]> granicus.if.org Git - postgresql/commit
Allow to reset execGrouping.c style tuple hashtables.
authorAndres Freund <andres@anarazel.de>
Sat, 9 Feb 2019 08:35:57 +0000 (00:35 -0800)
committerAndres Freund <andres@anarazel.de>
Sat, 9 Feb 2019 09:05:49 +0000 (01:05 -0800)
commit317ffdfeaac12e434b2befa24993dc1b52a140fd
treef53a3eae9594395bdf33ab77dafcf27da8c3fa51
parent3b632a58e7985c6589dbd0e6c0f32ba007783cfa
Allow to reset execGrouping.c style tuple hashtables.

This has the advantage that the comparator expression, the table's
slot, etc do not have to be rebuilt. Additionally the simplehash.h
hashtable within the tuple hashtable now keeps its previous size and
doesn't need to be reallocated. That both reduces allocator overhead,
and improves performance in cases where the input estimation was off
by a significant factor.

To avoid an API/ABI break, the new parameter is exposed via the new
BuildTupleHashTableExt(), and BuildTupleHashTable() now is a wrapper
around the former, that continues to allocate the table itself in the
tablecxt.

Using this fixes performance issues discovered in the two bugs
referenced. This commit however has not converted the callers, that's
done in a separate commit.

Bug: #15592 #15486
Reported-By: Jakub Janeček, Dmitry Marakasov
Author: Andres Freund
Discussion:
    https://postgr.es/m/15486-05850f065da42931@postgresql.org
    https://postgr.es/m/20190114180423.ywhdg2iagzvh43we@alap3.anarazel.de
Backpatch: 11, this is a prerequisite for other fixes
src/backend/executor/execGrouping.c
src/include/executor/executor.h