Gluster users - Apr 2015 - Synchronous replication, or no?

> I was under the impression that gluster replication was synchrounous, so
the
> appserver would not return back to the client until the created file was
> replicated to the other server. But this does not seem to be the case,
> because sleeping a little bit always seems to make the read failures go
> away. Is there any other reason why a file created is not immediately
> available on a second request?
It's quite possible that the replication is synchronous (the bits do hit
disk before returning) but that the results are not being seen immediately
due to caching at some level.  There are some GlusterFS mount options
(especially --negative-timeout) that might be relevant here, but it's also
possible that the culprit is somewhere above that in your app servers.

On 04/09/2015 07:33 PM, Jeff Darcy wrote:
>> I was under the impression that gluster replication was synchrounous,
so the
>> appserver would not return back to the client until the created file
was
>> replicated to the other server. But this does not seem to be the case,
>> because sleeping a little bit always seems to make the read failures go
>> away. Is there any other reason why a file created is not immediately
>> available on a second request?
>
> It's quite possible that the replication is synchronous (the bits do
hit
> disk before returning) but that the results are not being seen immediately
> due to caching at some level.  There are some GlusterFS mount options
> (especially --negative-timeout) that might be relevant here, but it's
also
> possible that the culprit is somewhere above that in your app servers.
>
Might be worth mounting with --entry-timeout=0 too.

-Vijay