Re: Load distributed checkpoint

On Thu, Dec 21, 2006 at 06:46:36PM +0900, ITAGAKI Takahiro wrote:
> > Oh, really, what an evil fsync is!  Yes, I sometimes saw a backend
> > waiting for lseek() to complete when it committed.  But why does the
> > backend which is syncing WAL/pg_control have to wait for syncing the
> > data file?  They are, not to mention, different files, and WAL and
> > data files are stored on separate disks.
> 
> Backends call lseek() in planning, so they have to wait fsync() to
> the table that they will access. Even if all of data in the file is in
> the cache, lseek() conflict with fsync(). You can see a lot of backends
> are waiting in planning phase in checkpoints, not executing phase.

Hmm, there are other ways to sync parts of a file. For example doing an
mmap()/msync()/munmap() cycle to start an asyncronous flush. But given
what you're saying that might suffer from the same problem.

Have a nice day,
-- 
Martijn van Oosterhout      http://svana.org/kleptog/
> From each according to his ability. To each according to his ability to litigate.