| From: | ITAGAKI Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp> |
|---|---|
| To: | Simon Riggs <simon(at)2ndquadrant(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Subject: | Re: Read Uncommitted |
| Date: | 2008-05-26 11:01:50 |
| Message-ID: | 20080526195344.C96A.52131E4D@oss.ntt.co.jp |
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| Lists: | pgsql-hackers |
Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> The use of this is clear though: allowing long running transactions
> against unchanging data to not interfere with other activities. It will
> also have importance in a Hot Standby mode.
I have an use of the dirty read -- pg_start_backup().
In 8.3, pg_start_backup takes long time, that is typically
{ checkpoint_timeout * checkpoint_completion_target }.
If we have some updating transaction during pg_start_backup,
updated tables cannot be vacuumed well. READ UNCOMMITTED mode
could help us in such a situation.
BEGIN;
SET TRANSACTION READ UNCOMMITTED;
SELECT pg_start_backup(timeofday());
END;
Regards,
---
ITAGAKI Takahiro
NTT Open Source Software Center
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