Wikimedia Bugzilla is closed!

Squid Cache 2.7 returns a "Connection: close" header which SquidPurgeClient doesn't recognize or recover from appropriately, resulting in a semi-infinite loop in the SquidPurgeClientPool.run() function, loading the CPU until the loop breaks for a timeout.  Besides the loading and slowing page edits, this bug also prevents some of the purge requests in the pool from being sent at all.

Also, SquirPurgeClientPool doesn't handle multiple squids (multiple entries in $wgSquidServers) because the indexing scheme for $readSockets and $writeSockets in SquidPurgeClientPool.run() is flattened by the socket_select function, and only the first server in the $wgSquidServers array actually receives the purge request.  Again, SquidPurgeClientPool.run() enters a semi-infinite loop as a result, loading the CPU and causing page edits to be very slow in their response.