Reading explain plans- row estimates/actuals on lower nodes vs next level up

From: Michael Lewis <mlewis(at)entrata(dot)com>
To: postgres performance list <pgsql-performance(at)postgresql(dot)org>
Subject: Reading explain plans- row estimates/actuals on lower nodes vs next level up
Date: 2019-10-17 21:15:21
Message-ID: CAHOFxGo1UAF45F_fdZML1QKmSjjvN_npLx52yQv7NV6Xk=COJg@mail.gmail.com
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https://explain.depesz.com/s/Caa5

I am looking at this explain analyze output and seeing a nested loop
towards the lowest levels with pretty bad estimate vs actual (2.3k vs 99k),
but the things that feed that nested loop seem like the estimates are
rather close (index scans with 11 estimated vs 30 actual and 3350 vs
3320)... why does the higher node have such a different estimate vs actual
ratio?

*Michael Lewis | Software Engineer*
*Entrata*

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