Re: pg_class.reltuples of brin indexes

On Tue, Mar 27, 2018 at 08:58:11PM +0900, Masahiko Sawada wrote:
> Hi,
>
> I found that pg_class.reltuples of brin indexes can be either the
> number of index tuples or the number of heap tuples.
>
> =# create table test as select generate_series(1,100000) as c;
> =# create index test_brin on test using brin (c);
> =# analyze test;
> =# select relname, reltuples, relpages from pg_class where relname in
> ('test', 'test_brin');
> relname | reltuples | relpages
> -----------+-----------+----------
> test | 100000 | 443
> test_brin | 100000 | 3
> (2 rows)
>
> =# vacuum test;
> =# select relname, reltuples, relpages from pg_class where relname in
> ('test', 'test_brin');
> relname | reltuples | relpages
> -----------+-----------+----------
> test | 100000 | 443
> test_brin | 3 | 3
> (2 rows)
>
> If I understand correctly pg_class.reltuples of indexes should have
> the number of index tuples but especially for brin indexes it would be
> hard to estimate it in the analyze code. I thought that we can change
> brinvacuumcleanup so that it returns the estimated number of index
> tuples and do vac_update_relstats using that value but it would break
> API contract. Better ideas?

I assume there is nothing to do on this issue.

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