Re: Read Uncommitted

Simon Riggs  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,
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ITAGAKI Takahiro
NTT Open Source Software Center