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Commitcff60f2

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Avoid creating PlaceHolderVars immediately within PlaceHolderVars.
Such a construction is useless since the lower PlaceHolderVar is alreadynullable; no need to make it more so. Noted while pursuing bug #6154.This is just a minor planner efficiency improvement, since the final planwill come out the same anyway after PHVs are flattened. So not worth therisk of back-patching.
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‎src/backend/optimizer/prep/prepjointree.c

Lines changed: 16 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1411,6 +1411,12 @@ pullup_replace_vars_callback(Var *var,
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/* Simple Vars always escape being wrapped */
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wrap= false;
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}
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elseif (newnode&&IsA(newnode,PlaceHolderVar)&&
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((PlaceHolderVar*)newnode)->phlevelsup==0)
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{
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/* No need to wrap a PlaceHolderVar with another one, either */
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wrap= false;
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}
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elseif (rcon->wrap_non_vars)
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{
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/* Wrap all non-Vars in a PlaceHolderVar */
@@ -1420,10 +1426,16 @@ pullup_replace_vars_callback(Var *var,
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{
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/*
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* If it contains a Var of current level, and does not contain
1423-
* any non-strict constructs, then it's certainly nullable and
1424-
* we don't need to insert a PlaceHolderVar. (Note: in future
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* maybe we should insert PlaceHolderVars anyway, when a tlist
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* item is expensive to evaluate?
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* any non-strict constructs, then it's certainly nullable so
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* we don't need to insert a PlaceHolderVar.
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*
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* This analysis could be tighter: in particular, a non-strict
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* construct hidden within a lower-level PlaceHolderVar is not
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* reason to add another PHV. But for now it doesn't seem
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* worth the code to be more exact.
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*
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* Note: in future maybe we should insert a PlaceHolderVar
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* anyway, if the tlist item is expensive to evaluate?
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*/
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if (contain_vars_of_level((Node*)newnode,0)&&
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!contain_nonstrict_functions((Node*)newnode))

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