We found the cause of this problem. It seems that the directory creation
was failing when the mod_disk_cache was trying to create the
subdirectory structure to store the header and data content . The reason
this failed was because mod_disk_cache had already created a large
number of directories and that number exceeded the max link count
allowed on a ext2/ext3 file system, i.e. 32000.
So i guess the solution here would be to use a different file system
,i.e ext4 or reiserfs or perhaps configure disk_cache to use shorter
directory lengths and more levels.
-M
Manik Taneja wrote:
Hi,
I have an apache server that is configured as an HTTP proxy, i.e.
mod_proxy is enabled. Along with this i have also enabled
mod_disk_cache and mod_mem_cache. The system that we are using in
ubuntu-server with 2.6.24 linux kernel version
We are doing some load tests on this system with web-polygraph, not a
very heavy load but around 120 tps. Initially we see that the apache
proxy server is able to cache 55% of the objects but as the tests go
on for more than 1/2 hr the cache hit ratio drops to around 1-2%. We
debugged this issue and we saw that after a while there are no objects
being written to the disk. All the cache hits come out of the
mem_cache. After enabling debug logging we saw a large number of the
following error messages being logged.
[Sat Sep 06 09:47:15 2008] [warn] (20)Not a directory: disk_cache:
rename tempfile to datafile failed: /cache/aptmpAglkI4 ->
/cache/72kYIz/6OraHr/pEFUJY/ZWkw.data
I am not sure what a "Not a directory" message is supposed to mean,
but i am guessing this happens because the directory inode is some
sort of inconsistent state. We initially saw these errors on a ext3
filesystem and so we created an ext2 fs, however these error messages
don't seem to go away.
I am wondering if this is a known problem or someone who has seen
these messages before and knows of a work-around can help us.
Oh and the apache version that we are using is 2.2.9 .
TIA
Regards,
Manik
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