| From: | Markus Wanner <markus(at)bluegap(dot)ch> |
|---|---|
| To: | Dimitri Fontaine <dfontaine(at)hi-media(dot)com> |
| Cc: | pgsql-hackers(at)postgresql(dot)org, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, ITAGAKI Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp> |
| Subject: | Re: Synchronous Log Shipping Replication |
| Date: | 2008-09-09 13:58:48 |
| Message-ID: | 48C68118.7030800@bluegap.ch |
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| Lists: | pgsql-hackers |
Hi,
Dimitri Fontaine wrote:
> Exactly the point. The process is now already waiting in all cases, so maybe
> we could just force waiting some WALSender signal before sending the fsync()
> order, so we now have Group Commit.
A single process can only wait on either fsync() or on select(), but not
on both concurrently, because both syscalls are blocking. So mixing
these into a single process is an inherently bad idea due to lack of
parallelism.
I fail to see how log shipping would ease or have any other impact on a
Group Commit feature, which should clearly also work for stand alone
servers, i.e. where there is no WAL sender process.
Regards
Markus Wanner
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