| From: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
|---|---|
| To: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
| Cc: | Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Separating bgwriter and checkpointer |
| Date: | 2011-09-20 09:03:51 |
| Message-ID: | 4E7856F7.4030004@enterprisedb.com |
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| Lists: | pgsql-hackers |
On 20.09.2011 11:18, Simon Riggs wrote:
> The bgwriter avoids I/O, if it is operating correctly. This patch
> ensures it continues to operate even during heavy checkpoints. So it
> helps avoid extra I/O during a period of very high I/O activity.
I don't see what difference it makes which process does the I/O. If a
write() by checkpointer process blocks, any write()s by the separate
bgwriter process at that time will block too. If the I/O is not
saturated, and the checkpoint write()s don't block, then even without
this patch, the bgwriter process can handle its usual bgwriter duties
during checkpoint just fine. (And if the I/O is not saturated, it's not
an I/O bound system anyway.)
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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