Re: Speeding up pg_upgrade

From: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
To: Stephen Frost <sfrost(at)snowman(dot)net>
Cc: Alexander Kukushkin <cyberdemn(at)gmail(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Speeding up pg_upgrade
Date: 2017-12-07 16:02:32
Message-ID: 20171207160232.auayfcnaexuudqy7@alvherre.pgsql
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Stephen Frost wrote:
> Alexander,

> * Alexander Kukushkin (cyberdemn(at)gmail(dot)com) wrote:

> > 2 ANALYZE phase is a pain. I think everybody agrees with it.
> >
> > 2.5 Usually ANALYZE stage 1 completes quite fast and performance becomes
> > reasonable, except one case: some of the columns might have non default
> > statistics target.
> Ok, if the stage-1 is very fast and performance is reasonable enough
> after that then perhaps it's not so bad to keep it as-is for now and
> focus on the dump/restore time. That said, we should certainly also
> work on improving this too.

It seems pretty clear to me that we should somehow transfer stats from
the old server to the new one. Shouldn't it just be a matter of
serializing the MCV/histogram/ndistinct values, then have capabilities
to load on the new server? I suppose it'd just be used during binary
upgrade, but the point seems painful enough for a lot of users.
Obviously it would not be the raw contents of pg_statistic{,_ext}, but
rather something a bit higher-level.

Álvaro Herrera
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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