[squid-users] rock storage and max-swap-rate

[Ivan Larionov]

Hello.

cache_dir max-swap-rate documentation says that swap in requests contribute
to measured swap rate. However in our squid 4 load test we see that
read_ops + write_ops significantly exceeds the max-swap-rate we set and
squid doesn't limit it.

I tried to set it to 200 to confirm that it actually works and saw that it
does. Squid started warning about exceeding max-swap-rate. But looks like
real limit is higher than the value we set in configuration.

Hardware:

AWS GP2 EBS (SSD) 600GB, 1500 iops baseline performance, 3000 iops
burstable.

Config:

cache_dir rock /mnt/services/squid/cache 435200 swap-timeout=500
max-swap-rate=1200 slot-size=16384

IOPS squid pushes under our load test:

read ~800 ops/sec
write ~1100 ops/sec

In summary it gives us ~1900 ops/sec which exceeds AWS limit of 1500
ops/sec and after spending too much "burst balance" we started getting
throttled from AWS side.

Could you please comment on this behavior? What the limit should we set to
stay under 1500 ops/sec for swap in + swap out operations?

Thanks.

Squid version:

Squid Cache: Version 4.0.22
Service Name: squid
configure options:  '--program-prefix=' '--prefix=/usr'
'--exec-prefix=/usr' '--bindir=/usr/sbin' '--sbindir=/usr/sbin'
'--sysconfdir=/etc/squid' '--libdir=/usr/lib' '--libexecdir=/usr/lib/squid'
'--includedir=/usr/include' '--datadir=/usr/share'
'--sharedstatedir=/usr/com' '--localstatedir=/var'
'--mandir=/usr/share/man' '--infodir=/usr/share/info' '--enable-epoll'
'--enable-removal-policies=heap,lru' '--enable-storeio=aufs,rock'
'--enable-delay-pools' '--with-pthreads' '--enable-cache-digests'
'--with-large-files' '--with-maxfd=16384' '--enable-htcp'

-- 
With best regards, Ivan Larionov.
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