/*------------------------------------------------------------------------- * * predicate.c * POSTGRES predicate locking * to support full serializable transaction isolation * * * The approach taken is to implement Serializable Snapshot Isolation (SSI) * as initially described in this paper: * * Michael J. Cahill, Uwe Röhm, and Alan D. Fekete. 2008. * Serializable isolation for snapshot databases. * In SIGMOD ’08: Proceedings of the 2008 ACM SIGMOD * international conference on Management of data, * pages 729–738, New York, NY, USA. ACM. * http://doi.acm.org/10.1145/1376616.1376690 * * and further elaborated in Cahill's doctoral thesis: * * Michael James Cahill. 2009. * Serializable Isolation for Snapshot Databases. * Sydney Digital Theses. * University of Sydney, School of Information Technologies. * http://hdl.handle.net/2123/5353 * * * Predicate locks for Serializable Snapshot Isolation (SSI) are SIREAD * locks, which are so different from normal locks that a distinct set of * structures is required to handle them. They are needed to detect * rw-conflicts when the read happens before the write. (When the write * occurs first, the reading transaction can check for a conflict by * examining the MVCC data.) * * (1) Besides tuples actually read, they must cover ranges of tuples * which would have been read based on the predicate. This will * require modelling the predicates through locks against database * objects such as pages, index ranges, or entire tables. * * (2) They must be kept in RAM for quick access. Because of this, it * isn't possible to always maintain tuple-level granularity -- when * the space allocated to store these approaches exhaustion, a * request for a lock may need to scan for situations where a single * transaction holds many fine-grained locks which can be coalesced * into a single coarser-grained lock. * * (3) They never block anything; they are more like flags than locks * in that regard; although they refer to database objects and are * used to identify rw-conflicts with normal write locks. * * (4) While they are associated with a transaction, they must survive * a successful COMMIT of that transaction, and remain until all * overlapping transactions complete. This even means that they * must survive termination of the transaction's process. If a * top level transaction is rolled back, however, it is immediately * flagged so that it can be ignored, and its SIREAD locks can be * released any time after that. * * (5) The only transactions which create SIREAD locks or check for * conflicts with them are serializable transactions. * * (6) When a write lock for a top level transaction is found to cover * an existing SIREAD lock for the same transaction, the SIREAD lock * can be deleted. * * (7) A write from a serializable transaction must ensure that a xact * record exists for the transaction, with the same lifespan (until * all concurrent transaction complete or the transaction is rolled * back) so that rw-dependencies to that transaction can be * detected. * * We use an optimization for read-only transactions. Under certain * circumstances, a read-only transaction's snapshot can be shown to * never have conflicts with other transactions. This is referred to * as a "safe" snapshot (and one known not to be is "unsafe"). * However, it can't be determined whether a snapshot is safe until * all concurrent read/write transactions complete. * * Once a read-only transaction is known to have a safe snapshot, it * can release its predicate locks and exempt itself from further * predicate lock tracking. READ ONLY DEFERRABLE transactions run only * on safe snapshots, waiting as necessary for one to be available. * * * Lightweight locks to manage access to the predicate locking shared * memory objects must be taken in this order, and should be released in * reverse order: * * SerializableFinishedListLock * - Protects the list of transactions which have completed but which * may yet matter because they overlap still-active transactions. * * SerializablePredicateLockListLock * - Protects the linked list of locks held by a transaction. Note * that the locks themselves are also covered by the partition * locks of their respective lock targets; this lock only affects * the linked list connecting the locks related to a transaction. * - All transactions share this single lock (with no partitioning). * - There is never a need for a process other than the one running * an active transaction to walk the list of locks held by that * transaction. * - It is relatively infrequent that another process needs to * modify the list for a transaction, but it does happen for such * things as index page splits for pages with predicate locks and * freeing of predicate locked pages by a vacuum process. When * removing a lock in such cases, the lock itself contains the * pointers needed to remove it from the list. When adding a * lock in such cases, the lock can be added using the anchor in * the transaction structure. Neither requires walking the list. * - Cleaning up the list for a terminated transaction is sometimes * not done on a retail basis, in which case no lock is required. * - Due to the above, a process accessing its active transaction's * list always uses a shared lock, regardless of whether it is * walking or maintaining the list. This improves concurrency * for the common access patterns. * - A process which needs to alter the list of a transaction other * than its own active transaction must acquire an exclusive * lock. * * FirstPredicateLockMgrLock based partition locks * - The same lock protects a target, all locks on that target, and * the linked list of locks on the target.. * - When more than one is needed, acquire in ascending order. * * SerializableXactHashLock * - Protects both PredXact and SerializableXidHash. * * PredicateLockNextRowLinkLock * - Protects the priorVersionOfRow and nextVersionOfRow fields of * PREDICATELOCKTARGET when linkage is being created or destroyed. * * * Portions Copyright (c) 1996-2011, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * * IDENTIFICATION * src/backend/storage/lmgr/predicate.c * *------------------------------------------------------------------------- */ /* * INTERFACE ROUTINES * * housekeeping for setting up shared memory predicate lock structures * InitPredicateLocks(void) * PredicateLockShmemSize(void) * * predicate lock reporting * GetPredicateLockStatusData(void) * PageIsPredicateLocked(Relation relation, BlockNumber blkno) * * predicate lock maintenance * RegisterSerializableTransaction(Snapshot snapshot) * RegisterPredicateLockingXid(void) * PredicateLockRelation(Relation relation) * PredicateLockPage(Relation relation, BlockNumber blkno) * PredicateLockTuple(Relation relation, HeapTuple tuple) * PredicateLockPageSplit(Relation relation, BlockNumber oldblkno, * BlockNumber newblkno); * PredicateLockPageCombine(Relation relation, BlockNumber oldblkno, * BlockNumber newblkno); * PredicateLockTupleRowVersionLink(const Relation relation, * const HeapTuple oldTuple, * const HeapTuple newTuple) * ReleasePredicateLocks(bool isCommit) * * conflict detection (may also trigger rollback) * CheckForSerializableConflictOut(bool visible, Relation relation, * HeapTupleData *tup, Buffer buffer) * CheckForSerializableConflictIn(Relation relation, HeapTupleData *tup, * Buffer buffer) * * final rollback checking * PreCommit_CheckForSerializationFailure(void) * * two-phase commit support * AtPrepare_PredicateLocks(void); * PostPrepare_PredicateLocks(TransactionId xid); * PredicateLockTwoPhaseFinish(TransactionId xid, bool isCommit); * predicatelock_twophase_recover(TransactionId xid, uint16 info, * void *recdata, uint32 len); */ #include "postgres.h" #include "access/slru.h" #include "access/subtrans.h" #include "access/transam.h" #include "access/twophase.h" #include "access/twophase_rmgr.h" #include "access/xact.h" #include "miscadmin.h" #include "storage/bufmgr.h" #include "storage/predicate.h" #include "storage/predicate_internals.h" #include "storage/procarray.h" #include "utils/rel.h" #include "utils/snapmgr.h" #include "utils/tqual.h" /* Uncomment the next line to test the graceful degradation code. */ /* #define TEST_OLDSERXID */ /* * Test the most selective fields first, for performance. * * a is covered by b if all of the following hold: * 1) a.database = b.database * 2) a.relation = b.relation * 3) b.offset is invalid (b is page-granularity or higher) * 4) either of the following: * 4a) a.offset is valid (a is tuple-granularity) and a.page = b.page * or 4b) a.offset is invalid and b.page is invalid (a is * page-granularity and b is relation-granularity */ #define TargetTagIsCoveredBy(covered_target, covering_target) \ ((GET_PREDICATELOCKTARGETTAG_RELATION(covered_target) == /* (2) */ \ GET_PREDICATELOCKTARGETTAG_RELATION(covering_target)) \ && (GET_PREDICATELOCKTARGETTAG_OFFSET(covering_target) == \ InvalidOffsetNumber) /* (3) */ \ && (((GET_PREDICATELOCKTARGETTAG_OFFSET(covered_target) != \ InvalidOffsetNumber) /* (4a) */ \ && (GET_PREDICATELOCKTARGETTAG_PAGE(covering_target) == \ GET_PREDICATELOCKTARGETTAG_PAGE(covered_target))) \ || ((GET_PREDICATELOCKTARGETTAG_PAGE(covering_target) == \ InvalidBlockNumber) /* (4b) */ \ && (GET_PREDICATELOCKTARGETTAG_PAGE(covered_target) \ != InvalidBlockNumber))) \ && (GET_PREDICATELOCKTARGETTAG_DB(covered_target) == /* (1) */ \ GET_PREDICATELOCKTARGETTAG_DB(covering_target))) /* * The predicate locking target and lock shared hash tables are partitioned to * reduce contention. To determine which partition a given target belongs to, * compute the tag's hash code with PredicateLockTargetTagHashCode(), then * apply one of these macros. * NB: NUM_PREDICATELOCK_PARTITIONS must be a power of 2! */ #define PredicateLockHashPartition(hashcode) \ ((hashcode) % NUM_PREDICATELOCK_PARTITIONS) #define PredicateLockHashPartitionLock(hashcode) \ ((LWLockId) (FirstPredicateLockMgrLock + PredicateLockHashPartition(hashcode))) #define NPREDICATELOCKTARGETENTS() \ mul_size(max_predicate_locks_per_xact, add_size(MaxBackends, max_prepared_xacts)) #define SxactIsOnFinishedList(sxact) (!SHMQueueIsDetached(&((sxact)->finishedLink))) #define SxactIsPrepared(sxact) (((sxact)->flags & SXACT_FLAG_PREPARED) != 0) #define SxactIsCommitted(sxact) (((sxact)->flags & SXACT_FLAG_COMMITTED) != 0) #define SxactIsRolledBack(sxact) (((sxact)->flags & SXACT_FLAG_ROLLED_BACK) != 0) #define SxactIsReadOnly(sxact) (((sxact)->flags & SXACT_FLAG_READ_ONLY) != 0) #define SxactHasSummaryConflictIn(sxact) (((sxact)->flags & SXACT_FLAG_SUMMARY_CONFLICT_IN) != 0) #define SxactHasSummaryConflictOut(sxact) (((sxact)->flags & SXACT_FLAG_SUMMARY_CONFLICT_OUT) != 0) #define SxactHasConflictOut(sxact) (((sxact)->flags & SXACT_FLAG_CONFLICT_OUT) != 0) #define SxactIsDeferrableWaiting(sxact) (((sxact)->flags & SXACT_FLAG_DEFERRABLE_WAITING) != 0) #define SxactIsROSafe(sxact) (((sxact)->flags & SXACT_FLAG_RO_SAFE) != 0) #define SxactIsROUnsafe(sxact) (((sxact)->flags & SXACT_FLAG_RO_UNSAFE) != 0) #define SxactIsMarkedForDeath(sxact) (((sxact)->flags & SXACT_FLAG_MARKED_FOR_DEATH) != 0) /* * When a public interface method is called for a split on an index relation, * this is the test to see if we should do a quick return. */ #define SkipSplitTracking(relation) \ (((relation)->rd_id < FirstBootstrapObjectId) \ || RelationUsesLocalBuffers(relation)) /* * When a public interface method is called for serializing a relation within * the current transaction, this is the test to see if we should do a quick * return. */ #define SkipSerialization(relation) \ ((!IsolationIsSerializable()) \ || ((MySerializableXact == InvalidSerializableXact)) \ || ReleasePredicateLocksIfROSafe() \ || SkipSplitTracking(relation)) /* * Compute the hash code associated with a PREDICATELOCKTARGETTAG. * * To avoid unnecessary recomputations of the hash code, we try to do this * just once per function, and then pass it around as needed. Aside from * passing the hashcode to hash_search_with_hash_value(), we can extract * the lock partition number from the hashcode. */ #define PredicateLockTargetTagHashCode(predicatelocktargettag) \ (tag_hash((predicatelocktargettag), sizeof(PREDICATELOCKTARGETTAG))) /* * Given a predicate lock tag, and the hash for its target, * compute the lock hash. * * To make the hash code also depend on the transaction, we xor the sxid * struct's address into the hash code, left-shifted so that the * partition-number bits don't change. Since this is only a hash, we * don't care if we lose high-order bits of the address; use an * intermediate variable to suppress cast-pointer-to-int warnings. */ #define PredicateLockHashCodeFromTargetHashCode(predicatelocktag, targethash) \ ((targethash) ^ ((uint32) PointerGetDatum((predicatelocktag)->myXact)) \ << LOG2_NUM_PREDICATELOCK_PARTITIONS) /* * The SLRU buffer area through which we access the old xids. */ static SlruCtlData OldSerXidSlruCtlData; #define OldSerXidSlruCtl (&OldSerXidSlruCtlData) #define OLDSERXID_PAGESIZE BLCKSZ #define OLDSERXID_ENTRYSIZE sizeof(SerCommitSeqNo) #define OLDSERXID_ENTRIESPERPAGE (OLDSERXID_PAGESIZE / OLDSERXID_ENTRYSIZE) #define OLDSERXID_MAX_PAGE (SLRU_PAGES_PER_SEGMENT * 0x10000 - 1) #define OldSerXidNextPage(page) (((page) >= OLDSERXID_MAX_PAGE) ? 0 : (page) + 1) #define OldSerXidValue(slotno, xid) (*((SerCommitSeqNo *) \ (OldSerXidSlruCtl->shared->page_buffer[slotno] + \ ((((uint32) (xid)) % OLDSERXID_ENTRIESPERPAGE) * OLDSERXID_ENTRYSIZE)))) #define OldSerXidPage(xid) ((((uint32) (xid)) / OLDSERXID_ENTRIESPERPAGE) % (OLDSERXID_MAX_PAGE + 1)) #define OldSerXidSegment(page) ((page) / SLRU_PAGES_PER_SEGMENT) typedef struct OldSerXidControlData { int headPage; int tailSegment; TransactionId headXid; TransactionId tailXid; bool warningIssued; } OldSerXidControlData; typedef struct OldSerXidControlData *OldSerXidControl; static OldSerXidControl oldSerXidControl; /* * When the oldest committed transaction on the "finished" list is moved to * SLRU, its predicate locks will be moved to this "dummy" transaction, * collapsing duplicate targets. When a duplicate is found, the later * commitSeqNo is used. */ static SERIALIZABLEXACT *OldCommittedSxact; /* This configuration variable is used to set the predicate lock table size */ int max_predicate_locks_per_xact; /* set by guc.c */ /* * This provides a list of objects in order to track transactions * participating in predicate locking. Entries in the list are fixed size, * and reside in shared memory. The memory address of an entry must remain * fixed during its lifetime. The list will be protected from concurrent * update externally; no provision is made in this code to manage that. The * number of entries in the list, and the size allowed for each entry is * fixed upon creation. */ static PredXactList PredXact; /* * This provides a pool of RWConflict data elements to use in conflict lists * between transactions. */ static RWConflictPoolHeader RWConflictPool; /* * The predicate locking hash tables are in shared memory. * Each backend keeps pointers to them. */ static HTAB *SerializableXidHash; static HTAB *PredicateLockTargetHash; static HTAB *PredicateLockHash; static SHM_QUEUE *FinishedSerializableTransactions; /* * Tag for a reserved entry in PredicateLockTargetHash; used to ensure * there's an element available for scratch space if we need it, * e.g. in PredicateLockPageSplit. This is an otherwise-invalid tag. */ static const PREDICATELOCKTARGETTAG ReservedTargetTag = {0, 0, 0, 0, 0}; /* * The local hash table used to determine when to combine multiple fine- * grained locks into a single courser-grained lock. */ static HTAB *LocalPredicateLockHash = NULL; /* * Keep a pointer to the currently-running serializable transaction (if any) * for quick reference. * TODO SSI: Remove volatile qualifier and the then-unnecessary casts? */ static volatile SERIALIZABLEXACT *MySerializableXact = InvalidSerializableXact; /* local functions */ static SERIALIZABLEXACT *CreatePredXact(void); static void ReleasePredXact(SERIALIZABLEXACT *sxact); static SERIALIZABLEXACT *FirstPredXact(void); static SERIALIZABLEXACT *NextPredXact(SERIALIZABLEXACT *sxact); static bool RWConflictExists(const SERIALIZABLEXACT *reader, const SERIALIZABLEXACT *writer); static void SetRWConflict(SERIALIZABLEXACT *reader, SERIALIZABLEXACT *writer); static void SetPossibleUnsafeConflict(SERIALIZABLEXACT *roXact, SERIALIZABLEXACT *activeXact); static void ReleaseRWConflict(RWConflict conflict); static void FlagSxactUnsafe(SERIALIZABLEXACT *sxact); static bool OldSerXidPagePrecedesLogically(int p, int q); static void OldSerXidInit(void); static void OldSerXidAdd(TransactionId xid, SerCommitSeqNo minConflictCommitSeqNo); static SerCommitSeqNo OldSerXidGetMinConflictCommitSeqNo(TransactionId xid); static void OldSerXidSetActiveSerXmin(TransactionId xid); static uint32 predicatelock_hash(const void *key, Size keysize); static void SummarizeOldestCommittedSxact(void); static Snapshot GetSafeSnapshot(Snapshot snapshot); static Snapshot RegisterSerializableTransactionInt(Snapshot snapshot); static bool PredicateLockExists(const PREDICATELOCKTARGETTAG *targettag); static bool GetParentPredicateLockTag(const PREDICATELOCKTARGETTAG *tag, PREDICATELOCKTARGETTAG *parent); static bool CoarserLockCovers(const PREDICATELOCKTARGETTAG *newtargettag); static void RemoveTargetIfNoLongerUsed(PREDICATELOCKTARGET *target, uint32 targettaghash); static void DeleteChildTargetLocks(const PREDICATELOCKTARGETTAG *newtargettag); static int PredicateLockPromotionThreshold(const PREDICATELOCKTARGETTAG *tag); static bool CheckAndPromotePredicateLockRequest(const PREDICATELOCKTARGETTAG *reqtag); static void DecrementParentLocks(const PREDICATELOCKTARGETTAG *targettag); static void CreatePredicateLock(const PREDICATELOCKTARGETTAG *targettag, uint32 targettaghash, SERIALIZABLEXACT *sxact); static void DeleteLockTarget(PREDICATELOCKTARGET *target, uint32 targettaghash); static bool TransferPredicateLocksToNewTarget(const PREDICATELOCKTARGETTAG oldtargettag, const PREDICATELOCKTARGETTAG newtargettag, bool removeOld); static void PredicateLockAcquire(const PREDICATELOCKTARGETTAG *targettag); static void SetNewSxactGlobalXmin(void); static bool ReleasePredicateLocksIfROSafe(void); static void ClearOldPredicateLocks(void); static void ReleaseOneSerializableXact(SERIALIZABLEXACT *sxact, bool partial, bool summarize); static bool XidIsConcurrent(TransactionId xid); static void CheckTargetForConflictsIn(PREDICATELOCKTARGETTAG *targettag); static bool CheckSingleTargetForConflictsIn(PREDICATELOCKTARGETTAG *targettag, PREDICATELOCKTARGETTAG *nexttargettag); static void FlagRWConflict(SERIALIZABLEXACT *reader, SERIALIZABLEXACT *writer); static void OnConflict_CheckForSerializationFailure(const SERIALIZABLEXACT *reader, SERIALIZABLEXACT *writer); /*------------------------------------------------------------------------*/ /* * These functions are a simple implementation of a list for this specific * type of struct. If there is ever a generalized shared memory list, we * should probably switch to that. */ static SERIALIZABLEXACT * CreatePredXact(void) { PredXactListElement ptle; ptle = (PredXactListElement) SHMQueueNext(&PredXact->availableList, &PredXact->availableList, offsetof(PredXactListElementData, link)); if (!ptle) return NULL; SHMQueueDelete(&ptle->link); SHMQueueInsertBefore(&PredXact->activeList, &ptle->link); return &ptle->sxact; } static void ReleasePredXact(SERIALIZABLEXACT *sxact) { PredXactListElement ptle; Assert(ShmemAddrIsValid(sxact)); ptle = (PredXactListElement) (((char *) sxact) - offsetof(PredXactListElementData, sxact) +offsetof(PredXactListElementData, link)); SHMQueueDelete(&ptle->link); SHMQueueInsertBefore(&PredXact->availableList, &ptle->link); } static SERIALIZABLEXACT * FirstPredXact(void) { PredXactListElement ptle; ptle = (PredXactListElement) SHMQueueNext(&PredXact->activeList, &PredXact->activeList, offsetof(PredXactListElementData, link)); if (!ptle) return NULL; return &ptle->sxact; } static SERIALIZABLEXACT * NextPredXact(SERIALIZABLEXACT *sxact) { PredXactListElement ptle; Assert(ShmemAddrIsValid(sxact)); ptle = (PredXactListElement) (((char *) sxact) - offsetof(PredXactListElementData, sxact) +offsetof(PredXactListElementData, link)); ptle = (PredXactListElement) SHMQueueNext(&PredXact->activeList, &ptle->link, offsetof(PredXactListElementData, link)); if (!ptle) return NULL; return &ptle->sxact; } /*------------------------------------------------------------------------*/ /* * These functions manage primitive access to the RWConflict pool and lists. */ static bool RWConflictExists(const SERIALIZABLEXACT *reader, const SERIALIZABLEXACT *writer) { RWConflict conflict; Assert(reader != writer); /* Check the ends of the purported conflict first. */ if (SxactIsRolledBack(reader) || SxactIsRolledBack(writer) || SHMQueueEmpty(&reader->outConflicts) || SHMQueueEmpty(&writer->inConflicts)) return false; /* A conflict is possible; walk the list to find out. */ conflict = (RWConflict) SHMQueueNext(&reader->outConflicts, &reader->outConflicts, offsetof(RWConflictData, outLink)); while (conflict) { if (conflict->sxactIn == writer) return true; conflict = (RWConflict) SHMQueueNext(&reader->outConflicts, &conflict->outLink, offsetof(RWConflictData, outLink)); } /* No conflict found. */ return false; } static void SetRWConflict(SERIALIZABLEXACT *reader, SERIALIZABLEXACT *writer) { RWConflict conflict; Assert(reader != writer); Assert(!RWConflictExists(reader, writer)); conflict = (RWConflict) SHMQueueNext(&RWConflictPool->availableList, &RWConflictPool->availableList, offsetof(RWConflictData, outLink)); if (!conflict) ereport(ERROR, (errcode(ERRCODE_OUT_OF_MEMORY), errmsg("not enough elements in RWConflictPool to record a rw-conflict"), errhint("You might need to run fewer transactions at a time or increase max_connections."))); SHMQueueDelete(&conflict->outLink); conflict->sxactOut = reader; conflict->sxactIn = writer; SHMQueueInsertBefore(&reader->outConflicts, &conflict->outLink); SHMQueueInsertBefore(&writer->inConflicts, &conflict->inLink); } static void SetPossibleUnsafeConflict(SERIALIZABLEXACT *roXact, SERIALIZABLEXACT *activeXact) { RWConflict conflict; Assert(roXact != activeXact); Assert(SxactIsReadOnly(roXact)); Assert(!SxactIsReadOnly(activeXact)); conflict = (RWConflict) SHMQueueNext(&RWConflictPool->availableList, &RWConflictPool->availableList, offsetof(RWConflictData, outLink)); if (!conflict) ereport(ERROR, (errcode(ERRCODE_OUT_OF_MEMORY), errmsg("not enough elements in RWConflictPool to record a potential rw-conflict"), errhint("You might need to run fewer transactions at a time or increase max_connections."))); SHMQueueDelete(&conflict->outLink); conflict->sxactOut = activeXact; conflict->sxactIn = roXact; SHMQueueInsertBefore(&activeXact->possibleUnsafeConflicts, &conflict->outLink); SHMQueueInsertBefore(&roXact->possibleUnsafeConflicts, &conflict->inLink); } static void ReleaseRWConflict(RWConflict conflict) { SHMQueueDelete(&conflict->inLink); SHMQueueDelete(&conflict->outLink); SHMQueueInsertBefore(&RWConflictPool->availableList, &conflict->outLink); } static void FlagSxactUnsafe(SERIALIZABLEXACT *sxact) { RWConflict conflict, nextConflict; Assert(SxactIsReadOnly(sxact)); Assert(!SxactIsROSafe(sxact)); sxact->flags |= SXACT_FLAG_RO_UNSAFE; /* * We know this isn't a safe snapshot, so we can stop looking for other * potential conflicts. */ conflict = (RWConflict) SHMQueueNext(&sxact->possibleUnsafeConflicts, &sxact->possibleUnsafeConflicts, offsetof(RWConflictData, inLink)); while (conflict) { nextConflict = (RWConflict) SHMQueueNext(&sxact->possibleUnsafeConflicts, &conflict->inLink, offsetof(RWConflictData, inLink)); Assert(!SxactIsReadOnly(conflict->sxactOut)); Assert(sxact == conflict->sxactIn); ReleaseRWConflict(conflict); conflict = nextConflict; } } /*------------------------------------------------------------------------*/ /* * We will work on the page range of 0..OLDSERXID_MAX_PAGE. * Compares using wraparound logic, as is required by slru.c. */ static bool OldSerXidPagePrecedesLogically(int p, int q) { int diff; /* * We have to compare modulo (OLDSERXID_MAX_PAGE+1)/2. Both inputs should * be in the range 0..OLDSERXID_MAX_PAGE. */ Assert(p >= 0 && p <= OLDSERXID_MAX_PAGE); Assert(q >= 0 && q <= OLDSERXID_MAX_PAGE); diff = p - q; if (diff >= ((OLDSERXID_MAX_PAGE + 1) / 2)) diff -= OLDSERXID_MAX_PAGE + 1; else if (diff < -((OLDSERXID_MAX_PAGE + 1) / 2)) diff += OLDSERXID_MAX_PAGE + 1; return diff < 0; } /* * Initialize for the tracking of old serializable committed xids. */ static void OldSerXidInit(void) { bool found; /* * Set up SLRU management of the pg_serial data. */ OldSerXidSlruCtl->PagePrecedes = OldSerXidPagePrecedesLogically; SimpleLruInit(OldSerXidSlruCtl, "OldSerXid SLRU Ctl", NUM_OLDSERXID_BUFFERS, 0, OldSerXidLock, "pg_serial"); /* Override default assumption that writes should be fsync'd */ OldSerXidSlruCtl->do_fsync = false; /* * Create or attach to the OldSerXidControl structure. */ oldSerXidControl = (OldSerXidControl) ShmemInitStruct("OldSerXidControlData", sizeof(OldSerXidControlData), &found); if (!found) { /* * Set control information to reflect empty SLRU. */ oldSerXidControl->headPage = -1; oldSerXidControl->tailSegment = -1; oldSerXidControl->headXid = InvalidTransactionId; oldSerXidControl->tailXid = InvalidTransactionId; oldSerXidControl->warningIssued = false; } } /* * Record a committed read write serializable xid and the minimum * commitSeqNo of any transactions to which this xid had a rw-conflict out. * A zero seqNo means that there were no conflicts out from xid. * * The return value is normally false -- true means that we're about to * wrap around our space for tracking these xids, so the caller might want * to take action to prevent that. */ static void OldSerXidAdd(TransactionId xid, SerCommitSeqNo minConflictCommitSeqNo) { TransactionId tailXid; int targetPage; int slotno; int page; int xidSpread; bool isNewPage; Assert(TransactionIdIsValid(xid)); targetPage = OldSerXidPage(xid); LWLockAcquire(OldSerXidLock, LW_EXCLUSIVE); /* * If no serializable transactions are active, there shouldn't be anything * to push out to this SLRU. Hitting this assert would mean there's * something wrong with the earlier cleanup logic. */ tailXid = oldSerXidControl->tailXid; Assert(TransactionIdIsValid(tailXid)); if (oldSerXidControl->headPage < 0) { page = OldSerXidPage(tailXid); oldSerXidControl->tailSegment = OldSerXidSegment(page); page = oldSerXidControl->tailSegment * OLDSERXID_ENTRIESPERPAGE; isNewPage = true; } else { page = OldSerXidNextPage(oldSerXidControl->headPage); isNewPage = OldSerXidPagePrecedesLogically(oldSerXidControl->headPage, targetPage); } if (!TransactionIdIsValid(oldSerXidControl->headXid) || TransactionIdFollows(xid, oldSerXidControl->headXid)) oldSerXidControl->headXid = xid; if (oldSerXidControl->headPage < 0 || OldSerXidPagePrecedesLogically(oldSerXidControl->headPage, targetPage)) oldSerXidControl->headPage = targetPage; xidSpread = (((uint32) xid) - ((uint32) tailXid)); if (oldSerXidControl->warningIssued) { if (xidSpread < 800000000) oldSerXidControl->warningIssued = false; } else if (xidSpread >= 1000000000) { oldSerXidControl->warningIssued = true; ereport(WARNING, (errmsg("memory for serializable conflict tracking is nearly exhausted"), errhint("There may be an idle transaction or a forgotten prepared transaction causing this."))); } if (isNewPage) { /* Initialize intervening pages. */ while (page != targetPage) { (void) SimpleLruZeroPage(OldSerXidSlruCtl, page); page = OldSerXidNextPage(page); } slotno = SimpleLruZeroPage(OldSerXidSlruCtl, targetPage); } else slotno = SimpleLruReadPage(OldSerXidSlruCtl, targetPage, true, xid); OldSerXidValue(slotno, xid) = minConflictCommitSeqNo; LWLockRelease(OldSerXidLock); } /* * Get the minimum commitSeqNo for any conflict out for the given xid. For * a transaction which exists but has no conflict out, InvalidSerCommitSeqNo * will be returned. */ static SerCommitSeqNo OldSerXidGetMinConflictCommitSeqNo(TransactionId xid) { TransactionId headXid; TransactionId tailXid; SerCommitSeqNo val; int slotno; Assert(TransactionIdIsValid(xid)); LWLockAcquire(OldSerXidLock, LW_SHARED); headXid = oldSerXidControl->headXid; tailXid = oldSerXidControl->tailXid; LWLockRelease(OldSerXidLock); if (!TransactionIdIsValid(headXid)) return 0; Assert(TransactionIdIsValid(tailXid)); if (TransactionIdPrecedes(xid, tailXid) || TransactionIdFollows(xid, headXid)) return 0; /* * The following function must be called without holding OldSerXidLock, * but will return with that lock held, which must then be released. */ slotno = SimpleLruReadPage_ReadOnly(OldSerXidSlruCtl, OldSerXidPage(xid), xid); val = OldSerXidValue(slotno, xid); LWLockRelease(OldSerXidLock); return val; } /* * Call this whenever there is a new xmin for active serializable * transactions. We don't need to keep information on transactions which * preceed that. InvalidTransactionId means none active, so everything in * the SLRU should be discarded. */ static void OldSerXidSetActiveSerXmin(TransactionId xid) { int newTailPage; int newTailSegment; LWLockAcquire(OldSerXidLock, LW_EXCLUSIVE); /* * When no sxacts are active, nothing overlaps, set the xid values to * invalid to show that there are no valid entries. Don't clear the * segment/page information, though. A new xmin might still land in an * existing segment, and we don't want to repeatedly delete and re-create * the same segment file. */ if (!TransactionIdIsValid(xid)) { if (TransactionIdIsValid(oldSerXidControl->tailXid)) { oldSerXidControl->headXid = InvalidTransactionId; oldSerXidControl->tailXid = InvalidTransactionId; } LWLockRelease(OldSerXidLock); return; } /* * When we're recovering prepared transactions, the global xmin might move * backwards depending on the order they're recovered. Normally that's not * OK, but during recovery no serializable transactions will commit, so * the SLRU is empty and we can get away with it. */ if (RecoveryInProgress()) { Assert(oldSerXidControl->headPage < 0); if (!TransactionIdIsValid(oldSerXidControl->tailXid) || TransactionIdPrecedes(xid, oldSerXidControl->tailXid)) oldSerXidControl->tailXid = xid; LWLockRelease(OldSerXidLock); return; } Assert(!TransactionIdIsValid(oldSerXidControl->tailXid) || TransactionIdFollows(xid, oldSerXidControl->tailXid)); oldSerXidControl->tailXid = xid; /* Exit quickly if there are no segments active. */ if (oldSerXidControl->headPage < 0) { LWLockRelease(OldSerXidLock); return; } newTailPage = OldSerXidPage(xid); newTailSegment = OldSerXidSegment(newTailPage); /* Exit quickly if we're still on the same segment. */ if (newTailSegment == oldSerXidControl->tailSegment) { LWLockRelease(OldSerXidLock); return; } oldSerXidControl->tailSegment = newTailSegment; /* See if that has cleared the last segment. */ if (OldSerXidPagePrecedesLogically(oldSerXidControl->headPage, newTailSegment * SLRU_PAGES_PER_SEGMENT)) { oldSerXidControl->headXid = InvalidTransactionId; oldSerXidControl->headPage = -1; oldSerXidControl->tailSegment = -1; } LWLockRelease(OldSerXidLock); SimpleLruTruncate(OldSerXidSlruCtl, newTailPage); } /*------------------------------------------------------------------------*/ /* * InitPredicateLocks -- Initialize the predicate locking data structures. * * This is called from CreateSharedMemoryAndSemaphores(), which see for * more comments. In the normal postmaster case, the shared hash tables * are created here. Backends inherit the pointers * to the shared tables via fork(). In the EXEC_BACKEND case, each * backend re-executes this code to obtain pointers to the already existing * shared hash tables. */ void InitPredicateLocks(void) { HASHCTL info; int hash_flags; long init_table_size, max_table_size; Size requestSize; bool found; /* * Compute init/max size to request for predicate lock target hashtable. * Note these calculations must agree with PredicateLockShmemSize! */ max_table_size = NPREDICATELOCKTARGETENTS(); init_table_size = max_table_size / 2; /* * Allocate hash table for PREDICATELOCKTARGET structs. This stores * per-predicate-lock-target information. */ MemSet(&info, 0, sizeof(info)); info.keysize = sizeof(PREDICATELOCKTARGETTAG); info.entrysize = sizeof(PREDICATELOCKTARGET); info.hash = tag_hash; info.num_partitions = NUM_PREDICATELOCK_PARTITIONS; hash_flags = (HASH_ELEM | HASH_FUNCTION | HASH_PARTITION); PredicateLockTargetHash = ShmemInitHash("PREDICATELOCKTARGET hash", init_table_size, max_table_size, &info, hash_flags); /* Assume an average of 2 xacts per target */ max_table_size *= 2; init_table_size *= 2; /* * Reserve an entry in the hash table; we use it to make sure there's * always one entry available when we need to split or combine a page, * because running out of space there could mean aborting a * non-serializable transaction. */ hash_search(PredicateLockTargetHash, &ReservedTargetTag, HASH_ENTER, NULL); /* * Allocate hash table for PREDICATELOCK structs. This stores per * xact-lock-of-a-target information. */ MemSet(&info, 0, sizeof(info)); info.keysize = sizeof(PREDICATELOCKTAG); info.entrysize = sizeof(PREDICATELOCK); info.hash = predicatelock_hash; info.num_partitions = NUM_PREDICATELOCK_PARTITIONS; hash_flags = (HASH_ELEM | HASH_FUNCTION | HASH_PARTITION); PredicateLockHash = ShmemInitHash("PREDICATELOCK hash", init_table_size, max_table_size, &info, hash_flags); /* * Compute init/max size to request for serializable transaction * hashtable. Note these calculations must agree with * PredicateLockShmemSize! */ max_table_size = (MaxBackends + max_prepared_xacts); /* * Allocate a list to hold information on transactions participating in * predicate locking. * * Assume an average of 10 predicate locking transactions per backend. * This allows aggressive cleanup while detail is present before data must * be summarized for storage in SLRU and the "dummy" transaction. */ max_table_size *= 10; PredXact = ShmemInitStruct("PredXactList", PredXactListDataSize, &found); if (!found) { int i; SHMQueueInit(&PredXact->availableList); SHMQueueInit(&PredXact->activeList); PredXact->SxactGlobalXmin = InvalidTransactionId; PredXact->SxactGlobalXminCount = 0; PredXact->WritableSxactCount = 0; PredXact->LastSxactCommitSeqNo = FirstNormalSerCommitSeqNo - 1; PredXact->CanPartialClearThrough = 0; PredXact->HavePartialClearedThrough = 0; PredXact->NeedTargetLinkCleanup = false; requestSize = mul_size((Size) max_table_size, PredXactListElementDataSize); PredXact->element = ShmemAlloc(requestSize); if (PredXact->element == NULL) ereport(ERROR, (errcode(ERRCODE_OUT_OF_MEMORY), errmsg("not enough shared memory for elements of data structure" " \"%s\" (%lu bytes requested)", "PredXactList", (unsigned long) requestSize))); /* Add all elements to available list, clean. */ memset(PredXact->element, 0, requestSize); for (i = 0; i < max_table_size; i++) { SHMQueueInsertBefore(&(PredXact->availableList), &(PredXact->element[i].link)); } PredXact->OldCommittedSxact = CreatePredXact(); SetInvalidVirtualTransactionId(PredXact->OldCommittedSxact->vxid); PredXact->OldCommittedSxact->commitSeqNo = 0; PredXact->OldCommittedSxact->SeqNo.lastCommitBeforeSnapshot = 0; SHMQueueInit(&PredXact->OldCommittedSxact->outConflicts); SHMQueueInit(&PredXact->OldCommittedSxact->inConflicts); SHMQueueInit(&PredXact->OldCommittedSxact->predicateLocks); SHMQueueInit(&PredXact->OldCommittedSxact->finishedLink); SHMQueueInit(&PredXact->OldCommittedSxact->possibleUnsafeConflicts); PredXact->OldCommittedSxact->topXid = InvalidTransactionId; PredXact->OldCommittedSxact->finishedBefore = InvalidTransactionId; PredXact->OldCommittedSxact->xmin = InvalidTransactionId; PredXact->OldCommittedSxact->flags = SXACT_FLAG_COMMITTED; PredXact->OldCommittedSxact->pid = 0; } /* This never changes, so let's keep a local copy. */ OldCommittedSxact = PredXact->OldCommittedSxact; /* * Allocate hash table for SERIALIZABLEXID structs. This stores per-xid * information for serializable transactions which have accessed data. */ MemSet(&info, 0, sizeof(info)); info.keysize = sizeof(SERIALIZABLEXIDTAG); info.entrysize = sizeof(SERIALIZABLEXID); info.hash = tag_hash; hash_flags = (HASH_ELEM | HASH_FUNCTION); SerializableXidHash = ShmemInitHash("SERIALIZABLEXID hash", max_table_size, max_table_size, &info, hash_flags); /* * Allocate space for tracking rw-conflicts in lists attached to the * transactions. * * Assume an average of 5 conflicts per transaction. Calculations suggest * that this will prevent resource exhaustion in even the most pessimal * loads up to max_connections = 200 with all 200 connections pounding the * database with serializable transactions. Beyond that, there may be * occassional transactions canceled when trying to flag conflicts. That's * probably OK. */ max_table_size *= 5; RWConflictPool = ShmemInitStruct("RWConflictPool", RWConflictPoolHeaderDataSize, &found); if (!found) { int i; SHMQueueInit(&RWConflictPool->availableList); requestSize = mul_size((Size) max_table_size, RWConflictDataSize); RWConflictPool->element = ShmemAlloc(requestSize); if (RWConflictPool->element == NULL) ereport(ERROR, (errcode(ERRCODE_OUT_OF_MEMORY), errmsg("not enough shared memory for elements of data structure" " \"%s\" (%lu bytes requested)", "RWConflictPool", (unsigned long) requestSize))); /* Add all elements to available list, clean. */ memset(RWConflictPool->element, 0, requestSize); for (i = 0; i < max_table_size; i++) { SHMQueueInsertBefore(&(RWConflictPool->availableList), &(RWConflictPool->element[i].outLink)); } } /* * Create or attach to the header for the list of finished serializable * transactions. */ FinishedSerializableTransactions = (SHM_QUEUE *) ShmemInitStruct("FinishedSerializableTransactions", sizeof(SHM_QUEUE), &found); if (!found) SHMQueueInit(FinishedSerializableTransactions); /* * Initialize the SLRU storage for old committed serializable * transactions. */ OldSerXidInit(); } /* * Estimate shared-memory space used for predicate lock table */ Size PredicateLockShmemSize(void) { Size size = 0; long max_table_size; /* predicate lock target hash table */ max_table_size = NPREDICATELOCKTARGETENTS(); size = add_size(size, hash_estimate_size(max_table_size, sizeof(PREDICATELOCKTARGET))); /* predicate lock hash table */ max_table_size *= 2; size = add_size(size, hash_estimate_size(max_table_size, sizeof(PREDICATELOCK))); /* * Since NPREDICATELOCKTARGETENTS is only an estimate, add 10% safety * margin. */ size = add_size(size, size / 10); /* transaction list */ max_table_size = MaxBackends + max_prepared_xacts; max_table_size *= 10; size = add_size(size, PredXactListDataSize); size = add_size(size, mul_size((Size) max_table_size, PredXactListElementDataSize)); /* transaction xid table */ size = add_size(size, hash_estimate_size(max_table_size, sizeof(SERIALIZABLEXID))); /* rw-conflict pool */ max_table_size *= 5; size = add_size(size, RWConflictPoolHeaderDataSize); size = add_size(size, mul_size((Size) max_table_size, RWConflictDataSize)); /* Head for list of finished serializable transactions. */ size = add_size(size, sizeof(SHM_QUEUE)); /* Shared memory structures for SLRU tracking of old committed xids. */ size = add_size(size, sizeof(OldSerXidControlData)); size = add_size(size, SimpleLruShmemSize(NUM_OLDSERXID_BUFFERS, 0)); return size; } /* * Compute the hash code associated with a PREDICATELOCKTAG. * * Because we want to use just one set of partition locks for both the * PREDICATELOCKTARGET and PREDICATELOCK hash tables, we have to make sure * that PREDICATELOCKs fall into the same partition number as their * associated PREDICATELOCKTARGETs. dynahash.c expects the partition number * to be the low-order bits of the hash code, and therefore a * PREDICATELOCKTAG's hash code must have the same low-order bits as the * associated PREDICATELOCKTARGETTAG's hash code. We achieve this with this * specialized hash function. */ static uint32 predicatelock_hash(const void *key, Size keysize) { const PREDICATELOCKTAG *predicatelocktag = (const PREDICATELOCKTAG *) key; uint32 targethash; Assert(keysize == sizeof(PREDICATELOCKTAG)); /* Look into the associated target object, and compute its hash code */ targethash = PredicateLockTargetTagHashCode(&predicatelocktag->myTarget->tag); return PredicateLockHashCodeFromTargetHashCode(predicatelocktag, targethash); } /* * GetPredicateLockStatusData * Return a table containing the internal state of the predicate * lock manager for use in pg_lock_status. * * Like GetLockStatusData, this function tries to hold the partition LWLocks * for as short a time as possible by returning two arrays that simply * contain the PREDICATELOCKTARGETTAG and SERIALIZABLEXACT for each lock * table entry. Multiple copies of the same PREDICATELOCKTARGETTAG and * SERIALIZABLEXACT will likely appear. */ PredicateLockData * GetPredicateLockStatusData(void) { PredicateLockData *data; int i; int els, el; HASH_SEQ_STATUS seqstat; PREDICATELOCK *predlock; data = (PredicateLockData *) palloc(sizeof(PredicateLockData)); /* * To ensure consistency, take simultaneous locks on all partition locks * in ascending order, then SerializableXactHashLock. */ for (i = 0; i < NUM_PREDICATELOCK_PARTITIONS; i++) LWLockAcquire(FirstPredicateLockMgrLock + i, LW_SHARED); LWLockAcquire(SerializableXactHashLock, LW_SHARED); /* Get number of locks and allocate appropriately-sized arrays. */ els = hash_get_num_entries(PredicateLockHash); data->nelements = els; data->locktags = (PREDICATELOCKTARGETTAG *) palloc(sizeof(PREDICATELOCKTARGETTAG) * els); data->xacts = (SERIALIZABLEXACT *) palloc(sizeof(SERIALIZABLEXACT) * els); /* Scan through PredicateLockHash and copy contents */ hash_seq_init(&seqstat, PredicateLockHash); el = 0; while ((predlock = (PREDICATELOCK *) hash_seq_search(&seqstat))) { data->locktags[el] = predlock->tag.myTarget->tag; data->xacts[el] = *predlock->tag.myXact; el++; } Assert(el == els); /* Release locks in reverse order */ LWLockRelease(SerializableXactHashLock); for (i = NUM_PREDICATELOCK_PARTITIONS - 1; i >= 0; i--) LWLockRelease(FirstPredicateLockMgrLock + i); return data; } /* * Free up shared memory structures by pushing the oldest sxact (the one at * the front of the SummarizeOldestCommittedSxact queue) into summary form. * Each call will free exactly one SERIALIZABLEXACT structure and may also * free one or more of these structures: SERIALIZABLEXID, PREDICATELOCK, * PREDICATELOCKTARGET, RWConflictData. */ static void SummarizeOldestCommittedSxact(void) { SERIALIZABLEXACT *sxact; LWLockAcquire(SerializableFinishedListLock, LW_EXCLUSIVE); #ifdef TEST_OLDSERXID if (SHMQueueEmpty(FinishedSerializableTransactions)) { LWLockRelease(SerializableFinishedListLock); return; } #else Assert(!SHMQueueEmpty(FinishedSerializableTransactions)); #endif /* * Grab the first sxact off the finished list -- this will be the earliest * commit. Remove it from the list. */ sxact = (SERIALIZABLEXACT *) SHMQueueNext(FinishedSerializableTransactions, FinishedSerializableTransactions, offsetof(SERIALIZABLEXACT, finishedLink)); SHMQueueDelete(&(sxact->finishedLink)); /* Add to SLRU summary information. */ if (TransactionIdIsValid(sxact->topXid) && !SxactIsReadOnly(sxact)) OldSerXidAdd(sxact->topXid, SxactHasConflictOut(sxact) ? sxact->SeqNo.earliestOutConflictCommit : InvalidSerCommitSeqNo); /* Summarize and release the detail. */ ReleaseOneSerializableXact(sxact, false, true); LWLockRelease(SerializableFinishedListLock); } /* * GetSafeSnapshot * Obtain and register a snapshot for a READ ONLY DEFERRABLE * transaction. Ensures that the snapshot is "safe", i.e. a * read-only transaction running on it can execute serializably * without further checks. This requires waiting for concurrent * transactions to complete, and retrying with a new snapshot if * one of them could possibly create a conflict. */ static Snapshot GetSafeSnapshot(Snapshot origSnapshot) { Snapshot snapshot; Assert(XactReadOnly && XactDeferrable); while (true) { /* * RegisterSerializableTransactionInt is going to call * GetSnapshotData, so we need to provide it the static snapshot our * caller passed to us. It returns a copy of that snapshot and * registers it on TopTransactionResourceOwner. */ snapshot = RegisterSerializableTransactionInt(origSnapshot); if (MySerializableXact == InvalidSerializableXact) return snapshot; /* no concurrent r/w xacts; it's safe */ MySerializableXact->flags |= SXACT_FLAG_DEFERRABLE_WAITING; /* * Wait for concurrent transactions to finish. Stop early if one of * them marked us as conflicted. */ while (!(SHMQueueEmpty((SHM_QUEUE *) &MySerializableXact->possibleUnsafeConflicts) || SxactIsROUnsafe(MySerializableXact))) ProcWaitForSignal(); MySerializableXact->flags &= ~SXACT_FLAG_DEFERRABLE_WAITING; if (!SxactIsROUnsafe(MySerializableXact)) break; /* success */ /* else, need to retry... */ ereport(DEBUG2, (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE), errmsg("deferrable snapshot was unsafe; trying a new one"))); ReleasePredicateLocks(false); UnregisterSnapshotFromOwner(snapshot, TopTransactionResourceOwner); } /* * Now we have a safe snapshot, so we don't need to do any further checks. */ Assert(SxactIsROSafe(MySerializableXact)); ReleasePredicateLocks(false); return snapshot; } /* * Acquire and register a snapshot which can be used for this transaction.. * Make sure we have a SERIALIZABLEXACT reference in MySerializableXact. * It should be current for this process and be contained in PredXact. */ Snapshot RegisterSerializableTransaction(Snapshot snapshot) { Assert(IsolationIsSerializable()); /* * A special optimization is available for SERIALIZABLE READ ONLY * DEFERRABLE transactions -- we can wait for a suitable snapshot and * thereby avoid all SSI overhead once it's running.. */ if (XactReadOnly && XactDeferrable) return GetSafeSnapshot(snapshot); return RegisterSerializableTransactionInt(snapshot); } static Snapshot RegisterSerializableTransactionInt(Snapshot snapshot) { PGPROC *proc; VirtualTransactionId vxid; SERIALIZABLEXACT *sxact, *othersxact; HASHCTL hash_ctl; /* We only do this for serializable transactions. Once. */ Assert(MySerializableXact == InvalidSerializableXact); Assert(!RecoveryInProgress()); proc = MyProc; Assert(proc != NULL); GET_VXID_FROM_PGPROC(vxid, *proc); /* * First we get the sxact structure, which may involve looping and access * to the "finished" list to free a structure for use. */ #ifdef TEST_OLDSERXID SummarizeOldestCommittedSxact(); #endif LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE); do { sxact = CreatePredXact(); /* If null, push out committed sxact to SLRU summary & retry. */ if (!sxact) { LWLockRelease(SerializableXactHashLock); SummarizeOldestCommittedSxact(); LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE); } } while (!sxact); /* Get and register a snapshot */ snapshot = GetSnapshotData(snapshot); snapshot = RegisterSnapshotOnOwner(snapshot, TopTransactionResourceOwner); /* * If there are no serializable transactions which are not read-only, we * can "opt out" of predicate locking and conflict checking for a * read-only transaction. * * The reason this is safe is that a read-only transaction can only become * part of a dangerous structure if it overlaps a writable transaction * which in turn overlaps a writable transaction which committed before * the read-only transaction started. A new writable transaction can * overlap this one, but it can't meet the other condition of overlapping * a transaction which committed before this one started. */ if (XactReadOnly && PredXact->WritableSxactCount == 0) { ReleasePredXact(sxact); LWLockRelease(SerializableXactHashLock); return snapshot; } /* Maintain serializable global xmin info. */ if (!TransactionIdIsValid(PredXact->SxactGlobalXmin)) { Assert(PredXact->SxactGlobalXminCount == 0); PredXact->SxactGlobalXmin = snapshot->xmin; PredXact->SxactGlobalXminCount = 1; OldSerXidSetActiveSerXmin(snapshot->xmin); } else if (TransactionIdEquals(snapshot->xmin, PredXact->SxactGlobalXmin)) { Assert(PredXact->SxactGlobalXminCount > 0); PredXact->SxactGlobalXminCount++; } else { Assert(TransactionIdFollows(snapshot->xmin, PredXact->SxactGlobalXmin)); } /* Initialize the structure. */ sxact->vxid = vxid; sxact->SeqNo.lastCommitBeforeSnapshot = PredXact->LastSxactCommitSeqNo; sxact->commitSeqNo = InvalidSerCommitSeqNo; SHMQueueInit(&(sxact->outConflicts)); SHMQueueInit(&(sxact->inConflicts)); SHMQueueInit(&(sxact->possibleUnsafeConflicts)); sxact->topXid = GetTopTransactionIdIfAny(); sxact->finishedBefore = InvalidTransactionId; sxact->xmin = snapshot->xmin; sxact->pid = MyProcPid; SHMQueueInit(&(sxact->predicateLocks)); SHMQueueElemInit(&(sxact->finishedLink)); sxact->flags = 0; if (XactReadOnly) { sxact->flags |= SXACT_FLAG_READ_ONLY; /* * Register all concurrent r/w transactions as possible conflicts; if * all of them commit without any outgoing conflicts to earlier * transactions then this snapshot can be deemed safe (and we can run * without tracking predicate locks). */ for (othersxact = FirstPredXact(); othersxact != NULL; othersxact = NextPredXact(othersxact)) { if (!SxactIsOnFinishedList(othersxact) && !SxactIsReadOnly(othersxact)) { SetPossibleUnsafeConflict(sxact, othersxact); } } } else { ++(PredXact->WritableSxactCount); Assert(PredXact->WritableSxactCount <= (MaxBackends + max_prepared_xacts)); } MySerializableXact = sxact; LWLockRelease(SerializableXactHashLock); /* Initialize the backend-local hash table of parent locks */ Assert(LocalPredicateLockHash == NULL); MemSet(&hash_ctl, 0, sizeof(hash_ctl)); hash_ctl.keysize = sizeof(PREDICATELOCKTARGETTAG); hash_ctl.entrysize = sizeof(LOCALPREDICATELOCK); hash_ctl.hash = tag_hash; LocalPredicateLockHash = hash_create("Local predicate lock", max_predicate_locks_per_xact, &hash_ctl, HASH_ELEM | HASH_FUNCTION); return snapshot; } /* * Register the top level XID in SerializableXidHash. * Also store it for easy reference in MySerializableXact. */ void RegisterPredicateLockingXid(const TransactionId xid) { SERIALIZABLEXIDTAG sxidtag; SERIALIZABLEXID *sxid; bool found; /* * If we're not tracking predicate lock data for this transaction, we * should ignore the request and return quickly. */ if (MySerializableXact == InvalidSerializableXact) return; /* This should only be done once per transaction. */ Assert(MySerializableXact->topXid == InvalidTransactionId); /* We should have a valid XID and be at the top level. */ Assert(TransactionIdIsValid(xid)); MySerializableXact->topXid = xid; sxidtag.xid = xid; LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE); sxid = (SERIALIZABLEXID *) hash_search(SerializableXidHash, &sxidtag, HASH_ENTER, &found); if (!sxid) /* This should not be possible, based on allocation. */ ereport(ERROR, (errcode(ERRCODE_OUT_OF_MEMORY), errmsg("out of shared memory"))); Assert(!found); /* Initialize the structure. */ sxid->myXact = (SERIALIZABLEXACT *) MySerializableXact; LWLockRelease(SerializableXactHashLock); } /* * Check whether there are any predicate locks held by any transaction * for the page at the given block number. * * Note that the transaction may be completed but not yet subject to * cleanup due to overlapping serializable transactions. This must * return valid information regardless of transaction isolation level. * * Also note that this doesn't check for a conflicting relation lock, * just a lock specifically on the given page. * * One use is to support proper behavior during GiST index vacuum. */ bool PageIsPredicateLocked(const Relation relation, const BlockNumber blkno) { PREDICATELOCKTARGETTAG targettag; uint32 targettaghash; LWLockId partitionLock; PREDICATELOCKTARGET *target; SET_PREDICATELOCKTARGETTAG_PAGE(targettag, relation->rd_node.dbNode, relation->rd_id, blkno); targettaghash = PredicateLockTargetTagHashCode(&targettag); partitionLock = PredicateLockHashPartitionLock(targettaghash); LWLockAcquire(partitionLock, LW_SHARED); target = (PREDICATELOCKTARGET *) hash_search_with_hash_value(PredicateLockTargetHash, &targettag, targettaghash, HASH_FIND, NULL); LWLockRelease(partitionLock); return (target != NULL); } /* * Check whether a particular lock is held by this transaction. * * Important note: this function may return false even if the lock is * being held, because it uses the local lock table which is not * updated if another transaction modifies our lock list (e.g. to * split an index page). However, it will never return true if the * lock is not held. We only use this function in circumstances where * such false negatives are acceptable. */ static bool PredicateLockExists(const PREDICATELOCKTARGETTAG *targettag) { LOCALPREDICATELOCK *lock; /* check local hash table */ lock = (LOCALPREDICATELOCK *) hash_search(LocalPredicateLockHash, targettag, HASH_FIND, NULL); if (!lock) return false; /* * Found entry in the table, but still need to check whether it's actually * held -- it could just be a parent of some held lock. */ return lock->held; } /* * Return the parent lock tag in the lock hierarchy: the next coarser * lock that covers the provided tag. * * Returns true and sets *parent to the parent tag if one exists, * returns false if none exists. */ static bool GetParentPredicateLockTag(const PREDICATELOCKTARGETTAG *tag, PREDICATELOCKTARGETTAG *parent) { switch (GET_PREDICATELOCKTARGETTAG_TYPE(*tag)) { case PREDLOCKTAG_RELATION: /* relation locks have no parent lock */ return false; case PREDLOCKTAG_PAGE: /* parent lock is relation lock */ SET_PREDICATELOCKTARGETTAG_RELATION(*parent, GET_PREDICATELOCKTARGETTAG_DB(*tag), GET_PREDICATELOCKTARGETTAG_RELATION(*tag)); return true; case PREDLOCKTAG_TUPLE: /* parent lock is page lock */ SET_PREDICATELOCKTARGETTAG_PAGE(*parent, GET_PREDICATELOCKTARGETTAG_DB(*tag), GET_PREDICATELOCKTARGETTAG_RELATION(*tag), GET_PREDICATELOCKTARGETTAG_PAGE(*tag)); return true; } /* not reachable */ Assert(false); return false; } /* * Check whether the lock we are considering is already covered by a * coarser lock for our transaction. */ static bool CoarserLockCovers(const PREDICATELOCKTARGETTAG *newtargettag) { PREDICATELOCKTARGETTAG targettag, parenttag; targettag = *newtargettag; /* check parents iteratively until no more */ while (GetParentPredicateLockTag(&targettag, &parenttag)) { targettag = parenttag; if (PredicateLockExists(&targettag)) return true; } /* no more parents to check; lock is not covered */ return false; } /* * Check whether both the list of related predicate locks and the pointer to * a prior version of the row (if this is a tuple lock target) are empty for * a predicate lock target, and remove the target if they are. */ static void RemoveTargetIfNoLongerUsed(PREDICATELOCKTARGET *target, uint32 targettaghash) { PREDICATELOCKTARGET *rmtarget; PREDICATELOCKTARGET *next; Assert(LWLockHeldByMe(SerializablePredicateLockListLock)); /* Can't remove it until no locks at this target. */ if (!SHMQueueEmpty(&target->predicateLocks)) return; /* Can't remove it if there are locks for a prior row version. */ LWLockAcquire(PredicateLockNextRowLinkLock, LW_EXCLUSIVE); if (target->priorVersionOfRow != NULL) { LWLockRelease(PredicateLockNextRowLinkLock); return; } /* * We are going to release this target, This requires that we let the * next version of the row (if any) know that it's previous version is * done. * * It might be that the link was all that was keeping the other target * from cleanup, but we can't clean that up here -- LW locking is all * wrong for that. We'll pass the HTAB in the general cleanup function to * get rid of such "dead" targets. */ next = target->nextVersionOfRow; if (next != NULL) { next->priorVersionOfRow = NULL; if (SHMQueueEmpty(&next->predicateLocks)) PredXact->NeedTargetLinkCleanup = true; } LWLockRelease(PredicateLockNextRowLinkLock); /* Actually remove the target. */ rmtarget = hash_search_with_hash_value(PredicateLockTargetHash, &target->tag, targettaghash, HASH_REMOVE, NULL); Assert(rmtarget == target); } /* * Delete child target locks owned by this process. * This implementation is assuming that the usage of each target tag field * is uniform. No need to make this hard if we don't have to. * * We aren't acquiring lightweight locks for the predicate lock or lock * target structures associated with this transaction unless we're going * to modify them, because no other process is permitted to modify our * locks. */ static void DeleteChildTargetLocks(const PREDICATELOCKTARGETTAG *newtargettag) { SERIALIZABLEXACT *sxact; PREDICATELOCK *predlock; LWLockAcquire(SerializablePredicateLockListLock, LW_SHARED); sxact = (SERIALIZABLEXACT *) MySerializableXact; predlock = (PREDICATELOCK *) SHMQueueNext(&(sxact->predicateLocks), &(sxact->predicateLocks), offsetof(PREDICATELOCK, xactLink)); while (predlock) { SHM_QUEUE *predlocksxactlink; PREDICATELOCK *nextpredlock; PREDICATELOCKTAG oldlocktag; PREDICATELOCKTARGET *oldtarget; PREDICATELOCKTARGETTAG oldtargettag; predlocksxactlink = &(predlock->xactLink); nextpredlock = (PREDICATELOCK *) SHMQueueNext(&(sxact->predicateLocks), predlocksxactlink, offsetof(PREDICATELOCK, xactLink)); oldlocktag = predlock->tag; Assert(oldlocktag.myXact == sxact); oldtarget = oldlocktag.myTarget; oldtargettag = oldtarget->tag; if (TargetTagIsCoveredBy(oldtargettag, *newtargettag)) { uint32 oldtargettaghash; LWLockId partitionLock; PREDICATELOCK *rmpredlock; oldtargettaghash = PredicateLockTargetTagHashCode(&oldtargettag); partitionLock = PredicateLockHashPartitionLock(oldtargettaghash); LWLockAcquire(partitionLock, LW_EXCLUSIVE); SHMQueueDelete(predlocksxactlink); SHMQueueDelete(&(predlock->targetLink)); rmpredlock = hash_search_with_hash_value (PredicateLockHash, &oldlocktag, PredicateLockHashCodeFromTargetHashCode(&oldlocktag, oldtargettaghash), HASH_REMOVE, NULL); Assert(rmpredlock == predlock); RemoveTargetIfNoLongerUsed(oldtarget, oldtargettaghash); LWLockRelease(partitionLock); DecrementParentLocks(&oldtargettag); } predlock = nextpredlock; } LWLockRelease(SerializablePredicateLockListLock); } /* * Returns the promotion threshold for a given predicate lock * target. This is the number of descendant locks required to promote * to the specified tag. Note that the threshold includes non-direct * descendants, e.g. both tuples and pages for a relation lock. * * TODO SSI: We should do something more intelligent about what the * thresholds are, either making it proportional to the number of * tuples in a page & pages in a relation, or at least making it a * GUC. Currently the threshold is 3 for a page lock, and * max_pred_locks_per_transaction/2 for a relation lock, chosen * entirely arbitrarily (and without benchmarking). */ static int PredicateLockPromotionThreshold(const PREDICATELOCKTARGETTAG *tag) { switch (GET_PREDICATELOCKTARGETTAG_TYPE(*tag)) { case PREDLOCKTAG_RELATION: return max_predicate_locks_per_xact / 2; case PREDLOCKTAG_PAGE: return 3; case PREDLOCKTAG_TUPLE: /* * not reachable: nothing is finer-granularity than a tuple, so we * should never try to promote to it. */ Assert(false); return 0; } /* not reachable */ Assert(false); return 0; } /* * For all ancestors of a newly-acquired predicate lock, increment * their child count in the parent hash table. If any of them have * more descendants than their promotion threshold, acquire the * coarsest such lock. * * Returns true if a parent lock was acquired and false otherwise. */ static bool CheckAndPromotePredicateLockRequest(const PREDICATELOCKTARGETTAG *reqtag) { PREDICATELOCKTARGETTAG targettag, nexttag, promotiontag; LOCALPREDICATELOCK *parentlock; bool found, promote; promote = false; targettag = *reqtag; /* check parents iteratively */ while (GetParentPredicateLockTag(&targettag, &nexttag)) { targettag = nexttag; parentlock = (LOCALPREDICATELOCK *) hash_search(LocalPredicateLockHash, &targettag, HASH_ENTER, &found); if (!found) { parentlock->held = false; parentlock->childLocks = 1; } else parentlock->childLocks++; if (parentlock->childLocks >= PredicateLockPromotionThreshold(&targettag)) { /* * We should promote to this parent lock. Continue to check its * ancestors, however, both to get their child counts right and to * check whether we should just go ahead and promote to one of * them. */ promotiontag = targettag; promote = true; } } if (promote) { /* acquire coarsest ancestor eligible for promotion */ PredicateLockAcquire(&promotiontag); return true; } else return false; } /* * When releasing a lock, decrement the child count on all ancestor * locks. * * This is called only when releasing a lock via * DeleteChildTargetLocks (i.e. when a lock becomes redundant because * we've acquired its parent, possibly due to promotion) or when a new * MVCC write lock makes the predicate lock unnecessary. There's no * point in calling it when locks are released at transaction end, as * this information is no longer needed. */ static void DecrementParentLocks(const PREDICATELOCKTARGETTAG *targettag) { PREDICATELOCKTARGETTAG parenttag, nexttag; parenttag = *targettag; while (GetParentPredicateLockTag(&parenttag, &nexttag)) { uint32 targettaghash; LOCALPREDICATELOCK *parentlock, *rmlock; parenttag = nexttag; targettaghash = PredicateLockTargetTagHashCode(&parenttag); parentlock = (LOCALPREDICATELOCK *) hash_search_with_hash_value(LocalPredicateLockHash, &parenttag, targettaghash, HASH_FIND, NULL); /* * There's a small chance the parent lock doesn't exist in the lock * table. This can happen if we prematurely removed it because an * index split caused the child refcount to be off. */ if (parentlock == NULL) continue; parentlock->childLocks--; /* * Under similar circumstances the parent lock's refcount might be * zero. This only happens if we're holding that lock (otherwise we * would have removed the entry). */ if (parentlock->childLocks < 0) { Assert(parentlock->held); parentlock->childLocks = 0; } if ((parentlock->childLocks == 0) && (!parentlock->held)) { rmlock = (LOCALPREDICATELOCK *) hash_search_with_hash_value(LocalPredicateLockHash, &parenttag, targettaghash, HASH_REMOVE, NULL); Assert(rmlock == parentlock); } } } /* * Indicate that a predicate lock on the given target is held by the * specified transaction. Has no effect if the lock is already held. * * This updates the lock table and the sxact's lock list, and creates * the lock target if necessary, but does *not* do anything related to * granularity promotion or the local lock table. See * PredicateLockAcquire for that. */ static void CreatePredicateLock(const PREDICATELOCKTARGETTAG *targettag, uint32 targettaghash, SERIALIZABLEXACT *sxact) { PREDICATELOCKTARGET *target; PREDICATELOCKTAG locktag; PREDICATELOCK *lock; LWLockId partitionLock; bool found; partitionLock = PredicateLockHashPartitionLock(targettaghash); LWLockAcquire(SerializablePredicateLockListLock, LW_SHARED); LWLockAcquire(partitionLock, LW_EXCLUSIVE); /* Make sure that the target is represented. */ target = (PREDICATELOCKTARGET *) hash_search_with_hash_value(PredicateLockTargetHash, targettag, targettaghash, HASH_ENTER, &found); if (!target) ereport(ERROR, (errcode(ERRCODE_OUT_OF_MEMORY), errmsg("out of shared memory"), errhint("You might need to increase max_pred_locks_per_transaction."))); if (!found) { SHMQueueInit(&(target->predicateLocks)); target->priorVersionOfRow = NULL; target->nextVersionOfRow = NULL; } /* We've got the sxact and target, make sure they're joined. */ locktag.myTarget = target; locktag.myXact = sxact; lock = (PREDICATELOCK *) hash_search_with_hash_value(PredicateLockHash, &locktag, PredicateLockHashCodeFromTargetHashCode(&locktag, targettaghash), HASH_ENTER, &found); if (!lock) ereport(ERROR, (errcode(ERRCODE_OUT_OF_MEMORY), errmsg("out of shared memory"), errhint("You might need to increase max_pred_locks_per_transaction."))); if (!found) { SHMQueueInsertBefore(&(target->predicateLocks), &(lock->targetLink)); SHMQueueInsertBefore(&(sxact->predicateLocks), &(lock->xactLink)); lock->commitSeqNo = 0; } LWLockRelease(partitionLock); LWLockRelease(SerializablePredicateLockListLock); } /* * Acquire a predicate lock on the specified target for the current * connection if not already held. This updates the local lock table * and uses it to implement granularity promotion. It will consolidate * multiple locks into a coarser lock if warranted, and will release * any finer-grained locks covered by the new one. */ static void PredicateLockAcquire(const PREDICATELOCKTARGETTAG *targettag) { uint32 targettaghash; bool found; LOCALPREDICATELOCK *locallock; /* Do we have the lock already, or a covering lock? */ if (PredicateLockExists(targettag)) return; if (CoarserLockCovers(targettag)) return; /* the same hash and LW lock apply to the lock target and the local lock. */ targettaghash = PredicateLockTargetTagHashCode(targettag); /* Acquire lock in local table */ locallock = (LOCALPREDICATELOCK *) hash_search_with_hash_value(LocalPredicateLockHash, targettag, targettaghash, HASH_ENTER, &found); /* We should not hold the lock (but its entry might still exist) */ Assert(!found || !locallock->held); locallock->held = true; if (!found) locallock->childLocks = 0; /* Actually create the lock */ CreatePredicateLock(targettag, targettaghash, (SERIALIZABLEXACT *) MySerializableXact); /* * Lock has been acquired. Check whether it should be promoted to a * coarser granularity, or whether there are finer-granularity locks to * clean up. */ if (CheckAndPromotePredicateLockRequest(targettag)) { /* * Lock request was promoted to a coarser-granularity lock, and that * lock was acquired. It will delete this lock and any of its * children, so we're done. */ } else { /* Clean up any finer-granularity locks */ if (GET_PREDICATELOCKTARGETTAG_TYPE(*targettag) != PREDLOCKTAG_TUPLE) DeleteChildTargetLocks(targettag); } } /* * PredicateLockRelation * * Gets a predicate lock at the relation level. * Skip if not in full serializable transaction isolation level. * Skip if this is a temporary table. * Clear any finer-grained predicate locks this session has on the relation. */ void PredicateLockRelation(const Relation relation) { PREDICATELOCKTARGETTAG tag; if (SkipSerialization(relation)) return; SET_PREDICATELOCKTARGETTAG_RELATION(tag, relation->rd_node.dbNode, relation->rd_id); PredicateLockAcquire(&tag); } /* * PredicateLockPage * * Gets a predicate lock at the page level. * Skip if not in full serializable transaction isolation level. * Skip if this is a temporary table. * Skip if a coarser predicate lock already covers this page. * Clear any finer-grained predicate locks this session has on the relation. */ void PredicateLockPage(const Relation relation, const BlockNumber blkno) { PREDICATELOCKTARGETTAG tag; if (SkipSerialization(relation)) return; SET_PREDICATELOCKTARGETTAG_PAGE(tag, relation->rd_node.dbNode, relation->rd_id, blkno); PredicateLockAcquire(&tag); } /* * PredicateLockTuple * * Gets a predicate lock at the tuple level. * Skip if not in full serializable transaction isolation level. * Skip if this is a temporary table. */ void PredicateLockTuple(const Relation relation, const HeapTuple tuple) { PREDICATELOCKTARGETTAG tag; ItemPointer tid; if (SkipSerialization(relation)) return; /* * If it's a heap tuple, return if this xact wrote it. */ if (relation->rd_index == NULL) { TransactionId myxid = GetTopTransactionIdIfAny(); if (TransactionIdIsValid(myxid)) { TransactionId xid = HeapTupleHeaderGetXmin(tuple->t_data); if (TransactionIdFollowsOrEquals(xid, TransactionXmin)) { xid = SubTransGetTopmostTransaction(xid); if (TransactionIdEquals(xid, myxid)) { /* We wrote it; we already have a write lock. */ return; } } } } /* * Do quick-but-not-definitive test for a relation lock first. This will * never cause a return when the relation is *not* locked, but will * occasionally let the check continue when there really *is* a relation * level lock. */ SET_PREDICATELOCKTARGETTAG_RELATION(tag, relation->rd_node.dbNode, relation->rd_id); if (PredicateLockExists(&tag)) return; tid = &(tuple->t_self); SET_PREDICATELOCKTARGETTAG_TUPLE(tag, relation->rd_node.dbNode, relation->rd_id, ItemPointerGetBlockNumber(tid), ItemPointerGetOffsetNumber(tid)); PredicateLockAcquire(&tag); } /* * If the old tuple has any predicate locks, create a lock target for the * new tuple and point them at each other. Conflict detection needs to * look for locks against prior versions of the row. */ void PredicateLockTupleRowVersionLink(const Relation relation, const HeapTuple oldTuple, const HeapTuple newTuple) { PREDICATELOCKTARGETTAG oldtargettag; PREDICATELOCKTARGETTAG newtargettag; PREDICATELOCKTARGET *oldtarget; PREDICATELOCKTARGET *newtarget; PREDICATELOCKTARGET *next; uint32 oldtargettaghash; LWLockId oldpartitionLock; uint32 newtargettaghash; LWLockId newpartitionLock; bool found; SET_PREDICATELOCKTARGETTAG_TUPLE(oldtargettag, relation->rd_node.dbNode, relation->rd_id, ItemPointerGetBlockNumber(&(oldTuple->t_self)), ItemPointerGetOffsetNumber(&(oldTuple->t_self))); oldtargettaghash = PredicateLockTargetTagHashCode(&oldtargettag); oldpartitionLock = PredicateLockHashPartitionLock(oldtargettaghash); SET_PREDICATELOCKTARGETTAG_TUPLE(newtargettag, relation->rd_node.dbNode, relation->rd_id, ItemPointerGetBlockNumber(&(newTuple->t_self)), ItemPointerGetOffsetNumber(&(newTuple->t_self))); newtargettaghash = PredicateLockTargetTagHashCode(&newtargettag); newpartitionLock = PredicateLockHashPartitionLock(newtargettaghash); /* Lock lower numbered partition first. */ if (oldpartitionLock < newpartitionLock) { LWLockAcquire(oldpartitionLock, LW_SHARED); LWLockAcquire(newpartitionLock, LW_EXCLUSIVE); } else if (newpartitionLock < oldpartitionLock) { LWLockAcquire(newpartitionLock, LW_EXCLUSIVE); LWLockAcquire(oldpartitionLock, LW_SHARED); } else LWLockAcquire(newpartitionLock, LW_EXCLUSIVE); oldtarget = (PREDICATELOCKTARGET *) hash_search_with_hash_value(PredicateLockTargetHash, &oldtargettag, oldtargettaghash, HASH_FIND, NULL); /* Only need to link if there is an old target already. */ if (oldtarget) { LWLockAcquire(PredicateLockNextRowLinkLock, LW_EXCLUSIVE); /* Guard against stale pointers from rollback. */ next = oldtarget->nextVersionOfRow; if (next != NULL) { next->priorVersionOfRow = NULL; oldtarget->nextVersionOfRow = NULL; } /* Find or create the new target, and link old and new. */ newtarget = (PREDICATELOCKTARGET *) hash_search_with_hash_value(PredicateLockTargetHash, &newtargettag, newtargettaghash, HASH_ENTER, &found); if (!newtarget) ereport(ERROR, (errcode(ERRCODE_OUT_OF_MEMORY), errmsg("out of shared memory"), errhint("You might need to increase max_pred_locks_per_transaction."))); if (!found) { SHMQueueInit(&(newtarget->predicateLocks)); newtarget->nextVersionOfRow = NULL; } else Assert(newtarget->priorVersionOfRow == NULL); newtarget->priorVersionOfRow = oldtarget; oldtarget->nextVersionOfRow = newtarget; LWLockRelease(PredicateLockNextRowLinkLock); } /* Release lower number partition last. */ if (oldpartitionLock < newpartitionLock) { LWLockRelease(newpartitionLock); LWLockRelease(oldpartitionLock); } else if (newpartitionLock < oldpartitionLock) { LWLockRelease(oldpartitionLock); LWLockRelease(newpartitionLock); } else LWLockRelease(newpartitionLock); } /* * DeleteLockTarget * * Remove a predicate lock target along with any locks held for it. * * Caller must hold SerializablePredicateLockListLock and the * appropriate hash partition lock for the target. */ static void DeleteLockTarget(PREDICATELOCKTARGET *target, uint32 targettaghash) { PREDICATELOCK *predlock; SHM_QUEUE *predlocktargetlink; PREDICATELOCK *nextpredlock; bool found; Assert(LWLockHeldByMe(SerializablePredicateLockListLock)); Assert(LWLockHeldByMe(PredicateLockHashPartitionLock(targettaghash))); predlock = (PREDICATELOCK *) SHMQueueNext(&(target->predicateLocks), &(target->predicateLocks), offsetof(PREDICATELOCK, targetLink)); LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE); while (predlock) { predlocktargetlink = &(predlock->targetLink); nextpredlock = (PREDICATELOCK *) SHMQueueNext(&(target->predicateLocks), predlocktargetlink, offsetof(PREDICATELOCK, targetLink)); SHMQueueDelete(&(predlock->xactLink)); SHMQueueDelete(&(predlock->targetLink)); hash_search_with_hash_value (PredicateLockHash, &predlock->tag, PredicateLockHashCodeFromTargetHashCode(&predlock->tag, targettaghash), HASH_REMOVE, &found); Assert(found); predlock = nextpredlock; } LWLockRelease(SerializableXactHashLock); /* Remove the target itself, if possible. */ RemoveTargetIfNoLongerUsed(target, targettaghash); } /* * TransferPredicateLocksToNewTarget * * Move or copy all the predicate locks for a lock target, for use by * index page splits/combines and other things that create or replace * lock targets. If 'removeOld' is true, the old locks and the target * will be removed. * * Returns true on success, or false if we ran out of shared memory to * allocate the new target or locks. Guaranteed to always succeed if * removeOld is set (by using the reserved entry in * PredicateLockTargetHash for scratch space). * * Caller must hold SerializablePredicateLockListLock. */ static bool TransferPredicateLocksToNewTarget(const PREDICATELOCKTARGETTAG oldtargettag, const PREDICATELOCKTARGETTAG newtargettag, bool removeOld) { uint32 oldtargettaghash; LWLockId oldpartitionLock; PREDICATELOCKTARGET *oldtarget; uint32 newtargettaghash; LWLockId newpartitionLock; bool found; bool outOfShmem = false; uint32 reservedtargettaghash; LWLockId reservedpartitionLock; Assert(LWLockHeldByMe(SerializablePredicateLockListLock)); oldtargettaghash = PredicateLockTargetTagHashCode(&oldtargettag); newtargettaghash = PredicateLockTargetTagHashCode(&newtargettag); oldpartitionLock = PredicateLockHashPartitionLock(oldtargettaghash); newpartitionLock = PredicateLockHashPartitionLock(newtargettaghash); reservedtargettaghash = 0; /* Quiet compiler warnings. */ reservedpartitionLock = 0; /* Quiet compiler warnings. */ if (removeOld) { /* * Remove the reserved entry to give us scratch space, so we know * we'll be able to create the new lock target. */ reservedtargettaghash = PredicateLockTargetTagHashCode(&ReservedTargetTag); reservedpartitionLock = PredicateLockHashPartitionLock(reservedtargettaghash); LWLockAcquire(reservedpartitionLock, LW_EXCLUSIVE); hash_search_with_hash_value(PredicateLockTargetHash, &ReservedTargetTag, reservedtargettaghash, HASH_REMOVE, &found); Assert(found); LWLockRelease(reservedpartitionLock); } /* * We must get the partition locks in ascending sequence to avoid * deadlocks. If old and new partitions are the same, we must request the * lock only once. */ if (oldpartitionLock < newpartitionLock) { LWLockAcquire(oldpartitionLock, (removeOld ? LW_EXCLUSIVE : LW_SHARED)); LWLockAcquire(newpartitionLock, LW_EXCLUSIVE); } else if (oldpartitionLock > newpartitionLock) { LWLockAcquire(newpartitionLock, LW_EXCLUSIVE); LWLockAcquire(oldpartitionLock, (removeOld ? LW_EXCLUSIVE : LW_SHARED)); } else LWLockAcquire(newpartitionLock, LW_EXCLUSIVE); /* * Look for the old target. If not found, that's OK; no predicate locks * are affected, so we can just clean up and return. If it does exist, * walk its list of predicate locks and move or copy them to the new * target. */ oldtarget = hash_search_with_hash_value(PredicateLockTargetHash, &oldtargettag, oldtargettaghash, HASH_FIND, NULL); if (oldtarget) { PREDICATELOCKTARGET *newtarget; PREDICATELOCK *oldpredlock; PREDICATELOCKTAG newpredlocktag; newtarget = hash_search_with_hash_value(PredicateLockTargetHash, &newtargettag, newtargettaghash, HASH_ENTER_NULL, &found); if (!newtarget) { /* Failed to allocate due to insufficient shmem */ outOfShmem = true; goto exit; } /* If we created a new entry, initialize it */ if (!found) { SHMQueueInit(&(newtarget->predicateLocks)); newtarget->priorVersionOfRow = NULL; newtarget->nextVersionOfRow = NULL; } newpredlocktag.myTarget = newtarget; oldpredlock = (PREDICATELOCK *) SHMQueueNext(&(oldtarget->predicateLocks), &(oldtarget->predicateLocks), offsetof(PREDICATELOCK, targetLink)); LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE); while (oldpredlock) { SHM_QUEUE *predlocktargetlink; PREDICATELOCK *nextpredlock; PREDICATELOCK *newpredlock; predlocktargetlink = &(oldpredlock->targetLink); nextpredlock = (PREDICATELOCK *) SHMQueueNext(&(oldtarget->predicateLocks), predlocktargetlink, offsetof(PREDICATELOCK, targetLink)); newpredlocktag.myXact = oldpredlock->tag.myXact; if (removeOld) { SHMQueueDelete(&(oldpredlock->xactLink)); SHMQueueDelete(&(oldpredlock->targetLink)); hash_search_with_hash_value (PredicateLockHash, &oldpredlock->tag, PredicateLockHashCodeFromTargetHashCode(&oldpredlock->tag, oldtargettaghash), HASH_REMOVE, &found); Assert(found); } newpredlock = (PREDICATELOCK *) hash_search_with_hash_value (PredicateLockHash, &newpredlocktag, PredicateLockHashCodeFromTargetHashCode(&newpredlocktag, newtargettaghash), HASH_ENTER_NULL, &found); if (!newpredlock) { /* Out of shared memory. Undo what we've done so far. */ LWLockRelease(SerializableXactHashLock); DeleteLockTarget(newtarget, newtargettaghash); outOfShmem = true; goto exit; } if (!found) { SHMQueueInsertBefore(&(newtarget->predicateLocks), &(newpredlock->targetLink)); SHMQueueInsertBefore(&(newpredlocktag.myXact->predicateLocks), &(newpredlock->xactLink)); newpredlock->commitSeqNo = InvalidSerCommitSeqNo; } oldpredlock = nextpredlock; } LWLockRelease(SerializableXactHashLock); if (removeOld) { Assert(SHMQueueEmpty(&oldtarget->predicateLocks)); RemoveTargetIfNoLongerUsed(oldtarget, oldtargettaghash); } } exit: /* Release partition locks in reverse order of acquisition. */ if (oldpartitionLock < newpartitionLock) { LWLockRelease(newpartitionLock); LWLockRelease(oldpartitionLock); } else if (oldpartitionLock > newpartitionLock) { LWLockRelease(oldpartitionLock); LWLockRelease(newpartitionLock); } else LWLockRelease(newpartitionLock); if (removeOld) { /* We shouldn't run out of memory if we're moving locks */ Assert(!outOfShmem); /* Put the reserved entry back */ LWLockAcquire(reservedpartitionLock, LW_EXCLUSIVE); hash_search_with_hash_value(PredicateLockTargetHash, &ReservedTargetTag, reservedtargettaghash, HASH_ENTER, &found); Assert(!found); LWLockRelease(reservedpartitionLock); } return !outOfShmem; } /* * PredicateLockPageSplit * * Copies any predicate locks for the old page to the new page. * Skip if this is a temporary table or toast table. * * NOTE: A page split (or overflow) affects all serializable transactions, * even if it occurs in the context of another transaction isolation level. * * NOTE: This currently leaves the local copy of the locks without * information on the new lock which is in shared memory. This could cause * problems if enough page splits occur on locked pages without the processes * which hold the locks getting in and noticing. */ void PredicateLockPageSplit(const Relation relation, const BlockNumber oldblkno, const BlockNumber newblkno) { PREDICATELOCKTARGETTAG oldtargettag; PREDICATELOCKTARGETTAG newtargettag; bool success; if (SkipSplitTracking(relation)) return; Assert(oldblkno != newblkno); Assert(BlockNumberIsValid(oldblkno)); Assert(BlockNumberIsValid(newblkno)); SET_PREDICATELOCKTARGETTAG_PAGE(oldtargettag, relation->rd_node.dbNode, relation->rd_id, oldblkno); SET_PREDICATELOCKTARGETTAG_PAGE(newtargettag, relation->rd_node.dbNode, relation->rd_id, newblkno); LWLockAcquire(SerializablePredicateLockListLock, LW_EXCLUSIVE); /* * Try copying the locks over to the new page's tag, creating it if * necessary. */ success = TransferPredicateLocksToNewTarget(oldtargettag, newtargettag, false); if (!success) { /* * No more predicate lock entries are available. Failure isn't an * option here, so promote the page lock to a relation lock. */ /* Get the parent relation lock's lock tag */ success = GetParentPredicateLockTag(&oldtargettag, &newtargettag); Assert(success); /* Move the locks to the parent. This shouldn't fail. */ success = TransferPredicateLocksToNewTarget(oldtargettag, newtargettag, true); Assert(success); } LWLockRelease(SerializablePredicateLockListLock); } /* * PredicateLockPageCombine * * Combines predicate locks for two existing pages. * Skip if this is a temporary table or toast table. * * NOTE: A page combine affects all serializable transactions, even if it * occurs in the context of another transaction isolation level. */ void PredicateLockPageCombine(const Relation relation, const BlockNumber oldblkno, const BlockNumber newblkno) { PREDICATELOCKTARGETTAG oldtargettag; PREDICATELOCKTARGETTAG newtargettag; bool success; if (SkipSplitTracking(relation)) return; Assert(oldblkno != newblkno); Assert(BlockNumberIsValid(oldblkno)); Assert(BlockNumberIsValid(newblkno)); SET_PREDICATELOCKTARGETTAG_PAGE(oldtargettag, relation->rd_node.dbNode, relation->rd_id, oldblkno); SET_PREDICATELOCKTARGETTAG_PAGE(newtargettag, relation->rd_node.dbNode, relation->rd_id, newblkno); LWLockAcquire(SerializablePredicateLockListLock, LW_EXCLUSIVE); /* Move the locks. This shouldn't fail. */ success = TransferPredicateLocksToNewTarget(oldtargettag, newtargettag, true); Assert(success); LWLockRelease(SerializablePredicateLockListLock); } /* * Walk the hash table and find the new xmin. */ static void SetNewSxactGlobalXmin(void) { SERIALIZABLEXACT *sxact; Assert(LWLockHeldByMe(SerializableXactHashLock)); PredXact->SxactGlobalXmin = InvalidTransactionId; PredXact->SxactGlobalXminCount = 0; for (sxact = FirstPredXact(); sxact != NULL; sxact = NextPredXact(sxact)) { if (!SxactIsRolledBack(sxact) && !SxactIsCommitted(sxact) && sxact != OldCommittedSxact) { Assert(sxact->xmin != InvalidTransactionId); if (!TransactionIdIsValid(PredXact->SxactGlobalXmin) || TransactionIdPrecedes(sxact->xmin, PredXact->SxactGlobalXmin)) { PredXact->SxactGlobalXmin = sxact->xmin; PredXact->SxactGlobalXminCount = 1; } else if (TransactionIdEquals(sxact->xmin, PredXact->SxactGlobalXmin)) PredXact->SxactGlobalXminCount++; } } OldSerXidSetActiveSerXmin(PredXact->SxactGlobalXmin); } /* * ReleasePredicateLocks * * Releases predicate locks based on completion of the current transaction, * whether committed or rolled back. It can also be called for a read only * transaction when it becomes impossible for the transaction to become * part of a dangerous structure. * * We do nothing unless this is a serializable transaction. * * This method must ensure that shared memory hash tables are cleaned * up in some relatively timely fashion. * * If this transaction is committing and is holding any predicate locks, * it must be added to a list of completed serializable transaction still * holding locks. */ void ReleasePredicateLocks(const bool isCommit) { bool needToClear; RWConflict conflict, nextConflict, possibleUnsafeConflict; SERIALIZABLEXACT *roXact; /* * We can't trust XactReadOnly here, because a transaction which started * as READ WRITE can show as READ ONLY later, e.g., within * substransactions. We want to flag a transaction as READ ONLY if it * commits without writing so that de facto READ ONLY transactions get the * benefit of some RO optimizations, so we will use this local variable to * get some cleanup logic right which is based on whether the transaction * was declared READ ONLY at the top level. */ bool topLevelIsDeclaredReadOnly; if (MySerializableXact == InvalidSerializableXact) { Assert(LocalPredicateLockHash == NULL); return; } Assert(!isCommit || SxactIsPrepared(MySerializableXact)); Assert(!SxactIsRolledBack(MySerializableXact)); Assert(!SxactIsCommitted(MySerializableXact)); /* may not be serializable during COMMIT/ROLLBACK PREPARED */ if (MySerializableXact->pid != 0) Assert(IsolationIsSerializable()); /* We'd better not already be on the cleanup list. */ Assert(!SxactIsOnFinishedList((SERIALIZABLEXACT *) MySerializableXact)); topLevelIsDeclaredReadOnly = SxactIsReadOnly(MySerializableXact); LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE); /* * We don't hold a lock here, assuming that TransactionId is atomic! * * If this value is changing, we don't care that much whether we get the * old or new value -- it is just used to determine how far * GlobalSerizableXmin must advance before this transaction can be cleaned * fully cleaned up. The worst that could happen is we wait for ome more * transaction to complete before freeing some RAM; correctness of visible * behavior is not affected. */ MySerializableXact->finishedBefore = ShmemVariableCache->nextXid; /* * If it's not a commit it's a rollback, and we can clear our locks * immediately. */ if (isCommit) { MySerializableXact->flags |= SXACT_FLAG_COMMITTED; MySerializableXact->commitSeqNo = ++(PredXact->LastSxactCommitSeqNo); /* Recognize implicit read-only transaction (commit without write). */ if (!(MySerializableXact->flags & SXACT_FLAG_DID_WRITE)) MySerializableXact->flags |= SXACT_FLAG_READ_ONLY; } else { MySerializableXact->flags |= SXACT_FLAG_ROLLED_BACK; } if (!topLevelIsDeclaredReadOnly) { Assert(PredXact->WritableSxactCount > 0); if (--(PredXact->WritableSxactCount) == 0) { /* * Release predicate locks and rw-conflicts in for all committed * transactions. There are no longer any transactions which might * conflict with the locks and no chance for new transactions to * overlap. Similarly, existing conflicts in can't cause pivots, * and any conflicts in which could have completed a dangerous * structure would already have caused a rollback, so any * remaining ones must be benign. */ PredXact->CanPartialClearThrough = PredXact->LastSxactCommitSeqNo; } } else { /* * Read-only transactions: clear the list of transactions that might * make us unsafe. Note that we use 'inLink' for the iteration as * opposed to 'outLink' for the r/w xacts. */ possibleUnsafeConflict = (RWConflict) SHMQueueNext((SHM_QUEUE *) &MySerializableXact->possibleUnsafeConflicts, (SHM_QUEUE *) &MySerializableXact->possibleUnsafeConflicts, offsetof(RWConflictData, inLink)); while (possibleUnsafeConflict) { nextConflict = (RWConflict) SHMQueueNext((SHM_QUEUE *) &MySerializableXact->possibleUnsafeConflicts, &possibleUnsafeConflict->inLink, offsetof(RWConflictData, inLink)); Assert(!SxactIsReadOnly(possibleUnsafeConflict->sxactOut)); Assert(MySerializableXact == possibleUnsafeConflict->sxactIn); ReleaseRWConflict(possibleUnsafeConflict); possibleUnsafeConflict = nextConflict; } } /* Check for conflict out to old committed transactions. */ if (isCommit && !SxactIsReadOnly(MySerializableXact) && SxactHasSummaryConflictOut(MySerializableXact)) { MySerializableXact->SeqNo.earliestOutConflictCommit = FirstNormalSerCommitSeqNo; MySerializableXact->flags |= SXACT_FLAG_CONFLICT_OUT; } /* * Release all outConflicts to committed transactions. If we're rolling * back clear them all. Set SXACT_FLAG_CONFLICT_OUT if any point to * previously committed transactions. */ conflict = (RWConflict) SHMQueueNext((SHM_QUEUE *) &MySerializableXact->outConflicts, (SHM_QUEUE *) &MySerializableXact->outConflicts, offsetof(RWConflictData, outLink)); while (conflict) { nextConflict = (RWConflict) SHMQueueNext((SHM_QUEUE *) &MySerializableXact->outConflicts, &conflict->outLink, offsetof(RWConflictData, outLink)); if (isCommit && !SxactIsReadOnly(MySerializableXact) && SxactIsCommitted(conflict->sxactIn)) { if ((MySerializableXact->flags & SXACT_FLAG_CONFLICT_OUT) == 0 || conflict->sxactIn->commitSeqNo < MySerializableXact->SeqNo.earliestOutConflictCommit) MySerializableXact->SeqNo.earliestOutConflictCommit = conflict->sxactIn->commitSeqNo; MySerializableXact->flags |= SXACT_FLAG_CONFLICT_OUT; } if (!isCommit || SxactIsCommitted(conflict->sxactIn) || (conflict->sxactIn->SeqNo.lastCommitBeforeSnapshot >= PredXact->LastSxactCommitSeqNo)) ReleaseRWConflict(conflict); conflict = nextConflict; } /* * Release all inConflicts from committed and read-only transactions. If * we're rolling back, clear them all. */ conflict = (RWConflict) SHMQueueNext((SHM_QUEUE *) &MySerializableXact->inConflicts, (SHM_QUEUE *) &MySerializableXact->inConflicts, offsetof(RWConflictData, inLink)); while (conflict) { nextConflict = (RWConflict) SHMQueueNext((SHM_QUEUE *) &MySerializableXact->inConflicts, &conflict->inLink, offsetof(RWConflictData, inLink)); if (!isCommit || SxactIsCommitted(conflict->sxactOut) || SxactIsReadOnly(conflict->sxactOut)) ReleaseRWConflict(conflict); conflict = nextConflict; } if (!topLevelIsDeclaredReadOnly) { /* * Remove ourselves from the list of possible conflicts for concurrent * READ ONLY transactions, flagging them as unsafe if we have a * conflict out. If any are waiting DEFERRABLE transactions, wake them * up if they are known safe or known unsafe. */ possibleUnsafeConflict = (RWConflict) SHMQueueNext((SHM_QUEUE *) &MySerializableXact->possibleUnsafeConflicts, (SHM_QUEUE *) &MySerializableXact->possibleUnsafeConflicts, offsetof(RWConflictData, outLink)); while (possibleUnsafeConflict) { nextConflict = (RWConflict) SHMQueueNext((SHM_QUEUE *) &MySerializableXact->possibleUnsafeConflicts, &possibleUnsafeConflict->outLink, offsetof(RWConflictData, outLink)); roXact = possibleUnsafeConflict->sxactIn; Assert(MySerializableXact == possibleUnsafeConflict->sxactOut); Assert(SxactIsReadOnly(roXact)); /* Mark conflicted if necessary. */ if (isCommit && (MySerializableXact->flags & SXACT_FLAG_DID_WRITE) && SxactHasConflictOut(MySerializableXact) && (MySerializableXact->SeqNo.earliestOutConflictCommit <= roXact->SeqNo.lastCommitBeforeSnapshot)) { /* * This releases possibleUnsafeConflict (as well as all other * possible conflicts for roXact) */ FlagSxactUnsafe(roXact); } else { ReleaseRWConflict(possibleUnsafeConflict); /* * If we were the last possible conflict, flag it safe. The * transaction can now safely release its predicate locks (but * that transaction's backend has to do that itself). */ if (SHMQueueEmpty(&roXact->possibleUnsafeConflicts)) roXact->flags |= SXACT_FLAG_RO_SAFE; } /* * Wake up the process for a waiting DEFERRABLE transaction if we * now know it's either safe or conflicted. */ if (SxactIsDeferrableWaiting(roXact) && (SxactIsROUnsafe(roXact) || SxactIsROSafe(roXact))) ProcSendSignal(roXact->pid); possibleUnsafeConflict = nextConflict; } } /* * Check whether it's time to clean up old transactions. This can only be * done when the last serializable transaction with the oldest xmin among * serializable transactions completes. We then find the "new oldest" * xmin and purge any transactions which finished before this transaction * was launched. */ needToClear = false; if (TransactionIdEquals(MySerializableXact->xmin, PredXact->SxactGlobalXmin)) { Assert(PredXact->SxactGlobalXminCount > 0); if (--(PredXact->SxactGlobalXminCount) == 0) { SetNewSxactGlobalXmin(); needToClear = true; } } LWLockRelease(SerializableXactHashLock); LWLockAcquire(SerializableFinishedListLock, LW_EXCLUSIVE); /* Add this to the list of transactions to check for later cleanup. */ if (isCommit) SHMQueueInsertBefore(FinishedSerializableTransactions, (SHM_QUEUE *) &(MySerializableXact->finishedLink)); if (!isCommit) ReleaseOneSerializableXact((SERIALIZABLEXACT *) MySerializableXact, false, false); LWLockRelease(SerializableFinishedListLock); if (needToClear) ClearOldPredicateLocks(); MySerializableXact = InvalidSerializableXact; /* Delete per-transaction lock table */ if (LocalPredicateLockHash != NULL) { hash_destroy(LocalPredicateLockHash); LocalPredicateLockHash = NULL; } } /* * ReleasePredicateLocksIfROSafe * Check if the current transaction is read only and operating on * a safe snapshot. If so, release predicate locks and return * true. * * A transaction is flagged as RO_SAFE if all concurrent R/W * transactions commit without having conflicts out to an earlier * snapshot, thus ensuring that no conflicts are possible for this * transaction. Thus, we call this function as part of the * SkipSerialization check on all public interface methods. */ static bool ReleasePredicateLocksIfROSafe(void) { if (SxactIsROSafe(MySerializableXact)) { ReleasePredicateLocks(false); return true; } else return false; } /* * Clear old predicate locks. */ static void ClearOldPredicateLocks(void) { SERIALIZABLEXACT *finishedSxact; PREDICATELOCK *predlock; int i; HASH_SEQ_STATUS seqstat; PREDICATELOCKTARGET *locktarget; LWLockAcquire(SerializableFinishedListLock, LW_EXCLUSIVE); finishedSxact = (SERIALIZABLEXACT *) SHMQueueNext(FinishedSerializableTransactions, FinishedSerializableTransactions, offsetof(SERIALIZABLEXACT, finishedLink)); LWLockAcquire(SerializableXactHashLock, LW_SHARED); while (finishedSxact) { SERIALIZABLEXACT *nextSxact; nextSxact = (SERIALIZABLEXACT *) SHMQueueNext(FinishedSerializableTransactions, &(finishedSxact->finishedLink), offsetof(SERIALIZABLEXACT, finishedLink)); if (!TransactionIdIsValid(PredXact->SxactGlobalXmin) || TransactionIdPrecedesOrEquals(finishedSxact->finishedBefore, PredXact->SxactGlobalXmin)) { LWLockRelease(SerializableXactHashLock); SHMQueueDelete(&(finishedSxact->finishedLink)); ReleaseOneSerializableXact(finishedSxact, false, false); LWLockAcquire(SerializableXactHashLock, LW_SHARED); } else if (finishedSxact->commitSeqNo > PredXact->HavePartialClearedThrough && finishedSxact->commitSeqNo <= PredXact->CanPartialClearThrough) { LWLockRelease(SerializableXactHashLock); ReleaseOneSerializableXact(finishedSxact, !SxactIsReadOnly(finishedSxact), false); PredXact->HavePartialClearedThrough = finishedSxact->commitSeqNo; LWLockAcquire(SerializableXactHashLock, LW_SHARED); } else break; finishedSxact = nextSxact; } LWLockRelease(SerializableXactHashLock); /* * Loop through predicate locks on dummy transaction for summarized data. */ predlock = (PREDICATELOCK *) SHMQueueNext(&OldCommittedSxact->predicateLocks, &OldCommittedSxact->predicateLocks, offsetof(PREDICATELOCK, xactLink)); LWLockAcquire(SerializablePredicateLockListLock, LW_SHARED); while (predlock) { PREDICATELOCK *nextpredlock; bool canDoPartialCleanup; nextpredlock = (PREDICATELOCK *) SHMQueueNext(&OldCommittedSxact->predicateLocks, &predlock->xactLink, offsetof(PREDICATELOCK, xactLink)); LWLockAcquire(SerializableXactHashLock, LW_SHARED); canDoPartialCleanup = (predlock->commitSeqNo <= PredXact->CanPartialClearThrough); LWLockRelease(SerializableXactHashLock); if (canDoPartialCleanup) { PREDICATELOCKTAG tag; SHM_QUEUE *targetLink; PREDICATELOCKTARGET *target; PREDICATELOCKTARGETTAG targettag; uint32 targettaghash; LWLockId partitionLock; tag = predlock->tag; targetLink = &(predlock->targetLink); target = tag.myTarget; targettag = target->tag; targettaghash = PredicateLockTargetTagHashCode(&targettag); partitionLock = PredicateLockHashPartitionLock(targettaghash); LWLockAcquire(partitionLock, LW_EXCLUSIVE); SHMQueueDelete(targetLink); SHMQueueDelete(&(predlock->xactLink)); hash_search_with_hash_value(PredicateLockHash, &tag, PredicateLockHashCodeFromTargetHashCode(&tag, targettaghash), HASH_REMOVE, NULL); RemoveTargetIfNoLongerUsed(target, targettaghash); LWLockRelease(partitionLock); } predlock = nextpredlock; } LWLockRelease(SerializablePredicateLockListLock); LWLockRelease(SerializableFinishedListLock); if (!PredXact->NeedTargetLinkCleanup) return; /* * Clean up any targets which were disconnected from a prior version with * no predicate locks attached. */ for (i = 0; i < NUM_PREDICATELOCK_PARTITIONS; i++) LWLockAcquire(FirstPredicateLockMgrLock + i, LW_EXCLUSIVE); LWLockAcquire(PredicateLockNextRowLinkLock, LW_SHARED); hash_seq_init(&seqstat, PredicateLockTargetHash); while ((locktarget = (PREDICATELOCKTARGET *) hash_seq_search(&seqstat))) { if (SHMQueueEmpty(&locktarget->predicateLocks) && locktarget->priorVersionOfRow == NULL && locktarget->nextVersionOfRow == NULL) { hash_search(PredicateLockTargetHash, &locktarget->tag, HASH_REMOVE, NULL); } } PredXact->NeedTargetLinkCleanup = false; LWLockRelease(PredicateLockNextRowLinkLock); for (i = NUM_PREDICATELOCK_PARTITIONS - 1; i >= 0; i--) LWLockRelease(FirstPredicateLockMgrLock + i); } /* * This is the normal way to delete anything from any of the predicate * locking hash tables. Given a transaction which we know can be deleted: * delete all predicate locks held by that transaction and any predicate * lock targets which are now unreferenced by a lock; delete all conflicts * for the transaction; delete all xid values for the transaction; then * delete the transaction. * * When the partial flag is set, we can release all predicate locks and * out-conflict information -- we've established that there are no longer * any overlapping read write transactions for which this transaction could * matter. * * When the summarize flag is set, we've run short of room for sxact data * and must summarize to the SLRU. Predicate locks are transferred to a * dummy "old" transaction, with duplicate locks on a single target * collapsing to a single lock with the "latest" commitSeqNo from among * the conflicting locks.. */ static void ReleaseOneSerializableXact(SERIALIZABLEXACT *sxact, bool partial, bool summarize) { PREDICATELOCK *predlock; SERIALIZABLEXIDTAG sxidtag; RWConflict conflict, nextConflict; Assert(sxact != NULL); Assert(SxactIsRolledBack(sxact) || SxactIsCommitted(sxact)); Assert(LWLockHeldByMe(SerializableFinishedListLock)); LWLockAcquire(SerializablePredicateLockListLock, LW_SHARED); predlock = (PREDICATELOCK *) SHMQueueNext(&(sxact->predicateLocks), &(sxact->predicateLocks), offsetof(PREDICATELOCK, xactLink)); while (predlock) { PREDICATELOCK *nextpredlock; PREDICATELOCKTAG tag; SHM_QUEUE *targetLink; PREDICATELOCKTARGET *target; PREDICATELOCKTARGETTAG targettag; uint32 targettaghash; LWLockId partitionLock; nextpredlock = (PREDICATELOCK *) SHMQueueNext(&(sxact->predicateLocks), &(predlock->xactLink), offsetof(PREDICATELOCK, xactLink)); tag = predlock->tag; targetLink = &(predlock->targetLink); target = tag.myTarget; targettag = target->tag; targettaghash = PredicateLockTargetTagHashCode(&targettag); partitionLock = PredicateLockHashPartitionLock(targettaghash); LWLockAcquire(partitionLock, LW_EXCLUSIVE); SHMQueueDelete(targetLink); hash_search_with_hash_value(PredicateLockHash, &tag, PredicateLockHashCodeFromTargetHashCode(&tag, targettaghash), HASH_REMOVE, NULL); if (summarize) { bool found; /* Fold into dummy transaction list. */ tag.myXact = OldCommittedSxact; predlock = hash_search_with_hash_value(PredicateLockHash, &tag, PredicateLockHashCodeFromTargetHashCode(&tag, targettaghash), HASH_ENTER, &found); if (!predlock) ereport(ERROR, (errcode(ERRCODE_OUT_OF_MEMORY), errmsg("out of shared memory"), errhint("You might need to increase max_pred_locks_per_transaction."))); if (found) { if (predlock->commitSeqNo < sxact->commitSeqNo) predlock->commitSeqNo = sxact->commitSeqNo; } else { SHMQueueInsertBefore(&(target->predicateLocks), &(predlock->targetLink)); SHMQueueInsertBefore(&(OldCommittedSxact->predicateLocks), &(predlock->xactLink)); predlock->commitSeqNo = sxact->commitSeqNo; } } else RemoveTargetIfNoLongerUsed(target, targettaghash); LWLockRelease(partitionLock); predlock = nextpredlock; } /* * Rather than retail removal, just re-init the head after we've run * through the list. */ SHMQueueInit(&sxact->predicateLocks); LWLockRelease(SerializablePredicateLockListLock); sxidtag.xid = sxact->topXid; LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE); if (!partial) { /* Release all outConflicts. */ conflict = (RWConflict) SHMQueueNext(&sxact->outConflicts, &sxact->outConflicts, offsetof(RWConflictData, outLink)); while (conflict) { nextConflict = (RWConflict) SHMQueueNext(&sxact->outConflicts, &conflict->outLink, offsetof(RWConflictData, outLink)); if (summarize) conflict->sxactIn->flags |= SXACT_FLAG_SUMMARY_CONFLICT_IN; ReleaseRWConflict(conflict); conflict = nextConflict; } } /* Release all inConflicts. */ conflict = (RWConflict) SHMQueueNext(&sxact->inConflicts, &sxact->inConflicts, offsetof(RWConflictData, inLink)); while (conflict) { nextConflict = (RWConflict) SHMQueueNext(&sxact->inConflicts, &conflict->inLink, offsetof(RWConflictData, inLink)); if (summarize) conflict->sxactOut->flags |= SXACT_FLAG_SUMMARY_CONFLICT_OUT; ReleaseRWConflict(conflict); conflict = nextConflict; } if (!partial) { /* Get rid of the xid and the record of the transaction itself. */ if (sxidtag.xid != InvalidTransactionId) hash_search(SerializableXidHash, &sxidtag, HASH_REMOVE, NULL); ReleasePredXact(sxact); } LWLockRelease(SerializableXactHashLock); } /* * Tests whether the given top level transaction is concurrent with * (overlaps) our current transaction. * * We need to identify the top level transaction for SSI, anyway, so pass * that to this function to save the overhead of checking the snapshot's * subxip array. */ static bool XidIsConcurrent(TransactionId xid) { Snapshot snap; uint32 i; Assert(TransactionIdIsValid(xid)); Assert(!TransactionIdEquals(xid, GetTopTransactionIdIfAny())); snap = GetTransactionSnapshot(); if (TransactionIdPrecedes(xid, snap->xmin)) return false; if (TransactionIdFollowsOrEquals(xid, snap->xmax)) return true; for (i = 0; i < snap->xcnt; i++) { if (xid == snap->xip[i]) return true; } return false; } /* * CheckForSerializableConflictOut * We are reading a tuple which has been modified. If it is visible to * us but has been deleted, that indicates a rw-conflict out. If it's * not visible and was created by a concurrent (overlapping) * serializable transaction, that is also a rw-conflict out, * * We will determine the top level xid of the writing transaction with which * we may be in conflict, and check for overlap with our own transaction. * If the transactions overlap (i.e., they cannot see each other's writes), * then we have a conflict out. * * This function should be called just about anywhere in heapam.c that a * tuple has been read. There is currently no known reason to call this * function from an index AM. */ void CheckForSerializableConflictOut(const bool visible, const Relation relation, const HeapTuple tuple, const Buffer buffer) { TransactionId xid; SERIALIZABLEXIDTAG sxidtag; SERIALIZABLEXID *sxid; SERIALIZABLEXACT *sxact; HTSV_Result htsvResult; if (SkipSerialization(relation)) return; if (SxactIsMarkedForDeath(MySerializableXact)) { ereport(ERROR, (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE), errmsg("could not serialize access due to read/write dependencies among transactions"), errdetail("Cancelled on identification as a pivot, during conflict out checking."), errhint("The transaction might succeed if retried."))); } /* * Check to see whether the tuple has been written to by a concurrent * transaction, either to create it not visible to us, or to delete it * while it is visible to us. The "visible" bool indicates whether the * tuple is visible to us, while HeapTupleSatisfiesVacuum checks what else * is going on with it. */ htsvResult = HeapTupleSatisfiesVacuum(tuple->t_data, TransactionXmin, buffer); switch (htsvResult) { case HEAPTUPLE_LIVE: if (visible) return; xid = HeapTupleHeaderGetXmin(tuple->t_data); break; case HEAPTUPLE_RECENTLY_DEAD: if (!visible) return; xid = HeapTupleHeaderGetXmax(tuple->t_data); break; case HEAPTUPLE_DELETE_IN_PROGRESS: xid = HeapTupleHeaderGetXmax(tuple->t_data); break; case HEAPTUPLE_INSERT_IN_PROGRESS: xid = HeapTupleHeaderGetXmin(tuple->t_data); break; case HEAPTUPLE_DEAD: return; default: /* * The only way to get to this default clause is if a new value is * added to the enum type without adding it to this switch * statement. That's a bug, so elog. */ elog(ERROR, "unrecognized return value from HeapTupleSatisfiesVacuum: %u", htsvResult); /* * In spite of having all enum values covered and calling elog on * this default, some compilers think this is a code path which * allows xid to be used below without initialization. Silence * that warning. */ xid = InvalidTransactionId; } Assert(TransactionIdIsValid(xid)); Assert(TransactionIdFollowsOrEquals(xid, TransactionXmin)); /* * Find top level xid. Bail out if xid is too early to be a conflict, or * if it's our own xid. */ if (TransactionIdEquals(xid, GetTopTransactionIdIfAny())) return; xid = SubTransGetTopmostTransaction(xid); if (TransactionIdPrecedes(xid, TransactionXmin)) return; if (TransactionIdEquals(xid, GetTopTransactionIdIfAny())) return; /* * Find sxact or summarized info for the top level xid. */ sxidtag.xid = xid; LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE); sxid = (SERIALIZABLEXID *) hash_search(SerializableXidHash, &sxidtag, HASH_FIND, NULL); if (!sxid) { /* * Transaction not found in "normal" SSI structures. Check whether it * got pushed out to SLRU storage for "old committed" transactions. */ SerCommitSeqNo conflictCommitSeqNo; conflictCommitSeqNo = OldSerXidGetMinConflictCommitSeqNo(xid); if (conflictCommitSeqNo != 0) { if (conflictCommitSeqNo != InvalidSerCommitSeqNo && (!SxactIsReadOnly(MySerializableXact) || conflictCommitSeqNo <= MySerializableXact->SeqNo.lastCommitBeforeSnapshot)) ereport(ERROR, (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE), errmsg("could not serialize access due to read/write dependencies among transactions"), errdetail("Cancelled on conflict out to old pivot %u.", xid), errhint("The transaction might succeed if retried."))); if (SxactHasSummaryConflictIn(MySerializableXact) || !SHMQueueEmpty((SHM_QUEUE *) &MySerializableXact->inConflicts)) ereport(ERROR, (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE), errmsg("could not serialize access due to read/write dependencies among transactions"), errdetail("Cancelled on identification as a pivot, with conflict out to old committed transaction %u.", xid), errhint("The transaction might succeed if retried."))); MySerializableXact->flags |= SXACT_FLAG_SUMMARY_CONFLICT_OUT; } /* It's not serializable or otherwise not important. */ LWLockRelease(SerializableXactHashLock); return; } sxact = sxid->myXact; Assert(TransactionIdEquals(sxact->topXid, xid)); if (sxact == MySerializableXact || SxactIsRolledBack(sxact) || SxactIsMarkedForDeath(sxact)) { /* We can't conflict with our own transaction or one rolled back. */ LWLockRelease(SerializableXactHashLock); return; } /* * We have a conflict out to a transaction which has a conflict out to a * summarized transaction. That summarized transaction must have * committed first, and we can't tell when it committed in relation to our * snapshot acquisition, so something needs to be cancelled. */ if (SxactHasSummaryConflictOut(sxact)) { if (!SxactIsPrepared(sxact)) { sxact->flags |= SXACT_FLAG_MARKED_FOR_DEATH; LWLockRelease(SerializableXactHashLock); return; } else { LWLockRelease(SerializableXactHashLock); ereport(ERROR, (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE), errmsg("could not serialize access due to read/write dependencies among transactions"), errdetail("Cancelled on conflict out to old pivot."), errhint("The transaction might succeed if retried."))); } } /* * If this is a read-only transaction and the writing transaction has * committed, and it doesn't have a rw-conflict to a transaction which * committed before it, no conflict. */ if (SxactIsReadOnly(MySerializableXact) && SxactIsCommitted(sxact) && !SxactHasSummaryConflictOut(sxact) && (!SxactHasConflictOut(sxact) || MySerializableXact->SeqNo.lastCommitBeforeSnapshot < sxact->SeqNo.earliestOutConflictCommit)) { /* Read-only transaction will appear to run first. No conflict. */ LWLockRelease(SerializableXactHashLock); return; } if (!XidIsConcurrent(xid)) { /* This write was already in our snapshot; no conflict. */ LWLockRelease(SerializableXactHashLock); return; } if (RWConflictExists((SERIALIZABLEXACT *) MySerializableXact, sxact)) { /* We don't want duplicate conflict records in the list. */ LWLockRelease(SerializableXactHashLock); return; } /* * Flag the conflict. But first, if this conflict creates a dangerous * structure, ereport an error. */ FlagRWConflict((SERIALIZABLEXACT *) MySerializableXact, sxact); LWLockRelease(SerializableXactHashLock); } /* * Check a particular target for rw-dependency conflict in. This will * also check prior versions of a tuple, if any. */ static void CheckTargetForConflictsIn(PREDICATELOCKTARGETTAG *targettag) { PREDICATELOCKTARGETTAG nexttargettag = { 0 }; PREDICATELOCKTARGETTAG thistargettag; for (;;) { if (!CheckSingleTargetForConflictsIn(targettag, &nexttargettag)) break; thistargettag = nexttargettag; targettag = &thistargettag; } } /* * Check a particular target for rw-dependency conflict in. If the tuple * has prior versions, returns true and *nexttargettag is set to the tag * of the prior tuple version. */ static bool CheckSingleTargetForConflictsIn(PREDICATELOCKTARGETTAG *targettag, PREDICATELOCKTARGETTAG *nexttargettag) { uint32 targettaghash; LWLockId partitionLock; PREDICATELOCKTARGET *target; PREDICATELOCK *predlock; bool hasnexttarget = false; Assert(MySerializableXact != InvalidSerializableXact); /* * The same hash and LW lock apply to the lock target and the lock itself. */ targettaghash = PredicateLockTargetTagHashCode(targettag); partitionLock = PredicateLockHashPartitionLock(targettaghash); LWLockAcquire(partitionLock, LW_SHARED); LWLockAcquire(PredicateLockNextRowLinkLock, LW_SHARED); target = (PREDICATELOCKTARGET *) hash_search_with_hash_value(PredicateLockTargetHash, targettag, targettaghash, HASH_FIND, NULL); if (!target) { /* Nothing has this target locked; we're done here. */ LWLockRelease(PredicateLockNextRowLinkLock); LWLockRelease(partitionLock); return false; } /* * If the target is linked to a prior version of the row, save the tag so * that it can be used for iterative calls to this function. */ if (target->priorVersionOfRow != NULL) { *nexttargettag = target->priorVersionOfRow->tag; hasnexttarget = true; } LWLockRelease(PredicateLockNextRowLinkLock); /* * Each lock for an overlapping transaction represents a conflict: a * rw-dependency in to this transaction. */ predlock = (PREDICATELOCK *) SHMQueueNext(&(target->predicateLocks), &(target->predicateLocks), offsetof(PREDICATELOCK, targetLink)); LWLockAcquire(SerializableXactHashLock, LW_SHARED); while (predlock) { SHM_QUEUE *predlocktargetlink; PREDICATELOCK *nextpredlock; SERIALIZABLEXACT *sxact; predlocktargetlink = &(predlock->targetLink); nextpredlock = (PREDICATELOCK *) SHMQueueNext(&(target->predicateLocks), predlocktargetlink, offsetof(PREDICATELOCK, targetLink)); sxact = predlock->tag.myXact; if (sxact == MySerializableXact) { /* * If we're getting a write lock on the tuple, we don't need a * predicate (SIREAD) lock. At this point our transaction already * has an ExclusiveRowLock on the relation, so we are OK to drop * the predicate lock on the tuple, if found, without fearing that * another write against the tuple will occur before the MVCC * information makes it to the buffer. */ if (GET_PREDICATELOCKTARGETTAG_OFFSET(*targettag)) { uint32 predlockhashcode; PREDICATELOCKTARGET *rmtarget = NULL; PREDICATELOCK *rmpredlock; LOCALPREDICATELOCK *locallock, *rmlocallock; /* * This is a tuple on which we have a tuple predicate lock. We * only have shared LW locks now; release those, and get * exclusive locks only while we modify things. */ LWLockRelease(SerializableXactHashLock); LWLockRelease(partitionLock); LWLockAcquire(SerializablePredicateLockListLock, LW_SHARED); LWLockAcquire(partitionLock, LW_EXCLUSIVE); LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE); /* * Remove the predicate lock from shared memory, if it wasn't * removed while the locks were released. One way that could * happen is from autovacuum cleaning up an index. */ predlockhashcode = PredicateLockHashCodeFromTargetHashCode (&(predlock->tag), targettaghash); rmpredlock = (PREDICATELOCK *) hash_search_with_hash_value(PredicateLockHash, &(predlock->tag), predlockhashcode, HASH_FIND, NULL); if (rmpredlock) { Assert(rmpredlock == predlock); SHMQueueDelete(predlocktargetlink); SHMQueueDelete(&(predlock->xactLink)); rmpredlock = (PREDICATELOCK *) hash_search_with_hash_value(PredicateLockHash, &(predlock->tag), predlockhashcode, HASH_REMOVE, NULL); Assert(rmpredlock == predlock); RemoveTargetIfNoLongerUsed(target, targettaghash); LWLockRelease(SerializableXactHashLock); LWLockRelease(partitionLock); LWLockRelease(SerializablePredicateLockListLock); locallock = (LOCALPREDICATELOCK *) hash_search_with_hash_value(LocalPredicateLockHash, targettag, targettaghash, HASH_FIND, NULL); Assert(locallock != NULL); Assert(locallock->held); locallock->held = false; if (locallock->childLocks == 0) { rmlocallock = (LOCALPREDICATELOCK *) hash_search_with_hash_value(LocalPredicateLockHash, targettag, targettaghash, HASH_REMOVE, NULL); Assert(rmlocallock == locallock); } DecrementParentLocks(targettag); /* * If we've cleaned up the last of the predicate locks for * the target, bail out before re-acquiring the locks. */ if (rmtarget) return hasnexttarget; /* * The list has been altered. Start over at the front. */ LWLockAcquire(partitionLock, LW_SHARED); nextpredlock = (PREDICATELOCK *) SHMQueueNext(&(target->predicateLocks), &(target->predicateLocks), offsetof(PREDICATELOCK, targetLink)); LWLockAcquire(SerializableXactHashLock, LW_SHARED); } else { /* * The predicate lock was cleared while we were attempting * to upgrade our lightweight locks. Revert to the shared * locks. */ LWLockRelease(SerializableXactHashLock); LWLockRelease(partitionLock); LWLockRelease(SerializablePredicateLockListLock); LWLockAcquire(partitionLock, LW_SHARED); LWLockAcquire(SerializableXactHashLock, LW_SHARED); } } } else if (!SxactIsRolledBack(sxact) && (!SxactIsCommitted(sxact) || TransactionIdPrecedes(GetTransactionSnapshot()->xmin, sxact->finishedBefore)) && !RWConflictExists(sxact, (SERIALIZABLEXACT *) MySerializableXact)) { LWLockRelease(SerializableXactHashLock); LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE); FlagRWConflict(sxact, (SERIALIZABLEXACT *) MySerializableXact); LWLockRelease(SerializableXactHashLock); LWLockAcquire(SerializableXactHashLock, LW_SHARED); } predlock = nextpredlock; } LWLockRelease(SerializableXactHashLock); LWLockRelease(partitionLock); return hasnexttarget; } /* * CheckForSerializableConflictIn * We are writing the given tuple. If that indicates a rw-conflict * in from another serializable transaction, take appropriate action. * * Skip checking for any granularity for which a parameter is missing. * * A tuple update or delete is in conflict if we have a predicate lock * against the relation or page in which the tuple exists, or against the * tuple itself. */ void CheckForSerializableConflictIn(const Relation relation, const HeapTuple tuple, const Buffer buffer) { PREDICATELOCKTARGETTAG targettag; if (SkipSerialization(relation)) return; if (SxactIsMarkedForDeath(MySerializableXact)) ereport(ERROR, (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE), errmsg("could not serialize access due to read/write dependencies among transactions"), errdetail("Cancelled on identification as a pivot, during conflict in checking."), errhint("The transaction might succeed if retried."))); MySerializableXact->flags |= SXACT_FLAG_DID_WRITE; /* * It is important that we check for locks from the finest granularity to * the coarsest granularity, so that granularity promotion doesn't cause * us to miss a lock. The new (coarser) lock will be acquired before the * old (finer) locks are released. * * It is not possible to take and hold a lock across the checks for all * granularities because each target could be in a separate partition. */ if (tuple != NULL) { SET_PREDICATELOCKTARGETTAG_TUPLE(targettag, relation->rd_node.dbNode, relation->rd_id, ItemPointerGetBlockNumber(&(tuple->t_data->t_ctid)), ItemPointerGetOffsetNumber(&(tuple->t_data->t_ctid))); CheckTargetForConflictsIn(&targettag); } if (BufferIsValid(buffer)) { SET_PREDICATELOCKTARGETTAG_PAGE(targettag, relation->rd_node.dbNode, relation->rd_id, BufferGetBlockNumber(buffer)); CheckTargetForConflictsIn(&targettag); } SET_PREDICATELOCKTARGETTAG_RELATION(targettag, relation->rd_node.dbNode, relation->rd_id); CheckTargetForConflictsIn(&targettag); } /* * Flag a rw-dependency between two serializable transactions. * * The caller is responsible for ensuring that we have a LW lock on * the transaction hash table. */ static void FlagRWConflict(SERIALIZABLEXACT *reader, SERIALIZABLEXACT *writer) { Assert(reader != writer); /* First, see if this conflict causes failure. */ OnConflict_CheckForSerializationFailure(reader, writer); /* Actually do the conflict flagging. */ if (reader == OldCommittedSxact) writer->flags |= SXACT_FLAG_SUMMARY_CONFLICT_IN; else if (writer == OldCommittedSxact) reader->flags |= SXACT_FLAG_SUMMARY_CONFLICT_OUT; else SetRWConflict(reader, writer); } /* * Check whether we should roll back one of these transactions * instead of flagging a new rw-conflict. */ static void OnConflict_CheckForSerializationFailure(const SERIALIZABLEXACT *reader, SERIALIZABLEXACT *writer) { bool failure; RWConflict conflict; Assert(LWLockHeldByMe(SerializableXactHashLock)); failure = false; /* * Check for already-committed writer with rw-conflict out flagged. This * means that the reader must immediately fail. */ if (SxactIsCommitted(writer) && (SxactHasConflictOut(writer) || SxactHasSummaryConflictOut(writer))) failure = true; /* * Check whether the reader has become a pivot with a committed writer. If * so, we must roll back unless every in-conflict either committed before * the writer committed or is READ ONLY and overlaps the writer. */ if (!failure && SxactIsCommitted(writer) && !SxactIsReadOnly(reader)) { if (SxactHasSummaryConflictIn(reader)) { failure = true; conflict = NULL; } else conflict = (RWConflict) SHMQueueNext(&reader->inConflicts, &reader->inConflicts, offsetof(RWConflictData, inLink)); while (conflict) { if (!SxactIsRolledBack(conflict->sxactOut) && (!SxactIsCommitted(conflict->sxactOut) || conflict->sxactOut->commitSeqNo >= writer->commitSeqNo) && (!SxactIsReadOnly(conflict->sxactOut) || conflict->sxactOut->SeqNo.lastCommitBeforeSnapshot >= writer->commitSeqNo)) { failure = true; break; } conflict = (RWConflict) SHMQueueNext(&reader->inConflicts, &conflict->inLink, offsetof(RWConflictData, inLink)); } } /* * Check whether the writer has become a pivot with an out-conflict * committed transaction, while neither reader nor writer is committed. If * the reader is a READ ONLY transaction, there is only a serialization * failure if an out-conflict transaction causing the pivot committed * before the reader acquired its snapshot. (That is, the reader must not * have been concurrent with the out-conflict transaction.) */ if (!failure && !SxactIsCommitted(writer)) { if (SxactHasSummaryConflictOut(reader)) { failure = true; conflict = NULL; } else conflict = (RWConflict) SHMQueueNext(&writer->outConflicts, &writer->outConflicts, offsetof(RWConflictData, outLink)); while (conflict) { if ((reader == conflict->sxactIn && SxactIsCommitted(reader)) || (SxactIsCommitted(conflict->sxactIn) && !SxactIsCommitted(reader) && (!SxactIsReadOnly(reader) || conflict->sxactIn->commitSeqNo <= reader->SeqNo.lastCommitBeforeSnapshot))) { failure = true; break; } conflict = (RWConflict) SHMQueueNext(&writer->outConflicts, &conflict->outLink, offsetof(RWConflictData, outLink)); } } if (failure) { if (MySerializableXact == writer) { LWLockRelease(SerializableXactHashLock); ereport(ERROR, (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE), errmsg("could not serialize access due to read/write dependencies among transactions"), errdetail("Cancelled on identification as pivot, during write."), errhint("The transaction might succeed if retried."))); } else if (SxactIsPrepared(writer)) { LWLockRelease(SerializableXactHashLock); ereport(ERROR, (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE), errmsg("could not serialize access due to read/write dependencies among transactions"), errdetail("Cancelled on conflict out to pivot %u, during read.", writer->topXid), errhint("The transaction might succeed if retried."))); } writer->flags |= SXACT_FLAG_MARKED_FOR_DEATH; } } /* * PreCommit_CheckForSerializableConflicts * Check for dangerous structures in a serializable transaction * at commit. * * We're checking for a dangerous structure as each conflict is recorded. * The only way we could have a problem at commit is if this is the "out" * side of a pivot, and neither the "in" side nor the pivot has yet * committed. * * If a dangerous structure is found, the pivot (the near conflict) is * marked for death, because rolling back another transaction might mean * that we flail without ever making progress. This transaction is * committing writes, so letting it commit ensures progress. If we * cancelled the far conflict, it might immediately fail again on retry. */ void PreCommit_CheckForSerializationFailure(void) { RWConflict nearConflict; if (MySerializableXact == InvalidSerializableXact) return; Assert(IsolationIsSerializable()); LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE); if (SxactIsMarkedForDeath(MySerializableXact)) { LWLockRelease(SerializableXactHashLock); ereport(ERROR, (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE), errmsg("could not serialize access due to read/write dependencies among transactions"), errdetail("Cancelled on identification as a pivot, during commit attempt."), errhint("The transaction might succeed if retried."))); } nearConflict = (RWConflict) SHMQueueNext((SHM_QUEUE *) &MySerializableXact->inConflicts, (SHM_QUEUE *) &MySerializableXact->inConflicts, offsetof(RWConflictData, inLink)); while (nearConflict) { if (!SxactIsCommitted(nearConflict->sxactOut) && !SxactIsRolledBack(nearConflict->sxactOut) && !SxactIsMarkedForDeath(nearConflict->sxactOut)) { RWConflict farConflict; farConflict = (RWConflict) SHMQueueNext(&nearConflict->sxactOut->inConflicts, &nearConflict->sxactOut->inConflicts, offsetof(RWConflictData, inLink)); while (farConflict) { if (farConflict->sxactOut == MySerializableXact || (!SxactIsCommitted(farConflict->sxactOut) && !SxactIsReadOnly(farConflict->sxactOut) && !SxactIsRolledBack(farConflict->sxactOut) && !SxactIsMarkedForDeath(farConflict->sxactOut))) { nearConflict->sxactOut->flags |= SXACT_FLAG_MARKED_FOR_DEATH; break; } farConflict = (RWConflict) SHMQueueNext(&nearConflict->sxactOut->inConflicts, &farConflict->inLink, offsetof(RWConflictData, inLink)); } } nearConflict = (RWConflict) SHMQueueNext((SHM_QUEUE *) &MySerializableXact->inConflicts, &nearConflict->inLink, offsetof(RWConflictData, inLink)); } MySerializableXact->flags |= SXACT_FLAG_PREPARED; LWLockRelease(SerializableXactHashLock); } /*------------------------------------------------------------------------*/ /* * Two-phase commit support */ /* * AtPrepare_Locks * Do the preparatory work for a PREPARE: make 2PC state file * records for all predicate locks currently held. */ void AtPrepare_PredicateLocks(void) { PREDICATELOCK *predlock; SERIALIZABLEXACT *sxact; TwoPhasePredicateRecord record; TwoPhasePredicateXactRecord *xactRecord; TwoPhasePredicateLockRecord *lockRecord; sxact = (SERIALIZABLEXACT *) MySerializableXact; xactRecord = &(record.data.xactRecord); lockRecord = &(record.data.lockRecord); if (MySerializableXact == InvalidSerializableXact) return; /* Generate a xact record for our SERIALIZABLEXACT */ record.type = TWOPHASEPREDICATERECORD_XACT; xactRecord->xmin = MySerializableXact->xmin; xactRecord->flags = MySerializableXact->flags; /* * Tweak the flags. Since we're not going to output the inConflicts and * outConflicts lists, if they're non-empty we'll represent that by * setting the appropriate summary conflict flags. */ if (!SHMQueueEmpty((SHM_QUEUE *) &MySerializableXact->inConflicts)) xactRecord->flags |= SXACT_FLAG_SUMMARY_CONFLICT_IN; if (!SHMQueueEmpty((SHM_QUEUE *) &MySerializableXact->outConflicts)) xactRecord->flags |= SXACT_FLAG_SUMMARY_CONFLICT_OUT; RegisterTwoPhaseRecord(TWOPHASE_RM_PREDICATELOCK_ID, 0, &record, sizeof(record)); /* * Generate a lock record for each lock. * * To do this, we need to walk the predicate lock list in our sxact rather * than using the local predicate lock table because the latter is not * guaranteed to be accurate. */ LWLockAcquire(SerializablePredicateLockListLock, LW_SHARED); predlock = (PREDICATELOCK *) SHMQueueNext(&(sxact->predicateLocks), &(sxact->predicateLocks), offsetof(PREDICATELOCK, xactLink)); while (predlock != NULL) { record.type = TWOPHASEPREDICATERECORD_LOCK; lockRecord->target = predlock->tag.myTarget->tag; RegisterTwoPhaseRecord(TWOPHASE_RM_PREDICATELOCK_ID, 0, &record, sizeof(record)); predlock = (PREDICATELOCK *) SHMQueueNext(&(sxact->predicateLocks), &(predlock->xactLink), offsetof(PREDICATELOCK, xactLink)); } LWLockRelease(SerializablePredicateLockListLock); } /* * PostPrepare_Locks * Clean up after successful PREPARE. Unlike the non-predicate * lock manager, we do not need to transfer locks to a dummy * PGPROC because our SERIALIZABLEXACT will stay around * anyway. We only need to clean up our local state. */ void PostPrepare_PredicateLocks(TransactionId xid) { if (MySerializableXact == InvalidSerializableXact) return; Assert(SxactIsPrepared(MySerializableXact)); MySerializableXact->pid = 0; hash_destroy(LocalPredicateLockHash); LocalPredicateLockHash = NULL; MySerializableXact = InvalidSerializableXact; } /* * PredicateLockTwoPhaseFinish * Release a prepared transaction's predicate locks once it * commits or aborts. */ void PredicateLockTwoPhaseFinish(TransactionId xid, bool isCommit) { SERIALIZABLEXID *sxid; SERIALIZABLEXIDTAG sxidtag; sxidtag.xid = xid; LWLockAcquire(SerializableXactHashLock, LW_SHARED); sxid = (SERIALIZABLEXID *) hash_search(SerializableXidHash, &sxidtag, HASH_FIND, NULL); LWLockRelease(SerializableXactHashLock); /* xid will not be found if it wasn't a serializable transaction */ if (sxid == NULL) return; /* Release its locks */ MySerializableXact = sxid->myXact; ReleasePredicateLocks(isCommit); } /* * Re-acquire a predicate lock belonging to a transaction that was prepared. */ void predicatelock_twophase_recover(TransactionId xid, uint16 info, void *recdata, uint32 len) { TwoPhasePredicateRecord *record; Assert(len == sizeof(TwoPhasePredicateRecord)); record = (TwoPhasePredicateRecord *) recdata; Assert((record->type == TWOPHASEPREDICATERECORD_XACT) || (record->type == TWOPHASEPREDICATERECORD_LOCK)); if (record->type == TWOPHASEPREDICATERECORD_XACT) { /* Per-transaction record. Set up a SERIALIZABLEXACT. */ TwoPhasePredicateXactRecord *xactRecord; SERIALIZABLEXACT *sxact; SERIALIZABLEXID *sxid; SERIALIZABLEXIDTAG sxidtag; bool found; xactRecord = (TwoPhasePredicateXactRecord *) &record->data.xactRecord; LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE); sxact = CreatePredXact(); if (!sxact) ereport(ERROR, (errcode(ERRCODE_OUT_OF_MEMORY), errmsg("out of shared memory"))); /* vxid for a prepared xact is InvalidBackendId/xid; no pid */ sxact->vxid.backendId = InvalidBackendId; sxact->vxid.localTransactionId = (LocalTransactionId) xid; sxact->pid = 0; /* a prepared xact hasn't committed yet */ sxact->commitSeqNo = InvalidSerCommitSeqNo; sxact->finishedBefore = InvalidTransactionId; sxact->SeqNo.lastCommitBeforeSnapshot = RecoverySerCommitSeqNo; /* * We don't need the details of a prepared transaction's conflicts, * just whether it had conflicts in or out (which we get from the * flags) */ SHMQueueInit(&(sxact->outConflicts)); SHMQueueInit(&(sxact->inConflicts)); /* * Don't need to track this; no transactions running at the time the * recovered xact started are still active, except possibly other * prepared xacts and we don't care whether those are RO_SAFE or not. */ SHMQueueInit(&(sxact->possibleUnsafeConflicts)); SHMQueueInit(&(sxact->predicateLocks)); SHMQueueElemInit(&(sxact->finishedLink)); sxact->topXid = xid; sxact->xmin = xactRecord->xmin; sxact->flags = xactRecord->flags; Assert(SxactIsPrepared(sxact)); if (!SxactIsReadOnly(sxact)) { ++(PredXact->WritableSxactCount); Assert(PredXact->WritableSxactCount <= (MaxBackends + max_prepared_xacts)); } /* Register the transaction's xid */ sxidtag.xid = xid; sxid = (SERIALIZABLEXID *) hash_search(SerializableXidHash, &sxidtag, HASH_ENTER, &found); if (!sxid) ereport(ERROR, (errcode(ERRCODE_OUT_OF_MEMORY), errmsg("out of shared memory"))); Assert(!found); sxid->myXact = (SERIALIZABLEXACT *) sxact; /* * Update global xmin. Note that this is a special case compared to * registering a normal transaction, because the global xmin might go * backwards. That's OK, because until recovery is over we're not * going to complete any transactions or create any non-prepared * transactions, so there's no danger of throwing away. */ if ((!TransactionIdIsValid(PredXact->SxactGlobalXmin)) || (TransactionIdFollows(PredXact->SxactGlobalXmin, sxact->xmin))) { PredXact->SxactGlobalXmin = sxact->xmin; PredXact->SxactGlobalXminCount = 1; OldSerXidSetActiveSerXmin(sxact->xmin); } else if (TransactionIdEquals(sxact->xmin, PredXact->SxactGlobalXmin)) { Assert(PredXact->SxactGlobalXminCount > 0); PredXact->SxactGlobalXminCount++; } LWLockRelease(SerializableXactHashLock); } else if (record->type == TWOPHASEPREDICATERECORD_LOCK) { /* Lock record. Recreate the PREDICATELOCK */ TwoPhasePredicateLockRecord *lockRecord; SERIALIZABLEXID *sxid; SERIALIZABLEXACT *sxact; SERIALIZABLEXIDTAG sxidtag; uint32 targettaghash; lockRecord = (TwoPhasePredicateLockRecord *) &record->data.lockRecord; targettaghash = PredicateLockTargetTagHashCode(&lockRecord->target); LWLockAcquire(SerializableXactHashLock, LW_SHARED); sxidtag.xid = xid; sxid = (SERIALIZABLEXID *) hash_search(SerializableXidHash, &sxidtag, HASH_FIND, NULL); LWLockRelease(SerializableXactHashLock); Assert(sxid != NULL); sxact = sxid->myXact; Assert(sxact != InvalidSerializableXact); CreatePredicateLock(&lockRecord->target, targettaghash, sxact); } }