Cache questions

[Igor Sysoev]

On Mon, Jul 13, 2009 at 03:33:21PM +0400, Maxim Dounin wrote:

> Hello!
> 
> On Fri, Jul 10, 2009 at 07:39:46PM -0400, Jim Ohlstein wrote:
> 
> > I'm using the fastcgi cache for static files (images, javascript,css)  
> > and just found multiple lines in the error log like this one:
> >
> > 2009/07/10 10:22:54 [crit] 22476#0: ngx_slab_alloc() failed: no memory  
> > in cache keys zone "one"
> >
> > So I increased the memory available for the zone and reloaded nginx. It  
> > took over five hours to go through the cache but these are the relevant  
> > entries:
> >
> > 2009/07/10 12:11:03 [notice] 21038#0: start cache manager process 32730
> > 2009/07/10 12:11:04 [notice] 21038#0: cache manager process 22480 exited  
> > with code 0
> >
> > and finally
> >
> > 2009/07/10 17:43:27 [notice] 32730#0: http file cache:  
> > /usr/local/nginx/cache 11638.289M, bsize: 4096
> >
> > My questions are:
> >
> > Is that simply the total (11638.289MB or 11.4GB) of all of the file  
> > sizes, or is that the actual disk space consumed taking into account  
> > total number of blocks used multiplied by the block size? The number  
> 
> It's size on disk (i.e. number of blocks * block size), but for 
> files only (it doesn't take directories into account).

Just note: nginx rounds a file size to the bsize.
bsize is f_bsize from statfs() or f_frsize from statvfs().
I'm not sure that bsize matches always a filesystem allocation unit.

> > could be quite different given what I estimate are nearly one million  
> > mostly small files in the cache at this point.
> >
> > When I next upgrade nginx (I'm running 0.8.4), and I attempt a "graceful  
> > upgrade" will it have to go through this entire process again?
> 
> Yes.  Binary upgrade doesn't preserve shared memory zones, so 
> cache will be rescanned again.
> 
> Note that nginx uses cache even before it was completely scanned, 
> so it shouldn't be a problem.
> 
> Maxim Dounin


-- 
Igor Sysoev
http://sysoev.ru/en/