[squid-users] squid doesn't cache objects in memory when using SMP and shared memory cache

[Ivan Larionov]

Hello!

After migrating squid from non-SMP/aufs to SMP/rock memory cache hit ratio
dropped significantly. Like from 50-100% to 1-5%. And disk cache hit ratio
went up from 15-50% to stable 60-65%. From the brief log file check it
looks like in SMP/rock mode squid avoids using memory for small files like
1-3KB but uses it for 10KB+ files.

I started tracking down the issue with disabling disk cache completely and
it didn't change anything, I just started to get MISS every time for the
URL which was getting MEM_HIT with an old configuration. Then I changed
"workers 2" to "workers 1" and started getting memory hits as before.

So it seems like the issue is with shared memory:

When squid doesn't use shared memory it works as expected. Even with
multiple workers.
When squid uses shared memory it caches very small amount of objects.

Am I doing anything wrong? Which debug options should I enable to provide
more information if it seems like a bug?

Config diff:

--- squid.conf.old  2018-01-14 02:01:19.000000000 -0800
+++ squid.conf.new  2018-01-14 02:01:16.000000000 -0800
@@ -1,5 +1,8 @@
 http_port 0.0.0.0:3128

+workers 2
+cpu_affinity_map process_numbers=1,2 cores=1,2
+
 acl localnet src 10.0.0.0/8     # RFC1918 possible internal network
 acl localnet src 172.16.0.0/12  # RFC1918 possible internal network
 acl localnet src 192.168.0.0/16 # RFC1918 possible internal network
@@ -94,13 +97,12 @@

 never_direct allow all

-cache_mem 9420328 KB
-maximum_object_size_in_memory 32 KB
+cache_mem 12560438 KB
+maximum_object_size_in_memory 64 KB
 memory_replacement_policy heap LRU
 cache_replacement_policy heap LRU

-cache_dir aufs /mnt/services/squid/cache/cache0 261120 16 256
-cache_dir aufs /mnt/services/squid/cache/cache1 261120 16 256
+cache_dir rock /mnt/services/squid/cache 522240 swap-timeout=500
max-swap-rate=1200 slot-size=16384

 minimum_object_size 64 bytes # none-zero so we dont cache mistakes
 maximum_object_size 102400 KB


All relevant config options together (SMP/rock):

workers 2
cpu_affinity_map process_numbers=1,2 cores=1,2

cache_mem 12560438 KB
maximum_object_size_in_memory 64 KB
memory_replacement_policy heap LRU
cache_replacement_policy heap LRU

cache_dir rock /mnt/services/squid/cache 522240 swap-timeout=500
max-swap-rate=1200 slot-size=16384

minimum_object_size 64 bytes # none-zero so we dont cache mistakes
maximum_object_size 102400 KB

negative_ttl 0 seconds
range_offset_limit none


Squid version:

Squid Cache: Version 3.5.27
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.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.squid-cache.org/pipermail/squid-users/attachments/20180114/b306ade4/attachment.html>