Re: A few questions to real pgsql gurus
От | Dennis Gearon |
---|---|
Тема | Re: A few questions to real pgsql gurus |
Дата | |
Msg-id | C7TYWA72ZLJ93HB2UHFQ839TQNLRQ.3e5a474f@cal-lab обсуждение исходный текст |
Ответ на | Re: A few questions to real pgsql gurus (Dmitry Tkach <dmitry@openratings.com>) |
Ответы |
Re: A few questions to real pgsql gurus
Re: A few questions to real pgsql gurus |
Список | pgsql-general |
And what about all the stuff in memory, pending transactions, etc? 2/24/2003 9:33:55 AM, Dmitry Tkach <dmitry@openratings.com> wrote: >Tom Lane wrote: > >>Dmitry Tkach <dmitry@openratings.com> writes: >> >> >>>- The database files sit on a NetApp box (this is a very reliable disk array with parity control etc... >>>plus, it has a 'snapshot' capability, that allows you to take a live snapshot of any directory in real time - that creates >>>a read-only copy of the content of that directory within a second or so). >>>- The snapshots are taken hourly by a cron job on the whole database (older snapshots get removed after a while), and the most recent snapshot >>>gets backed up to the tape every night. >>> >>> >> >>Have you ever actually restored one of those snapshots? I don't believe >>this will work, unless you shut down the database while taking the >>snapshot. Or unless the snapshot is instantaneous across all files in >>the $PGDATA directory tree --- but your "within a second or so" doesn't >>sound real promising. If there's any time skew between copying >>different files, you've got problems. >> >> >> >Yes, it *is* instanteneous, that's the point! >The idea is, that it does not really copy anything at all - just freezes >all the stuff under that directory exactly the way it is, and then, if >somebody (like postmaster) is writing to that directory, it replaces the >particular block that's is neing modified, so that the snapshot contiues >to look at the old block, and the 'real thing' referes to the new one... > >That 'under a second' time is what it needs to setup its bookeeping >recors, and it freezes all writes to the directory during that time... > >Dima > > > > >---------------------------(end of broadcast)--------------------------- >TIP 6: Have you searched our list archives? > >http://archives.postgresql.org >
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