Re: Multivariate MCV lists -- pg_mcv_list_items() seems to be broken

On Mon, Apr 15, 2019 at 05:02:43PM +0100, Dean Rasheed wrote:
>I just noticed the following:
>
>CREATE TABLE foo (a int, b int);
>INSERT INTO foo SELECT x/10, x/100 FROM generate_series(1, 100) x;
>CREATE STATISTICS foo_s ON a,b FROM foo;
>ANALYSE foo;
>
>SELECT pg_mcv_list_items(stxmcv) from pg_statistic_ext WHERE stxname = 'foo_s';
>
>which fails with
>
>ERROR: cache lookup failed for type 0
>
>That definitely used to work, so I'm guessing it got broken by the
>recent reworking of the serialisation code, but I've not looked into
>it.
>

Yeah, that seems like a bug. I'll take a look.

>There should probably be regression test coverage of that function.
>

Agreed. I plan to rework the existing tests to use the same approach as
the MCV, so I'll add a test for this function too.

regards

--
Tomas Vondra http://www.2ndQuadrant.com
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