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amcheck: Don't load the right sibling page into BtreeCheckState

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5ae2087202 implemented a cross-page unique constraint check by loading
the right sibling to the BtreeCheckState.target variable.  This is wrong,
because bt_target_page_check() shouldn't change the target page.  Also,
BtreeCheckState.target shouldn't be changed alone without
BtreeCheckState.targetblock.

However, the above didn't cause any visible bugs for the following reasons.
1. We do a cross-page unique constraint check only for leaf index pages.
2. The only way target page get accessed after a cross-page unique constraint
   check is loading of the lowkey.
3. The only place lowkey is used is bt_child_highkey_check(), and that applies
   only to non-leafs.

The reasons above don't diminish the fact that changing BtreeCheckState.target
for a cross-page unique constraint check is wrong.  This commit changes this
check to temporarily store the right sibling to the local variable.

Reported-by: Peter Geoghegan
Discussion: https://postgr.es/m/CAH2-Wzk%2B2116uOXdOViA27SHcr31WKPgmjsxXLBs_aTxAeThzg%40mail.gmail.com
Author: Pavel Borisov
This commit is contained in:
Alexander Korotkov 2024-05-23 02:12:45 +03:00
parent 532d94fec3
commit 0b5c161248
1 changed files with 9 additions and 5 deletions
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14
contrib/amcheck/verify_nbtree.c
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@ -1892,20 +1892,24 @@ bt_target_page_check(BtreeCheckState *state)
/* The first key on the next page is the same */ /* 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;
elog(DEBUG2, "cross page equal keys"); elog(DEBUG2, "cross page equal keys");
state->target = palloc_btree_page(state, rightpage = palloc_btree_page(state,
rightblock_number); rightblock_number);
topaque = BTPageGetOpaque(state->target); topaque = BTPageGetOpaque(rightpage);
if (P_IGNORE(topaque) || !P_ISLEAF(topaque)) if (P_IGNORE(topaque) || !P_ISLEAF(topaque))
break; break;
itemid = PageGetItemIdCareful(state, rightblock_number, itemid = PageGetItemIdCareful(state, rightblock_number,
state->target, rightpage,
rightfirstoffset); rightfirstoffset);
itup = (IndexTuple) PageGetItem(state->target, itemid); itup = (IndexTuple) PageGetItem(rightpage, itemid);
bt_entry_unique_check(state, itup, rightblock_number, rightfirstoffset, &lVis); bt_entry_unique_check(state, itup, rightblock_number, rightfirstoffset, &lVis);
pfree(rightpage);
} }
} }
} }