[Gluster-users] Low (<0.2ms) latency reads, is it possible at all?

Willem gwillem at gmail.com
Wed Apr 24 12:41:52 UTC 2013

Meanwhile, I have made a csync2 test setup and I must say, I'm positively
surprised by its performance. It keeps a local meta database (in SQLlite)
of file checksums. Deleting and adding files works fine. Automatic conflict
resolution works also acceptably well (in my setup: younger files
win). Synchronization check of 180K files takes 10 seconds. Which could be
further optimized by inotify hooks (lsyncd) which requires only
partial synchronization.

Still, I'd prefer the beauty of an integrated Gluster setup. My dream
scenario is that Gluster would cooperate well with the kernel FSCache so
that all small I/O requests could be served from memory. At the moment -
AFAIK - this only works for the NFS client and then again only for a subset
of I/O functions (which is understandable from a consistency perspective).


On Wed, Apr 24, 2013 at 2:18 PM, Marcus Bointon
<marcus at synchromedia.co.uk>wrote:

> On 24 Apr 2013, at 14:00, "Willem" <gwillem at gmail.com> wrote:
> >> I'm testing GlusterFS viability for use with a typical PHP webapp (ie.
> lots
> >> of small files). I don't care so much for the C in the CAP theorem, as I
> >> have very few writes. I could live with a write propagation delay of 5
> >> minutes (or dirty caches for up to 5 minutes).
> We know that gluster's small-file performance isn't good, and since you
> can live with such long write propagation, reciprocal rsync could be a
> better and simpler solution. That way you'd get much faster local
> performance. The only issue really is that deletes aren't possible to
> propagate correctly with 2-way rsync (because a delete at one end is
> indistinguishable from an add at the other), but you may be able to live
> with it. csync2 aims to solve the delete issue with a transaction database,
> but I could never make it work.
> To get a consistent 0.2ms off anything you're going to need to be on SSDs
> - you can't fit everything in your cache.
> Marcus
> --
> Marcus Bointon
> Synchromedia Limited: Creators of http://www.smartmessages.net/
> UK info at hand CRM solutions
> marcus at synchromedia.co.uk | http://www.synchromedia.co.uk/
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