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Re: sync_file_range()

From: Simon Riggs <simon(at)2ndquadrant(dot)com>
To: Greg Stark <gsstark(at)mit(dot)edu>
Cc: Qingqing Zhou <zhouqq(at)cs(dot)toronto(dot)edu>, ITAGAKI Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: sync_file_range()
Date: 2006-06-19 19:53:32
Message-ID: 1150746813.2587.98.camel@localhost.localdomain (view raw or flat)
Thread:
Lists: pgsql-hackers
On Mon, 2006-06-19 at 15:04 -0400, Greg Stark wrote:

> > We fsync the xlog at transaction commit, so only the leading edge needs
> > to be synced - would the call help there? Presumably the OS can already
> > locate all blocks associated with a particular file fairly quickly
> > without doing a full cache scan.
> 
> Well in theory the transaction being committed isn't necessarily the "leading
> edge", there could be more work from other transactions since the last work
> this transaction actually did. 

Near enough.

> > Other files are fsynced at checkpoint - always all dirty blocks in the
> > whole file.
> 
> Well couldn't it be useful for checkpoints if it there was some way to know
> which buffers had been touched since the last checkpoint? There could be a lot
> of buffers dirtied since the checkpoint began and those don't really need to
> be synced do they?

Qingqing had a proposal for something like that, but seemed not worth it
after analysis.

-- 
  Simon Riggs
  EnterpriseDB          http://www.enterprisedb.com


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