On 2019-Nov-05, Tatsuro Yamada wrote:
> ==============
> [Session1]
> \! pgbench -i
> create statistics pg_ext1 (dependencies) ON aid, bid from pgbench_accounts;
> create statistics pg_ext2 (mcv) ON aid, bid from pgbench_accounts;
> create statistics pg_ext3 (ndistinct) ON aid, bid from pgbench_accounts;
Wow, it takes a long time to compute these ...
Hmm, you normally wouldn't define stats that way; you'd do this instead:
create statistics pg_ext1 (dependencies, mcv,ndistinct) ON aid, bid from pgbench_accounts;
I'm not sure if this has an important impact in practice. What I'm
saying is that I'm not sure that "number of ext stats" is necessarily a
useful number as shown. I wonder if it's possible to count the number
of items that have been computed for each stats object. So if you do
this
create statistics pg_ext1 (dependencies, mcv) ON aid, bid from pgbench_accounts;
create statistics pg_ext2 (ndistinct,histogram) ON aid, bid from pgbench_accounts;
then the counter goes to 4. But I also wonder if we need to publish
_which_ type of ext stats is currently being built, in a separate
column.
--
Álvaro Herrera https://www.2ndQuadrant.com/
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