Reducing overflowed and dropped work requests

Simon Males sime at
Thu Jul 14 14:18:44 CEST 2011


The Varnish munin plugins have alerted me a number of times (say less
then 5) that N dropped work requests (n_wrk_drop) is greater then 1.

According to Kristian Lyngstol's post [1] this is represents when the
request queue it full. Additionally I believe the overflowed work
requests (n_wrk_overflow) will always be greater then n_wrk_drop.

I think I should be trying to tackle two issues: Limit requests
overflowing, followed by increasing the size of the request queue.

Of the below startup parameters I believe thread_pools should match
the number of cores the server has and increase the maximum number of
threads to possibly double (from 25 to 50?).

DAEMON_OPTS="-a :80 \
             -T localhost:6082 \
             -f /etc/varnish/default.vcl \
             -S /etc/varnish/secret \
             -w 10,25,120 \
             -p listen_depth=8192 \
             -p log_hashstring=off \
             -p lru_interval=60 \
             -p sess_timeout=10 \
             -p shm_workspace=32768 \
             -p ping_interval=1 \
             -p thread_pools=4 \
             -s malloc,2G"

Varnish 2.1.5, x86_64, 4 GB, 8 or 16 cores.


Simon Males

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