Re: sync_file_range()

On Mon, 2006-06-19 at 15:32 +0800, Qingqing Zhou wrote:
> "ITAGAKI Takahiro" <itagaki.takahiro@oss.ntt.co.jp> wrote
> >
> >
> > I'm interested in it, with which we could improve responsiveness during
> > checkpoints. Though it is Linux specific system call, but we could use
> > the combination of mmap() and msync() instead of it; I mean we can use
> > mmap only to flush dirty pages, not to read or write pages.
> >
> 
> Can you specify details? As the TODO item inidcates, if we mmap data file, a
> serious problem is that we don't know when the data pages hit the disks -- 
> so that we may voilate the WAL rule.

Can't see where we'd use it.

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.

Other files are fsynced at checkpoint - always all dirty blocks in the
whole file.

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