On 7/1/13 3:41 PM, Scott Harris wrote:
Hi,
We are currently looking at upgrading to ats from some bluecoat web caches
and trying to find out if ats has a hard limit on max number of stored
objects? (Not single object size, I know there is a setting to control that)
I ask this because our bluecoats have a hard limit of 32 million objects.
It's a calculation based on the size of your disk cache, and the setting
proxy.config.cache.min_average_object_size from records.config. Basically,
you get one "directory entry" in memory for every 8KB of disk cache. You
always consume at least one directory entry per cache object, but it can be
more.
Example: 2TB disk, default settings -> 275 million directory entries.
this happens to also consume 275MM * 10 bytes = ~2.5GB of RAM just for the
directory entries. The easiest way to think of this is to think of our
directory entries as I-nodes. There's a fixed number of I-nodes, and you can
tweak it via that config, but doing so will be the same as doing an "mkfs"
(i.e. blow the cache).
Note that more directory entries will consume a bit more disk resources as
well as RAM, when it syncs (and reads) the directory to (and from) disk. So
having a huge amount of unused directory entries is a waste too, but you
don't want to risk running out of them either.
-- leif
