Re: [PERFORM] Backup taking long time !!!

От: Stephen Frost
Тема: Re: [PERFORM] Backup taking long time !!!
Дата: ,
Msg-id: 20170123172301.GH18360@tamriel.snowman.net
(см: обсуждение, исходный текст)
Ответ на: Re: [PERFORM] Backup taking long time !!!  (Jeff Janes)
Список: pgsql-performance

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[PERFORM] Backup taking long time !!!  (Dinesh Chandra 12108, )
 Re: [PERFORM] Backup taking long time !!!  ("Madusudanan.B.N", )
  Re: [PERFORM] Backup taking long time !!!  (Dinesh Chandra 12108, )
   Re: [PERFORM] Backup taking long time !!!  (Pavel Stehule, )
    Re: [PERFORM] Backup taking long time !!!  ("Madusudanan.B.N", )
    Re: [PERFORM] Backup taking long time !!!  (Dinesh Chandra 12108, )
     Re: [PERFORM] Backup taking long time !!!  (Pavel Stehule, )
      Re: [PERFORM] Backup taking long time !!!  (Stephen Frost, )
  Re: [PERFORM] Backup taking long time !!!  (Vladimir Borodin, )
   Re: [PERFORM] Backup taking long time !!!  (Stephen Frost, )
 Re: [PERFORM] Backup taking long time !!!  (Vladimir Borodin, )
  Re: [PERFORM] Backup taking long time !!!  (Stephen Frost, )
 Re: [PERFORM] Backup taking long time !!!  (Vladimir Borodin, )
  Re: [PERFORM] Backup taking long time !!!  (Stephen Frost, )
   Re: [PERFORM] Backup taking long time !!!  (Jim Nasby, )
    Re: [PERFORM] Backup taking long time !!!  (Stephen Frost, )
     Re: [PERFORM] Backup taking long time !!!  (Jim Nasby, )
   Re: [PERFORM] Backup taking long time !!!  (David Steele, )
  Re: [PERFORM] Backup taking long time !!!  (Torsten Zuehlsdorff, )
   Re: [PERFORM] Backup taking long time !!!  (Stephen Frost, )
 Re: [PERFORM] Backup taking long time !!!  (Vladimir Borodin, )
  Re: [PERFORM] Backup taking long time !!!  (Stephen Frost, )
 Re: [PERFORM] Backup taking long time !!!  (julyanto SUTANDANG, )
  Re: [PERFORM] Backup taking long time !!!  (julyanto SUTANDANG, )
   Re: [PERFORM] Backup taking long time !!!  (Stephen Frost, )
    Re: [PERFORM] Backup taking long time !!!  (Jeff Janes, )
     Re: [PERFORM] Backup taking long time !!!  (Stephen Frost, )
     Re: [PERFORM] Backup taking long time !!!  (Simon Riggs, )
      Re: [PERFORM] Backup taking long time !!!  (Stephen Frost, )
      Re: [PERFORM] Backup taking long time !!!  (Jeff Janes, )
       Re: [PERFORM] Backup taking long time !!!  (Rick Otten, )
        Re: [PERFORM] Backup taking long time !!!  (Stephen Frost, )
     Re: [PERFORM] Backup taking long time !!!  (julyanto SUTANDANG, )
  Re: [PERFORM] Backup taking long time !!!  (Stephen Frost, )
 Re: [PERFORM] Backup taking long time !!!  (julyanto SUTANDANG, )
  Re: [PERFORM] Backup taking long time !!!  (Stephen Frost, )
 Re: [PERFORM] Backup taking long time !!!  (julyanto SUTANDANG, )
  Re: [PERFORM] Backup taking long time !!!  (Stephen Frost, )
   Re: [PERFORM] Backup taking long time !!!  (Jim Nasby, )
    Re: [PERFORM] Backup taking long time !!!  (Jeff Janes, )
     Re: [PERFORM] Backup taking long time !!!  (Stephen Frost, )
 Re: [PERFORM] Backup taking long time !!!  (julyanto SUTANDANG, )

* Jeff Janes () wrote:
> On Sun, Jan 22, 2017 at 6:57 AM, Stephen Frost <> wrote:
> > Just to make sure anyone reading the mailing list archives isn't
> > confused, running pg_start_backup does *not* make PG stop writing to
> > BASEDIR (or DATADIR, or anything, really).  PG *will* continue to write
> > data into BASEDIR after pg_start_backup has been called.
>
> Correct.  Unfortunately it is a very common myth that it does cause
> PostgreSQL to stop writing to the base dir.

I would love a way to dispel that myth. :/

If you have any suggestions of how we could improve the docs, I'd
certainly be happy to take a look and try to help.

> > The only thing that pg_start_backup does is identify an entry in the WAL
> > stream, from which point all WAL must be replayed when restoring the
> > backup.  All WAL generated from that point (pg_start_backup point) until
> > the pg_stop_backup point *must* be replayed when restoring the backup or
> > the database will not be consistent.
>
> pg_start_backup also forces full_page_writes to be effectively 'on' for the
> duration of the backup, if it is not already explicitly on (which it
> usually will already be).  This affects pg_xlog, of course, not base.  But
> it is an essential step for people who run with full_page_writes=off, as it
> ensures that anything in base which got changed mid-copy will be fixed up
> during replay of the WAL.

Agreed.

Thanks!

Stephen

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