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| author | Tom Lane <tgl@sss.pgh.pa.us> | 2011-08-09 11:33:46 -0400 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2011-08-09 11:34:20 -0400 |
| commit | cff60f2dfa470d5736a19d36eb910844e31db764 (patch) | |
| tree | 96d1218ac40d39c7aa2ea94e732f8aaa4660e8bd /src | |
| parent | f4a9da0a150ead846be33c38f665f4337a81054e (diff) | |
| download | postgresql-cff60f2dfa470d5736a19d36eb910844e31db764.tar.gz postgresql-cff60f2dfa470d5736a19d36eb910844e31db764.zip | |
Avoid creating PlaceHolderVars immediately within PlaceHolderVars.
Such a construction is useless since the lower PlaceHolderVar is already
nullable; no need to make it more so. Noted while pursuing bug #6154.
This is just a minor planner efficiency improvement, since the final plan
will come out the same anyway after PHVs are flattened. So not worth the
risk of back-patching.
Diffstat (limited to 'src')
| -rw-r--r-- | src/backend/optimizer/prep/prepjointree.c | 20 |
1 files changed, 16 insertions, 4 deletions
diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c index ac622a34d9d..63a52f2d976 100644 --- a/src/backend/optimizer/prep/prepjointree.c +++ b/src/backend/optimizer/prep/prepjointree.c @@ -1411,6 +1411,12 @@ pullup_replace_vars_callback(Var *var, /* Simple Vars always escape being wrapped */ wrap = false; } + else if (newnode && IsA(newnode, PlaceHolderVar) && + ((PlaceHolderVar *) newnode)->phlevelsup == 0) + { + /* No need to wrap a PlaceHolderVar with another one, either */ + wrap = false; + } else if (rcon->wrap_non_vars) { /* Wrap all non-Vars in a PlaceHolderVar */ @@ -1420,10 +1426,16 @@ pullup_replace_vars_callback(Var *var, { /* * If it contains a Var of current level, and does not contain - * any non-strict constructs, then it's certainly nullable and - * we don't need to insert a PlaceHolderVar. (Note: in future - * maybe we should insert PlaceHolderVars anyway, when a tlist - * item is expensive to evaluate? + * any non-strict constructs, then it's certainly nullable so + * we don't need to insert a PlaceHolderVar. + * + * This analysis could be tighter: in particular, a non-strict + * construct hidden within a lower-level PlaceHolderVar is not + * reason to add another PHV. But for now it doesn't seem + * worth the code to be more exact. + * + * Note: in future maybe we should insert a PlaceHolderVar + * anyway, if the tlist item is expensive to evaluate? */ if (contain_vars_of_level((Node *) newnode, 0) && !contain_nonstrict_functions((Node *) newnode)) |