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Fix misuse of table_index_fetch_tuple_check().

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Commit 0d861bbb, which added deduplication to nbtree, had
_bt_check_unique() pass a TID to table_index_fetch_tuple_check() that
isn't safe to mutate.  table_index_fetch_tuple_check()'s tid argument is
modified when the TID in question is not the latest visible tuple in a
hot chain, though this wasn't documented.

To fix, go back to using a local copy of the TID in _bt_check_unique(),
and update comments above table_index_fetch_tuple_check().

Backpatch: 13-, where B-Tree deduplication was introduced.
This commit is contained in:
Peter Geoghegan
2020-06-25 10:55:28 -07:00
parent 463b808e75
commit 10f1ab2cb8
3 changed files with 9 additions and 2 deletions
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3
src/backend/access/nbtree/nbtinsert.c
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@@ -597,7 +597,8 @@ _bt_check_unique(Relation rel, BTInsertState insertstate, Relation heapRel,
* not part of this chain because it had a different index
* entry.
*/
if (table_index_fetch_tuple_check(heapRel, &itup->t_tid,
htid = itup->t_tid;
if (table_index_fetch_tuple_check(heapRel, &htid,
SnapshotSelf, NULL))
{
/* Normal case --- it's still live */