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Fix unnecessary use of moving-aggregate mode with non-moving frame.

2024年3月27日 17:39:03 +0000 (13:39 -0400)

When a plain aggregate is used as a window function, and the window
frame start is specified as UNBOUNDED PRECEDING, the frame's head
cannot move so we do not need to use moving-aggregate mode. The check
for that was put into initialize_peragg(), failing to notice that
ExecInitWindowAgg() calls that function before it's filled in
winstate->frameOptions. Since makeNode() would have zeroed the field,
this didn't provoke uninitialized-value complaints, nor would the
erroneous decision have resulted in more than a little inefficiency.
Still, it's wrong, so move the initialization of
winstate->frameOptions earlier to make it work properly.

While here, also fix a thinko in a comment. Both errors crept in in
commit a9d9acbf2 which introduced the moving-aggregate mode.

Spotted by Vallimaharajan G. Back-patch to all supported branches.

Discussion: https://postgr.es/m/18e7f2a5167.fe36253866818.977923893562469143@zohocorp.com

src/backend/executor/nodeWindowAgg.c patch | blob | blame | history

diff --git a/src/backend/executor/nodeWindowAgg.c b/src/backend/executor/nodeWindowAgg.c

index 62d028379bec9c31c473210214ddd2d5402722ce..3221fa1522a3a2ae46e709193e13cbc3349dfcf0 100644 (file)

--- a/src/backend/executor/nodeWindowAgg.c

+++ b/src/backend/executor/nodeWindowAgg.c

@@ -2399,6 +2399,9 @@ ExecInitWindowAgg(WindowAgg *node, EState *estate, int eflags)

winstate->ss.ps.state = estate;

winstate->ss.ps.ExecProcNode = ExecWindowAgg;

+ /* copy frame options to state node for easy access */

+ winstate->frameOptions = frameOptions;

* Create expression contexts. We need two, one for per-input-tuple

* processing and one for per-output-tuple processing. We cheat a little