Re: Speeding up query pulling comments from pg_catalog

On Sat, Jul 20, 2019 at 7:46 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> But if you do so manually you'll end up with something like
>
> SELECT c.relname AS table, a.attname AS column, d.description AS comment
> FROM
> pg_catalog.pg_attribute a JOIN pg_catalog.pg_class c ON a.attrelid =
> c.oid
> LEFT JOIN pg_catalog.pg_description d ON d.classoid = c.tableoid and
> d.objoid = c.oid and d.objsubid = a.attnum
> WHERE d.description IS NOT NULL;
>
> For me, that formulation is quite a bit faster than the original ---
>

A lot faster for me too (~30-40 ms). Thanks!

and then to add insult to injury, has to search pg_description a second
> time for each hit.
>

Not sure if I'm understanding this correctly, but are you saying that
because col_description() is specified in two places in the query, that it
actually will get called twice? I was under the impression that a function
(at least a non-volatile one) specified multiple times, but with the same
arguments, would only get called once. Is that just wishful thinking?

Cheers,

Ken

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