🔗 What to do when there are way too many cache misses

In normal operation Squid gives very few (typically well less than 1%) code TCP_SWAPFAIL_MISS indicating an object was thought to be in the cache but couldn’t be found. Once in a while though this occurs very very frequently. When lots of errors occur, the problem is the Squid cache index (probably in a file named something like swap.state at the top level of the Squid cache directory structure) is out of sync with the actual cache contents.

Here’s a script I use to make sure this doesn’t happen. It’s way too paranoid, doing a lot of unnecessary things including throwing away what’s in the cache every time. But it always works.

🔗 sample script

    # restart Squid
    # (probably after making arbitrary config changes)
    
    echo temporarily stopping Dans Guardian [Squid user]
    dansguardian -q
    while [[ `ps aux | grep dansguardian | wc -l` -gt 1 ]]; do
            sleep 1
    done
    sleep 2
    echo stopping Squid so can make arbitrary changes
    squid -k shutdown
    while [[ `ps aux | grep squid | wc -l` -gt 1 ]]; do
            sleep 1
    done
    sleep 2
    echo flushing-by-deleting old Squid cache including index
    rm -rf /var/spool/squid/*
    sleep 2
    echo creating new Squid disk cache directories and index
    squid -z
    sleep 2
    echo starting Squid again with new configuration
    squid
    sleep 2
    echo starting Dans Guardian [Squid user] again
    dansguardian

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