Odd Output from Varnishstat

Poul-Henning Kamp phk at phk.freebsd.dk
Mon Oct 15 23:55:45 CEST 2007

In message <4713DEDB.9040409 at nyi.net>, James Quacinella writes:
>Hello everyone,
>Curious if anyone has ever seen varnishstat give strange output for the 
>line 'active struct srcaddr'? In my cluster, they all seem to output the 
>line '0 . .', but one instance the number keeps going from 0 to 
>18446744073709551615 and vice versa, at seemingly random times. Any 
>ideas what might be causing this? Restarting varnishstat did not help.

Some of the counters varnishstat shows are not locked in varnishd,
and so in rare (or not so rare) cases, they can get out of lock-step
with reality because to treads tweak them at the same time.

In general, I've tried to update stats counters while a relevant
lock was held anyway, but there are a few cases, and srcaddr is one
of them, where it would cost two extra lock operations to update
the counter atomically, and I have decided not to take that cost.

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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