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Commit10f1ab2

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Fix misuse of table_index_fetch_tuple_check().
Commit0d861bb, which added deduplication to nbtree, had_bt_check_unique() pass a TID to table_index_fetch_tuple_check() thatisn't safe to mutate. table_index_fetch_tuple_check()'s tid argument ismodified when the TID in question is not the latest visible tuple in ahot 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.
1 parent463b808 commit10f1ab2

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3 files changed

+9
-2
lines changed

3 files changed

+9
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‎src/backend/access/nbtree/nbtinsert.c

Lines changed: 2 additions & 1 deletion
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@@ -597,7 +597,8 @@ _bt_check_unique(Relation rel, BTInsertState insertstate, Relation heapRel,
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* not part of this chain because it had a different index
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* entry.
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*/
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if (table_index_fetch_tuple_check(heapRel,&itup->t_tid,
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htid=itup->t_tid;
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if (table_index_fetch_tuple_check(heapRel,&htid,
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SnapshotSelf,NULL))
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{
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/* Normal case --- it's still live */

‎src/backend/access/table/tableam.c

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Original file line numberDiff line numberDiff line change
@@ -196,6 +196,10 @@ table_beginscan_parallel(Relation relation, ParallelTableScanDesc parallel_scan)
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* optimized, but is unlikely to matter from a performance POV. If there
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* frequently are live index pointers also matching a unique index key, the
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* CPU overhead of this routine is unlikely to matter.
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*
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* Note that *tid may be modified when we return true if the AM supports
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* storing multiple row versions reachable via a single index entry (like
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* heap's HOT).
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*/
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bool
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table_index_fetch_tuple_check(Relationrel,

‎src/include/access/tableam.h

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -989,7 +989,9 @@ table_index_fetch_end(struct IndexFetchTableData *scan)
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/*
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* Fetches, as part of an index scan, tuple at `tid` into `slot`, after doing
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* a visibility test according to `snapshot`. If a tuple was found and passed
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* the visibility test, returns true, false otherwise.
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* the visibility test, returns true, false otherwise. Note that *tid may be
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* modified when we return true (see later remarks on multiple row versions
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* reachable via a single index entry).
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*
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* *call_again needs to be false on the first call to table_index_fetch_tuple() for
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* a tid. If there potentially is another tuple matching the tid, *call_again

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