Re: Extremely slow HashAggregate in simple UNION query

Hi,

On August 24, 2019 12:41:03 PM PDT, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>Jeff Janes <jeff(dot)janes(at)gmail(dot)com> writes:
>> Most of the time is not after the clock stops, but before the
>stepwise
>> ANALYZE clock starts. If you just do an EXPLAIN rather than EXPLAIN
>> ANALYZE, that is also slow. The giant hash table is created during
>the
>> planning step (or somewhere around there
>
>It's in executor startup, I believe.

I'm sure personally interested in doing so, but it'd not be hard to measure the executor startup time separately. And display it either on a per node basis, or as a total number.

Quite unconvinced this thread is a convincing reason to do so (or really do anything). But for some other workloads executor startup is a very large fraction of the total time, without massive misestimations. Optimizing that could be easier with that information available.

Andres
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