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| author | Tom Lane <tgl@sss.pgh.pa.us> | 2016-03-27 18:06:53 -0400 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2016-03-27 18:07:16 -0400 |
| commit | fa09f8935156533584b4e215bdf70ec1ff968dad (patch) | |
| tree | ac391eb6237aac234ff9aeaf43f0b199c41bac3d /src/backend/utils/adt/selfuncs.c | |
| parent | 408f0438531eec17ac62f91fc23f72bcfc48dd36 (diff) | |
| download | postgresql-fa09f8935156533584b4e215bdf70ec1ff968dad.tar.gz postgresql-fa09f8935156533584b4e215bdf70ec1ff968dad.zip | |
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.
Diffstat (limited to 'src/backend/utils/adt/selfuncs.c')
| -rw-r--r-- | src/backend/utils/adt/selfuncs.c | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c index b2c57e87a5e..30751fc8ac6 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 |