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tableam: Add helper for indexes to check if a corresponding table tuples exist.

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This is, likely exclusively, useful to verify that conflicts detected
in a unique index are with live tuples, rather than dead ones.

Author: Andres Freund
Discussion: https://postgr.es/m/20180703070645.wchpu5muyto5n647@alap3.anarazel.de
This commit is contained in:
Andres Freund
2019-03-25 16:52:55 -07:00
parent aa1419e63f
commit 71bdc99d0d
4 changed files with 64 additions and 14 deletions
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34
src/backend/access/table/tableam.c
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@@ -176,6 +176,40 @@ table_beginscan_parallel(Relation relation, ParallelTableScanDesc parallel_scan)
}
/* ----------------------------------------------------------------------------
* Index scan related functions.
* ----------------------------------------------------------------------------
*/
/*
* To perform that check simply start an index scan, create the necessary
* slot, do the heap lookup, and shut everything down again. This could be
* optimized, but is unlikely to matter from a performance POV. If there
* frequently are live index pointers also matching a unique index key, the
* CPU overhead of this routine is unlikely to matter.
*/
bool
table_index_fetch_tuple_check(Relation rel,
ItemPointer tid,
Snapshot snapshot,
bool *all_dead)
{
IndexFetchTableData *scan;
TupleTableSlot *slot;
bool call_again = false;
bool found;
slot = table_slot_create(rel, NULL);
scan = table_index_fetch_begin(rel);
found = table_index_fetch_tuple(scan, tid, snapshot, slot, &call_again,
all_dead);
table_index_fetch_end(scan);
ExecDropSingleTupleTableSlot(slot);
return found;
}
/* ----------------------------------------------------------------------------
* Functions to make modifications a bit simpler.
* ----------------------------------------------------------------------------