Fault in LRU mechanism

From: Gero J. Dittmer <Gero.Dittmer@dont-contact.us>
Date: Wed, 05 Aug 1998 11:00:32 +0200

For more than a year I have suspected that squid LRU algorithm contains some
design flaws throughout all 1.1. versions (currently running 1.1.22).

My observations :

1. Sometimes I had MISSES on files that had been loaded very recently for no
apparent reason.
2. Listing the oldest files in the cache using
ls -luR /usr/local/squid/cache/ | grep 0000 | sort +5M -6 +6n -7 | head
consistently returned nearly the same files over weeks, showing that the
oldest files were not removed. I doublechecked that these files were still
listed in cache/log.

Then I found the reason for this : Directly after a 10 MB download the
Storage LRU Expiration Age dropped to 0.10 days and 1000 files, most of them
recent, got unlinked. During a couple of minutes the value rose back to its
usual 30 days. Judging from the parameters there was no reason for
aggressive deletion of files.

Can anybody tell, if this is considered to be a serious bug or if there is
some parameter to ease the problem. At current traffic levels cache contents
is fairly static with a a maximum of 5 % being replaced each day, so I want
to stay the Storage LRU Expiration Age well beyond 20 days all the time.

Regards, Gero

--- Ammirati Puris Lintas ---
--- Gero Dittmer, Mittelweg 177, 21048 Hamburg, Germany ---
--- phone: +49 40 41441217 fax: +49 40 41441616 ---
--- Email: Gero.Dittmer@hamburg.aplnet.com ---
--- ... waiting for a unicorn under chapter eleven ... ---
Received on Wed Aug 05 1998 - 02:15:52 MDT

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