On Tue, Feb 26, 2013 at 11:58 AM, Kevin Decherf <kevin@xxxxxxxxxxxx> wrote:
> We have one folder per application (php, java, ruby). Every application has
> small (<1M) files. The folder is mounted by only one client by default.
>
> In case of overload, another clients spawn to mount the same folder and
> access the same files.
>
> In the following test, only one client was used to serve the
> application (a website using wordpress).
>
> I made the test with strace to see the time of each IO request (strace -T
> -e trace=file) and I noticed the same pattern:
>
> ...
> [pid 4378] stat("/data/wp-includes/user.php", {st_mode=S_IFREG|0750, st_size=28622, ...}) = 0 <0.033409>
> [pid 4378] lstat("/data/wp-includes/user.php", {st_mode=S_IFREG|0750, st_size=28622, ...}) = 0 <0.081642>
> [pid 4378] open("/data/wp-includes/user.php", O_RDONLY) = 5 <0.041138>
> [pid 4378] stat("/data/wp-includes/meta.php", {st_mode=S_IFREG|0750, st_size=10896, ...}) = 0 <0.082303>
> [pid 4378] lstat("/data/wp-includes/meta.php", {st_mode=S_IFREG|0750, st_size=10896, ...}) = 0 <0.004090>
> [pid 4378] open("/data/wp-includes/meta.php", O_RDONLY) = 5 <0.081929>
> ...
>
> ~250 files were accessed for only one request (thanks Wordpress.).
Okay, that is slower than I'd expect, even for an across-the-wire request...
> The fs is mounted with these options: rw,noatime,name=<hidden>,secret=<hidden>,nodcache.
What kernel and why are you using nodcache? Did you have problems
without that mount option? That's forcing an MDS access for most
operations, rather than using local data.
> I have a debug (debug_mds=20) log of the active mds during this test if you want.
Yeah, can you post it somewhere?
-Greg
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