Sent to a Squid developer I just had a discussion with on IRC...

-------- Original Message -------- Subject: Squid: Conversion of disk cache reads into cache misses when disk bandwidth is saturated Date: Sun, 30 Apr 2006 14:07:29 +0200 From: Mark Bergsma <mark@...>

Hi. As discussed on IRC, a summary:

We are having some problems efficiently using disk caches in our Wikimedia Squid cache cluster. When the disk cache is too big, disk cache reads can easily saturate all of the available disk bandwidth on all disks. This makes Squid very slow as it keeps queuing up the requests. Therefore we deploy many Squids without disk caches and have them memory only, which results in much faster Squids (lower request times with much shorter distribution tails), but the total hit rate suffers.

It would be neat if Squid could decide to convert a disk cache read to a cache miss when the relevant cache_dir is overloaded. That would make Squid more load-tolerant reduces the need for administrators to tune and readjust disk caches for each server over time.

As Squid already does this for cache *writes*, this should be fairly easy to implement for reads too. Let me know when you have something, I'll be happy to test patches on a test server in our cluster. I'll stick around on IRC too...

Thanks,