From d65b665d524a67273b075f468bf3d60ce31f4040 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sun, 27 Mar 2016 18:21:03 -0400
Subject: [PATCH] Guard against zero vardata.rel->tuples in
estimate_hash_bucketsize().
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.
---
src/backend/utils/adt/selfuncs.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c
index 30751fc8ac..a6555e91b7 100644
--- a/src/backend/utils/adt/selfuncs.c
+++ b/src/backend/utils/adt/selfuncs.c
@@ -3540,7 +3540,7 @@ estimate_hash_bucketsize(PlannerInfo *root, Node *hashkey, double nbuckets)
* XXX Possibly better way, but much more expensive: multiply by
* 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 = clamp_row_est(ndistinct);
--
2.49.0