Fix unnecessary use of moving-aggregate mode with non-moving frame.
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
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@ -2399,6 +2399,9 @@ ExecInitWindowAgg(WindowAgg *node, EState *estate, int eflags)
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winstate->ss.ps.state = estate;
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winstate->ss.ps.ExecProcNode = ExecWindowAgg;
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/* copy frame options to state node for easy access */
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winstate->frameOptions = frameOptions;
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/*
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* Create expression contexts. We need two, one for per-input-tuple
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* processing and one for per-output-tuple processing. We cheat a little
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@ -2649,9 +2652,6 @@ ExecInitWindowAgg(WindowAgg *node, EState *estate, int eflags)
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/* Set the status to running */
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winstate->status = WINDOWAGG_RUN;
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/* copy frame options to state node for easy access */
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winstate->frameOptions = frameOptions;
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/* initialize frame bound offset expressions */
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winstate->startOffset = ExecInitExpr((Expr *) node->startOffset,
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(PlanState *) winstate);
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@ -2785,7 +2785,7 @@ initialize_peragg(WindowAggState *winstate, WindowFunc *wfunc,
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/*
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* Figure out whether we want to use the moving-aggregate implementation,
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* and collect the right set of fields from the pg_attribute entry.
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* and collect the right set of fields from the pg_aggregate entry.
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*
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* It's possible that an aggregate would supply a safe moving-aggregate
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* implementation and an unsafe normal one, in which case our hand is
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