Re: Slow statement using parallelism after 9.6>11 upgrade

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: arnaud(dot)listes(at)codata(dot)eu
Cc: pgsql-general <pgsql-general(at)lists(dot)postgresql(dot)org>
Subject: Re: Slow statement using parallelism after 9.6>11 upgrade
Date: 2019-09-03 13:43:11
Message-ID: 23865.1567518191@sss.pgh.pa.us
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"Arnaud L." <arnaud(dot)listes(at)codata(dot)eu> writes:
> We have upgraded our database from 9.6 to 11 (and updated PostGIS from
> 2.3 to 2.5 as well).
> ...

Have you re-ANALYZEd the database? The problem with this query
seems to be the spectacularly awful rowcount estimate here:

> -> Bitmap Index Scan on planet_osm_ways_nodes_idx
> (cost=0.00..11190.36 rows=1420982 width=0) (actual time=0.268..0.268
> rows=1 loops=1)
> Index Cond: (nodes && '{1}'::bigint[])

The planner should be able to do better than that, given up-to-date
statistics on the "nodes" column.

regards, tom lane

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