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amcheck: Optimize speed of checking for unique constraint violation 

Currently, when amcheck validates a unique constraint, it visits the heap for
each index tuple.  This commit implements skipping keys, which have only one
non-dedeuplicated index tuple (quite common case for unique indexes). That
gives substantial economy on index checking time.

Reported-by: Noah Misch
Discussion: https://postgr.es/m/20240325020323.fd.nmisch%40google.com
Author: Alexander Korotkov, Pavel Borisov
This commit is contained in:
Alexander Korotkov 2024-07-28 13:50:57 +03:00
parent b181062aa5
commit cdd6ab9d1f
1 changed files with 33 additions and 3 deletions
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36
contrib/amcheck/verify_nbtree.c
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@ -1433,6 +1433,13 @@ bt_target_page_check(BtreeCheckState *state)
bool lowersizelimit;
ItemPointer scantid;
/*
* True if we already called bt_entry_unique_check() for the current
* item. This helps to avoid visiting the heap for keys, which are
* anyway presented only once and can't comprise a unique violation.
*/
bool unique_checked = false;
CHECK_FOR_INTERRUPTS();
itemid = PageGetItemIdCareful(state, state->targetblock,
@ -1775,12 +1782,18 @@ bt_target_page_check(BtreeCheckState *state)
/*
* If the index is unique verify entries uniqueness by checking the
* heap tuples visibility.
* heap tuples visibility. Immediately check posting tuples and
* tuples with repeated keys. Postpone check for keys, which have the
* first appearance.
*/
if (state->checkunique && state->indexinfo->ii_Unique &&
P_ISLEAF(topaque) && !skey->anynullkeys)
P_ISLEAF(topaque) && !skey->anynullkeys &&
(BTreeTupleIsPosting(itup) || ItemPointerIsValid(lVis.tid)))
{
bt_entry_unique_check(state, itup, state->targetblock, offset,
&lVis);
unique_checked = true;
}
if (state->checkunique && state->indexinfo->ii_Unique &&
P_ISLEAF(topaque) && OffsetNumberNext(offset) <= max)
@ -1799,6 +1812,9 @@ bt_target_page_check(BtreeCheckState *state)
* data (whole index tuple or last posting in index tuple). Key
* containing null value does not violate unique constraint and
* treated as different to any other key.
*
* If the next key is the same as the previous one, do the
* bt_entry_unique_check() call if it was postponed.
*/
if (_bt_compare(state->rel, skey, state->target,
OffsetNumberNext(offset)) != 0 || skey->anynullkeys)
@ -1808,6 +1824,11 @@ bt_target_page_check(BtreeCheckState *state)
lVis.postingIndex = -1;
lVis.tid = NULL;
}
else if (!unique_checked)
{
bt_entry_unique_check(state, itup, state->targetblock, offset,
&lVis);
}
skey->scantid = scantid; /* Restore saved scan key state */
}
@ -1890,10 +1911,19 @@ bt_target_page_check(BtreeCheckState *state)
rightkey->scantid = NULL;
/* The first key on the next page is the same */
if (_bt_compare(state->rel, rightkey, state->target, max) == 0 && !rightkey->anynullkeys)
if (_bt_compare(state->rel, rightkey, state->target, max) == 0 &&
!rightkey->anynullkeys)
{
Page rightpage;
/*
* Do the bt_entry_unique_check() call if it was
* postponed.
*/
if (!unique_checked)
bt_entry_unique_check(state, itup, state->targetblock,
offset, &lVis);
elog(DEBUG2, "cross page equal keys");
rightpage = palloc_btree_page(state,
rightblock_number);