Re: Re: Faster CREATE DATABASE by delaying fsync (was 8.4.1 ubuntu karmic slow createdb)

On Sunday 14 February 2010 18:11:39 Tom Lane wrote:
> Greg Stark <gsstark@mit.edu> writes:
> > So I think we have a bigger problem than just copydir.c. It seems to
> > me we should be fsyncing the table space data directories on every
> > checkpoint.
> 
> Is there any evidence that anyone anywhere has ever lost data because
> of a lack of directory fsyncs?  I sure don't recall any bug reports
> that seem to match that theory.
I have actually seen the issue during create database at least. In a 
virtualized hw though...
~1GB template database, lots and lots of small tables, the crash occured maybe 
a minute after CREATE DB, filesystem was xfs, kernel 2.6.30.y.
> It seems to me that we're talking about a huge hit in both code
> complexity and performance to deal with a problem that doesn't actually
> occur in the field; and which furthermore is trivially solved on any
> modern filesystem by choosing the right filesystem options.  Why don't
> we just document those options, instead?
Which options would that be? I am not aware that there any for any of the 
recent linux filesystems.
Well, except "sync" that is, but that sure would be more of a performance hit 
than fsyncing the directory...

Andres