1558 lines
46 KiB
C
1558 lines
46 KiB
C
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/*-------------------------------------------------------------------------
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*
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* multixact.c
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* PostgreSQL multi-transaction-log manager
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*
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* The pg_multixact manager is a pg_clog-like manager that stores an array
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* of TransactionIds for each MultiXactId. It is a fundamental part of the
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* shared-row-lock implementation. A share-locked tuple stores a
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* MultiXactId in its Xmax, and a transaction that needs to wait for the
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* tuple to be unlocked can sleep on the potentially-several TransactionIds
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* that compose the MultiXactId.
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*
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* We use two SLRU areas, one for storing the offsets on which the data
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* starts for each MultiXactId in the other one. This trick allows us to
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* store variable length arrays of TransactionIds. (We could alternatively
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* use one area containing counts and TransactionIds, with valid MultiXactId
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* values pointing at slots containing counts; but that way seems less robust
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* since it would get completely confused if someone inquired about a bogus
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* MultiXactId that pointed to an intermediate slot containing an XID.)
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*
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* This code is based on subtrans.c; see it for additional discussion.
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* Like the subtransaction manager, we only need to remember multixact
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* information for currently-open transactions. Thus, there is
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* no need to preserve data over a crash and restart.
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*
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* The only XLOG interaction we need to take care of is that generated
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* MultiXactId values must continue to increase across a system crash.
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* Thus we log groups of MultiXactIds acquisition in the same fashion we do
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* for Oids (see XLogPutNextMultiXactId).
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*
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* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/backend/access/transam/multixact.c,v 1.1 2005/04/28 21:47:10 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "access/multixact.h"
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#include "access/slru.h"
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#include "access/xact.h"
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#include "miscadmin.h"
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#include "utils/memutils.h"
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#include "storage/backendid.h"
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#include "storage/lmgr.h"
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#include "storage/sinval.h"
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/*
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* Defines for MultiXactOffset page sizes. A page is the same BLCKSZ as is
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* used everywhere else in Postgres.
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*
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* Note: because both uint32 and TransactionIds are 32 bits and wrap around at
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* 0xFFFFFFFF, MultiXact page numbering also wraps around at
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* 0xFFFFFFFF/MULTIXACT_*_PER_PAGE, and segment numbering at
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* 0xFFFFFFFF/MULTIXACT_*_PER_PAGE/SLRU_SEGMENTS_PER_PAGE. We need take no
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* explicit notice of that fact in this module, except when comparing segment
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* and page numbers in TruncateMultiXact
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* (see MultiXact{Offset,Member}PagePrecedes).
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*/
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/* We need four bytes per offset and also four bytes per member */
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#define MULTIXACT_OFFSETS_PER_PAGE (BLCKSZ / sizeof(uint32))
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#define MULTIXACT_MEMBERS_PER_PAGE (BLCKSZ / sizeof(TransactionId))
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#define MultiXactIdToOffsetPage(xid) \
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((xid) / (uint32) MULTIXACT_OFFSETS_PER_PAGE)
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#define MultiXactIdToOffsetEntry(xid) \
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((xid) % (uint32) MULTIXACT_OFFSETS_PER_PAGE)
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#define MXOffsetToMemberPage(xid) \
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((xid) / (TransactionId) MULTIXACT_MEMBERS_PER_PAGE)
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#define MXOffsetToMemberEntry(xid) \
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((xid) % (TransactionId) MULTIXACT_MEMBERS_PER_PAGE)
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/* Arbitrary number of MultiXactIds to allocate at each XLog call */
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#define MXACT_PREFETCH 8192
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/*
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* Links to shared-memory data structures for MultiXact control
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*/
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static SlruCtlData MultiXactOffsetCtlData;
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static SlruCtlData MultiXactMemberCtlData;
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#define MultiXactOffsetCtl (&MultiXactOffsetCtlData)
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#define MultiXactMemberCtl (&MultiXactMemberCtlData)
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/*
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* MultiXact state shared across all backends. All this state is protected
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* by MultiXactGenLock. (We also use MultiXactOffsetControlLock and
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* MultiXactMemberControlLock to guard accesses to the two sets of SLRU
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* buffers. For concurrency's sake, we avoid holding more than one of these
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* locks at a time.)
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*/
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typedef struct MultiXactStateData
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{
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/* next-to-be-assigned MultiXactId */
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MultiXactId nextMXact;
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/* MultiXactIds we have left before logging more */
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uint32 mXactCount;
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/* next-to-be-assigned offset */
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uint32 nextOffset;
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/* the Offset SLRU area was last truncated at this MultiXactId */
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MultiXactId lastTruncationPoint;
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/*
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* Per-backend data starts here. We have two arrays stored in
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* the area immediately following the MultiXactStateData struct.
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* Each is indexed by BackendId. (Note: valid BackendIds run from 1 to
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* MaxBackends; element zero of each array is never used.)
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*
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* OldestMemberMXactId[k] is the oldest MultiXactId each backend's
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* current transaction(s) could possibly be a member of, or
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* InvalidMultiXactId when the backend has no live transaction that
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* could possibly be a member of a MultiXact. Each backend sets its
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* entry to the current nextMXact counter just before first acquiring a
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* shared lock in a given transaction, and clears it at transaction end.
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* (This works because only during or after acquiring a shared lock
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* could an XID possibly become a member of a MultiXact, and that
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* MultiXact would have to be created during or after the lock
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* acquisition.)
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*
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* OldestVisibleMXactId[k] is the oldest MultiXactId each backend's
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* current transaction(s) think is potentially live, or InvalidMultiXactId
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* when not in a transaction or not in a transaction that's paid any
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* attention to MultiXacts yet. This is computed when first needed in
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* a given transaction, and cleared at transaction end. We can compute
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* it as the minimum of the valid OldestMemberMXactId[] entries at the
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* time we compute it (using nextMXact if none are valid). Each backend
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* is required not to attempt to access any SLRU data for MultiXactIds
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* older than its own OldestVisibleMXactId[] setting; this is necessary
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* because the checkpointer could truncate away such data at any instant.
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*
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* The checkpointer can compute the safe truncation point as the oldest
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* valid value among all the OldestMemberMXactId[] and
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* OldestVisibleMXactId[] entries, or nextMXact if none are valid.
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* Clearly, it is not possible for any later-computed OldestVisibleMXactId
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* value to be older than this, and so there is no risk of truncating
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* data that is still needed.
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*/
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MultiXactId perBackendXactIds[1]; /* VARIABLE LENGTH ARRAY */
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} MultiXactStateData;
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/* Pointers to the state data in shared memory */
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static MultiXactStateData *MultiXactState;
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static MultiXactId *OldestMemberMXactId;
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static MultiXactId *OldestVisibleMXactId;
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/*
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* Definitions for the backend-local MultiXactId cache.
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*
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* We use this cache to store known MultiXacts, so we don't need to go to
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* SLRU areas everytime.
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*
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* The cache lasts for the duration of a single transaction, the rationale
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* for this being that most entries will contain our own TransactionId and
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* so they will be uninteresting by the time our next transaction starts.
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* (XXX not clear that this is correct --- other members of the MultiXact
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* could hang around longer than we did.)
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*
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* We allocate the cache entries in a memory context that is deleted at
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* transaction end, so we don't need to do retail freeing of entries.
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*/
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typedef struct mXactCacheEnt
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{
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struct mXactCacheEnt *next;
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MultiXactId multi;
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int nxids;
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TransactionId xids[1]; /* VARIABLE LENGTH ARRAY */
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} mXactCacheEnt;
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static mXactCacheEnt *MXactCache = NULL;
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static MemoryContext MXactContext = NULL;
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#ifdef MULTIXACT_DEBUG
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#define debug_elog2(a,b) elog(a,b)
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#define debug_elog3(a,b,c) elog(a,b,c)
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#define debug_elog4(a,b,c,d) elog(a,b,c,d)
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#define debug_elog5(a,b,c,d,e) elog(a,b,c,d,e)
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#else
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#define debug_elog2(a,b)
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#define debug_elog3(a,b,c)
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#define debug_elog4(a,b,c,d)
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#define debug_elog5(a,b,c,d,e)
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#endif
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/* internal MultiXactId management */
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static void MultiXactIdSetOldestVisible(void);
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static MultiXactId CreateMultiXactId(int nxids, TransactionId *xids);
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static int GetMultiXactIdMembers(MultiXactId multi, TransactionId **xids);
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static MultiXactId GetNewMultiXactId(int nxids, uint32 *offset);
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/* MultiXact cache management */
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static MultiXactId mXactCacheGetBySet(int nxids, TransactionId *xids);
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static int mXactCacheGetById(MultiXactId multi, TransactionId **xids);
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static void mXactCachePut(MultiXactId multi, int nxids, TransactionId *xids);
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static int xidComparator(const void *arg1, const void *arg2);
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#ifdef MULTIXACT_DEBUG
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static char *mxid_to_string(MultiXactId multi, int nxids, TransactionId *xids);
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#endif
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/* management of SLRU infrastructure */
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static int ZeroMultiXactOffsetPage(int pageno);
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static int ZeroMultiXactMemberPage(int pageno);
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static bool MultiXactOffsetPagePrecedes(int page1, int page2);
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static bool MultiXactMemberPagePrecedes(int page1, int page2);
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static bool MultiXactIdPrecedes(MultiXactId multi1, MultiXactId multi2);
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static bool MultiXactOffsetPrecedes(uint32 offset1, uint32 offset2);
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static void ExtendMultiXactOffset(MultiXactId multi);
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static void ExtendMultiXactMember(uint32 offset);
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static void TruncateMultiXact(void);
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/*
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* MultiXactIdExpand
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* Add a TransactionId to a possibly-already-existing MultiXactId.
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*
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* We abuse the notation for the first argument: if "isMulti" is true, then
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* it's really a MultiXactId; else it's a TransactionId. We are already
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* storing MultiXactId in HeapTupleHeader's xmax so assuming the datatypes
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* are equivalent is necessary anyway.
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*
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* If isMulti is true, then get the members of the passed MultiXactId, add
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* the passed TransactionId, and create a new MultiXactId. If isMulti is
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* false, then take the two TransactionIds and create a new MultiXactId with
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* them. The caller must ensure that the multi and xid are different
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* in the latter case.
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*
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* If the TransactionId is already a member of the passed MultiXactId,
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* just return it as-is.
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*
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* Note that we do NOT actually modify the membership of a pre-existing
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* MultiXactId; instead we create a new one. This is necessary to avoid
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* a race condition against MultiXactIdWait (see notes there).
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*
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* NB - we don't worry about our local MultiXactId cache here, because that
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* is handled by the lower-level routines.
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*/
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MultiXactId
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MultiXactIdExpand(MultiXactId multi, bool isMulti, TransactionId xid)
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{
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MultiXactId newMulti;
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TransactionId *members;
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TransactionId *newMembers;
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int nmembers;
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int i;
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int j;
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AssertArg(MultiXactIdIsValid(multi));
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AssertArg(TransactionIdIsValid(xid));
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debug_elog5(DEBUG2, "Expand: received %s %u, xid %u",
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isMulti ? "MultiXactId" : "TransactionId",
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multi, xid);
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if (!isMulti)
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{
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/*
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* The first argument is a TransactionId, not a MultiXactId.
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*/
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TransactionId xids[2];
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Assert(!TransactionIdEquals(multi, xid));
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xids[0] = multi;
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xids[1] = xid;
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newMulti = CreateMultiXactId(2, xids);
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debug_elog5(DEBUG2, "Expand: returning %u two-elem %u/%u",
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newMulti, multi, xid);
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return newMulti;
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}
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nmembers = GetMultiXactIdMembers(multi, &members);
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if (nmembers < 0)
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{
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/*
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* The MultiXactId is obsolete. This can only happen if all the
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* MultiXactId members stop running between the caller checking and
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* passing it to us. It would be better to return that fact to the
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* caller, but it would complicate the API and it's unlikely to happen
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* too often, so just deal with it by creating a singleton MultiXact.
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*/
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newMulti = CreateMultiXactId(1, &xid);
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debug_elog4(DEBUG2, "Expand: %u has no members, create singleton %u",
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multi, newMulti);
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return newMulti;
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}
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/*
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* If the TransactionId is already a member of the MultiXactId,
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* just return the existing MultiXactId.
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*/
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for (i = 0; i < nmembers; i++)
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{
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if (TransactionIdEquals(members[i], xid))
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{
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pfree(members);
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debug_elog4(DEBUG2, "Expand: %u is already a member of %u",
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xid, multi);
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return multi;
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}
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}
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/*
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* Determine which of the members of the MultiXactId are still running,
|
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* and use them to create a new one. (Removing dead members is just
|
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* an optimization, but a useful one. Note we have the same race
|
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* condition here as above: j could be 0 at the end of the loop.)
|
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*/
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newMembers = (TransactionId *)
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palloc(sizeof(TransactionId) * (nmembers + 1));
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for (i = 0, j = 0; i < nmembers; i++)
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{
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if (TransactionIdIsInProgress(members[i]))
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newMembers[j++] = members[i];
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}
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newMembers[j++] = xid;
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newMulti = CreateMultiXactId(j, newMembers);
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pfree(members);
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pfree(newMembers);
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debug_elog3(DEBUG2, "Expand: returning new multi %u", newMulti);
|
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return newMulti;
|
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}
|
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|
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/*
|
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* MultiXactIdIsRunning
|
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* Returns whether a MultiXactId is "running".
|
||
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*
|
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* We return true if at least one member of the given MultiXactId is still
|
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* running. Note that a "false" result is certain not to change,
|
||
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* because it is not legal to add members to an existing MultiXactId.
|
||
|
*/
|
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bool
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MultiXactIdIsRunning(MultiXactId multi)
|
||
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{
|
||
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TransactionId *members;
|
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TransactionId myXid;
|
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|
int nmembers;
|
||
|
int i;
|
||
|
|
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debug_elog3(DEBUG2, "IsRunning %u?", multi);
|
||
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|
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nmembers = GetMultiXactIdMembers(multi, &members);
|
||
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|
||
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if (nmembers < 0)
|
||
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{
|
||
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debug_elog2(DEBUG2, "IsRunning: no members");
|
||
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return false;
|
||
|
}
|
||
|
|
||
|
/* checking for myself is cheap */
|
||
|
myXid = GetTopTransactionId();
|
||
|
|
||
|
for (i = 0; i < nmembers; i++)
|
||
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{
|
||
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if (TransactionIdEquals(members[i], myXid))
|
||
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{
|
||
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pfree(members);
|
||
|
debug_elog3(DEBUG2, "IsRunning: I (%d) am running!", i);
|
||
|
return true;
|
||
|
}
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* This could be made better by having a special entry point in sinval.c,
|
||
|
* walking the PGPROC array only once for the whole array. But in most
|
||
|
* cases nmembers should be small enough that it doesn't much matter.
|
||
|
*/
|
||
|
for (i = 0; i < nmembers; i++)
|
||
|
{
|
||
|
if (TransactionIdIsInProgress(members[i]))
|
||
|
{
|
||
|
pfree(members);
|
||
|
debug_elog4(DEBUG2, "IsRunning: member %d (%u) is running",
|
||
|
i, members[i]);
|
||
|
return true;
|
||
|
}
|
||
|
}
|
||
|
|
||
|
pfree(members);
|
||
|
debug_elog3(DEBUG2, "IsRunning: %u is not running", multi);
|
||
|
|
||
|
return false;
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* MultiXactIdSetOldestMember
|
||
|
* Save the oldest MultiXactId this transaction could be a member of.
|
||
|
*
|
||
|
* We set the OldestMemberMXactId for a given transaction the first time
|
||
|
* it's going to acquire a shared lock. We need to do this even if we end
|
||
|
* up using a TransactionId instead of a MultiXactId, because there is a
|
||
|
* chance that another transaction would add our XID to a MultiXactId.
|
||
|
*
|
||
|
* The value to set is the next-to-be-assigned MultiXactId, so this is meant
|
||
|
* to be called just before acquiring a shared lock.
|
||
|
*/
|
||
|
void
|
||
|
MultiXactIdSetOldestMember(void)
|
||
|
{
|
||
|
if (!MultiXactIdIsValid(OldestMemberMXactId[MyBackendId]))
|
||
|
{
|
||
|
MultiXactId nextMXact;
|
||
|
|
||
|
/*
|
||
|
* You might think we don't need to acquire a lock here, since
|
||
|
* fetching and storing of TransactionIds is probably atomic,
|
||
|
* but in fact we do: suppose we pick up nextMXact and then
|
||
|
* lose the CPU for a long time. Someone else could advance
|
||
|
* nextMXact, and then another someone else could compute an
|
||
|
* OldestVisibleMXactId that would be after the value we are
|
||
|
* going to store when we get control back. Which would be wrong.
|
||
|
*/
|
||
|
LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
|
||
|
|
||
|
/*
|
||
|
* We have to beware of the possibility that nextMXact is in the
|
||
|
* wrapped-around state. We don't fix the counter itself here,
|
||
|
* but we must be sure to store a valid value in our array entry.
|
||
|
*/
|
||
|
nextMXact = MultiXactState->nextMXact;
|
||
|
if (nextMXact < FirstMultiXactId)
|
||
|
nextMXact = FirstMultiXactId;
|
||
|
|
||
|
OldestMemberMXactId[MyBackendId] = nextMXact;
|
||
|
|
||
|
LWLockRelease(MultiXactGenLock);
|
||
|
|
||
|
debug_elog4(DEBUG2, "MultiXact: setting OldestMember[%d] = %u",
|
||
|
MyBackendId, nextMXact);
|
||
|
}
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* MultiXactIdSetOldestVisible
|
||
|
* Save the oldest MultiXactId this transaction considers possibly live.
|
||
|
*
|
||
|
* We set the OldestVisibleMXactId for a given transaction the first time
|
||
|
* it's going to inspect any MultiXactId. Once we have set this, we are
|
||
|
* guaranteed that the checkpointer won't truncate off SLRU data for
|
||
|
* MultiXactIds at or after our OldestVisibleMXactId.
|
||
|
*
|
||
|
* The value to set is the oldest of nextMXact and all the valid per-backend
|
||
|
* OldestMemberMXactId[] entries. Because of the locking we do, we can be
|
||
|
* certain that no subsequent call to MultiXactIdSetOldestMember can set
|
||
|
* an OldestMemberMXactId[] entry older than what we compute here. Therefore
|
||
|
* there is no live transaction, now or later, that can be a member of any
|
||
|
* MultiXactId older than the OldestVisibleMXactId we compute here.
|
||
|
*/
|
||
|
static void
|
||
|
MultiXactIdSetOldestVisible(void)
|
||
|
{
|
||
|
if (!MultiXactIdIsValid(OldestVisibleMXactId[MyBackendId]))
|
||
|
{
|
||
|
MultiXactId oldestMXact;
|
||
|
int i;
|
||
|
|
||
|
LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
|
||
|
|
||
|
/*
|
||
|
* We have to beware of the possibility that nextMXact is in the
|
||
|
* wrapped-around state. We don't fix the counter itself here,
|
||
|
* but we must be sure to store a valid value in our array entry.
|
||
|
*/
|
||
|
oldestMXact = MultiXactState->nextMXact;
|
||
|
if (oldestMXact < FirstMultiXactId)
|
||
|
oldestMXact = FirstMultiXactId;
|
||
|
|
||
|
for (i = 1; i <= MaxBackends; i++)
|
||
|
{
|
||
|
MultiXactId thisoldest = OldestMemberMXactId[i];
|
||
|
|
||
|
if (MultiXactIdIsValid(thisoldest) &&
|
||
|
MultiXactIdPrecedes(thisoldest, oldestMXact))
|
||
|
oldestMXact = thisoldest;
|
||
|
}
|
||
|
|
||
|
OldestVisibleMXactId[MyBackendId] = oldestMXact;
|
||
|
|
||
|
LWLockRelease(MultiXactGenLock);
|
||
|
|
||
|
debug_elog4(DEBUG2, "MultiXact: setting OldestVisible[%d] = %u",
|
||
|
MyBackendId, oldestMXact);
|
||
|
}
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* MultiXactIdWait
|
||
|
* Sleep on a MultiXactId.
|
||
|
*
|
||
|
* We do this by sleeping on each member using XactLockTableWait. Any
|
||
|
* members that belong to the current backend are *not* waited for, however;
|
||
|
* this would not merely be useless but would lead to Assert failure inside
|
||
|
* XactLockTableWait. By the time this returns, it is certain that all
|
||
|
* transactions *of other backends* that were members of the MultiXactId
|
||
|
* are dead (and no new ones can have been added, since it is not legal
|
||
|
* to add members to an existing MultiXactId).
|
||
|
*
|
||
|
* But by the time we finish sleeping, someone else may have changed the Xmax
|
||
|
* of the containing tuple, so the caller needs to iterate on us somehow.
|
||
|
*/
|
||
|
void
|
||
|
MultiXactIdWait(MultiXactId multi)
|
||
|
{
|
||
|
TransactionId *members;
|
||
|
int nmembers;
|
||
|
|
||
|
nmembers = GetMultiXactIdMembers(multi, &members);
|
||
|
|
||
|
if (nmembers >= 0)
|
||
|
{
|
||
|
int i;
|
||
|
|
||
|
for (i = 0; i < nmembers; i++)
|
||
|
{
|
||
|
TransactionId member = members[i];
|
||
|
|
||
|
debug_elog4(DEBUG2, "MultiXactIdWait: waiting for %d (%u)",
|
||
|
i, member);
|
||
|
if (!TransactionIdIsCurrentTransactionId(member))
|
||
|
XactLockTableWait(member);
|
||
|
}
|
||
|
|
||
|
pfree(members);
|
||
|
}
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* CreateMultiXactId
|
||
|
* Make a new MultiXactId
|
||
|
*
|
||
|
* Make SLRU and cache entries for a new MultiXactId, recording the given
|
||
|
* TransactionIds as members. Returns the newly created MultiXactId.
|
||
|
*
|
||
|
* NB: the passed xids[] array will be sorted in-place.
|
||
|
*/
|
||
|
static MultiXactId
|
||
|
CreateMultiXactId(int nxids, TransactionId *xids)
|
||
|
{
|
||
|
MultiXactId multi;
|
||
|
int pageno;
|
||
|
int prev_pageno;
|
||
|
int entryno;
|
||
|
int slotno;
|
||
|
uint32 *offptr;
|
||
|
uint32 offset;
|
||
|
int i;
|
||
|
|
||
|
debug_elog3(DEBUG2, "Create: %s",
|
||
|
mxid_to_string(InvalidMultiXactId, nxids, xids));
|
||
|
|
||
|
/*
|
||
|
* See if the same set of XIDs already exists in our cache; if so, just
|
||
|
* re-use that MultiXactId. (Note: it might seem that looking in our
|
||
|
* cache is insufficient, and we ought to search disk to see if a
|
||
|
* duplicate definition already exists. But since we only ever create
|
||
|
* MultiXacts containing our own XID, in most cases any such MultiXacts
|
||
|
* were in fact created by us, and so will be in our cache. There are
|
||
|
* corner cases where someone else added us to a MultiXact without our
|
||
|
* knowledge, but it's not worth checking for.)
|
||
|
*/
|
||
|
multi = mXactCacheGetBySet(nxids, xids);
|
||
|
if (MultiXactIdIsValid(multi))
|
||
|
{
|
||
|
debug_elog2(DEBUG2, "Create: in cache!");
|
||
|
return multi;
|
||
|
}
|
||
|
|
||
|
multi = GetNewMultiXactId(nxids, &offset);
|
||
|
|
||
|
LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
|
||
|
|
||
|
ExtendMultiXactOffset(multi);
|
||
|
|
||
|
pageno = MultiXactIdToOffsetPage(multi);
|
||
|
entryno = MultiXactIdToOffsetEntry(multi);
|
||
|
|
||
|
/*
|
||
|
* Note: we pass the MultiXactId to SimpleLruReadPage as the "transaction"
|
||
|
* to complain about if there's any I/O error. This is kinda bogus, but
|
||
|
* since the errors will always give the full pathname, it should be
|
||
|
* clear enough that a MultiXactId is really involved. Perhaps someday
|
||
|
* we'll take the trouble to generalize the slru.c error reporting code.
|
||
|
*/
|
||
|
slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, multi);
|
||
|
offptr = (uint32 *) MultiXactOffsetCtl->shared->page_buffer[slotno];
|
||
|
offptr += entryno;
|
||
|
*offptr = offset;
|
||
|
|
||
|
MultiXactOffsetCtl->shared->page_status[slotno] = SLRU_PAGE_DIRTY;
|
||
|
|
||
|
/* Exchange our lock */
|
||
|
LWLockRelease(MultiXactOffsetControlLock);
|
||
|
|
||
|
debug_elog3(DEBUG2, "Create: got offset %u", offset);
|
||
|
|
||
|
LWLockAcquire(MultiXactMemberControlLock, LW_EXCLUSIVE);
|
||
|
|
||
|
prev_pageno = -1;
|
||
|
|
||
|
for (i = 0; i < nxids; i++, offset++)
|
||
|
{
|
||
|
TransactionId *memberptr;
|
||
|
|
||
|
ExtendMultiXactMember(offset);
|
||
|
|
||
|
pageno = MXOffsetToMemberPage(offset);
|
||
|
entryno = MXOffsetToMemberEntry(offset);
|
||
|
|
||
|
if (pageno != prev_pageno)
|
||
|
{
|
||
|
slotno = SimpleLruReadPage(MultiXactMemberCtl, pageno, multi);
|
||
|
prev_pageno = pageno;
|
||
|
}
|
||
|
|
||
|
memberptr = (TransactionId *)
|
||
|
MultiXactMemberCtl->shared->page_buffer[slotno];
|
||
|
memberptr += entryno;
|
||
|
|
||
|
*memberptr = xids[i];
|
||
|
MultiXactMemberCtl->shared->page_status[slotno] = SLRU_PAGE_DIRTY;
|
||
|
}
|
||
|
|
||
|
LWLockRelease(MultiXactMemberControlLock);
|
||
|
|
||
|
/* Store the new MultiXactId in the local cache, too */
|
||
|
mXactCachePut(multi, nxids, xids);
|
||
|
debug_elog2(DEBUG2, "Create: all done");
|
||
|
|
||
|
return multi;
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* GetNewMultiXactId
|
||
|
* Get the next MultiXactId.
|
||
|
*
|
||
|
* Get the next MultiXactId, XLogging if needed. Also, reserve the needed
|
||
|
* amount of space in the "members" area. The starting offset of the
|
||
|
* reserved space is returned in *offset.
|
||
|
*/
|
||
|
static MultiXactId
|
||
|
GetNewMultiXactId(int nxids, uint32 *offset)
|
||
|
{
|
||
|
MultiXactId result;
|
||
|
|
||
|
debug_elog3(DEBUG2, "GetNew: for %d xids", nxids);
|
||
|
|
||
|
/* MultiXactIdSetOldestMember() must have been called already */
|
||
|
Assert(MultiXactIdIsValid(OldestMemberMXactId[MyBackendId]));
|
||
|
|
||
|
LWLockAcquire(MultiXactGenLock, LW_EXCLUSIVE);
|
||
|
|
||
|
/* Handle wraparound of the nextMXact counter */
|
||
|
if (MultiXactState->nextMXact < FirstMultiXactId)
|
||
|
{
|
||
|
MultiXactState->nextMXact = FirstMultiXactId;
|
||
|
MultiXactState->mXactCount = 0;
|
||
|
}
|
||
|
|
||
|
/* If we run out of logged for use multixacts then we must log more */
|
||
|
if (MultiXactState->mXactCount == 0)
|
||
|
{
|
||
|
XLogPutNextMultiXactId(MultiXactState->nextMXact + MXACT_PREFETCH);
|
||
|
MultiXactState->mXactCount = MXACT_PREFETCH;
|
||
|
}
|
||
|
|
||
|
result = MultiXactState->nextMXact;
|
||
|
|
||
|
/*
|
||
|
* We don't care about MultiXactId wraparound here; it will be handled by
|
||
|
* the next iteration. But note that nextMXact may be InvalidMultiXactId
|
||
|
* after this routine exits, so anyone else looking at the variable must
|
||
|
* be prepared to deal with that.
|
||
|
*/
|
||
|
(MultiXactState->nextMXact)++;
|
||
|
(MultiXactState->mXactCount)--;
|
||
|
|
||
|
/*
|
||
|
* Reserve the members space.
|
||
|
*/
|
||
|
*offset = MultiXactState->nextOffset;
|
||
|
MultiXactState->nextOffset += nxids;
|
||
|
|
||
|
LWLockRelease(MultiXactGenLock);
|
||
|
|
||
|
debug_elog4(DEBUG2, "GetNew: returning %u offset %u", result, *offset);
|
||
|
return result;
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* GetMultiXactIdMembers
|
||
|
* Returns the set of TransactionIds that make up a MultiXactId
|
||
|
*
|
||
|
* We return -1 if the MultiXactId is too old to possibly have any members
|
||
|
* still running; in that case we have not actually looked them up, and
|
||
|
* *xids is not set.
|
||
|
*/
|
||
|
static int
|
||
|
GetMultiXactIdMembers(MultiXactId multi, TransactionId **xids)
|
||
|
{
|
||
|
int pageno;
|
||
|
int prev_pageno;
|
||
|
int entryno;
|
||
|
int slotno;
|
||
|
uint32 *offptr;
|
||
|
uint32 offset;
|
||
|
int length;
|
||
|
int i;
|
||
|
MultiXactId nextMXact;
|
||
|
MultiXactId tmpMXact;
|
||
|
uint32 nextOffset;
|
||
|
TransactionId *ptr;
|
||
|
|
||
|
debug_elog3(DEBUG2, "GetMembers: asked for %u", multi);
|
||
|
|
||
|
Assert(MultiXactIdIsValid(multi));
|
||
|
|
||
|
/* See if the MultiXactId is in the local cache */
|
||
|
length = mXactCacheGetById(multi, xids);
|
||
|
if (length >= 0)
|
||
|
{
|
||
|
debug_elog3(DEBUG2, "GetMembers: found %s in the cache",
|
||
|
mxid_to_string(multi, length, *xids));
|
||
|
return length;
|
||
|
}
|
||
|
|
||
|
/* Set our OldestVisibleMXactId[] entry if we didn't already */
|
||
|
MultiXactIdSetOldestVisible();
|
||
|
|
||
|
/*
|
||
|
* We check known limits on MultiXact before resorting to the SLRU area.
|
||
|
*
|
||
|
* An ID older than our OldestVisibleMXactId[] entry can't possibly still
|
||
|
* be running, and we'd run the risk of trying to read already-truncated
|
||
|
* SLRU data if we did try to examine it.
|
||
|
*
|
||
|
* Conversely, an ID >= nextMXact shouldn't ever be seen here; if it is
|
||
|
* seen, it implies undetected ID wraparound has occurred. We just
|
||
|
* silently assume that such an ID is no longer running.
|
||
|
*
|
||
|
* Shared lock is enough here since we aren't modifying any global state.
|
||
|
* Also, we can examine our own OldestVisibleMXactId without the lock,
|
||
|
* since no one else is allowed to change it.
|
||
|
*/
|
||
|
if (MultiXactIdPrecedes(multi, OldestVisibleMXactId[MyBackendId]))
|
||
|
{
|
||
|
debug_elog2(DEBUG2, "GetMembers: it's too old");
|
||
|
*xids = NULL;
|
||
|
return -1;
|
||
|
}
|
||
|
|
||
|
LWLockAcquire(MultiXactGenLock, LW_SHARED);
|
||
|
|
||
|
if (!MultiXactIdPrecedes(multi, MultiXactState->nextMXact))
|
||
|
{
|
||
|
LWLockRelease(MultiXactGenLock);
|
||
|
debug_elog2(DEBUG2, "GetMembers: it's too new!");
|
||
|
*xids = NULL;
|
||
|
return -1;
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* Before releasing the lock, save the current counter values, because
|
||
|
* the target MultiXactId may be just one less than nextMXact. We will
|
||
|
* need to use nextOffset as the endpoint if so.
|
||
|
*/
|
||
|
nextMXact = MultiXactState->nextMXact;
|
||
|
nextOffset = MultiXactState->nextOffset;
|
||
|
|
||
|
LWLockRelease(MultiXactGenLock);
|
||
|
|
||
|
/* Get the offset at which we need to start reading MultiXactMembers */
|
||
|
LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
|
||
|
|
||
|
pageno = MultiXactIdToOffsetPage(multi);
|
||
|
entryno = MultiXactIdToOffsetEntry(multi);
|
||
|
|
||
|
slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, multi);
|
||
|
offptr = (uint32 *) MultiXactOffsetCtl->shared->page_buffer[slotno];
|
||
|
offptr += entryno;
|
||
|
offset = *offptr;
|
||
|
|
||
|
/*
|
||
|
* How many members do we need to read? If we are at the end of the
|
||
|
* assigned MultiXactIds, use the offset just saved above. Else we
|
||
|
* need to check the MultiXactId following ours.
|
||
|
*
|
||
|
* Use the same increment rule as GetNewMultiXactId(), that is, don't
|
||
|
* handle wraparound explicitly until needed.
|
||
|
*/
|
||
|
tmpMXact = multi + 1;
|
||
|
|
||
|
if (nextMXact == tmpMXact)
|
||
|
length = nextOffset - offset;
|
||
|
else
|
||
|
{
|
||
|
/* handle wraparound if needed */
|
||
|
if (tmpMXact < FirstMultiXactId)
|
||
|
tmpMXact = FirstMultiXactId;
|
||
|
|
||
|
prev_pageno = pageno;
|
||
|
|
||
|
pageno = MultiXactIdToOffsetPage(tmpMXact);
|
||
|
entryno = MultiXactIdToOffsetEntry(tmpMXact);
|
||
|
|
||
|
if (pageno != prev_pageno)
|
||
|
slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, tmpMXact);
|
||
|
|
||
|
offptr = (uint32 *) MultiXactOffsetCtl->shared->page_buffer[slotno];
|
||
|
offptr += entryno;
|
||
|
length = *offptr - offset;
|
||
|
}
|
||
|
|
||
|
LWLockRelease(MultiXactOffsetControlLock);
|
||
|
|
||
|
ptr = (TransactionId *) palloc(length * sizeof(TransactionId));
|
||
|
*xids = ptr;
|
||
|
|
||
|
/* Now get the members themselves. */
|
||
|
LWLockAcquire(MultiXactMemberControlLock, LW_EXCLUSIVE);
|
||
|
|
||
|
prev_pageno = -1;
|
||
|
for (i = 0; i < length; i++, offset++)
|
||
|
{
|
||
|
TransactionId *xactptr;
|
||
|
|
||
|
pageno = MXOffsetToMemberPage(offset);
|
||
|
entryno = MXOffsetToMemberEntry(offset);
|
||
|
|
||
|
if (pageno != prev_pageno)
|
||
|
{
|
||
|
slotno = SimpleLruReadPage(MultiXactMemberCtl, pageno, multi);
|
||
|
prev_pageno = pageno;
|
||
|
}
|
||
|
|
||
|
xactptr = (TransactionId *)
|
||
|
MultiXactMemberCtl->shared->page_buffer[slotno];
|
||
|
xactptr += entryno;
|
||
|
|
||
|
ptr[i] = *xactptr;
|
||
|
}
|
||
|
|
||
|
LWLockRelease(MultiXactMemberControlLock);
|
||
|
|
||
|
/*
|
||
|
* Copy the result into the local cache.
|
||
|
*/
|
||
|
mXactCachePut(multi, length, ptr);
|
||
|
|
||
|
debug_elog3(DEBUG2, "GetMembers: no cache for %s",
|
||
|
mxid_to_string(multi, length, ptr));
|
||
|
return length;
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* mXactCacheGetBySet
|
||
|
* returns a MultiXactId from the cache based on the set of
|
||
|
* TransactionIds that compose it, or InvalidMultiXactId if
|
||
|
* none matches.
|
||
|
*
|
||
|
* This is helpful, for example, if two transactions want to lock a huge
|
||
|
* table. By using the cache, the second will use the same MultiXactId
|
||
|
* for the majority of tuples, thus keeping MultiXactId usage low (saving
|
||
|
* both I/O and wraparound issues).
|
||
|
*
|
||
|
* NB: the passed xids[] array will be sorted in-place.
|
||
|
*/
|
||
|
static MultiXactId
|
||
|
mXactCacheGetBySet(int nxids, TransactionId *xids)
|
||
|
{
|
||
|
mXactCacheEnt *entry;
|
||
|
|
||
|
debug_elog3(DEBUG2, "CacheGet: looking for %s",
|
||
|
mxid_to_string(InvalidMultiXactId, nxids, xids));
|
||
|
|
||
|
/* sort the array so comparison is easy */
|
||
|
qsort(xids, nxids, sizeof(TransactionId), xidComparator);
|
||
|
|
||
|
for (entry = MXactCache; entry != NULL; entry = entry->next)
|
||
|
{
|
||
|
if (entry->nxids != nxids)
|
||
|
continue;
|
||
|
|
||
|
/* We assume the cache entries are sorted */
|
||
|
if (memcmp(xids, entry->xids, nxids * sizeof(TransactionId)) == 0)
|
||
|
{
|
||
|
debug_elog3(DEBUG2, "CacheGet: found %u", entry->multi);
|
||
|
return entry->multi;
|
||
|
}
|
||
|
}
|
||
|
|
||
|
debug_elog2(DEBUG2, "CacheGet: not found :-(");
|
||
|
return InvalidMultiXactId;
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* mXactCacheGetById
|
||
|
* returns the composing TransactionId set from the cache for a
|
||
|
* given MultiXactId, if present.
|
||
|
*
|
||
|
* If successful, *xids is set to the address of a palloc'd copy of the
|
||
|
* TransactionId set. Return value is number of members, or -1 on failure.
|
||
|
*/
|
||
|
static int
|
||
|
mXactCacheGetById(MultiXactId multi, TransactionId **xids)
|
||
|
{
|
||
|
mXactCacheEnt *entry;
|
||
|
|
||
|
debug_elog3(DEBUG2, "CacheGet: looking for %u", multi);
|
||
|
|
||
|
for (entry = MXactCache; entry != NULL; entry = entry->next)
|
||
|
{
|
||
|
if (entry->multi == multi)
|
||
|
{
|
||
|
TransactionId *ptr;
|
||
|
Size size;
|
||
|
|
||
|
size = sizeof(TransactionId) * entry->nxids;
|
||
|
ptr = (TransactionId *) palloc(size);
|
||
|
*xids = ptr;
|
||
|
|
||
|
memcpy(ptr, entry->xids, size);
|
||
|
|
||
|
debug_elog3(DEBUG2, "CacheGet: found %s",
|
||
|
mxid_to_string(multi, entry->nxids, entry->xids));
|
||
|
return entry->nxids;
|
||
|
}
|
||
|
}
|
||
|
|
||
|
debug_elog2(DEBUG2, "CacheGet: not found");
|
||
|
return -1;
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* mXactCachePut
|
||
|
* Add a new MultiXactId and its composing set into the local cache.
|
||
|
*/
|
||
|
static void
|
||
|
mXactCachePut(MultiXactId multi, int nxids, TransactionId *xids)
|
||
|
{
|
||
|
mXactCacheEnt *entry;
|
||
|
|
||
|
debug_elog3(DEBUG2, "CachePut: storing %s",
|
||
|
mxid_to_string(multi, nxids, xids));
|
||
|
|
||
|
if (MXactContext == NULL)
|
||
|
{
|
||
|
/* The cache only lives as long as the current transaction */
|
||
|
debug_elog2(DEBUG2, "CachePut: initializing memory context");
|
||
|
MXactContext = AllocSetContextCreate(TopTransactionContext,
|
||
|
"MultiXact Cache Context",
|
||
|
ALLOCSET_SMALL_MINSIZE,
|
||
|
ALLOCSET_SMALL_INITSIZE,
|
||
|
ALLOCSET_SMALL_MAXSIZE);
|
||
|
}
|
||
|
|
||
|
entry = (mXactCacheEnt *)
|
||
|
MemoryContextAlloc(MXactContext,
|
||
|
offsetof(mXactCacheEnt, xids) +
|
||
|
nxids * sizeof(TransactionId));
|
||
|
|
||
|
entry->multi = multi;
|
||
|
entry->nxids = nxids;
|
||
|
memcpy(entry->xids, xids, nxids * sizeof(TransactionId));
|
||
|
|
||
|
/* mXactCacheGetBySet assumes the entries are sorted, so sort them */
|
||
|
qsort(entry->xids, nxids, sizeof(TransactionId), xidComparator);
|
||
|
|
||
|
entry->next = MXactCache;
|
||
|
MXactCache = entry;
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* xidComparator
|
||
|
* qsort comparison function for XIDs
|
||
|
*
|
||
|
* We don't need to use wraparound comparison for XIDs, and indeed must
|
||
|
* not do so since that does not respect the triangle inequality! Any
|
||
|
* old sort order will do.
|
||
|
*/
|
||
|
static int
|
||
|
xidComparator(const void *arg1, const void *arg2)
|
||
|
{
|
||
|
TransactionId xid1 = * (const TransactionId *) arg1;
|
||
|
TransactionId xid2 = * (const TransactionId *) arg2;
|
||
|
|
||
|
if (xid1 > xid2)
|
||
|
return 1;
|
||
|
if (xid1 < xid2)
|
||
|
return -1;
|
||
|
return 0;
|
||
|
}
|
||
|
|
||
|
#ifdef MULTIXACT_DEBUG
|
||
|
static char *
|
||
|
mxid_to_string(MultiXactId multi, int nxids, TransactionId *xids)
|
||
|
{
|
||
|
char *str = palloc(15 * (nxids + 1) + 4);
|
||
|
int i;
|
||
|
snprintf(str, 47, "%u %d[%u", multi, nxids, xids[0]);
|
||
|
|
||
|
for (i = 1; i < nxids; i++)
|
||
|
snprintf(str + strlen(str), 17, ", %u", xids[i]);
|
||
|
|
||
|
strcat(str, "]");
|
||
|
return str;
|
||
|
}
|
||
|
#endif
|
||
|
|
||
|
/*
|
||
|
* AtEOXact_MultiXact
|
||
|
* Handle transaction end for MultiXact
|
||
|
*
|
||
|
* This is called at top transaction commit or abort (we don't care which).
|
||
|
*/
|
||
|
void
|
||
|
AtEOXact_MultiXact(void)
|
||
|
{
|
||
|
/*
|
||
|
* Reset our OldestMemberMXactId and OldestVisibleMXactId values,
|
||
|
* both of which should only be valid while within a transaction.
|
||
|
*
|
||
|
* We assume that storing a MultiXactId is atomic and so we need
|
||
|
* not take MultiXactGenLock to do this.
|
||
|
*/
|
||
|
OldestMemberMXactId[MyBackendId] = InvalidMultiXactId;
|
||
|
OldestVisibleMXactId[MyBackendId] = InvalidMultiXactId;
|
||
|
|
||
|
/*
|
||
|
* Discard the local MultiXactId cache. Since MXactContext was created
|
||
|
* as a child of TopTransactionContext, we needn't delete it explicitly.
|
||
|
*/
|
||
|
MXactContext = NULL;
|
||
|
MXactCache = NULL;
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* Initialization of shared memory for MultiXact. We use two SLRU areas,
|
||
|
* thus double memory. Also, reserve space for the shared MultiXactState
|
||
|
* struct and the per-backend MultiXactId arrays (two of those, too).
|
||
|
*/
|
||
|
int
|
||
|
MultiXactShmemSize(void)
|
||
|
{
|
||
|
#define SHARED_MULTIXACT_STATE_SIZE \
|
||
|
(sizeof(MultiXactStateData) + sizeof(MultiXactId) * 2 * MaxBackends)
|
||
|
|
||
|
return (SimpleLruShmemSize() * 2 + SHARED_MULTIXACT_STATE_SIZE);
|
||
|
}
|
||
|
|
||
|
void
|
||
|
MultiXactShmemInit(void)
|
||
|
{
|
||
|
bool found;
|
||
|
|
||
|
debug_elog2(DEBUG2, "Shared Memory Init for MultiXact");
|
||
|
|
||
|
MultiXactOffsetCtl->PagePrecedes = MultiXactOffsetPagePrecedes;
|
||
|
MultiXactMemberCtl->PagePrecedes = MultiXactMemberPagePrecedes;
|
||
|
|
||
|
SimpleLruInit(MultiXactOffsetCtl, "MultiXactOffset Ctl",
|
||
|
MultiXactOffsetControlLock, "pg_multixact/offsets");
|
||
|
SimpleLruInit(MultiXactMemberCtl, "MultiXactMember Ctl",
|
||
|
MultiXactMemberControlLock, "pg_multixact/members");
|
||
|
|
||
|
/* Override default assumption that writes should be fsync'd */
|
||
|
MultiXactOffsetCtl->do_fsync = false;
|
||
|
MultiXactMemberCtl->do_fsync = false;
|
||
|
|
||
|
/* Initialize our shared state struct */
|
||
|
MultiXactState = ShmemInitStruct("Shared MultiXact State",
|
||
|
SHARED_MULTIXACT_STATE_SIZE,
|
||
|
&found);
|
||
|
if (!IsUnderPostmaster)
|
||
|
{
|
||
|
Assert(!found);
|
||
|
|
||
|
/* Make sure we zero out the per-backend state */
|
||
|
MemSet(MultiXactState, 0, SHARED_MULTIXACT_STATE_SIZE);
|
||
|
}
|
||
|
else
|
||
|
Assert(found);
|
||
|
|
||
|
/*
|
||
|
* Set up array pointers. Note that perBackendXactIds[0] is wasted
|
||
|
* space since we only use indexes 1..MaxBackends in each array.
|
||
|
*/
|
||
|
OldestMemberMXactId = MultiXactState->perBackendXactIds;
|
||
|
OldestVisibleMXactId = OldestMemberMXactId + MaxBackends;
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* This func must be called ONCE on system install. It creates the initial
|
||
|
* MultiXact segments. (The MultiXacts directories are assumed to have been
|
||
|
* created by initdb, and MultiXactShmemInit must have been called already.)
|
||
|
*
|
||
|
* Note: it's not really necessary to create the initial segments now,
|
||
|
* since slru.c would create 'em on first write anyway. But we may as well
|
||
|
* do it to be sure the directories are set up correctly.
|
||
|
*/
|
||
|
void
|
||
|
BootStrapMultiXact(void)
|
||
|
{
|
||
|
int slotno;
|
||
|
|
||
|
LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
|
||
|
|
||
|
/* Offsets first page */
|
||
|
slotno = ZeroMultiXactOffsetPage(0);
|
||
|
SimpleLruWritePage(MultiXactOffsetCtl, slotno, NULL);
|
||
|
Assert(MultiXactOffsetCtl->shared->page_status[slotno] == SLRU_PAGE_CLEAN);
|
||
|
|
||
|
LWLockRelease(MultiXactOffsetControlLock);
|
||
|
|
||
|
LWLockAcquire(MultiXactMemberControlLock, LW_EXCLUSIVE);
|
||
|
|
||
|
/* Members first page */
|
||
|
slotno = ZeroMultiXactMemberPage(0);
|
||
|
SimpleLruWritePage(MultiXactMemberCtl, slotno, NULL);
|
||
|
Assert(MultiXactMemberCtl->shared->page_status[slotno] == SLRU_PAGE_CLEAN);
|
||
|
|
||
|
LWLockRelease(MultiXactMemberControlLock);
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* Initialize (or reinitialize) a page of MultiXactOffset to zeroes.
|
||
|
*
|
||
|
* The page is not actually written, just set up in shared memory.
|
||
|
* The slot number of the new page is returned.
|
||
|
*
|
||
|
* Control lock must be held at entry, and will be held at exit.
|
||
|
*/
|
||
|
static int
|
||
|
ZeroMultiXactOffsetPage(int pageno)
|
||
|
{
|
||
|
return SimpleLruZeroPage(MultiXactOffsetCtl, pageno);
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* Ditto, for MultiXactMember
|
||
|
*/
|
||
|
static int
|
||
|
ZeroMultiXactMemberPage(int pageno)
|
||
|
{
|
||
|
return SimpleLruZeroPage(MultiXactMemberCtl, pageno);
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* This must be called ONCE during postmaster or standalone-backend startup.
|
||
|
*
|
||
|
* StartupXLOG has already established nextMXact by calling
|
||
|
* MultiXactSetNextMXact and/or MultiXactAdvanceNextMXact.
|
||
|
*
|
||
|
* We don't need any locks here, really; the SLRU locks are taken
|
||
|
* only because slru.c expects to be called with locks held.
|
||
|
*/
|
||
|
void
|
||
|
StartupMultiXact(void)
|
||
|
{
|
||
|
int startPage;
|
||
|
int cutoffPage;
|
||
|
uint32 offset;
|
||
|
|
||
|
/*
|
||
|
* We start nextOffset at zero after every reboot; there is no need to
|
||
|
* avoid offset values that were used in the previous system lifecycle.
|
||
|
*/
|
||
|
MultiXactState->nextOffset = 0;
|
||
|
|
||
|
/*
|
||
|
* Because of the above, a shutdown and restart is likely to leave
|
||
|
* high-numbered MultiXactMember page files that would not get recycled
|
||
|
* for a long time (about as long as the system had been up in the
|
||
|
* previous cycle of life). To clean out such page files, we issue an
|
||
|
* artificial truncation call that will zap any page files in the first
|
||
|
* half of the offset cycle. Should there be any page files in the last
|
||
|
* half, they will get cleaned out by the first checkpoint.
|
||
|
*
|
||
|
* XXX it might be a good idea to disable this when debugging, since it
|
||
|
* will tend to destroy evidence after a crash. To not be *too* ruthless,
|
||
|
* we arbitrarily spare the first 64 pages. (Note this will get
|
||
|
* rounded off to a multiple of SLRU_PAGES_PER_SEGMENT ...)
|
||
|
*/
|
||
|
offset = ((~ (uint32) 0) >> 1) + 1;
|
||
|
|
||
|
cutoffPage = MXOffsetToMemberPage(offset) + 64;
|
||
|
|
||
|
/*
|
||
|
* Defeat safety interlock in SimpleLruTruncate; this hack will be
|
||
|
* cleaned up by ZeroMultiXactMemberPage call below.
|
||
|
*/
|
||
|
MultiXactMemberCtl->shared->latest_page_number = cutoffPage;
|
||
|
|
||
|
SimpleLruTruncate(MultiXactMemberCtl, cutoffPage);
|
||
|
|
||
|
/*
|
||
|
* Initialize lastTruncationPoint to invalid, ensuring that the first
|
||
|
* checkpoint will try to do truncation.
|
||
|
*/
|
||
|
MultiXactState->lastTruncationPoint = InvalidMultiXactId;
|
||
|
|
||
|
/*
|
||
|
* Since we don't expect MultiXact to be valid across crashes, we
|
||
|
* initialize the currently-active pages to zeroes during startup.
|
||
|
* Whenever we advance into a new page, both ExtendMultiXact routines
|
||
|
* will likewise zero the new page without regard to whatever was
|
||
|
* previously on disk.
|
||
|
*/
|
||
|
LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
|
||
|
|
||
|
startPage = MultiXactIdToOffsetPage(MultiXactState->nextMXact);
|
||
|
(void) ZeroMultiXactOffsetPage(startPage);
|
||
|
|
||
|
LWLockRelease(MultiXactOffsetControlLock);
|
||
|
|
||
|
LWLockAcquire(MultiXactMemberControlLock, LW_EXCLUSIVE);
|
||
|
|
||
|
startPage = MXOffsetToMemberPage(MultiXactState->nextOffset);
|
||
|
(void) ZeroMultiXactMemberPage(startPage);
|
||
|
|
||
|
LWLockRelease(MultiXactMemberControlLock);
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* This must be called ONCE during postmaster or standalone-backend shutdown
|
||
|
*/
|
||
|
void
|
||
|
ShutdownMultiXact(void)
|
||
|
{
|
||
|
/*
|
||
|
* Flush dirty MultiXact pages to disk
|
||
|
*
|
||
|
* This is not actually necessary from a correctness point of view. We do
|
||
|
* it merely as a debugging aid.
|
||
|
*/
|
||
|
SimpleLruFlush(MultiXactOffsetCtl, false);
|
||
|
SimpleLruFlush(MultiXactMemberCtl, false);
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* Get the next MultiXactId to save in a checkpoint record
|
||
|
*/
|
||
|
MultiXactId
|
||
|
MultiXactGetCheckptMulti(bool is_shutdown)
|
||
|
{
|
||
|
MultiXactId retval;
|
||
|
|
||
|
LWLockAcquire(MultiXactGenLock, LW_SHARED);
|
||
|
|
||
|
retval = MultiXactState->nextMXact;
|
||
|
if (!is_shutdown)
|
||
|
retval += MultiXactState->mXactCount;
|
||
|
|
||
|
LWLockRelease(MultiXactGenLock);
|
||
|
|
||
|
debug_elog3(DEBUG2, "MultiXact: MultiXact for checkpoint record is %u",
|
||
|
retval);
|
||
|
|
||
|
return retval;
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* Perform a checkpoint --- either during shutdown, or on-the-fly
|
||
|
*/
|
||
|
void
|
||
|
CheckPointMultiXact(void)
|
||
|
{
|
||
|
/*
|
||
|
* Flush dirty MultiXact pages to disk
|
||
|
*
|
||
|
* This is not actually necessary from a correctness point of view. We do
|
||
|
* it merely to improve the odds that writing of dirty pages is done
|
||
|
* by the checkpoint process and not by backends.
|
||
|
*/
|
||
|
SimpleLruFlush(MultiXactOffsetCtl, true);
|
||
|
SimpleLruFlush(MultiXactMemberCtl, true);
|
||
|
|
||
|
/*
|
||
|
* Truncate the SLRU files
|
||
|
*/
|
||
|
TruncateMultiXact();
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* Set the next-to-be-assigned MultiXactId
|
||
|
*
|
||
|
* This is used when we can determine the correct next Id exactly
|
||
|
* from an XLog record. We need no locking since it is only called
|
||
|
* during bootstrap and XLog replay.
|
||
|
*/
|
||
|
void
|
||
|
MultiXactSetNextMXact(MultiXactId nextMulti)
|
||
|
{
|
||
|
debug_elog3(DEBUG2, "MultiXact: setting next multi to %u", nextMulti);
|
||
|
MultiXactState->nextMXact = nextMulti;
|
||
|
MultiXactState->mXactCount = 0;
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* Ensure the next-to-be-assigned MultiXactId is at least minMulti
|
||
|
*
|
||
|
* This is used when we can determine a minimum safe value
|
||
|
* from an XLog record. We need no locking since it is only called
|
||
|
* during XLog replay.
|
||
|
*/
|
||
|
void
|
||
|
MultiXactAdvanceNextMXact(MultiXactId minMulti)
|
||
|
{
|
||
|
if (MultiXactIdPrecedes(MultiXactState->nextMXact, minMulti))
|
||
|
{
|
||
|
debug_elog3(DEBUG2, "MultiXact: setting next multi to %u", minMulti);
|
||
|
MultiXactState->nextMXact = minMulti;
|
||
|
MultiXactState->mXactCount = 0;
|
||
|
}
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* Make sure that MultiXactOffset has room for a newly-allocated MultiXactId.
|
||
|
*
|
||
|
* The MultiXactOffsetControlLock should be held at entry, and will
|
||
|
* be held at exit.
|
||
|
*/
|
||
|
void
|
||
|
ExtendMultiXactOffset(MultiXactId multi)
|
||
|
{
|
||
|
int pageno;
|
||
|
|
||
|
/*
|
||
|
* No work except at first MultiXactId of a page. But beware: just after
|
||
|
* wraparound, the first MultiXactId of page zero is FirstMultiXactId.
|
||
|
*/
|
||
|
if (MultiXactIdToOffsetEntry(multi) != 0 &&
|
||
|
multi != FirstMultiXactId)
|
||
|
return;
|
||
|
|
||
|
pageno = MultiXactIdToOffsetPage(multi);
|
||
|
|
||
|
/* Zero the page */
|
||
|
ZeroMultiXactOffsetPage(pageno);
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* Make sure that MultiXactMember has room for the members of a newly-
|
||
|
* allocated MultiXactId.
|
||
|
*
|
||
|
* The MultiXactMemberControlLock should be held at entry, and will be held
|
||
|
* at exit.
|
||
|
*/
|
||
|
void
|
||
|
ExtendMultiXactMember(uint32 offset)
|
||
|
{
|
||
|
int pageno;
|
||
|
|
||
|
/*
|
||
|
* No work except at first entry of a page.
|
||
|
*/
|
||
|
if (MXOffsetToMemberEntry(offset) != 0)
|
||
|
return;
|
||
|
|
||
|
pageno = MXOffsetToMemberPage(offset);
|
||
|
|
||
|
/* Zero the page */
|
||
|
ZeroMultiXactMemberPage(pageno);
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* Remove all MultiXactOffset and MultiXactMember segments before the oldest
|
||
|
* ones still of interest.
|
||
|
*
|
||
|
* This is called only during checkpoints. We assume no more than one
|
||
|
* backend does this at a time.
|
||
|
*/
|
||
|
static void
|
||
|
TruncateMultiXact(void)
|
||
|
{
|
||
|
MultiXactId nextMXact;
|
||
|
uint32 nextOffset;
|
||
|
MultiXactId oldestMXact;
|
||
|
uint32 oldestOffset;
|
||
|
int cutoffPage;
|
||
|
int i;
|
||
|
|
||
|
/*
|
||
|
* First, compute where we can safely truncate. Per notes above,
|
||
|
* this is the oldest valid value among all the OldestMemberMXactId[] and
|
||
|
* OldestVisibleMXactId[] entries, or nextMXact if none are valid.
|
||
|
*/
|
||
|
LWLockAcquire(MultiXactGenLock, LW_SHARED);
|
||
|
|
||
|
/*
|
||
|
* We have to beware of the possibility that nextMXact is in the
|
||
|
* wrapped-around state. We don't fix the counter itself here,
|
||
|
* but we must be sure to use a valid value in our calculation.
|
||
|
*/
|
||
|
nextMXact = MultiXactState->nextMXact;
|
||
|
if (nextMXact < FirstMultiXactId)
|
||
|
nextMXact = FirstMultiXactId;
|
||
|
|
||
|
oldestMXact = nextMXact;
|
||
|
for (i = 1; i <= MaxBackends; i++)
|
||
|
{
|
||
|
MultiXactId thisoldest;
|
||
|
|
||
|
thisoldest = OldestMemberMXactId[i];
|
||
|
if (MultiXactIdIsValid(thisoldest) &&
|
||
|
MultiXactIdPrecedes(thisoldest, oldestMXact))
|
||
|
oldestMXact = thisoldest;
|
||
|
thisoldest = OldestVisibleMXactId[i];
|
||
|
if (MultiXactIdIsValid(thisoldest) &&
|
||
|
MultiXactIdPrecedes(thisoldest, oldestMXact))
|
||
|
oldestMXact = thisoldest;
|
||
|
}
|
||
|
|
||
|
/* Save the current nextOffset too */
|
||
|
nextOffset = MultiXactState->nextOffset;
|
||
|
|
||
|
LWLockRelease(MultiXactGenLock);
|
||
|
|
||
|
debug_elog3(DEBUG2, "MultiXact: truncation point = %u", oldestMXact);
|
||
|
|
||
|
/*
|
||
|
* If we already truncated at this point, do nothing. This saves time
|
||
|
* when no MultiXacts are getting used, which is probably not uncommon.
|
||
|
*/
|
||
|
if (MultiXactState->lastTruncationPoint == oldestMXact)
|
||
|
return;
|
||
|
|
||
|
/*
|
||
|
* We need to determine where to truncate MultiXactMember. If we
|
||
|
* found a valid oldest MultiXactId, read its starting offset;
|
||
|
* otherwise we use the nextOffset value we saved above.
|
||
|
*/
|
||
|
if (oldestMXact == nextMXact)
|
||
|
oldestOffset = nextOffset;
|
||
|
else
|
||
|
{
|
||
|
int pageno;
|
||
|
int slotno;
|
||
|
int entryno;
|
||
|
uint32 *offptr;
|
||
|
|
||
|
LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
|
||
|
|
||
|
pageno = MultiXactIdToOffsetPage(oldestMXact);
|
||
|
entryno = MultiXactIdToOffsetEntry(oldestMXact);
|
||
|
|
||
|
slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, oldestMXact);
|
||
|
offptr = (uint32 *) MultiXactOffsetCtl->shared->page_buffer[slotno];
|
||
|
offptr += entryno;
|
||
|
oldestOffset = *offptr;
|
||
|
|
||
|
LWLockRelease(MultiXactOffsetControlLock);
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* The cutoff point is the start of the segment containing oldestMXact.
|
||
|
* We pass the *page* containing oldestMXact to SimpleLruTruncate.
|
||
|
*/
|
||
|
cutoffPage = MultiXactIdToOffsetPage(oldestMXact);
|
||
|
|
||
|
SimpleLruTruncate(MultiXactOffsetCtl, cutoffPage);
|
||
|
|
||
|
/*
|
||
|
* Also truncate MultiXactMember at the previously determined offset.
|
||
|
*/
|
||
|
cutoffPage = MXOffsetToMemberPage(oldestOffset);
|
||
|
|
||
|
SimpleLruTruncate(MultiXactMemberCtl, cutoffPage);
|
||
|
|
||
|
/*
|
||
|
* Set the last known truncation point. We don't need a lock for this
|
||
|
* since only one backend does checkpoints at a time.
|
||
|
*/
|
||
|
MultiXactState->lastTruncationPoint = oldestMXact;
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* Decide which of two MultiXactOffset page numbers is "older" for truncation
|
||
|
* purposes.
|
||
|
*
|
||
|
* We need to use comparison of MultiXactId here in order to do the right
|
||
|
* thing with wraparound. However, if we are asked about page number zero, we
|
||
|
* don't want to hand InvalidMultiXactId to MultiXactIdPrecedes: it'll get
|
||
|
* weird. So, offset both multis by FirstMultiXactId to avoid that.
|
||
|
* (Actually, the current implementation doesn't do anything weird with
|
||
|
* InvalidMultiXactId, but there's no harm in leaving this code like this.)
|
||
|
*/
|
||
|
static bool
|
||
|
MultiXactOffsetPagePrecedes(int page1, int page2)
|
||
|
{
|
||
|
MultiXactId multi1;
|
||
|
MultiXactId multi2;
|
||
|
|
||
|
multi1 = ((MultiXactId) page1) * MULTIXACT_OFFSETS_PER_PAGE;
|
||
|
multi1 += FirstMultiXactId;
|
||
|
multi2 = ((MultiXactId) page2) * MULTIXACT_OFFSETS_PER_PAGE;
|
||
|
multi2 += FirstMultiXactId;
|
||
|
|
||
|
return MultiXactIdPrecedes(multi1, multi2);
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* Decide which of two MultiXactMember page numbers is "older" for truncation
|
||
|
* purposes. There is no "invalid offset number" so use the numbers verbatim.
|
||
|
*/
|
||
|
static bool
|
||
|
MultiXactMemberPagePrecedes(int page1, int page2)
|
||
|
{
|
||
|
uint32 offset1;
|
||
|
uint32 offset2;
|
||
|
|
||
|
offset1 = ((uint32) page1) * MULTIXACT_MEMBERS_PER_PAGE;
|
||
|
offset2 = ((uint32) page2) * MULTIXACT_MEMBERS_PER_PAGE;
|
||
|
|
||
|
return MultiXactOffsetPrecedes(offset1, offset2);
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* Decide which of two MultiXactIds is earlier.
|
||
|
*
|
||
|
* XXX do we need to do something special for InvalidMultiXactId?
|
||
|
* (Doesn't look like it.)
|
||
|
*/
|
||
|
static bool
|
||
|
MultiXactIdPrecedes(MultiXactId multi1, MultiXactId multi2)
|
||
|
{
|
||
|
int32 diff = (int32) (multi1 - multi2);
|
||
|
|
||
|
return (diff < 0);
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* Decide which of two offsets is earlier.
|
||
|
*/
|
||
|
static bool
|
||
|
MultiXactOffsetPrecedes(uint32 offset1, uint32 offset2)
|
||
|
{
|
||
|
int32 diff = (int32) (offset1 - offset2);
|
||
|
|
||
|
return (diff < 0);
|
||
|
}
|