[COMMITTERS] pgsql: Fix AggGetAggref() so it won't lie to aggregate finalfunctions. - Mailing list pgsql-committers

From Tom Lane
Subject [COMMITTERS] pgsql: Fix AggGetAggref() so it won't lie to aggregate finalfunctions.
Date
Msg-id E1e2j26-0007mg-JH@gemulon.postgresql.org
Whole thread Raw
List pgsql-committers
Fix AggGetAggref() so it won't lie to aggregate final functions.

If we merge the transition calculations for two different aggregates,
it's reasonable to assume that the transition function should not care
which of those Aggref structs it gets from AggGetAggref().  It is not
reasonable to make the same assumption about an aggregate final function,
however.  Commit 804163bc2 broke this, as it will pass whichever Aggref
was first associated with the transition state in both cases.

This doesn't create an observable bug so far as the core system is
concerned, because the only existing uses of AggGetAggref() are in
ordered-set aggregates that happen to not pay attention to anything
but the input properties of the Aggref; and besides that, we disabled
sharing of transition calculations for OSAs yesterday.  Nonetheless,
if some third-party code were using AggGetAggref() in a normal aggregate,
they would be entitled to call this a bug.  Hence, back-patch the fix
to 9.6 where the problem was introduced.

In passing, improve some of the comments about transition state sharing.

Discussion: https://postgr.es/m/CAB4ELO5RZhOamuT9Xsf72ozbenDLLXZKSk07FiSVsuJNZB861A@mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/305cf1fd7239e0ffa9ae4ff54a7c66f36432c741

Modified Files
--------------
src/backend/executor/nodeAgg.c | 65 +++++++++++++++++++++++++++---------------
src/include/nodes/execnodes.h  |  3 +-
2 files changed, 44 insertions(+), 24 deletions(-)


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