On Fri, May 13, 2011 at 6:02 PM, Tom Lane <t...@sss.pgh.pa.us> wrote:
> Gurjeet Singh <singh.gurj...@gmail.com> writes: > > I am listing the query, it's explain output and explain analyze output at > > the end. > > > The EXPLAIN output shows the 'Subplan 2' node only once, whereas EXPLAIN > > ANALYZE output shows that the 'Subplan 2' is being executed twice . Is > that > > true? Or is it just the plan printer getting confused? Is the confusion > > because of the 2 conditions in the WHERE clause of the correlated > subquery? > > The reason it looks like that is that the SubPlan is referenced in the > index condition, and there are actually two copies of that (indxqual and > indxqualorig). They both point at the same physical subplan, but there > are two entries in the parent node's subPlan list. In EXPLAIN you only > see one because ExecInitIndexScan skips initializing the indxquals in > EXPLAIN_ONLY mode. > > In short: it's cosmetic. > That's a relief > > We could probably suppress the duplicate printout when both references > are in the same plan node, but in bitmap scans the indxqual and > indxqualorig expressions are actually in different plan nodes (the > indexscan and heapscan respectively). I'm not sure how we could > suppress the duplicate printout in that case, or whether it would even > make sense to do so --- after all, the subplan can in fact get called by > both nodes. > As long as it's not being re-evaluated, it's not a big deal. It does confuse the casual onlooker, though; and if there's any automatic tool to parse and report explain analyze output, it might get its numbers quite wrong. Regards, -- Gurjeet Singh EnterpriseDB Corporation The Enterprise PostgreSQL Company
