From e91a1643ac723477d6ec2d47c8486cd0013660bb Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Thu, 30 Jul 2015 12:11:23 -0400 Subject: Avoid some zero-divide hazards in the planner. Although I think on all modern machines floating division by zero results in Infinity not SIGFPE, we still don't want infinities running around in the planner's costing estimates; too much risk of that leading to insane behavior. grouping_planner() failed to consider the possibility that final_rel might be known dummy and hence have zero rowcount. (I wonder if it would be better to set a rows estimate of 1 for dummy relations? But at least in the back branches, changing this convention seems like a bad idea, so I'll leave that for another day.) Make certain that get_variable_numdistinct() produces a nonzero result. The case that can be shown to be broken is with stadistinct < 0.0 and small ntuples; we did not prevent the result from rounding to zero. For good luck I applied clamp_row_est() to all the nonconstant return values. In ExecChooseHashTableSize(), Assert that we compute positive nbuckets and nbatch. I know of no reason to think this isn't the case, but it seems like a good safety check. Per reports from Piotr Stefaniak. Back-patch to all active branches. --- src/backend/executor/nodeHash.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'src/backend/executor/nodeHash.c') diff --git a/src/backend/executor/nodeHash.c b/src/backend/executor/nodeHash.c index 906cb46b658..ee9298a157f 100644 --- a/src/backend/executor/nodeHash.c +++ b/src/backend/executor/nodeHash.c @@ -542,6 +542,9 @@ ExecChooseHashTableSize(double ntuples, int tupwidth, bool useskew, nbatch <<= 1; } + Assert(nbuckets > 0); + Assert(nbatch > 0); + *numbuckets = nbuckets; *numbatches = nbatch; } -- cgit v1.2.3