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Guard against zero vardata.rel->tuples in estimate_hash_bucketsize().

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If the referenced rel was proven empty, we'd compute 0/0 here, which
results in the function returning NaN.  That's a bit more serious
than the other zero-divide case.  Still, it only seems to be possible
in HEAD, so no back-patch.

Per report from Piotr Stefaniak.  I looked through the rest of selfuncs.c
and found no other likely trouble spots.
This commit is contained in:
Tom Lane
2016-03-27 18:21:03 -04:00
parent fa09f89351
commit d65b665d52
1 changed files with 1 additions and 1 deletions
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2
src/backend/utils/adt/selfuncs.c
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@ -3540,7 +3540,7 @@ estimate_hash_bucketsize(PlannerInfo *root, Node *hashkey, double nbuckets)
* XXX Possibly better way, but much more expensive: multiply by * XXX Possibly better way, but much more expensive: multiply by
* selectivity of rel's restriction clauses that mention the target Var. * selectivity of rel's restriction clauses that mention the target Var.
*/ */
if (vardata.rel) if (vardata.rel && vardata.rel->tuples > 0)
{ {
ndistinct *= vardata.rel->rows / vardata.rel->tuples; ndistinct *= vardata.rel->rows / vardata.rel->tuples;
ndistinct = clamp_row_est(ndistinct); ndistinct = clamp_row_est(ndistinct);