> I am helping someone to reconfigure PHP for a high-traffic site (well...
> high traffic for one PC to handle, at least).
>
> The server is hosted by Rackspace.com, running Linux kernel 2.2.19. I have
> done all the standard Apache/PHP/MySQL performance tweaks, and I have raised
> the filesystem and inode limits in /proc/sys/fs.
>
> I have read that one performance tweak for Linux is to mount the filesystem
> with the "noatime" option (meaning the kernel does not update the timestamp
> whenever files are accessed).
>
> The site relies highly on PHP sessions, and it seems to me that there would
> be trouble with the /tmp/ session files if I configure Linux to mount the
> filesystem with the "noatime" option. As I understand it, the PHP session
> mechanism runs a "stat" operation every time it evaluates whether to delete
> session files. This being the case, I guess the logical assumption here is
> that it reads the access timestamp to decide whether to delete the session
> file or not.
>
> Am I right here? Is there any way to use the default session mechanism if I
> mount the filesystem with noatime? If not, is my only option to create a
> custom session handler?
>
> Also, is there any problem using a RAMdisk partition for the directory to
> handle the session files. I suppose theoretically it would be possible to
> mount the main filesystem with "noatime", but to create a RAM partition
> which *does* update the access timestamp, and have PHP use that for the
> session files.
You could use the shared memory session store.
ie.
session.save_handler = mm
Or you could create a ramdisk and point PHP at that.
session.save_path = /your/ramdisk
But yes, if you use the standard "files" save_handler on a filesystem that
does not set the atime it will not work. You can see that for yourself in
the ext/session/mod_files.c file in the ps_files_cleanup_dir() function:
/* check whether its last access was more than maxlifet ago */
if (VCWD_STAT(buf, &sbuf) == 0 &&
(now - sbuf.st_atime) > maxlifetime) {
VCWD_UNLINK(buf);
nrdels++;
}
Of course, you could set the gc to 0 and do your own garbage collection on
your session files by some other criteria. Not quite sure how you would
determine old and non-active sessions without an atime though.
-Rasmus
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