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Re: Pg_upgrade speed for many tables

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>,Magnus Hagander <magnus(at)hagander(dot)net>,PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Pg_upgrade speed for many tables
Date: 2012-11-05 21:29:49
Message-ID: 20121105212949.GG19099@momjian.us (view raw or flat)
Thread:
Lists: pgsql-hackers
On Mon, Nov  5, 2012 at 01:23:58PM -0800, Jeff Janes wrote:
> On Mon, Nov 5, 2012 at 1:14 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> > On Mon, Nov 5, 2012 at 4:07 PM, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:
> >> Or have options for pg_dump and pg_restore to insert "set
> >> synchronous_commit=off" into the SQL stream?
> >
> > It would be kind of neat if we had a command that would force all
> > previously-asynchronous commits to complete.  It seems likely that
> > very, very few people would care about intermediate pg_dump states, so
> > we could do the whole dump asynchronously and then do "FORCE ALL
> > COMMITS;" or whatever at the end.
> 
> Yeah, I was wondering what a fool-proof way of doing that would be,
> without implementing a new feature.  Turning synchronous_commits back
> on and then doing and committing a transaction guaranteed to generate
> WAL would do it.
> 
> Would a simple 'select pg_switch_xlog();' always accomplish the desired flush?

That could generate a lot of WAL files if used regularly.  :-(  Does
SELECT txid_current() generate WAL?  I think it does.

-- 
  Bruce Momjian  <bruce(at)momjian(dot)us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +


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