From fa09f8935156533584b4e215bdf70ec1ff968dad Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Sun, 27 Mar 2016 18:06:53 -0400 Subject: [PATCH] Clamp adjusted ndistinct to positive integer in estimate_hash_bucketsize(). This avoids a possible divide-by-zero in the following calculation, and rounding the number to an integer seems like saner behavior anyway. Assuming IEEE math, the division would yield +Infinity which would get replaced by 1.0 at the bottom of the function, so nothing really interesting would ensue; but avoiding divide-by-zero seems like a good idea on general principles. Per report from Piotr Stefaniak. No back-patch since this seems mostly cosmetic. --- src/backend/utils/adt/selfuncs.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c index b2c57e87a5..30751fc8ac 100644 --- a/src/backend/utils/adt/selfuncs.c +++ b/src/backend/utils/adt/selfuncs.c @@ -3541,7 +3541,10 @@ estimate_hash_bucketsize(PlannerInfo *root, Node *hashkey, double nbuckets) * selectivity of rel's restriction clauses that mention the target Var. */ if (vardata.rel) + { ndistinct *= vardata.rel->rows / vardata.rel->tuples; + ndistinct = clamp_row_est(ndistinct); + } /* * Initial estimate of bucketsize fraction is 1/nbuckets as long as the