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Make _bt_keep_natts_fast() use datum_image_eq().

2019年11月12日 21:08:41 +0000 (13:08 -0800)

An upcoming patch that adds deduplication to the nbtree AM will rely on
_bt_keep_natts_fast() understanding that differences in TOAST input
state can never affect its answer. In particular, two opclass-equal
datums (with opclasses deemed safe for deduplication) should never be
treated as unequal by _bt_keep_natts_fast() due to TOAST input
differences.

This also seems like a good idea on general principle. nbtsplitloc.c
will now occasionally make better decisions about where to split a leaf
page. The behavior of _bt_keep_natts_fast() is now somewhat closer to
the behavior of _bt_keep_natts().

Discussion: https://postgr.es/m/CAH2-Wzn3Ee49Gmxb7V1VJ3-AC8fWn-Fr8pfWQebHe8rYRxt5OQ@mail.gmail.com

src/backend/access/nbtree/nbtutils.c patch | blob | blame | history

diff --git a/src/backend/access/nbtree/nbtutils.c b/src/backend/access/nbtree/nbtutils.c

index 6a3008dd48d8e7a471157441a300b90d2aeee486..7669a1a66f5a73891f3a7906ef4469d24ea6351a 100644 (file)

--- a/src/backend/access/nbtree/nbtutils.c

+++ b/src/backend/access/nbtree/nbtutils.c

@@ -2303,9 +2303,7 @@ _bt_keep_natts(Relation rel, IndexTuple lastleft, IndexTuple firstright,

* The approach taken here usually provides the same answer as _bt_keep_natts

* will (for the same pair of tuples from a heapkeyspace index), since the

* majority of btree opclasses can never indicate that two datums are equal

- * unless they're bitwise equal (once detoasted). Similarly, result may

- * differ from the _bt_keep_natts result when either tuple has TOASTed datums,

- * though this is barely possible in practice.