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postgresql/contrib/amcheck/verify_nbtree.c
Tom Lane f10f0ae420 Replace RelationOpenSmgr() with RelationGetSmgr(). 
The idea behind this patch is to design out bugs like the one fixed
by commit 9d523119f.  Previously, once one did RelationOpenSmgr(rel),
it was considered okay to access rel->rd_smgr directly for some
not-very-clear interval.  But since that pointer will be cleared by
relcache flushes, we had bugs arising from overreliance on a previous
RelationOpenSmgr call still being effective.

Now, very little code except that in rel.h and relcache.c should ever
touch the rd_smgr field directly.  The normal coding rule is to use
RelationGetSmgr(rel) and not expect the result to be valid for longer
than one smgr function call.  There are a couple of places where using
the function every single time seemed like overkill, but they are now
annotated with large warning comments.

Amul Sul, after an idea of mine.

Discussion: https://postgr.es/m/CANiYTQsU7yMFpQYnv=BrcRVqK_3U3mtAzAsJCaqtzsDHfsUbdQ@mail.gmail.com
2021-07-12 17:01:36 -04:00

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/*-------------------------------------------------------------------------
*
* verify_nbtree.c
* Verifies the integrity of nbtree indexes based on invariants.
*
* For B-Tree indexes, verification includes checking that each page in the
* target index has items in logical order as reported by an insertion scankey
* (the insertion scankey sort-wise NULL semantics are needed for
* verification).
*
* When index-to-heap verification is requested, a Bloom filter is used to
* fingerprint all tuples in the target index, as the index is traversed to
* verify its structure. A heap scan later uses Bloom filter probes to verify
* that every visible heap tuple has a matching index tuple.
*
*
* Copyright (c) 2017-2021, PostgreSQL Global Development Group
*
* IDENTIFICATION
* contrib/amcheck/verify_nbtree.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/htup_details.h"
#include "access/nbtree.h"
#include "access/table.h"
#include "access/tableam.h"
#include "access/transam.h"
#include "access/xact.h"
#include "catalog/index.h"
#include "catalog/pg_am.h"
#include "commands/tablecmds.h"
#include "lib/bloomfilter.h"
#include "miscadmin.h"
#include "storage/lmgr.h"
#include "storage/smgr.h"
#include "utils/memutils.h"
#include "utils/snapmgr.h"
PG_MODULE_MAGIC;
/*
* A B-Tree cannot possibly have this many levels, since there must be one
* block per level, which is bound by the range of BlockNumber:
*/
#define InvalidBtreeLevel ((uint32) InvalidBlockNumber)
#define BTreeTupleGetNKeyAtts(itup, rel) \
Min(IndexRelationGetNumberOfKeyAttributes(rel), BTreeTupleGetNAtts(itup, rel))
/*
* State associated with verifying a B-Tree index
*
* target is the point of reference for a verification operation.
*
* Other B-Tree pages may be allocated, but those are always auxiliary (e.g.,
* they are current target's child pages). Conceptually, problems are only
* ever found in the current target page (or for a particular heap tuple during
* heapallindexed verification). Each page found by verification's left/right,
* top/bottom scan becomes the target exactly once.
*/
typedef struct BtreeCheckState
{
/*
* Unchanging state, established at start of verification:
*/
/* B-Tree Index Relation and associated heap relation */
Relation rel;
Relation heaprel;
/* rel is heapkeyspace index? */
bool heapkeyspace;
/* ShareLock held on heap/index, rather than AccessShareLock? */
bool readonly;
/* Also verifying heap has no unindexed tuples? */
bool heapallindexed;
/* Also making sure non-pivot tuples can be found by new search? */
bool rootdescend;
/* Per-page context */
MemoryContext targetcontext;
/* Buffer access strategy */
BufferAccessStrategy checkstrategy;
/*
* Mutable state, for verification of particular page:
*/
/* Current target page */
Page target;
/* Target block number */
BlockNumber targetblock;
/* Target page's LSN */
XLogRecPtr targetlsn;
/*
* Low key: high key of left sibling of target page. Used only for child
* verification. So, 'lowkey' is kept only when 'readonly' is set.
*/
IndexTuple lowkey;
/*
* The rightlink and incomplete split flag of block one level down to the
* target page, which was visited last time via downlink from taget page.
* We use it to check for missing downlinks.
*/
BlockNumber prevrightlink;
bool previncompletesplit;
/*
* Mutable state, for optional heapallindexed verification:
*/
/* Bloom filter fingerprints B-Tree index */
bloom_filter *filter;
/* Debug counter */
int64 heaptuplespresent;
} BtreeCheckState;
/*
* Starting point for verifying an entire B-Tree index level
*/
typedef struct BtreeLevel
{
/* Level number (0 is leaf page level). */
uint32 level;
/* Left most block on level. Scan of level begins here. */
BlockNumber leftmost;
/* Is this level reported as "true" root level by meta page? */
bool istruerootlevel;
} BtreeLevel;
PG_FUNCTION_INFO_V1(bt_index_check);
PG_FUNCTION_INFO_V1(bt_index_parent_check);
static void bt_index_check_internal(Oid indrelid, bool parentcheck,
bool heapallindexed, bool rootdescend);
static inline void btree_index_checkable(Relation rel);
static inline bool btree_index_mainfork_expected(Relation rel);
static void bt_check_every_level(Relation rel, Relation heaprel,
bool heapkeyspace, bool readonly, bool heapallindexed,
bool rootdescend);
static BtreeLevel bt_check_level_from_leftmost(BtreeCheckState *state,
BtreeLevel level);
static void bt_recheck_sibling_links(BtreeCheckState *state,
BlockNumber btpo_prev_from_target,
BlockNumber leftcurrent);
static void bt_target_page_check(BtreeCheckState *state);
static BTScanInsert bt_right_page_check_scankey(BtreeCheckState *state);
static void bt_child_check(BtreeCheckState *state, BTScanInsert targetkey,
OffsetNumber downlinkoffnum);
static void bt_child_highkey_check(BtreeCheckState *state,
OffsetNumber target_downlinkoffnum,
Page loaded_child,
uint32 target_level);
static void bt_downlink_missing_check(BtreeCheckState *state, bool rightsplit,
BlockNumber targetblock, Page target);
static void bt_tuple_present_callback(Relation index, ItemPointer tid,
Datum *values, bool *isnull,
bool tupleIsAlive, void *checkstate);
static IndexTuple bt_normalize_tuple(BtreeCheckState *state,
IndexTuple itup);
static inline IndexTuple bt_posting_plain_tuple(IndexTuple itup, int n);
static bool bt_rootdescend(BtreeCheckState *state, IndexTuple itup);
static inline bool offset_is_negative_infinity(BTPageOpaque opaque,
OffsetNumber offset);
static inline bool invariant_l_offset(BtreeCheckState *state, BTScanInsert key,
OffsetNumber upperbound);
static inline bool invariant_leq_offset(BtreeCheckState *state,
BTScanInsert key,
OffsetNumber upperbound);
static inline bool invariant_g_offset(BtreeCheckState *state, BTScanInsert key,
OffsetNumber lowerbound);
static inline bool invariant_l_nontarget_offset(BtreeCheckState *state,
BTScanInsert key,
BlockNumber nontargetblock,
Page nontarget,
OffsetNumber upperbound);
static Page palloc_btree_page(BtreeCheckState *state, BlockNumber blocknum);
static inline BTScanInsert bt_mkscankey_pivotsearch(Relation rel,
IndexTuple itup);
static ItemId PageGetItemIdCareful(BtreeCheckState *state, BlockNumber block,
Page page, OffsetNumber offset);
static inline ItemPointer BTreeTupleGetHeapTIDCareful(BtreeCheckState *state,
IndexTuple itup, bool nonpivot);
static inline ItemPointer BTreeTupleGetPointsToTID(IndexTuple itup);
/*
* bt_index_check(index regclass, heapallindexed boolean)
*
* Verify integrity of B-Tree index.
*
* Acquires AccessShareLock on heap & index relations. Does not consider
* invariants that exist between parent/child pages. Optionally verifies
* that heap does not contain any unindexed or incorrectly indexed tuples.
*/
Datum
bt_index_check(PG_FUNCTION_ARGS)
{
Oid indrelid = PG_GETARG_OID(0);
bool heapallindexed = false;
if (PG_NARGS() == 2)
heapallindexed = PG_GETARG_BOOL(1);
bt_index_check_internal(indrelid, false, heapallindexed, false);
PG_RETURN_VOID();
}
/*
* bt_index_parent_check(index regclass, heapallindexed boolean)
*
* Verify integrity of B-Tree index.
*
* Acquires ShareLock on heap & index relations. Verifies that downlinks in
* parent pages are valid lower bounds on child pages. Optionally verifies
* that heap does not contain any unindexed or incorrectly indexed tuples.
*/
Datum
bt_index_parent_check(PG_FUNCTION_ARGS)
{
Oid indrelid = PG_GETARG_OID(0);
bool heapallindexed = false;
bool rootdescend = false;
if (PG_NARGS() >= 2)
heapallindexed = PG_GETARG_BOOL(1);
if (PG_NARGS() == 3)
rootdescend = PG_GETARG_BOOL(2);
bt_index_check_internal(indrelid, true, heapallindexed, rootdescend);
PG_RETURN_VOID();
}
/*
* Helper for bt_index_[parent_]check, coordinating the bulk of the work.
*/
static void
bt_index_check_internal(Oid indrelid, bool parentcheck, bool heapallindexed,
bool rootdescend)
{
Oid heapid;
Relation indrel;
Relation heaprel;
LOCKMODE lockmode;
if (parentcheck)
lockmode = ShareLock;
else
lockmode = AccessShareLock;
/*
* We must lock table before index to avoid deadlocks. However, if the
* passed indrelid isn't an index then IndexGetRelation() will fail.
* Rather than emitting a not-very-helpful error message, postpone
* complaining, expecting that the is-it-an-index test below will fail.
*
* In hot standby mode this will raise an error when parentcheck is true.
*/
heapid = IndexGetRelation(indrelid, true);
if (OidIsValid(heapid))
heaprel = table_open(heapid, lockmode);
else
heaprel = NULL;
/*
* Open the target index relations separately (like relation_openrv(), but
* with heap relation locked first to prevent deadlocking). In hot
* standby mode this will raise an error when parentcheck is true.
*
* There is no need for the usual indcheckxmin usability horizon test
* here, even in the heapallindexed case, because index undergoing
* verification only needs to have entries for a new transaction snapshot.
* (If this is a parentcheck verification, there is no question about
* committed or recently dead heap tuples lacking index entries due to
* concurrent activity.)
*/
indrel = index_open(indrelid, lockmode);
/*
* Since we did the IndexGetRelation call above without any lock, it's
* barely possible that a race against an index drop/recreation could have
* netted us the wrong table.
*/
if (heaprel == NULL || heapid != IndexGetRelation(indrelid, false))
ereport(ERROR,
(errcode(ERRCODE_UNDEFINED_TABLE),
errmsg("could not open parent table of index \"%s\"",
RelationGetRelationName(indrel))));
/* Relation suitable for checking as B-Tree? */
btree_index_checkable(indrel);
if (btree_index_mainfork_expected(indrel))
{
bool heapkeyspace,
allequalimage;
if (!smgrexists(RelationGetSmgr(indrel), MAIN_FORKNUM))
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("index \"%s\" lacks a main relation fork",
RelationGetRelationName(indrel))));
/* Extract metadata from metapage, and sanitize it in passing */
_bt_metaversion(indrel, &heapkeyspace, &allequalimage);
if (allequalimage && !heapkeyspace)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("index \"%s\" metapage has equalimage field set on unsupported nbtree version",
RelationGetRelationName(indrel))));
if (allequalimage && !_bt_allequalimage(indrel, false))
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("index \"%s\" metapage incorrectly indicates that deduplication is safe",
RelationGetRelationName(indrel))));
/* Check index, possibly against table it is an index on */
bt_check_every_level(indrel, heaprel, heapkeyspace, parentcheck,
heapallindexed, rootdescend);
}
/*
* Release locks early. That's ok here because nothing in the called
* routines will trigger shared cache invalidations to be sent, so we can
* relax the usual pattern of only releasing locks after commit.
*/
index_close(indrel, lockmode);
if (heaprel)
table_close(heaprel, lockmode);
}
/*
* Basic checks about the suitability of a relation for checking as a B-Tree
* index.
*
* NB: Intentionally not checking permissions, the function is normally not
* callable by non-superusers. If granted, it's useful to be able to check a
* whole cluster.
*/
static inline void
btree_index_checkable(Relation rel)
{
if (rel->rd_rel->relkind != RELKIND_INDEX ||
rel->rd_rel->relam != BTREE_AM_OID)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("only B-Tree indexes are supported as targets for verification"),
errdetail("Relation \"%s\" is not a B-Tree index.",
RelationGetRelationName(rel))));
if (RELATION_IS_OTHER_TEMP(rel))
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot access temporary tables of other sessions"),
errdetail("Index \"%s\" is associated with temporary relation.",
RelationGetRelationName(rel))));
if (!rel->rd_index->indisvalid)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot check index \"%s\"",
RelationGetRelationName(rel)),
errdetail("Index is not valid.")));
}
/*
* Check if B-Tree index relation should have a file for its main relation
* fork. Verification uses this to skip unlogged indexes when in hot standby
* mode, where there is simply nothing to verify.
*
* NB: Caller should call btree_index_checkable() before calling here.
*/
static inline bool
btree_index_mainfork_expected(Relation rel)
{
if (rel->rd_rel->relpersistence != RELPERSISTENCE_UNLOGGED ||
!RecoveryInProgress())
return true;
ereport(NOTICE,
(errcode(ERRCODE_READ_ONLY_SQL_TRANSACTION),
errmsg("cannot verify unlogged index \"%s\" during recovery, skipping",
RelationGetRelationName(rel))));
return false;
}
/*
* Main entry point for B-Tree SQL-callable functions. Walks the B-Tree in
* logical order, verifying invariants as it goes. Optionally, verification
* checks if the heap relation contains any tuples that are not represented in
* the index but should be.
*
* It is the caller's responsibility to acquire appropriate heavyweight lock on
* the index relation, and advise us if extra checks are safe when a ShareLock
* is held. (A lock of the same type must also have been acquired on the heap
* relation.)
*
* A ShareLock is generally assumed to prevent any kind of physical
* modification to the index structure, including modifications that VACUUM may
* make. This does not include setting of the LP_DEAD bit by concurrent index
* scans, although that is just metadata that is not able to directly affect
* any check performed here. Any concurrent process that might act on the
* LP_DEAD bit being set (recycle space) requires a heavyweight lock that
* cannot be held while we hold a ShareLock. (Besides, even if that could
* happen, the ad-hoc recycling when a page might otherwise split is performed
* per-page, and requires an exclusive buffer lock, which wouldn't cause us
* trouble. _bt_delitems_vacuum() may only delete leaf items, and so the extra
* parent/child check cannot be affected.)
*/
static void
bt_check_every_level(Relation rel, Relation heaprel, bool heapkeyspace,
bool readonly, bool heapallindexed, bool rootdescend)
{
BtreeCheckState *state;
Page metapage;
BTMetaPageData *metad;
uint32 previouslevel;
BtreeLevel current;
Snapshot snapshot = SnapshotAny;
if (!readonly)
elog(DEBUG1, "verifying consistency of tree structure for index \"%s\"",
RelationGetRelationName(rel));
else
elog(DEBUG1, "verifying consistency of tree structure for index \"%s\" with cross-level checks",
RelationGetRelationName(rel));
/*
* This assertion matches the one in index_getnext_tid(). See page
* recycling/"visible to everyone" notes in nbtree README.
*/
Assert(TransactionIdIsValid(RecentXmin));
/*
* Initialize state for entire verification operation
*/
state = palloc0(sizeof(BtreeCheckState));
state->rel = rel;
state->heaprel = heaprel;
state->heapkeyspace = heapkeyspace;
state->readonly = readonly;
state->heapallindexed = heapallindexed;
state->rootdescend = rootdescend;
if (state->heapallindexed)
{
int64 total_pages;
int64 total_elems;
uint64 seed;
/*
* Size Bloom filter based on estimated number of tuples in index,
* while conservatively assuming that each block must contain at least
* MaxTIDsPerBTreePage / 3 "plain" tuples -- see
* bt_posting_plain_tuple() for definition, and details of how posting
* list tuples are handled.
*/
total_pages = RelationGetNumberOfBlocks(rel);
total_elems = Max(total_pages * (MaxTIDsPerBTreePage / 3),
(int64) state->rel->rd_rel->reltuples);
/* Random seed relies on backend srandom() call to avoid repetition */
seed = random();
/* Create Bloom filter to fingerprint index */
state->filter = bloom_create(total_elems, maintenance_work_mem, seed);
state->heaptuplespresent = 0;
/*
* Register our own snapshot in !readonly case, rather than asking
* table_index_build_scan() to do this for us later. This needs to
* happen before index fingerprinting begins, so we can later be
* certain that index fingerprinting should have reached all tuples
* returned by table_index_build_scan().
*/
if (!state->readonly)
{
snapshot = RegisterSnapshot(GetTransactionSnapshot());
/*
* GetTransactionSnapshot() always acquires a new MVCC snapshot in
* READ COMMITTED mode. A new snapshot is guaranteed to have all
* the entries it requires in the index.
*
* We must defend against the possibility that an old xact
* snapshot was returned at higher isolation levels when that
* snapshot is not safe for index scans of the target index. This
* is possible when the snapshot sees tuples that are before the
* index's indcheckxmin horizon. Throwing an error here should be
* very rare. It doesn't seem worth using a secondary snapshot to
* avoid this.
*/
if (IsolationUsesXactSnapshot() && rel->rd_index->indcheckxmin &&
!TransactionIdPrecedes(HeapTupleHeaderGetXmin(rel->rd_indextuple->t_data),
snapshot->xmin))
ereport(ERROR,
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
errmsg("index \"%s\" cannot be verified using transaction snapshot",
RelationGetRelationName(rel))));
}
}
Assert(!state->rootdescend || state->readonly);
if (state->rootdescend && !state->heapkeyspace)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot verify that tuples from index \"%s\" can each be found by an independent index search",
RelationGetRelationName(rel)),
errhint("Only B-Tree version 4 indexes support rootdescend verification.")));
/* Create context for page */
state->targetcontext = AllocSetContextCreate(CurrentMemoryContext,
"amcheck context",
ALLOCSET_DEFAULT_SIZES);
state->checkstrategy = GetAccessStrategy(BAS_BULKREAD);
/* Get true root block from meta-page */
metapage = palloc_btree_page(state, BTREE_METAPAGE);
metad = BTPageGetMeta(metapage);
/*
* Certain deletion patterns can result in "skinny" B-Tree indexes, where
* the fast root and true root differ.
*
* Start from the true root, not the fast root, unlike conventional index
* scans. This approach is more thorough, and removes the risk of
* following a stale fast root from the meta page.
*/
if (metad->btm_fastroot != metad->btm_root)
ereport(DEBUG1,
(errcode(ERRCODE_NO_DATA),
errmsg_internal("harmless fast root mismatch in index \"%s\"",
RelationGetRelationName(rel)),
errdetail_internal("Fast root block %u (level %u) differs from true root block %u (level %u).",
metad->btm_fastroot, metad->btm_fastlevel,
metad->btm_root, metad->btm_level)));
/*
* Starting at the root, verify every level. Move left to right, top to
* bottom. Note that there may be no pages other than the meta page (meta
* page can indicate that root is P_NONE when the index is totally empty).
*/
previouslevel = InvalidBtreeLevel;
current.level = metad->btm_level;
current.leftmost = metad->btm_root;
current.istruerootlevel = true;
while (current.leftmost != P_NONE)
{
/*
* Verify this level, and get left most page for next level down, if
* not at leaf level
*/
current = bt_check_level_from_leftmost(state, current);
if (current.leftmost == InvalidBlockNumber)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("index \"%s\" has no valid pages on level below %u or first level",
RelationGetRelationName(rel), previouslevel)));
previouslevel = current.level;
}
/*
* * Check whether heap contains unindexed/malformed tuples *
*/
if (state->heapallindexed)
{
IndexInfo *indexinfo = BuildIndexInfo(state->rel);
TableScanDesc scan;
/*
* Create our own scan for table_index_build_scan(), rather than
* getting it to do so for us. This is required so that we can
* actually use the MVCC snapshot registered earlier in !readonly
* case.
*
* Note that table_index_build_scan() calls heap_endscan() for us.
*/
scan = table_beginscan_strat(state->heaprel, /* relation */
snapshot, /* snapshot */
0, /* number of keys */
NULL, /* scan key */
true, /* buffer access strategy OK */
true); /* syncscan OK? */
/*
* Scan will behave as the first scan of a CREATE INDEX CONCURRENTLY
* behaves in !readonly case.
*
* It's okay that we don't actually use the same lock strength for the
* heap relation as any other ii_Concurrent caller would in !readonly
* case. We have no reason to care about a concurrent VACUUM
* operation, since there isn't going to be a second scan of the heap
* that needs to be sure that there was no concurrent recycling of
* TIDs.
*/
indexinfo->ii_Concurrent = !state->readonly;
/*
* Don't wait for uncommitted tuple xact commit/abort when index is a
* unique index on a catalog (or an index used by an exclusion
* constraint). This could otherwise happen in the readonly case.
*/
indexinfo->ii_Unique = false;
indexinfo->ii_ExclusionOps = NULL;
indexinfo->ii_ExclusionProcs = NULL;
indexinfo->ii_ExclusionStrats = NULL;
elog(DEBUG1, "verifying that tuples from index \"%s\" are present in \"%s\"",
RelationGetRelationName(state->rel),
RelationGetRelationName(state->heaprel));
table_index_build_scan(state->heaprel, state->rel, indexinfo, true, false,
bt_tuple_present_callback, (void *) state, scan);
ereport(DEBUG1,
(errmsg_internal("finished verifying presence of " INT64_FORMAT " tuples from table \"%s\" with bitset %.2f%% set",
state->heaptuplespresent, RelationGetRelationName(heaprel),
100.0 * bloom_prop_bits_set(state->filter))));
if (snapshot != SnapshotAny)
UnregisterSnapshot(snapshot);
bloom_free(state->filter);
}
/* Be tidy: */
MemoryContextDelete(state->targetcontext);
}
/*
* Given a left-most block at some level, move right, verifying each page
* individually (with more verification across pages for "readonly"
* callers). Caller should pass the true root page as the leftmost initially,
* working their way down by passing what is returned for the last call here
* until level 0 (leaf page level) was reached.
*
* Returns state for next call, if any. This includes left-most block number
* one level lower that should be passed on next level/call, which is set to
* P_NONE on last call here (when leaf level is verified). Level numbers
* follow the nbtree convention: higher levels have higher numbers, because new
* levels are added only due to a root page split. Note that prior to the
* first root page split, the root is also a leaf page, so there is always a
* level 0 (leaf level), and it's always the last level processed.
*
* Note on memory management: State's per-page context is reset here, between
* each call to bt_target_page_check().
*/
static BtreeLevel
bt_check_level_from_leftmost(BtreeCheckState *state, BtreeLevel level)
{
/* State to establish early, concerning entire level */
BTPageOpaque opaque;
MemoryContext oldcontext;
BtreeLevel nextleveldown;
/* Variables for iterating across level using right links */
BlockNumber leftcurrent = P_NONE;
BlockNumber current = level.leftmost;
/* Initialize return state */
nextleveldown.leftmost = InvalidBlockNumber;
nextleveldown.level = InvalidBtreeLevel;
nextleveldown.istruerootlevel = false;
/* Use page-level context for duration of this call */
oldcontext = MemoryContextSwitchTo(state->targetcontext);
elog(DEBUG1, "verifying level %u%s", level.level,
level.istruerootlevel ?
" (true root level)" : level.level == 0 ? " (leaf level)" : "");
state->prevrightlink = InvalidBlockNumber;
state->previncompletesplit = false;
do
{
/* Don't rely on CHECK_FOR_INTERRUPTS() calls at lower level */
CHECK_FOR_INTERRUPTS();
/* Initialize state for this iteration */
state->targetblock = current;
state->target = palloc_btree_page(state, state->targetblock);
state->targetlsn = PageGetLSN(state->target);
opaque = (BTPageOpaque) PageGetSpecialPointer(state->target);
if (P_IGNORE(opaque))
{
/*
* Since there cannot be a concurrent VACUUM operation in readonly
* mode, and since a page has no links within other pages
* (siblings and parent) once it is marked fully deleted, it
* should be impossible to land on a fully deleted page in
* readonly mode. See bt_child_check() for further details.
*
* The bt_child_check() P_ISDELETED() check is repeated here so
* that pages that are only reachable through sibling links get
* checked.
*/
if (state->readonly && P_ISDELETED(opaque))
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("downlink or sibling link points to deleted block in index \"%s\"",
RelationGetRelationName(state->rel)),
errdetail_internal("Block=%u left block=%u left link from block=%u.",
current, leftcurrent, opaque->btpo_prev)));
if (P_RIGHTMOST(opaque))
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("block %u fell off the end of index \"%s\"",
current, RelationGetRelationName(state->rel))));
else
ereport(DEBUG1,
(errcode(ERRCODE_NO_DATA),
errmsg_internal("block %u of index \"%s\" concurrently deleted",
current, RelationGetRelationName(state->rel))));
goto nextpage;
}
else if (nextleveldown.leftmost == InvalidBlockNumber)
{
/*
* A concurrent page split could make the caller supplied leftmost
* block no longer contain the leftmost page, or no longer be the
* true root, but where that isn't possible due to heavyweight
* locking, check that the first valid page meets caller's
* expectations.
*/
if (state->readonly)
{
if (!P_LEFTMOST(opaque))
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("block %u is not leftmost in index \"%s\"",
current, RelationGetRelationName(state->rel))));
if (level.istruerootlevel && !P_ISROOT(opaque))
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("block %u is not true root in index \"%s\"",
current, RelationGetRelationName(state->rel))));
}
/*
* Before beginning any non-trivial examination of level, prepare
* state for next bt_check_level_from_leftmost() invocation for
* the next level for the next level down (if any).
*
* There should be at least one non-ignorable page per level,
* unless this is the leaf level, which is assumed by caller to be
* final level.
*/
if (!P_ISLEAF(opaque))
{
IndexTuple itup;
ItemId itemid;
/* Internal page -- downlink gets leftmost on next level */
itemid = PageGetItemIdCareful(state, state->targetblock,
state->target,
P_FIRSTDATAKEY(opaque));
itup = (IndexTuple) PageGetItem(state->target, itemid);
nextleveldown.leftmost = BTreeTupleGetDownLink(itup);
nextleveldown.level = opaque->btpo_level - 1;
}
else
{
/*
* Leaf page -- final level caller must process.
*
* Note that this could also be the root page, if there has
* been no root page split yet.
*/
nextleveldown.leftmost = P_NONE;
nextleveldown.level = InvalidBtreeLevel;
}
/*
* Finished setting up state for this call/level. Control will
* never end up back here in any future loop iteration for this
* level.
*/
}
/* Sibling links should be in mutual agreement */
if (opaque->btpo_prev != leftcurrent)
bt_recheck_sibling_links(state, opaque->btpo_prev, leftcurrent);
/* Check level */
if (level.level != opaque->btpo_level)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("leftmost down link for level points to block in index \"%s\" whose level is not one level down",
RelationGetRelationName(state->rel)),
errdetail_internal("Block pointed to=%u expected level=%u level in pointed to block=%u.",
current, level.level, opaque->btpo_level)));
/* Verify invariants for page */
bt_target_page_check(state);
nextpage:
/* Try to detect circular links */
if (current == leftcurrent || current == opaque->btpo_prev)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("circular link chain found in block %u of index \"%s\"",
current, RelationGetRelationName(state->rel))));
leftcurrent = current;
current = opaque->btpo_next;
if (state->lowkey)
{
Assert(state->readonly);
pfree(state->lowkey);
state->lowkey = NULL;
}
/*
* Copy current target high key as the low key of right sibling.
* Allocate memory in upper level context, so it would be cleared
* after reset of target context.
*
* We only need the low key in corner cases of checking child high
* keys. We use high key only when incomplete split on the child level
* falls to the boundary of pages on the target level. See
* bt_child_highkey_check() for details. So, typically we won't end
* up doing anything with low key, but it's simpler for general case
* high key verification to always have it available.
*
* The correctness of managing low key in the case of concurrent
* splits wasn't investigated yet. Thankfully we only need low key
* for readonly verification and concurrent splits won't happen.
*/
if (state->readonly && !P_RIGHTMOST(opaque))
{
IndexTuple itup;
ItemId itemid;
itemid = PageGetItemIdCareful(state, state->targetblock,
state->target, P_HIKEY);
itup = (IndexTuple) PageGetItem(state->target, itemid);
state->lowkey = MemoryContextAlloc(oldcontext, IndexTupleSize(itup));
memcpy(state->lowkey, itup, IndexTupleSize(itup));
}
/* Free page and associated memory for this iteration */
MemoryContextReset(state->targetcontext);
}
while (current != P_NONE);
if (state->lowkey)
{
Assert(state->readonly);
pfree(state->lowkey);
state->lowkey = NULL;
}
/* Don't change context for caller */
MemoryContextSwitchTo(oldcontext);
return nextleveldown;
}
/*
* Raise an error when target page's left link does not point back to the
* previous target page, called leftcurrent here. The leftcurrent page's
* right link was followed to get to the current target page, and we expect
* mutual agreement among leftcurrent and the current target page. Make sure
* that this condition has definitely been violated in the !readonly case,
* where concurrent page splits are something that we need to deal with.
*
* Cross-page inconsistencies involving pages that don't agree about being
* siblings are known to be a particularly good indicator of corruption
* involving partial writes/lost updates. The bt_right_page_check_scankey
* check also provides a way of detecting cross-page inconsistencies for
* !readonly callers, but it can only detect sibling pages that have an
* out-of-order keyspace, which can't catch many of the problems that we
* expect to catch here.
*
* The classic example of the kind of inconsistency that we can only catch
* with this check (when in !readonly mode) involves three sibling pages that
* were affected by a faulty page split at some point in the past. The
* effects of the split are reflected in the original page and its new right
* sibling page, with a lack of any accompanying changes for the _original_
* right sibling page. The original right sibling page's left link fails to
* point to the new right sibling page (its left link still points to the
* original page), even though the first phase of a page split is supposed to
* work as a single atomic action. This subtle inconsistency will probably
* only break backwards scans in practice.
*
* Note that this is the only place where amcheck will "couple" buffer locks
* (and only for !readonly callers). In general we prefer to avoid more
* thorough cross-page checks in !readonly mode, but it seems worth the
* complexity here. Also, the performance overhead of performing lock
* coupling here is negligible in practice. Control only reaches here with a
* non-corrupt index when there is a concurrent page split at the instant
* caller crossed over to target page from leftcurrent page.
*/
static void
bt_recheck_sibling_links(BtreeCheckState *state,
BlockNumber btpo_prev_from_target,
BlockNumber leftcurrent)
{
if (!state->readonly)
{
Buffer lbuf;
Buffer newtargetbuf;
Page page;
BTPageOpaque opaque;
BlockNumber newtargetblock;
/* Couple locks in the usual order for nbtree: Left to right */
lbuf = ReadBufferExtended(state->rel, MAIN_FORKNUM, leftcurrent,
RBM_NORMAL, state->checkstrategy);
LockBuffer(lbuf, BT_READ);
_bt_checkpage(state->rel, lbuf);
page = BufferGetPage(lbuf);
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
if (P_ISDELETED(opaque))
{
/*
* Cannot reason about concurrently deleted page -- the left link
* in the page to the right is expected to point to some other
* page to the left (not leftcurrent page).
*
* Note that we deliberately don't give up with a half-dead page.
*/
UnlockReleaseBuffer(lbuf);
return;
}
newtargetblock = opaque->btpo_next;
/* Avoid self-deadlock when newtargetblock == leftcurrent */
if (newtargetblock != leftcurrent)
{
newtargetbuf = ReadBufferExtended(state->rel, MAIN_FORKNUM,
newtargetblock, RBM_NORMAL,
state->checkstrategy);
LockBuffer(newtargetbuf, BT_READ);
_bt_checkpage(state->rel, newtargetbuf);
page = BufferGetPage(newtargetbuf);
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
/* btpo_prev_from_target may have changed; update it */
btpo_prev_from_target = opaque->btpo_prev;
}
else
{
/*
* leftcurrent right sibling points back to leftcurrent block.
* Index is corrupt. Easiest way to handle this is to pretend
* that we actually read from a distinct page that has an invalid
* block number in its btpo_prev.
*/
newtargetbuf = InvalidBuffer;
btpo_prev_from_target = InvalidBlockNumber;
}
/*
* No need to check P_ISDELETED here, since new target block cannot be
* marked deleted as long as we hold a lock on lbuf
*/
if (BufferIsValid(newtargetbuf))
UnlockReleaseBuffer(newtargetbuf);
UnlockReleaseBuffer(lbuf);
if (btpo_prev_from_target == leftcurrent)
{
/* Report split in left sibling, not target (or new target) */
ereport(DEBUG1,
(errcode(ERRCODE_INTERNAL_ERROR),
errmsg_internal("harmless concurrent page split detected in index \"%s\"",
RelationGetRelationName(state->rel)),
errdetail_internal("Block=%u new right sibling=%u original right sibling=%u.",
leftcurrent, newtargetblock,
state->targetblock)));
return;
}
/*
* Index is corrupt. Make sure that we report correct target page.
*
* This could have changed in cases where there was a concurrent page
* split, as well as index corruption (at least in theory). Note that
* btpo_prev_from_target was already updated above.
*/
state->targetblock = newtargetblock;
}
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("left link/right link pair in index \"%s\" not in agreement",
RelationGetRelationName(state->rel)),
errdetail_internal("Block=%u left block=%u left link from block=%u.",
state->targetblock, leftcurrent,
btpo_prev_from_target)));
}
/*
* Function performs the following checks on target page, or pages ancillary to
* target page:
*
* - That every "real" data item is less than or equal to the high key, which
* is an upper bound on the items on the page. Data items should be
* strictly less than the high key when the page is an internal page.
*
* - That within the page, every data item is strictly less than the item
* immediately to its right, if any (i.e., that the items are in order
* within the page, so that the binary searches performed by index scans are
* sane).
*
* - That the last data item stored on the page is strictly less than the
* first data item on the page to the right (when such a first item is
* available).
*
* - Various checks on the structure of tuples themselves. For example, check
* that non-pivot tuples have no truncated attributes.
*
* Furthermore, when state passed shows ShareLock held, function also checks:
*
* - That all child pages respect strict lower bound from parent's pivot
* tuple.
*
* - That downlink to block was encountered in parent where that's expected.
*
* - That high keys of child pages matches corresponding pivot keys in parent.
*
* This is also where heapallindexed callers use their Bloom filter to
* fingerprint IndexTuples for later table_index_build_scan() verification.
*
* Note: Memory allocated in this routine is expected to be released by caller
* resetting state->targetcontext.
*/
static void
bt_target_page_check(BtreeCheckState *state)
{
OffsetNumber offset;
OffsetNumber max;
BTPageOpaque topaque;
topaque = (BTPageOpaque) PageGetSpecialPointer(state->target);
max = PageGetMaxOffsetNumber(state->target);
elog(DEBUG2, "verifying %u items on %s block %u", max,
P_ISLEAF(topaque) ? "leaf" : "internal", state->targetblock);
/*
* Check the number of attributes in high key. Note, rightmost page
* doesn't contain a high key, so nothing to check
*/
if (!P_RIGHTMOST(topaque))
{
ItemId itemid;
IndexTuple itup;
/* Verify line pointer before checking tuple */
itemid = PageGetItemIdCareful(state, state->targetblock,
state->target, P_HIKEY);
if (!_bt_check_natts(state->rel, state->heapkeyspace, state->target,
P_HIKEY))
{
itup = (IndexTuple) PageGetItem(state->target, itemid);
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("wrong number of high key index tuple attributes in index \"%s\"",
RelationGetRelationName(state->rel)),
errdetail_internal("Index block=%u natts=%u block type=%s page lsn=%X/%X.",
state->targetblock,
BTreeTupleGetNAtts(itup, state->rel),
P_ISLEAF(topaque) ? "heap" : "index",
LSN_FORMAT_ARGS(state->targetlsn))));
}
}
/*
* Loop over page items, starting from first non-highkey item, not high
* key (if any). Most tests are not performed for the "negative infinity"
* real item (if any).
*/
for (offset = P_FIRSTDATAKEY(topaque);
offset <= max;
offset = OffsetNumberNext(offset))
{
ItemId itemid;
IndexTuple itup;
size_t tupsize;
BTScanInsert skey;
bool lowersizelimit;
ItemPointer scantid;
CHECK_FOR_INTERRUPTS();
itemid = PageGetItemIdCareful(state, state->targetblock,
state->target, offset);
itup = (IndexTuple) PageGetItem(state->target, itemid);
tupsize = IndexTupleSize(itup);
/*
* lp_len should match the IndexTuple reported length exactly, since
* lp_len is completely redundant in indexes, and both sources of
* tuple length are MAXALIGN()'d. nbtree does not use lp_len all that
* frequently, and is surprisingly tolerant of corrupt lp_len fields.
*/
if (tupsize != ItemIdGetLength(itemid))
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("index tuple size does not equal lp_len in index \"%s\"",
RelationGetRelationName(state->rel)),
errdetail_internal("Index tid=(%u,%u) tuple size=%zu lp_len=%u page lsn=%X/%X.",
state->targetblock, offset,
tupsize, ItemIdGetLength(itemid),
LSN_FORMAT_ARGS(state->targetlsn)),
errhint("This could be a torn page problem.")));
/* Check the number of index tuple attributes */
if (!_bt_check_natts(state->rel, state->heapkeyspace, state->target,
offset))
{
ItemPointer tid;
char *itid,
*htid;
itid = psprintf("(%u,%u)", state->targetblock, offset);
tid = BTreeTupleGetPointsToTID(itup);
htid = psprintf("(%u,%u)",
ItemPointerGetBlockNumberNoCheck(tid),
ItemPointerGetOffsetNumberNoCheck(tid));
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("wrong number of index tuple attributes in index \"%s\"",
RelationGetRelationName(state->rel)),
errdetail_internal("Index tid=%s natts=%u points to %s tid=%s page lsn=%X/%X.",
itid,
BTreeTupleGetNAtts(itup, state->rel),
P_ISLEAF(topaque) ? "heap" : "index",
htid,
LSN_FORMAT_ARGS(state->targetlsn))));
}
/*
* Don't try to generate scankey using "negative infinity" item on
* internal pages. They are always truncated to zero attributes.
*/
if (offset_is_negative_infinity(topaque, offset))
{
/*
* We don't call bt_child_check() for "negative infinity" items.
* But if we're performing downlink connectivity check, we do it
* for every item including "negative infinity" one.
*/
if (!P_ISLEAF(topaque) && state->readonly)
{
bt_child_highkey_check(state,
offset,
NULL,
topaque->btpo_level);
}
continue;
}
/*
* Readonly callers may optionally verify that non-pivot tuples can
* each be found by an independent search that starts from the root.
* Note that we deliberately don't do individual searches for each
* TID, since the posting list itself is validated by other checks.
*/
if (state->rootdescend && P_ISLEAF(topaque) &&
!bt_rootdescend(state, itup))
{
ItemPointer tid = BTreeTupleGetPointsToTID(itup);
char *itid,
*htid;
itid = psprintf("(%u,%u)", state->targetblock, offset);
htid = psprintf("(%u,%u)", ItemPointerGetBlockNumber(tid),
ItemPointerGetOffsetNumber(tid));
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("could not find tuple using search from root page in index \"%s\"",
RelationGetRelationName(state->rel)),
errdetail_internal("Index tid=%s points to heap tid=%s page lsn=%X/%X.",
itid, htid,
LSN_FORMAT_ARGS(state->targetlsn))));
}
/*
* If tuple is a posting list tuple, make sure posting list TIDs are
* in order
*/
if (BTreeTupleIsPosting(itup))
{
ItemPointerData last;
ItemPointer current;
ItemPointerCopy(BTreeTupleGetHeapTID(itup), &last);
for (int i = 1; i < BTreeTupleGetNPosting(itup); i++)
{
current = BTreeTupleGetPostingN(itup, i);
if (ItemPointerCompare(current, &last) <= 0)
{
char *itid = psprintf("(%u,%u)", state->targetblock, offset);
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg_internal("posting list contains misplaced TID in index \"%s\"",
RelationGetRelationName(state->rel)),
errdetail_internal("Index tid=%s posting list offset=%d page lsn=%X/%X.",
itid, i,
LSN_FORMAT_ARGS(state->targetlsn))));
}
ItemPointerCopy(current, &last);
}
}
/* Build insertion scankey for current page offset */
skey = bt_mkscankey_pivotsearch(state->rel, itup);
/*
* Make sure tuple size does not exceed the relevant BTREE_VERSION
* specific limit.
*
* BTREE_VERSION 4 (which introduced heapkeyspace rules) requisitioned
* a small amount of space from BTMaxItemSize() in order to ensure
* that suffix truncation always has enough space to add an explicit
* heap TID back to a tuple -- we pessimistically assume that every
* newly inserted tuple will eventually need to have a heap TID
* appended during a future leaf page split, when the tuple becomes
* the basis of the new high key (pivot tuple) for the leaf page.
*
* Since the reclaimed space is reserved for that purpose, we must not
* enforce the slightly lower limit when the extra space has been used
* as intended. In other words, there is only a cross-version
* difference in the limit on tuple size within leaf pages.
*
* Still, we're particular about the details within BTREE_VERSION 4
* internal pages. Pivot tuples may only use the extra space for its
* designated purpose. Enforce the lower limit for pivot tuples when
* an explicit heap TID isn't actually present. (In all other cases
* suffix truncation is guaranteed to generate a pivot tuple that's no
* larger than the firstright tuple provided to it by its caller.)
*/
lowersizelimit = skey->heapkeyspace &&
(P_ISLEAF(topaque) || BTreeTupleGetHeapTID(itup) == NULL);
if (tupsize > (lowersizelimit ? BTMaxItemSize(state->target) :
BTMaxItemSizeNoHeapTid(state->target)))
{
ItemPointer tid = BTreeTupleGetPointsToTID(itup);
char *itid,
*htid;
itid = psprintf("(%u,%u)", state->targetblock, offset);
htid = psprintf("(%u,%u)",
ItemPointerGetBlockNumberNoCheck(tid),
ItemPointerGetOffsetNumberNoCheck(tid));
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("index row size %zu exceeds maximum for index \"%s\"",
tupsize, RelationGetRelationName(state->rel)),
errdetail_internal("Index tid=%s points to %s tid=%s page lsn=%X/%X.",
itid,
P_ISLEAF(topaque) ? "heap" : "index",
htid,
LSN_FORMAT_ARGS(state->targetlsn))));
}
/* Fingerprint leaf page tuples (those that point to the heap) */
if (state->heapallindexed && P_ISLEAF(topaque) && !ItemIdIsDead(itemid))
{
IndexTuple norm;
if (BTreeTupleIsPosting(itup))
{
/* Fingerprint all elements as distinct "plain" tuples */
for (int i = 0; i < BTreeTupleGetNPosting(itup); i++)
{
IndexTuple logtuple;
logtuple = bt_posting_plain_tuple(itup, i);
norm = bt_normalize_tuple(state, logtuple);
bloom_add_element(state->filter, (unsigned char *) norm,
IndexTupleSize(norm));
/* Be tidy */
if (norm != logtuple)
pfree(norm);
pfree(logtuple);
}
}
else
{
norm = bt_normalize_tuple(state, itup);
bloom_add_element(state->filter, (unsigned char *) norm,
IndexTupleSize(norm));
/* Be tidy */
if (norm != itup)
pfree(norm);
}
}
/*
* * High key check *
*
* If there is a high key (if this is not the rightmost page on its
* entire level), check that high key actually is upper bound on all
* page items. If this is a posting list tuple, we'll need to set
* scantid to be highest TID in posting list.
*
* We prefer to check all items against high key rather than checking
* just the last and trusting that the operator class obeys the
* transitive law (which implies that all previous items also
* respected the high key invariant if they pass the item order
* check).
*
* Ideally, we'd compare every item in the index against every other
* item in the index, and not trust opclass obedience of the
* transitive law to bridge the gap between children and their
* grandparents (as well as great-grandparents, and so on). We don't
* go to those lengths because that would be prohibitively expensive,
* and probably not markedly more effective in practice.
*
* On the leaf level, we check that the key is <= the highkey.
* However, on non-leaf levels we check that the key is < the highkey,
* because the high key is "just another separator" rather than a copy
* of some existing key item; we expect it to be unique among all keys
* on the same level. (Suffix truncation will sometimes produce a
* leaf highkey that is an untruncated copy of the lastleft item, but
* never any other item, which necessitates weakening the leaf level
* check to <=.)
*
* Full explanation for why a highkey is never truly a copy of another
* item from the same level on internal levels:
*
* While the new left page's high key is copied from the first offset
* on the right page during an internal page split, that's not the
* full story. In effect, internal pages are split in the middle of
* the firstright tuple, not between the would-be lastleft and
* firstright tuples: the firstright key ends up on the left side as
* left's new highkey, and the firstright downlink ends up on the
* right side as right's new "negative infinity" item. The negative
* infinity tuple is truncated to zero attributes, so we're only left
* with the downlink. In other words, the copying is just an
* implementation detail of splitting in the middle of a (pivot)
* tuple. (See also: "Notes About Data Representation" in the nbtree
* README.)
*/
scantid = skey->scantid;
if (state->heapkeyspace && BTreeTupleIsPosting(itup))
skey->scantid = BTreeTupleGetMaxHeapTID(itup);
if (!P_RIGHTMOST(topaque) &&
!(P_ISLEAF(topaque) ? invariant_leq_offset(state, skey, P_HIKEY) :
invariant_l_offset(state, skey, P_HIKEY)))
{
ItemPointer tid = BTreeTupleGetPointsToTID(itup);
char *itid,
*htid;
itid = psprintf("(%u,%u)", state->targetblock, offset);
htid = psprintf("(%u,%u)",
ItemPointerGetBlockNumberNoCheck(tid),
ItemPointerGetOffsetNumberNoCheck(tid));
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("high key invariant violated for index \"%s\"",
RelationGetRelationName(state->rel)),
errdetail_internal("Index tid=%s points to %s tid=%s page lsn=%X/%X.",
itid,
P_ISLEAF(topaque) ? "heap" : "index",
htid,
LSN_FORMAT_ARGS(state->targetlsn))));
}
/* Reset, in case scantid was set to (itup) posting tuple's max TID */
skey->scantid = scantid;
/*
* * Item order check *
*
* Check that items are stored on page in logical order, by checking
* current item is strictly less than next item (if any).
*/
if (OffsetNumberNext(offset) <= max &&
!invariant_l_offset(state, skey, OffsetNumberNext(offset)))
{
ItemPointer tid;
char *itid,
*htid,
*nitid,
*nhtid;
itid = psprintf("(%u,%u)", state->targetblock, offset);
tid = BTreeTupleGetPointsToTID(itup);
htid = psprintf("(%u,%u)",
ItemPointerGetBlockNumberNoCheck(tid),
ItemPointerGetOffsetNumberNoCheck(tid));
nitid = psprintf("(%u,%u)", state->targetblock,
OffsetNumberNext(offset));
/* Reuse itup to get pointed-to heap location of second item */
itemid = PageGetItemIdCareful(state, state->targetblock,
state->target,
OffsetNumberNext(offset));
itup = (IndexTuple) PageGetItem(state->target, itemid);
tid = BTreeTupleGetPointsToTID(itup);
nhtid = psprintf("(%u,%u)",
ItemPointerGetBlockNumberNoCheck(tid),
ItemPointerGetOffsetNumberNoCheck(tid));
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("item order invariant violated for index \"%s\"",
RelationGetRelationName(state->rel)),
errdetail_internal("Lower index tid=%s (points to %s tid=%s) "
"higher index tid=%s (points to %s tid=%s) "
"page lsn=%X/%X.",
itid,
P_ISLEAF(topaque) ? "heap" : "index",
htid,
nitid,
P_ISLEAF(topaque) ? "heap" : "index",
nhtid,
LSN_FORMAT_ARGS(state->targetlsn))));
}
/*
* * Last item check *
*
* Check last item against next/right page's first data item's when
* last item on page is reached. This additional check will detect
* transposed pages iff the supposed right sibling page happens to
* belong before target in the key space. (Otherwise, a subsequent
* heap verification will probably detect the problem.)
*
* This check is similar to the item order check that will have
* already been performed for every other "real" item on target page
* when last item is checked. The difference is that the next item
* (the item that is compared to target's last item) needs to come
* from the next/sibling page. There may not be such an item
* available from sibling for various reasons, though (e.g., target is
* the rightmost page on level).
*/
else if (offset == max)
{
BTScanInsert rightkey;
/* Get item in next/right page */
rightkey = bt_right_page_check_scankey(state);
if (rightkey &&
!invariant_g_offset(state, rightkey, max))
{
/*
* As explained at length in bt_right_page_check_scankey(),
* there is a known !readonly race that could account for
* apparent violation of invariant, which we must check for
* before actually proceeding with raising error. Our canary
* condition is that target page was deleted.
*/
if (!state->readonly)
{
/* Get fresh copy of target page */
state->target = palloc_btree_page(state, state->targetblock);
/* Note that we deliberately do not update target LSN */
topaque = (BTPageOpaque) PageGetSpecialPointer(state->target);
/*
* All !readonly checks now performed; just return
*/
if (P_IGNORE(topaque))
return;
}
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("cross page item order invariant violated for index \"%s\"",
RelationGetRelationName(state->rel)),
errdetail_internal("Last item on page tid=(%u,%u) page lsn=%X/%X.",
state->targetblock, offset,
LSN_FORMAT_ARGS(state->targetlsn))));
}
}
/*
* * Downlink check *
*
* Additional check of child items iff this is an internal page and
* caller holds a ShareLock. This happens for every downlink (item)
* in target excluding the negative-infinity downlink (again, this is
* because it has no useful value to compare).
*/
if (!P_ISLEAF(topaque) && state->readonly)
bt_child_check(state, skey, offset);
}
/*
* Special case bt_child_highkey_check() call
*
* We don't pass an real downlink, but we've to finish the level
* processing. If condition is satisfied, we've already processed all the
* downlinks from the target level. But there still might be pages to the
* right of the child page pointer to by our rightmost downlink. And they
* might have missing downlinks. This final call checks for them.
*/
if (!P_ISLEAF(topaque) && P_RIGHTMOST(topaque) && state->readonly)
{
bt_child_highkey_check(state, InvalidOffsetNumber,
NULL, topaque->btpo_level);
}
}
/*
* Return a scankey for an item on page to right of current target (or the
* first non-ignorable page), sufficient to check ordering invariant on last
* item in current target page. Returned scankey relies on local memory
* allocated for the child page, which caller cannot pfree(). Caller's memory
* context should be reset between calls here.
*
* This is the first data item, and so all adjacent items are checked against
* their immediate sibling item (which may be on a sibling page, or even a
* "cousin" page at parent boundaries where target's rightlink points to page
* with different parent page). If no such valid item is available, return
* NULL instead.
*
* Note that !readonly callers must reverify that target page has not
* been concurrently deleted.
*/
static BTScanInsert
bt_right_page_check_scankey(BtreeCheckState *state)
{
BTPageOpaque opaque;
ItemId rightitem;
IndexTuple firstitup;
BlockNumber targetnext;
Page rightpage;
OffsetNumber nline;
/* Determine target's next block number */
opaque = (BTPageOpaque) PageGetSpecialPointer(state->target);
/* If target is already rightmost, no right sibling; nothing to do here */
if (P_RIGHTMOST(opaque))
return NULL;
/*
* General notes on concurrent page splits and page deletion:
*
* Routines like _bt_search() don't require *any* page split interlock
* when descending the tree, including something very light like a buffer
* pin. That's why it's okay that we don't either. This avoidance of any
* need to "couple" buffer locks is the raison d' etre of the Lehman & Yao
* algorithm, in fact.
*
* That leaves deletion. A deleted page won't actually be recycled by
* VACUUM early enough for us to fail to at least follow its right link
* (or left link, or downlink) and find its sibling, because recycling
* does not occur until no possible index scan could land on the page.
* Index scans can follow links with nothing more than their snapshot as
* an interlock and be sure of at least that much. (See page
* recycling/"visible to everyone" notes in nbtree README.)
*
* Furthermore, it's okay if we follow a rightlink and find a half-dead or
* dead (ignorable) page one or more times. There will either be a
* further right link to follow that leads to a live page before too long
* (before passing by parent's rightmost child), or we will find the end
* of the entire level instead (possible when parent page is itself the
* rightmost on its level).
*/
targetnext = opaque->btpo_next;
for (;;)
{
CHECK_FOR_INTERRUPTS();
rightpage = palloc_btree_page(state, targetnext);
opaque = (BTPageOpaque) PageGetSpecialPointer(rightpage);
if (!P_IGNORE(opaque) || P_RIGHTMOST(opaque))
break;
/*
* We landed on a deleted or half-dead sibling page. Step right until
* we locate a live sibling page.
*/
ereport(DEBUG2,
(errcode(ERRCODE_NO_DATA),
errmsg_internal("level %u sibling page in block %u of index \"%s\" was found deleted or half dead",
opaque->btpo_level, targetnext, RelationGetRelationName(state->rel)),
errdetail_internal("Deleted page found when building scankey from right sibling.")));
targetnext = opaque->btpo_next;
/* Be slightly more pro-active in freeing this memory, just in case */
pfree(rightpage);
}
/*
* No ShareLock held case -- why it's safe to proceed.
*
* Problem:
*
* We must avoid false positive reports of corruption when caller treats
* item returned here as an upper bound on target's last item. In
* general, false positives are disallowed. Avoiding them here when
* caller is !readonly is subtle.
*
* A concurrent page deletion by VACUUM of the target page can result in
* the insertion of items on to this right sibling page that would
* previously have been inserted on our target page. There might have
* been insertions that followed the target's downlink after it was made
* to point to right sibling instead of target by page deletion's first
* phase. The inserters insert items that would belong on target page.
* This race is very tight, but it's possible. This is our only problem.
*
* Non-problems:
*
* We are not hindered by a concurrent page split of the target; we'll
* never land on the second half of the page anyway. A concurrent split
* of the right page will also not matter, because the first data item
* remains the same within the left half, which we'll reliably land on. If
* we had to skip over ignorable/deleted pages, it cannot matter because
* their key space has already been atomically merged with the first
* non-ignorable page we eventually find (doesn't matter whether the page
* we eventually find is a true sibling or a cousin of target, which we go
* into below).
*
* Solution:
*
* Caller knows that it should reverify that target is not ignorable
* (half-dead or deleted) when cross-page sibling item comparison appears
* to indicate corruption (invariant fails). This detects the single race
* condition that exists for caller. This is correct because the
* continued existence of target block as non-ignorable (not half-dead or
* deleted) implies that target page was not merged into from the right by
* deletion; the key space at or after target never moved left. Target's
* parent either has the same downlink to target as before, or a <
* downlink due to deletion at the left of target. Target either has the
* same highkey as before, or a highkey < before when there is a page
* split. (The rightmost concurrently-split-from-target-page page will
* still have the same highkey as target was originally found to have,
* which for our purposes is equivalent to target's highkey itself never
* changing, since we reliably skip over
* concurrently-split-from-target-page pages.)
*
* In simpler terms, we allow that the key space of the target may expand
* left (the key space can move left on the left side of target only), but
* the target key space cannot expand right and get ahead of us without
* our detecting it. The key space of the target cannot shrink, unless it
* shrinks to zero due to the deletion of the original page, our canary
* condition. (To be very precise, we're a bit stricter than that because
* it might just have been that the target page split and only the
* original target page was deleted. We can be more strict, just not more
* lax.)
*
* Top level tree walk caller moves on to next page (makes it the new
* target) following recovery from this race. (cf. The rationale for
* child/downlink verification needing a ShareLock within
* bt_child_check(), where page deletion is also the main source of
* trouble.)
*
* Note that it doesn't matter if right sibling page here is actually a
* cousin page, because in order for the key space to be readjusted in a
* way that causes us issues in next level up (guiding problematic
* concurrent insertions to the cousin from the grandparent rather than to
* the sibling from the parent), there'd have to be page deletion of
* target's parent page (affecting target's parent's downlink in target's
* grandparent page). Internal page deletion only occurs when there are
* no child pages (they were all fully deleted), and caller is checking
* that the target's parent has at least one non-deleted (so
* non-ignorable) child: the target page. (Note that the first phase of
* deletion atomically marks the page to be deleted half-dead/ignorable at
* the same time downlink in its parent is removed, so caller will
* definitely not fail to detect that this happened.)
*
* This trick is inspired by the method backward scans use for dealing
* with concurrent page splits; concurrent page deletion is a problem that
* similarly receives special consideration sometimes (it's possible that
* the backwards scan will re-read its "original" block after failing to
* find a right-link to it, having already moved in the opposite direction
* (right/"forwards") a few times to try to locate one). Just like us,
* that happens only to determine if there was a concurrent page deletion
* of a reference page, and just like us if there was a page deletion of
* that reference page it means we can move on from caring about the
* reference page. See the nbtree README for a full description of how
* that works.
*/
nline = PageGetMaxOffsetNumber(rightpage);
/*
* Get first data item, if any
*/
if (P_ISLEAF(opaque) && nline >= P_FIRSTDATAKEY(opaque))
{
/* Return first data item (if any) */
rightitem = PageGetItemIdCareful(state, targetnext, rightpage,
P_FIRSTDATAKEY(opaque));
}
else if (!P_ISLEAF(opaque) &&
nline >= OffsetNumberNext(P_FIRSTDATAKEY(opaque)))
{
/*
* Return first item after the internal page's "negative infinity"
* item
*/
rightitem = PageGetItemIdCareful(state, targetnext, rightpage,
OffsetNumberNext(P_FIRSTDATAKEY(opaque)));
}
else
{
/*
* No first item. Page is probably empty leaf page, but it's also
* possible that it's an internal page with only a negative infinity
* item.
*/
ereport(DEBUG2,
(errcode(ERRCODE_NO_DATA),
errmsg_internal("%s block %u of index \"%s\" has no first data item",
P_ISLEAF(opaque) ? "leaf" : "internal", targetnext,
RelationGetRelationName(state->rel))));
return NULL;
}
/*
* Return first real item scankey. Note that this relies on right page
* memory remaining allocated.
*/
firstitup = (IndexTuple) PageGetItem(rightpage, rightitem);
return bt_mkscankey_pivotsearch(state->rel, firstitup);
}
/*
* Check if two tuples are binary identical except the block number. So,
* this function is capable to compare pivot keys on different levels.
*/
static bool
bt_pivot_tuple_identical(bool heapkeyspace, IndexTuple itup1, IndexTuple itup2)
{
if (IndexTupleSize(itup1) != IndexTupleSize(itup2))
return false;
if (heapkeyspace)
{
/*
* Offset number will contain important information in heapkeyspace
* indexes: the number of attributes left in the pivot tuple following
* suffix truncation. Don't skip over it (compare it too).
*/
if (memcmp(&itup1->t_tid.ip_posid, &itup2->t_tid.ip_posid,
IndexTupleSize(itup1) -
offsetof(ItemPointerData, ip_posid)) != 0)
return false;
}
else
{
/*
* Cannot rely on offset number field having consistent value across
* levels on pg_upgrade'd !heapkeyspace indexes. Compare contents of
* tuple starting from just after item pointer (i.e. after block
* number and offset number).
*/
if (memcmp(&itup1->t_info, &itup2->t_info,
IndexTupleSize(itup1) -
offsetof(IndexTupleData, t_info)) != 0)
return false;
}
return true;
}
/*---
* Check high keys on the child level. Traverse rightlinks from previous
* downlink to the current one. Check that there are no intermediate pages
* with missing downlinks.
*
* If 'loaded_child' is given, it's assumed to be the page pointed to by the
* downlink referenced by 'downlinkoffnum' of the target page.
*
* Basically this function is called for each target downlink and checks two
* invariants:
*
* 1) You can reach the next child from previous one via rightlinks;
* 2) Each child high key have matching pivot key on target level.
*
* Consider the sample tree picture.
*
* 1
* / \
* 2 <-> 3
* / \ / \
* 4 <> 5 <> 6 <> 7 <> 8
*
* This function will be called for blocks 4, 5, 6 and 8. Consider what is
* happening for each function call.
*
* - The function call for block 4 initializes data structure and matches high
* key of block 4 to downlink's pivot key of block 2.
* - The high key of block 5 is matched to the high key of block 2.
* - The block 6 has an incomplete split flag set, so its high key isn't
* matched to anything.
* - The function call for block 8 checks that block 8 can be found while
* following rightlinks from block 6. The high key of block 7 will be
* matched to downlink's pivot key in block 3.
*
* There is also final call of this function, which checks that there is no
* missing downlinks for children to the right of the child referenced by
* rightmost downlink in target level.
*/
static void
bt_child_highkey_check(BtreeCheckState *state,
OffsetNumber target_downlinkoffnum,
Page loaded_child,
uint32 target_level)
{
BlockNumber blkno = state->prevrightlink;
Page page;
BTPageOpaque opaque;
bool rightsplit = state->previncompletesplit;
bool first = true;
ItemId itemid;
IndexTuple itup;
BlockNumber downlink;
if (OffsetNumberIsValid(target_downlinkoffnum))
{
itemid = PageGetItemIdCareful(state, state->targetblock,
state->target, target_downlinkoffnum);
itup = (IndexTuple) PageGetItem(state->target, itemid);
downlink = BTreeTupleGetDownLink(itup);
}
else
{
downlink = P_NONE;
}
/*
* If no previous rightlink is memorized for current level just below
* target page's level, we are about to start from the leftmost page. We
* can't follow rightlinks from previous page, because there is no
* previous page. But we still can match high key.
*
* So we initialize variables for the loop above like there is previous
* page referencing current child. Also we imply previous page to not
* have incomplete split flag, that would make us require downlink for
* current child. That's correct, because leftmost page on the level
* should always have parent downlink.
*/
if (!BlockNumberIsValid(blkno))
{
blkno = downlink;
rightsplit = false;
}
/* Move to the right on the child level */
while (true)
{
/*
* Did we traverse the whole tree level and this is check for pages to
* the right of rightmost downlink?
*/
if (blkno == P_NONE && downlink == P_NONE)
{
state->prevrightlink = InvalidBlockNumber;
state->previncompletesplit = false;
return;
}
/* Did we traverse the whole tree level and don't find next downlink? */
if (blkno == P_NONE)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("can't traverse from downlink %u to downlink %u of index \"%s\"",
state->prevrightlink, downlink,
RelationGetRelationName(state->rel))));
/* Load page contents */
if (blkno == downlink && loaded_child)
page = loaded_child;
else
page = palloc_btree_page(state, blkno);
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
/* The first page we visit at the level should be leftmost */
if (first && !BlockNumberIsValid(state->prevrightlink) && !P_LEFTMOST(opaque))
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("the first child of leftmost target page is not leftmost of its level in index \"%s\"",
RelationGetRelationName(state->rel)),
errdetail_internal("Target block=%u child block=%u target page lsn=%X/%X.",
state->targetblock, blkno,
LSN_FORMAT_ARGS(state->targetlsn))));
/* Do level sanity check */
if ((!P_ISDELETED(opaque) || P_HAS_FULLXID(opaque)) &&
opaque->btpo_level != target_level - 1)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("block found while following rightlinks from child of index \"%s\" has invalid level",
RelationGetRelationName(state->rel)),
errdetail_internal("Block pointed to=%u expected level=%u level in pointed to block=%u.",
blkno, target_level - 1, opaque->btpo_level)));
/* Try to detect circular links */
if ((!first && blkno == state->prevrightlink) || blkno == opaque->btpo_prev)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("circular link chain found in block %u of index \"%s\"",
blkno, RelationGetRelationName(state->rel))));
if (blkno != downlink && !P_IGNORE(opaque))
{
/* blkno probably has missing parent downlink */
bt_downlink_missing_check(state, rightsplit, blkno, page);
}
rightsplit = P_INCOMPLETE_SPLIT(opaque);
/*
* If we visit page with high key, check that it is equal to the
* target key next to corresponding downlink.
*/
if (!rightsplit && !P_RIGHTMOST(opaque))
{
BTPageOpaque topaque;
IndexTuple highkey;
OffsetNumber pivotkey_offset;
/* Get high key */
itemid = PageGetItemIdCareful(state, blkno, page, P_HIKEY);
highkey = (IndexTuple) PageGetItem(page, itemid);
/*
* There might be two situations when we examine high key. If
* current child page is referenced by given target downlink, we
* should look to the next offset number for matching key from
* target page.
*
* Alternatively, we're following rightlinks somewhere in the
* middle between page referenced by previous target's downlink
* and the page referenced by current target's downlink. If
* current child page hasn't incomplete split flag set, then its
* high key should match to the target's key of current offset
* number. This happens when a previous call here (to
* bt_child_highkey_check()) found an incomplete split, and we
* reach a right sibling page without a downlink -- the right
* sibling page's high key still needs to be matched to a
* separator key on the parent/target level.
*
* Don't apply OffsetNumberNext() to target_downlinkoffnum when we
* already had to step right on the child level. Our traversal of
* the child level must try to move in perfect lockstep behind (to
* the left of) the target/parent level traversal.
*/
if (blkno == downlink)
pivotkey_offset = OffsetNumberNext(target_downlinkoffnum);
else
pivotkey_offset = target_downlinkoffnum;
topaque = (BTPageOpaque) PageGetSpecialPointer(state->target);
if (!offset_is_negative_infinity(topaque, pivotkey_offset))
{
/*
* If we're looking for the next pivot tuple in target page,
* but there is no more pivot tuples, then we should match to
* high key instead.
*/
if (pivotkey_offset > PageGetMaxOffsetNumber(state->target))
{
if (P_RIGHTMOST(topaque))
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("child high key is greater than rightmost pivot key on target level in index \"%s\"",
RelationGetRelationName(state->rel)),
errdetail_internal("Target block=%u child block=%u target page lsn=%X/%X.",
state->targetblock, blkno,
LSN_FORMAT_ARGS(state->targetlsn))));
pivotkey_offset = P_HIKEY;
}
itemid = PageGetItemIdCareful(state, state->targetblock,
state->target, pivotkey_offset);
itup = (IndexTuple) PageGetItem(state->target, itemid);
}
else
{
/*
* We cannot try to match child's high key to a negative
* infinity key in target, since there is nothing to compare.
* However, it's still possible to match child's high key
* outside of target page. The reason why we're are is that
* bt_child_highkey_check() was previously called for the
* cousin page of 'loaded_child', which is incomplete split.
* So, now we traverse to the right of that cousin page and
* current child level page under consideration still belongs
* to the subtree of target's left sibling. Thus, we need to
* match child's high key to it's left uncle page high key.
* Thankfully we saved it, it's called a "low key" of target
* page.
*/
if (!state->lowkey)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("can't find left sibling high key in index \"%s\"",
RelationGetRelationName(state->rel)),
errdetail_internal("Target block=%u child block=%u target page lsn=%X/%X.",
state->targetblock, blkno,
LSN_FORMAT_ARGS(state->targetlsn))));
itup = state->lowkey;
}
if (!bt_pivot_tuple_identical(state->heapkeyspace, highkey, itup))
{
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("mismatch between parent key and child high key in index \"%s\"",
RelationGetRelationName(state->rel)),
errdetail_internal("Target block=%u child block=%u target page lsn=%X/%X.",
state->targetblock, blkno,
LSN_FORMAT_ARGS(state->targetlsn))));
}
}
/* Exit if we already found next downlink */
if (blkno == downlink)
{
state->prevrightlink = opaque->btpo_next;
state->previncompletesplit = rightsplit;
return;
}
/* Traverse to the next page using rightlink */
blkno = opaque->btpo_next;
/* Free page contents if it's allocated by us */
if (page != loaded_child)
pfree(page);
first = false;
}
}
/*
* Checks one of target's downlink against its child page.
*
* Conceptually, the target page continues to be what is checked here. The
* target block is still blamed in the event of finding an invariant violation.
* The downlink insertion into the target is probably where any problem raised
* here arises, and there is no such thing as a parent link, so doing the
* verification this way around is much more practical.
*
* This function visits child page and it's sequentially called for each
* downlink of target page. Assuming this we also check downlink connectivity
* here in order to save child page visits.
*/
static void
bt_child_check(BtreeCheckState *state, BTScanInsert targetkey,
OffsetNumber downlinkoffnum)
{
ItemId itemid;
IndexTuple itup;
BlockNumber childblock;
OffsetNumber offset;
OffsetNumber maxoffset;
Page child;
BTPageOpaque copaque;
BTPageOpaque topaque;
itemid = PageGetItemIdCareful(state, state->targetblock,
state->target, downlinkoffnum);
itup = (IndexTuple) PageGetItem(state->target, itemid);
childblock = BTreeTupleGetDownLink(itup);
/*
* Caller must have ShareLock on target relation, because of
* considerations around page deletion by VACUUM.
*
* NB: In general, page deletion deletes the right sibling's downlink, not
* the downlink of the page being deleted; the deleted page's downlink is
* reused for its sibling. The key space is thereby consolidated between
* the deleted page and its right sibling. (We cannot delete a parent
* page's rightmost child unless it is the last child page, and we intend
* to also delete the parent itself.)
*
* If this verification happened without a ShareLock, the following race
* condition could cause false positives:
*
* In general, concurrent page deletion might occur, including deletion of
* the left sibling of the child page that is examined here. If such a
* page deletion were to occur, closely followed by an insertion into the
* newly expanded key space of the child, a window for the false positive
* opens up: the stale parent/target downlink originally followed to get
* to the child legitimately ceases to be a lower bound on all items in
* the page, since the key space was concurrently expanded "left".
* (Insertion followed the "new" downlink for the child, not our now-stale
* downlink, which was concurrently physically removed in target/parent as
* part of deletion's first phase.)
*
* While we use various techniques elsewhere to perform cross-page
* verification for !readonly callers, a similar trick seems difficult
* here. The tricks used by bt_recheck_sibling_links and by
* bt_right_page_check_scankey both involve verification of a same-level,
* cross-sibling invariant. Cross-level invariants are far more squishy,
* though. The nbtree REDO routines do not actually couple buffer locks
* across levels during page splits, so making any cross-level check work
* reliably in !readonly mode may be impossible.
*/
Assert(state->readonly);
/*
* Verify child page has the downlink key from target page (its parent) as
* a lower bound; downlink must be strictly less than all keys on the
* page.
*
* Check all items, rather than checking just the first and trusting that
* the operator class obeys the transitive law.
*/
topaque = (BTPageOpaque) PageGetSpecialPointer(state->target);
child = palloc_btree_page(state, childblock);
copaque = (BTPageOpaque) PageGetSpecialPointer(child);
maxoffset = PageGetMaxOffsetNumber(child);
/*
* Since we've already loaded the child block, combine this check with
* check for downlink connectivity.
*/
bt_child_highkey_check(state, downlinkoffnum,
child, topaque->btpo_level);
/*
* Since there cannot be a concurrent VACUUM operation in readonly mode,
* and since a page has no links within other pages (siblings and parent)
* once it is marked fully deleted, it should be impossible to land on a
* fully deleted page.
*
* It does not quite make sense to enforce that the page cannot even be
* half-dead, despite the fact the downlink is modified at the same stage
* that the child leaf page is marked half-dead. That's incorrect because
* there may occasionally be multiple downlinks from a chain of pages
* undergoing deletion, where multiple successive calls are made to
* _bt_unlink_halfdead_page() by VACUUM before it can finally safely mark
* the leaf page as fully dead. While _bt_mark_page_halfdead() usually
* removes the downlink to the leaf page that is marked half-dead, that's
* not guaranteed, so it's possible we'll land on a half-dead page with a
* downlink due to an interrupted multi-level page deletion.
*
* We go ahead with our checks if the child page is half-dead. It's safe
* to do so because we do not test the child's high key, so it does not
* matter that the original high key will have been replaced by a dummy
* truncated high key within _bt_mark_page_halfdead(). All other page
* items are left intact on a half-dead page, so there is still something
* to test.
*/
if (P_ISDELETED(copaque))
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("downlink to deleted page found in index \"%s\"",
RelationGetRelationName(state->rel)),
errdetail_internal("Parent block=%u child block=%u parent page lsn=%X/%X.",
state->targetblock, childblock,
LSN_FORMAT_ARGS(state->targetlsn))));
for (offset = P_FIRSTDATAKEY(copaque);
offset <= maxoffset;
offset = OffsetNumberNext(offset))
{
/*
* Skip comparison of target page key against "negative infinity"
* item, if any. Checking it would indicate that it's not a strict
* lower bound, but that's only because of the hard-coding for
* negative infinity items within _bt_compare().
*
* If nbtree didn't truncate negative infinity tuples during internal
* page splits then we'd expect child's negative infinity key to be
* equal to the scankey/downlink from target/parent (it would be a
* "low key" in this hypothetical scenario, and so it would still need
* to be treated as a special case here).
*
* Negative infinity items can be thought of as a strict lower bound
* that works transitively, with the last non-negative-infinity pivot
* followed during a descent from the root as its "true" strict lower
* bound. Only a small number of negative infinity items are truly
* negative infinity; those that are the first items of leftmost
* internal pages. In more general terms, a negative infinity item is
* only negative infinity with respect to the subtree that the page is
* at the root of.
*
* See also: bt_rootdescend(), which can even detect transitive
* inconsistencies on cousin leaf pages.
*/
if (offset_is_negative_infinity(copaque, offset))
continue;
if (!invariant_l_nontarget_offset(state, targetkey, childblock, child,
offset))
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("down-link lower bound invariant violated for index \"%s\"",
RelationGetRelationName(state->rel)),
errdetail_internal("Parent block=%u child index tid=(%u,%u) parent page lsn=%X/%X.",
state->targetblock, childblock, offset,
LSN_FORMAT_ARGS(state->targetlsn))));
}
pfree(child);
}
/*
* Checks if page is missing a downlink that it should have.
*
* A page that lacks a downlink/parent may indicate corruption. However, we
* must account for the fact that a missing downlink can occasionally be
* encountered in a non-corrupt index. This can be due to an interrupted page
* split, or an interrupted multi-level page deletion (i.e. there was a hard
* crash or an error during a page split, or while VACUUM was deleting a
* multi-level chain of pages).
*
* Note that this can only be called in readonly mode, so there is no need to
* be concerned about concurrent page splits or page deletions.
*/
static void
bt_downlink_missing_check(BtreeCheckState *state, bool rightsplit,
BlockNumber blkno, Page page)
{
BTPageOpaque opaque = (BTPageOpaque) PageGetSpecialPointer(page);
ItemId itemid;
IndexTuple itup;
Page child;
BTPageOpaque copaque;
uint32 level;
BlockNumber childblk;
XLogRecPtr pagelsn;
Assert(state->readonly);
Assert(!P_IGNORE(opaque));
/* No next level up with downlinks to fingerprint from the true root */
if (P_ISROOT(opaque))
return;
pagelsn = PageGetLSN(page);
/*
* Incomplete (interrupted) page splits can account for the lack of a
* downlink. Some inserting transaction should eventually complete the
* page split in passing, when it notices that the left sibling page is
* P_INCOMPLETE_SPLIT().
*
* In general, VACUUM is not prepared for there to be no downlink to a
* page that it deletes. This is the main reason why the lack of a
* downlink can be reported as corruption here. It's not obvious that an
* invalid missing downlink can result in wrong answers to queries,
* though, since index scans that land on the child may end up
* consistently moving right. The handling of concurrent page splits (and
* page deletions) within _bt_moveright() cannot distinguish
* inconsistencies that last for a moment from inconsistencies that are
* permanent and irrecoverable.
*
* VACUUM isn't even prepared to delete pages that have no downlink due to
* an incomplete page split, but it can detect and reason about that case
* by design, so it shouldn't be taken to indicate corruption. See
* _bt_pagedel() for full details.
*/
if (rightsplit)
{
ereport(DEBUG1,
(errcode(ERRCODE_NO_DATA),
errmsg_internal("harmless interrupted page split detected in index \"%s\"",
RelationGetRelationName(state->rel)),
errdetail_internal("Block=%u level=%u left sibling=%u page lsn=%X/%X.",
blkno, opaque->btpo_level,
opaque->btpo_prev,
LSN_FORMAT_ARGS(pagelsn))));
return;
}
/*
* Page under check is probably the "top parent" of a multi-level page
* deletion. We'll need to descend the subtree to make sure that
* descendant pages are consistent with that, though.
*
* If the page (which must be non-ignorable) is a leaf page, then clearly
* it can't be the top parent. The lack of a downlink is probably a
* symptom of a broad problem that could just as easily cause
* inconsistencies anywhere else.
*/
if (P_ISLEAF(opaque))
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("leaf index block lacks downlink in index \"%s\"",
RelationGetRelationName(state->rel)),
errdetail_internal("Block=%u page lsn=%X/%X.",
blkno,
LSN_FORMAT_ARGS(pagelsn))));
/* Descend from the given page, which is an internal page */
elog(DEBUG1, "checking for interrupted multi-level deletion due to missing downlink in index \"%s\"",
RelationGetRelationName(state->rel));
level = opaque->btpo_level;
itemid = PageGetItemIdCareful(state, blkno, page, P_FIRSTDATAKEY(opaque));
itup = (IndexTuple) PageGetItem(page, itemid);
childblk = BTreeTupleGetDownLink(itup);
for (;;)
{
CHECK_FOR_INTERRUPTS();
child = palloc_btree_page(state, childblk);
copaque = (BTPageOpaque) PageGetSpecialPointer(child);
if (P_ISLEAF(copaque))
break;
/* Do an extra sanity check in passing on internal pages */
if (copaque->btpo_level != level - 1)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg_internal("downlink points to block in index \"%s\" whose level is not one level down",
RelationGetRelationName(state->rel)),
errdetail_internal("Top parent/under check block=%u block pointed to=%u expected level=%u level in pointed to block=%u.",
blkno, childblk,
level - 1, copaque->btpo_level)));
level = copaque->btpo_level;
itemid = PageGetItemIdCareful(state, childblk, child,
P_FIRSTDATAKEY(copaque));
itup = (IndexTuple) PageGetItem(child, itemid);
childblk = BTreeTupleGetDownLink(itup);
/* Be slightly more pro-active in freeing this memory, just in case */
pfree(child);
}
/*
* Since there cannot be a concurrent VACUUM operation in readonly mode,
* and since a page has no links within other pages (siblings and parent)
* once it is marked fully deleted, it should be impossible to land on a
* fully deleted page. See bt_child_check() for further details.
*
* The bt_child_check() P_ISDELETED() check is repeated here because
* bt_child_check() does not visit pages reachable through negative
* infinity items. Besides, bt_child_check() is unwilling to descend
* multiple levels. (The similar bt_child_check() P_ISDELETED() check
* within bt_check_level_from_leftmost() won't reach the page either,
* since the leaf's live siblings should have their sibling links updated
* to bypass the deletion target page when it is marked fully dead.)
*
* If this error is raised, it might be due to a previous multi-level page
* deletion that failed to realize that it wasn't yet safe to mark the
* leaf page as fully dead. A "dangling downlink" will still remain when
* this happens. The fact that the dangling downlink's page (the leaf's
* parent/ancestor page) lacked a downlink is incidental.
*/
if (P_ISDELETED(copaque))
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg_internal("downlink to deleted leaf page found in index \"%s\"",
RelationGetRelationName(state->rel)),
errdetail_internal("Top parent/target block=%u leaf block=%u top parent/under check lsn=%X/%X.",
blkno, childblk,
LSN_FORMAT_ARGS(pagelsn))));
/*
* Iff leaf page is half-dead, its high key top parent link should point
* to what VACUUM considered to be the top parent page at the instant it
* was interrupted. Provided the high key link actually points to the
* page under check, the missing downlink we detected is consistent with
* there having been an interrupted multi-level page deletion. This means
* that the subtree with the page under check at its root (a page deletion
* chain) is in a consistent state, enabling VACUUM to resume deleting the
* entire chain the next time it encounters the half-dead leaf page.
*/
if (P_ISHALFDEAD(copaque) && !P_RIGHTMOST(copaque))
{
itemid = PageGetItemIdCareful(state, childblk, child, P_HIKEY);
itup = (IndexTuple) PageGetItem(child, itemid);
if (BTreeTupleGetTopParent(itup) == blkno)
return;
}
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("internal index block lacks downlink in index \"%s\"",
RelationGetRelationName(state->rel)),
errdetail_internal("Block=%u level=%u page lsn=%X/%X.",
blkno, opaque->btpo_level,
LSN_FORMAT_ARGS(pagelsn))));
}
/*
* Per-tuple callback from table_index_build_scan, used to determine if index has
* all the entries that definitely should have been observed in leaf pages of
* the target index (that is, all IndexTuples that were fingerprinted by our
* Bloom filter). All heapallindexed checks occur here.
*
* The redundancy between an index and the table it indexes provides a good
* opportunity to detect corruption, especially corruption within the table.
* The high level principle behind the verification performed here is that any
* IndexTuple that should be in an index following a fresh CREATE INDEX (based
* on the same index definition) should also have been in the original,
* existing index, which should have used exactly the same representation
*
* Since the overall structure of the index has already been verified, the most
* likely explanation for error here is a corrupt heap page (could be logical
* or physical corruption). Index corruption may still be detected here,
* though. Only readonly callers will have verified that left links and right
* links are in agreement, and so it's possible that a leaf page transposition
* within index is actually the source of corruption detected here (for
* !readonly callers). The checks performed only for readonly callers might
* more accurately frame the problem as a cross-page invariant issue (this
* could even be due to recovery not replaying all WAL records). The !readonly
* ERROR message raised here includes a HINT about retrying with readonly
* verification, just in case it's a cross-page invariant issue, though that
* isn't particularly likely.
*
* table_index_build_scan() expects to be able to find the root tuple when a
* heap-only tuple (the live tuple at the end of some HOT chain) needs to be
* indexed, in order to replace the actual tuple's TID with the root tuple's
* TID (which is what we're actually passed back here). The index build heap
* scan code will raise an error when a tuple that claims to be the root of the
* heap-only tuple's HOT chain cannot be located. This catches cases where the
* original root item offset/root tuple for a HOT chain indicates (for whatever
* reason) that the entire HOT chain is dead, despite the fact that the latest
* heap-only tuple should be indexed. When this happens, sequential scans may
* always give correct answers, and all indexes may be considered structurally
* consistent (i.e. the nbtree structural checks would not detect corruption).
* It may be the case that only index scans give wrong answers, and yet heap or
* SLRU corruption is the real culprit. (While it's true that LP_DEAD bit
* setting will probably also leave the index in a corrupt state before too
* long, the problem is nonetheless that there is heap corruption.)
*
* Heap-only tuple handling within table_index_build_scan() works in a way that
* helps us to detect index tuples that contain the wrong values (values that
* don't match the latest tuple in the HOT chain). This can happen when there
* is no superseding index tuple due to a faulty assessment of HOT safety,
* perhaps during the original CREATE INDEX. Because the latest tuple's
* contents are used with the root TID, an error will be raised when a tuple
* with the same TID but non-matching attribute values is passed back to us.
* Faulty assessment of HOT-safety was behind at least two distinct CREATE
* INDEX CONCURRENTLY bugs that made it into stable releases, one of which was
* undetected for many years. In short, the same principle that allows a
* REINDEX to repair corruption when there was an (undetected) broken HOT chain
* also allows us to detect the corruption in many cases.
*/
static void
bt_tuple_present_callback(Relation index, ItemPointer tid, Datum *values,
bool *isnull, bool tupleIsAlive, void *checkstate)
{
BtreeCheckState *state = (BtreeCheckState *) checkstate;
IndexTuple itup,
norm;
Assert(state->heapallindexed);
/* Generate a normalized index tuple for fingerprinting */
itup = index_form_tuple(RelationGetDescr(index), values, isnull);
itup->t_tid = *tid;
norm = bt_normalize_tuple(state, itup);
/* Probe Bloom filter -- tuple should be present */
if (bloom_lacks_element(state->filter, (unsigned char *) norm,
IndexTupleSize(norm)))
ereport(ERROR,
(errcode(ERRCODE_DATA_CORRUPTED),
errmsg("heap tuple (%u,%u) from table \"%s\" lacks matching index tuple within index \"%s\"",
ItemPointerGetBlockNumber(&(itup->t_tid)),
ItemPointerGetOffsetNumber(&(itup->t_tid)),
RelationGetRelationName(state->heaprel),
RelationGetRelationName(state->rel)),
!state->readonly
? errhint("Retrying verification using the function bt_index_parent_check() might provide a more specific error.")
: 0));
state->heaptuplespresent++;
pfree(itup);
/* Cannot leak memory here */
if (norm != itup)
pfree(norm);
}
/*
* Normalize an index tuple for fingerprinting.
*
* In general, index tuple formation is assumed to be deterministic by
* heapallindexed verification, and IndexTuples are assumed immutable. While
* the LP_DEAD bit is mutable in leaf pages, that's ItemId metadata, which is
* not fingerprinted. Normalization is required to compensate for corner
* cases where the determinism assumption doesn't quite work.
*
* There is currently one such case: index_form_tuple() does not try to hide
* the source TOAST state of input datums. The executor applies TOAST
* compression for heap tuples based on different criteria to the compression
* applied within btinsert()'s call to index_form_tuple(): it sometimes
* compresses more aggressively, resulting in compressed heap tuple datums but
* uncompressed corresponding index tuple datums. A subsequent heapallindexed
* verification will get a logically equivalent though bitwise unequal tuple
* from index_form_tuple(). False positive heapallindexed corruption reports
* could occur without normalizing away the inconsistency.
*
* Returned tuple is often caller's own original tuple. Otherwise, it is a
* new representation of caller's original index tuple, palloc()'d in caller's
* memory context.
*
* Note: This routine is not concerned with distinctions about the
* representation of tuples beyond those that might break heapallindexed
* verification. In particular, it won't try to normalize opclass-equal
* datums with potentially distinct representations (e.g., btree/numeric_ops
* index datums will not get their display scale normalized-away here).
* Caller does normalization for non-pivot tuples that have a posting list,
* since dummy CREATE INDEX callback code generates new tuples with the same
* normalized representation.
*/
static IndexTuple
bt_normalize_tuple(BtreeCheckState *state, IndexTuple itup)
{
TupleDesc tupleDescriptor = RelationGetDescr(state->rel);
Datum normalized[INDEX_MAX_KEYS];
bool isnull[INDEX_MAX_KEYS];
bool toast_free[INDEX_MAX_KEYS];
bool formnewtup = false;
IndexTuple reformed;
int i;
/* Caller should only pass "logical" non-pivot tuples here */
Assert(!BTreeTupleIsPosting(itup) && !BTreeTupleIsPivot(itup));
/* Easy case: It's immediately clear that tuple has no varlena datums */
if (!IndexTupleHasVarwidths(itup))
return itup;
for (i = 0; i < tupleDescriptor->natts; i++)
{
Form_pg_attribute att;
att = TupleDescAttr(tupleDescriptor, i);
/* Assume untoasted/already normalized datum initially */
toast_free[i] = false;
normalized[i] = index_getattr(itup, att->attnum,
tupleDescriptor,
&isnull[i]);
if (att->attbyval || att->attlen != -1 || isnull[i])
continue;
/*
* Callers always pass a tuple that could safely be inserted into the
* index without further processing, so an external varlena header
* should never be encountered here
*/
if (VARATT_IS_EXTERNAL(DatumGetPointer(normalized[i])))
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("external varlena datum in tuple that references heap row (%u,%u) in index \"%s\"",
ItemPointerGetBlockNumber(&(itup->t_tid)),
ItemPointerGetOffsetNumber(&(itup->t_tid)),
RelationGetRelationName(state->rel))));
else if (VARATT_IS_COMPRESSED(DatumGetPointer(normalized[i])))
{
formnewtup = true;
normalized[i] = PointerGetDatum(PG_DETOAST_DATUM(normalized[i]));
toast_free[i] = true;
}
}
/* Easier case: Tuple has varlena datums, none of which are compressed */
if (!formnewtup)
return itup;
/*
* Hard case: Tuple had compressed varlena datums that necessitate
* creating normalized version of the tuple from uncompressed input datums
* (normalized input datums). This is rather naive, but shouldn't be
* necessary too often.
*
* Note that we rely on deterministic index_form_tuple() TOAST compression
* of normalized input.
*/
reformed = index_form_tuple(tupleDescriptor, normalized, isnull);
reformed->t_tid = itup->t_tid;
/* Cannot leak memory here */
for (i = 0; i < tupleDescriptor->natts; i++)
if (toast_free[i])
pfree(DatumGetPointer(normalized[i]));
return reformed;
}
/*
* Produce palloc()'d "plain" tuple for nth posting list entry/TID.
*
* In general, deduplication is not supposed to change the logical contents of
* an index. Multiple index tuples are merged together into one equivalent
* posting list index tuple when convenient.
*
* heapallindexed verification must normalize-away this variation in
* representation by converting posting list tuples into two or more "plain"
* tuples. Each tuple must be fingerprinted separately -- there must be one
* tuple for each corresponding Bloom filter probe during the heap scan.
*
* Note: Caller still needs to call bt_normalize_tuple() with returned tuple.
*/
static inline IndexTuple
bt_posting_plain_tuple(IndexTuple itup, int n)
{
Assert(BTreeTupleIsPosting(itup));
/* Returns non-posting-list tuple */
return _bt_form_posting(itup, BTreeTupleGetPostingN(itup, n), 1);
}
/*
* Search for itup in index, starting from fast root page. itup must be a
* non-pivot tuple. This is only supported with heapkeyspace indexes, since
* we rely on having fully unique keys to find a match with only a single
* visit to a leaf page, barring an interrupted page split, where we may have
* to move right. (A concurrent page split is impossible because caller must
* be readonly caller.)
*
* This routine can detect very subtle transitive consistency issues across
* more than one level of the tree. Leaf pages all have a high key (even the
* rightmost page has a conceptual positive infinity high key), but not a low
* key. Their downlink in parent is a lower bound, which along with the high
* key is almost enough to detect every possible inconsistency. A downlink
* separator key value won't always be available from parent, though, because
* the first items of internal pages are negative infinity items, truncated
* down to zero attributes during internal page splits. While it's true that
* bt_child_check() and the high key check can detect most imaginable key
* space problems, there are remaining problems it won't detect with non-pivot
* tuples in cousin leaf pages. Starting a search from the root for every
* existing leaf tuple detects small inconsistencies in upper levels of the
* tree that cannot be detected any other way. (Besides all this, this is
* probably also useful as a direct test of the code used by index scans
* themselves.)
*/
static bool
bt_rootdescend(BtreeCheckState *state, IndexTuple itup)
{
BTScanInsert key;
BTStack stack;
Buffer lbuf;
bool exists;
key = _bt_mkscankey(state->rel, itup);
Assert(key->heapkeyspace && key->scantid != NULL);
/*
* Search from root.
*
* Ideally, we would arrange to only move right within _bt_search() when
* an interrupted page split is detected (i.e. when the incomplete split
* bit is found to be set), but for now we accept the possibility that
* that could conceal an inconsistency.
*/
Assert(state->readonly && state->rootdescend);
exists = false;
stack = _bt_search(state->rel, key, &lbuf, BT_READ, NULL);
if (BufferIsValid(lbuf))
{
BTInsertStateData insertstate;
OffsetNumber offnum;
Page page;
insertstate.itup = itup;
insertstate.itemsz = MAXALIGN(IndexTupleSize(itup));
insertstate.itup_key = key;
insertstate.postingoff = 0;
insertstate.bounds_valid = false;
insertstate.buf = lbuf;
/* Get matching tuple on leaf page */
offnum = _bt_binsrch_insert(state->rel, &insertstate);
/* Compare first >= matching item on leaf page, if any */
page = BufferGetPage(lbuf);
/* Should match on first heap TID when tuple has a posting list */
if (offnum <= PageGetMaxOffsetNumber(page) &&
insertstate.postingoff <= 0 &&
_bt_compare(state->rel, key, page, offnum) == 0)
exists = true;
_bt_relbuf(state->rel, lbuf);
}
_bt_freestack(stack);
pfree(key);
return exists;
}
/*
* Is particular offset within page (whose special state is passed by caller)
* the page negative-infinity item?
*
* As noted in comments above _bt_compare(), there is special handling of the
* first data item as a "negative infinity" item. The hard-coding within
* _bt_compare() makes comparing this item for the purposes of verification
* pointless at best, since the IndexTuple only contains a valid TID (a
* reference TID to child page).
*/
static inline bool
offset_is_negative_infinity(BTPageOpaque opaque, OffsetNumber offset)
{
/*
* For internal pages only, the first item after high key, if any, is
* negative infinity item. Internal pages always have a negative infinity
* item, whereas leaf pages never have one. This implies that negative
* infinity item is either first or second line item, or there is none
* within page.
*
* Negative infinity items are a special case among pivot tuples. They
* always have zero attributes, while all other pivot tuples always have
* nkeyatts attributes.
*
* Right-most pages don't have a high key, but could be said to
* conceptually have a "positive infinity" high key. Thus, there is a
* symmetry between down link items in parent pages, and high keys in
* children. Together, they represent the part of the key space that
* belongs to each page in the index. For example, all children of the
* root page will have negative infinity as a lower bound from root
* negative infinity downlink, and positive infinity as an upper bound
* (implicitly, from "imaginary" positive infinity high key in root).
*/
return !P_ISLEAF(opaque) && offset == P_FIRSTDATAKEY(opaque);
}
/*
* Does the invariant hold that the key is strictly less than a given upper
* bound offset item?
*
* Verifies line pointer on behalf of caller.
*
* If this function returns false, convention is that caller throws error due
* to corruption.
*/
static inline bool
invariant_l_offset(BtreeCheckState *state, BTScanInsert key,
OffsetNumber upperbound)
{
ItemId itemid;
int32 cmp;
Assert(key->pivotsearch);
/* Verify line pointer before checking tuple */
itemid = PageGetItemIdCareful(state, state->targetblock, state->target,
upperbound);
/* pg_upgrade'd indexes may legally have equal sibling tuples */
if (!key->heapkeyspace)
return invariant_leq_offset(state, key, upperbound);
cmp = _bt_compare(state->rel, key, state->target, upperbound);
/*
* _bt_compare() is capable of determining that a scankey with a
* filled-out attribute is greater than pivot tuples where the comparison
* is resolved at a truncated attribute (value of attribute in pivot is
* minus infinity). However, it is not capable of determining that a
* scankey is _less than_ a tuple on the basis of a comparison resolved at
* _scankey_ minus infinity attribute. Complete an extra step to simulate
* having minus infinity values for omitted scankey attribute(s).
*/
if (cmp == 0)
{
BTPageOpaque topaque;
IndexTuple ritup;
int uppnkeyatts;
ItemPointer rheaptid;
bool nonpivot;
ritup = (IndexTuple) PageGetItem(state->target, itemid);
topaque = (BTPageOpaque) PageGetSpecialPointer(state->target);
nonpivot = P_ISLEAF(topaque) && upperbound >= P_FIRSTDATAKEY(topaque);
/* Get number of keys + heap TID for item to the right */
uppnkeyatts = BTreeTupleGetNKeyAtts(ritup, state->rel);
rheaptid = BTreeTupleGetHeapTIDCareful(state, ritup, nonpivot);
/* Heap TID is tiebreaker key attribute */
if (key->keysz == uppnkeyatts)
return key->scantid == NULL && rheaptid != NULL;
return key->keysz < uppnkeyatts;
}
return cmp < 0;
}
/*
* Does the invariant hold that the key is less than or equal to a given upper
* bound offset item?
*
* Caller should have verified that upperbound's line pointer is consistent
* using PageGetItemIdCareful() call.
*
* If this function returns false, convention is that caller throws error due
* to corruption.
*/
static inline bool
invariant_leq_offset(BtreeCheckState *state, BTScanInsert key,
OffsetNumber upperbound)
{
int32 cmp;
Assert(key->pivotsearch);
cmp = _bt_compare(state->rel, key, state->target, upperbound);
return cmp <= 0;
}
/*
* Does the invariant hold that the key is strictly greater than a given lower
* bound offset item?
*
* Caller should have verified that lowerbound's line pointer is consistent
* using PageGetItemIdCareful() call.
*
* If this function returns false, convention is that caller throws error due
* to corruption.
*/
static inline bool
invariant_g_offset(BtreeCheckState *state, BTScanInsert key,
OffsetNumber lowerbound)
{
int32 cmp;
Assert(key->pivotsearch);
cmp = _bt_compare(state->rel, key, state->target, lowerbound);
/* pg_upgrade'd indexes may legally have equal sibling tuples */
if (!key->heapkeyspace)
return cmp >= 0;
/*
* No need to consider the possibility that scankey has attributes that we
* need to force to be interpreted as negative infinity. _bt_compare() is
* able to determine that scankey is greater than negative infinity. The
* distinction between "==" and "<" isn't interesting here, since
* corruption is indicated either way.
*/
return cmp > 0;
}
/*
* Does the invariant hold that the key is strictly less than a given upper
* bound offset item, with the offset relating to a caller-supplied page that
* is not the current target page?
*
* Caller's non-target page is a child page of the target, checked as part of
* checking a property of the target page (i.e. the key comes from the
* target). Verifies line pointer on behalf of caller.
*
* If this function returns false, convention is that caller throws error due
* to corruption.
*/
static inline bool
invariant_l_nontarget_offset(BtreeCheckState *state, BTScanInsert key,
BlockNumber nontargetblock, Page nontarget,
OffsetNumber upperbound)
{
ItemId itemid;
int32 cmp;
Assert(key->pivotsearch);
/* Verify line pointer before checking tuple */
itemid = PageGetItemIdCareful(state, nontargetblock, nontarget,
upperbound);
cmp = _bt_compare(state->rel, key, nontarget, upperbound);
/* pg_upgrade'd indexes may legally have equal sibling tuples */
if (!key->heapkeyspace)
return cmp <= 0;
/* See invariant_l_offset() for an explanation of this extra step */
if (cmp == 0)
{
IndexTuple child;
int uppnkeyatts;
ItemPointer childheaptid;
BTPageOpaque copaque;
bool nonpivot;
child = (IndexTuple) PageGetItem(nontarget, itemid);
copaque = (BTPageOpaque) PageGetSpecialPointer(nontarget);
nonpivot = P_ISLEAF(copaque) && upperbound >= P_FIRSTDATAKEY(copaque);
/* Get number of keys + heap TID for child/non-target item */
uppnkeyatts = BTreeTupleGetNKeyAtts(child, state->rel);
childheaptid = BTreeTupleGetHeapTIDCareful(state, child, nonpivot);
/* Heap TID is tiebreaker key attribute */
if (key->keysz == uppnkeyatts)
return key->scantid == NULL && childheaptid != NULL;
return key->keysz < uppnkeyatts;
}
return cmp < 0;
}
/*
* Given a block number of a B-Tree page, return page in palloc()'d memory.
* While at it, perform some basic checks of the page.
*
* There is never an attempt to get a consistent view of multiple pages using
* multiple concurrent buffer locks; in general, we only acquire a single pin
* and buffer lock at a time, which is often all that the nbtree code requires.
* (Actually, bt_recheck_sibling_links couples buffer locks, which is the only
* exception to this general rule.)
*
* Operating on a copy of the page is useful because it prevents control
* getting stuck in an uninterruptible state when an underlying operator class
* misbehaves.
*/
static Page
palloc_btree_page(BtreeCheckState *state, BlockNumber blocknum)
{
Buffer buffer;
Page page;
BTPageOpaque opaque;
OffsetNumber maxoffset;
page = palloc(BLCKSZ);
/*
* We copy the page into local storage to avoid holding pin on the buffer
* longer than we must.
*/
buffer = ReadBufferExtended(state->rel, MAIN_FORKNUM, blocknum, RBM_NORMAL,
state->checkstrategy);
LockBuffer(buffer, BT_READ);
/*
* Perform the same basic sanity checking that nbtree itself performs for
* every page:
*/
_bt_checkpage(state->rel, buffer);
/* Only use copy of page in palloc()'d memory */
memcpy(page, BufferGetPage(buffer), BLCKSZ);
UnlockReleaseBuffer(buffer);
opaque = (BTPageOpaque) PageGetSpecialPointer(page);
if (P_ISMETA(opaque) && blocknum != BTREE_METAPAGE)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("invalid meta page found at block %u in index \"%s\"",
blocknum, RelationGetRelationName(state->rel))));
/* Check page from block that ought to be meta page */
if (blocknum == BTREE_METAPAGE)
{
BTMetaPageData *metad = BTPageGetMeta(page);
if (!P_ISMETA(opaque) ||
metad->btm_magic != BTREE_MAGIC)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("index \"%s\" meta page is corrupt",
RelationGetRelationName(state->rel))));
if (metad->btm_version < BTREE_MIN_VERSION ||
metad->btm_version > BTREE_VERSION)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("version mismatch in index \"%s\": file version %d, "
"current version %d, minimum supported version %d",
RelationGetRelationName(state->rel),
metad->btm_version, BTREE_VERSION,
BTREE_MIN_VERSION)));
/* Finished with metapage checks */
return page;
}
/*
* Deleted pages that still use the old 32-bit XID representation have no
* sane "level" field because they type pun the field, but all other pages
* (including pages deleted on Postgres 14+) have a valid value.
*/
if (!P_ISDELETED(opaque) || P_HAS_FULLXID(opaque))
{
/* Okay, no reason not to trust btpo_level field from page */
if (P_ISLEAF(opaque) && opaque->btpo_level != 0)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg_internal("invalid leaf page level %u for block %u in index \"%s\"",
opaque->btpo_level, blocknum,
RelationGetRelationName(state->rel))));
if (!P_ISLEAF(opaque) && opaque->btpo_level == 0)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg_internal("invalid internal page level 0 for block %u in index \"%s\"",
blocknum,
RelationGetRelationName(state->rel))));
}
/*
* Sanity checks for number of items on page.
*
* As noted at the beginning of _bt_binsrch(), an internal page must have
* children, since there must always be a negative infinity downlink
* (there may also be a highkey). In the case of non-rightmost leaf
* pages, there must be at least a highkey. The exceptions are deleted
* pages, which contain no items.
*
* This is correct when pages are half-dead, since internal pages are
* never half-dead, and leaf pages must have a high key when half-dead
* (the rightmost page can never be deleted). It's also correct with
* fully deleted pages: _bt_unlink_halfdead_page() doesn't change anything
* about the target page other than setting the page as fully dead, and
* setting its xact field. In particular, it doesn't change the sibling
* links in the deletion target itself, since they're required when index
* scans land on the deletion target, and then need to move right (or need
* to move left, in the case of backward index scans).
*/
maxoffset = PageGetMaxOffsetNumber(page);
if (maxoffset > MaxIndexTuplesPerPage)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("Number of items on block %u of index \"%s\" exceeds MaxIndexTuplesPerPage (%u)",
blocknum, RelationGetRelationName(state->rel),
MaxIndexTuplesPerPage)));
if (!P_ISLEAF(opaque) && !P_ISDELETED(opaque) && maxoffset < P_FIRSTDATAKEY(opaque))
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("internal block %u in index \"%s\" lacks high key and/or at least one downlink",
blocknum, RelationGetRelationName(state->rel))));
if (P_ISLEAF(opaque) && !P_ISDELETED(opaque) && !P_RIGHTMOST(opaque) && maxoffset < P_HIKEY)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("non-rightmost leaf block %u in index \"%s\" lacks high key item",
blocknum, RelationGetRelationName(state->rel))));
/*
* In general, internal pages are never marked half-dead, except on
* versions of Postgres prior to 9.4, where it can be valid transient
* state. This state is nonetheless treated as corruption by VACUUM on
* from version 9.4 on, so do the same here. See _bt_pagedel() for full
* details.
*/
if (!P_ISLEAF(opaque) && P_ISHALFDEAD(opaque))
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("internal page block %u in index \"%s\" is half-dead",
blocknum, RelationGetRelationName(state->rel)),
errhint("This can be caused by an interrupted VACUUM in version 9.3 or older, before upgrade. Please REINDEX it.")));
/*
* Check that internal pages have no garbage items, and that no page has
* an invalid combination of deletion-related page level flags
*/
if (!P_ISLEAF(opaque) && P_HAS_GARBAGE(opaque))
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg_internal("internal page block %u in index \"%s\" has garbage items",
blocknum, RelationGetRelationName(state->rel))));
if (P_HAS_FULLXID(opaque) && !P_ISDELETED(opaque))
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg_internal("full transaction id page flag appears in non-deleted block %u in index \"%s\"",
blocknum, RelationGetRelationName(state->rel))));
if (P_ISDELETED(opaque) && P_ISHALFDEAD(opaque))
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg_internal("deleted page block %u in index \"%s\" is half-dead",
blocknum, RelationGetRelationName(state->rel))));
return page;
}
/*
* _bt_mkscankey() wrapper that automatically prevents insertion scankey from
* being considered greater than the pivot tuple that its values originated
* from (or some other identical pivot tuple) in the common case where there
* are truncated/minus infinity attributes. Without this extra step, there
* are forms of corruption that amcheck could theoretically fail to report.
*
* For example, invariant_g_offset() might miss a cross-page invariant failure
* on an internal level if the scankey built from the first item on the
* target's right sibling page happened to be equal to (not greater than) the
* last item on target page. The !pivotsearch tiebreaker in _bt_compare()
* might otherwise cause amcheck to assume (rather than actually verify) that
* the scankey is greater.
*/
static inline BTScanInsert
bt_mkscankey_pivotsearch(Relation rel, IndexTuple itup)
{
BTScanInsert skey;
skey = _bt_mkscankey(rel, itup);
skey->pivotsearch = true;
return skey;
}
/*
* PageGetItemId() wrapper that validates returned line pointer.
*
* Buffer page/page item access macros generally trust that line pointers are
* not corrupt, which might cause problems for verification itself. For
* example, there is no bounds checking in PageGetItem(). Passing it a
* corrupt line pointer can cause it to return a tuple/pointer that is unsafe
* to dereference.
*
* Validating line pointers before tuples avoids undefined behavior and
* assertion failures with corrupt indexes, making the verification process
* more robust and predictable.
*/
static ItemId
PageGetItemIdCareful(BtreeCheckState *state, BlockNumber block, Page page,
OffsetNumber offset)
{
ItemId itemid = PageGetItemId(page, offset);
if (ItemIdGetOffset(itemid) + ItemIdGetLength(itemid) >
BLCKSZ - MAXALIGN(sizeof(BTPageOpaqueData)))
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("line pointer points past end of tuple space in index \"%s\"",
RelationGetRelationName(state->rel)),
errdetail_internal("Index tid=(%u,%u) lp_off=%u, lp_len=%u lp_flags=%u.",
block, offset, ItemIdGetOffset(itemid),
ItemIdGetLength(itemid),
ItemIdGetFlags(itemid))));
/*
* Verify that line pointer isn't LP_REDIRECT or LP_UNUSED, since nbtree
* never uses either. Verify that line pointer has storage, too, since
* even LP_DEAD items should within nbtree.
*/
if (ItemIdIsRedirected(itemid) || !ItemIdIsUsed(itemid) ||
ItemIdGetLength(itemid) == 0)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("invalid line pointer storage in index \"%s\"",
RelationGetRelationName(state->rel)),
errdetail_internal("Index tid=(%u,%u) lp_off=%u, lp_len=%u lp_flags=%u.",
block, offset, ItemIdGetOffset(itemid),
ItemIdGetLength(itemid),
ItemIdGetFlags(itemid))));
return itemid;
}
/*
* BTreeTupleGetHeapTID() wrapper that enforces that a heap TID is present in
* cases where that is mandatory (i.e. for non-pivot tuples)
*/
static inline ItemPointer
BTreeTupleGetHeapTIDCareful(BtreeCheckState *state, IndexTuple itup,
bool nonpivot)
{
ItemPointer htid;
/*
* Caller determines whether this is supposed to be a pivot or non-pivot
* tuple using page type and item offset number. Verify that tuple
* metadata agrees with this.
*/
Assert(state->heapkeyspace);
if (BTreeTupleIsPivot(itup) && nonpivot)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg_internal("block %u or its right sibling block or child block in index \"%s\" has unexpected pivot tuple",
state->targetblock,
RelationGetRelationName(state->rel))));
if (!BTreeTupleIsPivot(itup) && !nonpivot)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg_internal("block %u or its right sibling block or child block in index \"%s\" has unexpected non-pivot tuple",
state->targetblock,
RelationGetRelationName(state->rel))));
htid = BTreeTupleGetHeapTID(itup);
if (!ItemPointerIsValid(htid) && nonpivot)
ereport(ERROR,
(errcode(ERRCODE_INDEX_CORRUPTED),
errmsg("block %u or its right sibling block or child block in index \"%s\" contains non-pivot tuple that lacks a heap TID",
state->targetblock,
RelationGetRelationName(state->rel))));
return htid;
}
/*
* Return the "pointed to" TID for itup, which is used to generate a
* descriptive error message. itup must be a "data item" tuple (it wouldn't
* make much sense to call here with a high key tuple, since there won't be a
* valid downlink/block number to display).
*
* Returns either a heap TID (which will be the first heap TID in posting list
* if itup is posting list tuple), or a TID that contains downlink block
* number, plus some encoded metadata (e.g., the number of attributes present
* in itup).
*/
static inline ItemPointer
BTreeTupleGetPointsToTID(IndexTuple itup)
{
/*
* Rely on the assumption that !heapkeyspace internal page data items will
* correctly return TID with downlink here -- BTreeTupleGetHeapTID() won't
* recognize it as a pivot tuple, but everything still works out because
* the t_tid field is still returned
*/
if (!BTreeTupleIsPivot(itup))
return BTreeTupleGetHeapTID(itup);
/* Pivot tuple returns TID with downlink block (heapkeyspace variant) */
return &itup->t_tid;
}
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