From caae9f764699e44e2e95394b90f48d4429b8ea3f 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/optimizer/plan/planmain.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'src/backend/optimizer/plan/planmain.c') diff --git a/src/backend/optimizer/plan/planmain.c b/src/backend/optimizer/plan/planmain.c index 16d3af32ed0..6647640b385 100644 --- a/src/backend/optimizer/plan/planmain.c +++ b/src/backend/optimizer/plan/planmain.c @@ -356,7 +356,7 @@ query_planner(PlannerInfo *root, List *tlist, * can be divided by the number of tuples. */ if (tuple_fraction >= 1.0) - tuple_fraction /= final_rel->rows; + tuple_fraction /= clamp_row_est(final_rel->rows); } /* -- cgit v1.2.3