Squid Web Cache wiki

Squid Web Cache documentation

πŸ”— AIO Queue Congestion

πŸ”— Symptoms

squidaio_queue_request: WARNING - Queue congestion

πŸ”— Explanation

Working with multi-threaded disk access (AIO) Squid queues the tasks to be performed and lets the disk controller work through it as fast as it can. This allows Squid to work on other processing tasks for the same request without being held up waiting for slow disks.

The queue starts off at a default length of 8 queue slots per thread. When that queue space is filled up, Squid will spit out the WARNING, and double the available queue length.

Up to a few of these is OK under very high load. But if you get them very frequently then it’s a sign that either the disk I/O is overloaded or you have run out of CPU cycles to handle it.

πŸ”— Workaround

πŸ”— Additional Info

:information_source: One should note before reading the below that XFS benchmarks in professional tests from 2004/2005 as the slowest FS to use underneath Squid. The mail below shows an interesting counter-result, but should be taken with care.

See <http://www.squid-cache.org/mail-archive/squid-users/200603/0903.html>
for some discussion on the topic

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