postgres.git / summary / log / commit / refs

commit    fa09f8935156533584b4e215bdf70ec1ff968dad
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Sun Mar 27 22:06:53 2016 +0000

    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 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


[parent: 408f0438531e]