| From: | Greg Stark <gsstark(at)mit(dot)edu> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Re: Synch Rep: direct transfer of WAL file from the primary to the standby |
| Date: | 2009-07-07 23:56:27 |
| Message-ID: | 407d949e0907071656q229d6d4ds7ed783acc49a8e25@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Jul 7, 2009 at 8:12 PM, Tom Lane<tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> (If nothing else, there is no point in keeping so much WAL that catching
> up by scanning it would take longer than taking a fresh base backup.
> My impression from recent complaints about our WAL-reading speed is that
> that might be a pretty tight threshold ...)
Well those are two independent variables. The time taken to scan WAL
is dependent on the transaction rate and the time to take a fresh
backup is dependent on the total database size. There are plenty of
low transaction rate humungous databases where it would be faster to
replay weeks of transactions than try to take a fresh base backup.
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