From: | David Gilman <davidgilman1(at)gmail(dot)com> |
---|---|
To: | pgsql-general(at)lists(dot)postgresql(dot)org |
Subject: | Query plan regression between CTE and views |
Date: | 2023-08-14 14:54:46 |
Message-ID: | CALBH9DDEFesJy-hS33dvS88krG0+XZDiPr1iG2_YQNyJZRwa-w@mail.gmail.com |
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Lists: | pgsql-general |
I have a query that was originally written as a handful of CTEs out of
convenience. It is producing a reasonable query plan because the CTE
materialization was kicking in at an appropriate place. The CTEs
aren't totally linear. The graph looks like this, where A, B, C and D
are CTEs, and B -> A means B selects from A. In Graphviz format:
G {
B -> A;
C -> A;
C -> B;
D -> C;
}
Out of curiosity I tried turning the query into a series of views and
ran that query. The query plan is vastly different, there is no
materialization and it runs much slower.
My question is: is this a valid bug? I am not sure if I should expect
the view version to find a way to materialize and produce a comparable
query plan. Also, making a minimal test case is going to take a bit
and I don't want to start unless this smells like a genuine bug.
--
David Gilman
:DG<
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