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Re: squid becomes slow (when cache_dir is full)

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On 06/07/11 21:30, Sergiu Tatar wrote:
Hello friends.... i have a problem with my squid server ( conf proc: Intel(R) Celeron(R) E3200  @ 2.40GHz, 6 GB ram dual-channel 800 Mhz, hdd S-ATA II 500 GB Cache 32 Mb ) , when cache_dir is full squid becomes slow.... i have 60 Mbps bandwith and i can't use only 10-15 Mbps with squid up. Linux kernel is: 2.6.33.7-desktop-2mnb #1 SMP Mon Sep 20 18:19:20 UTC 2010 x86_64 x86_64 x86_64 GNU/Linux
Squid Configure Options:
Squid Cache: Version 3.1.12.1-20110503
configure options:  '--enable-cache-digests' '--disable-icmp' '--disable-delay-pools' '--enable-storeio=ufs,aufs' '--disable-ident-lookups' '--prefix=/squid2' '--enable-removal-policies=heap,lru' '--with-filedescriptors=16384' '--disable-snmp' '--enable-linux-netfilter' '--enable-follow-x-forwarded-for' '--disable-translation' '--with-large-files' --enable-ltdl-convenience

Squid config:
cache_dir aufs /mnt/squid 92160 64 512
cache_mem 2048 MB
maximum_object_size_in_memory 96 KB
maximum_object_size 24 MB
fqdncache_size 4096
ipcache_size 4096
ipcache_low 95
ipcache_high 97

Squid info:
Squid Object Cache: Version 3.1.12.1-20110503
Start Time:     Wed, 29 Jun 2011 03:56:36 GMT
Current Time:   Wed, 06 Jul 2011 09:07:51 GMT
Connection information for squid:
         Number of clients accessing cache:      0
         Number of HTTP requests received:       7677294
         Number of ICP messages received:        0
         Number of ICP messages sent:    0
         Number of queued ICP replies:   0
         Number of HTCP messages received:       0
         Number of HTCP messages sent:   0
         Request failure ratio:   0.00
         Average HTTP requests per minute since start:   738.8

Only 12 req/sec? That does not compute with 60Mbps.

Your avg. object size indicates an avg around 276 Kbps. Weird, or most of your requests are not cacheable and will be stressing the disks.

         Average ICP messages per minute since start:    0.0
         Select loop called: 886726996 times, 0.703 ms avg
Cache information for squid:
         Hits as % of all requests:      5min: 36.1%, 60min: 40.9%
         Hits as % of bytes sent:        5min: 6.4%, 60min: 8.8%
         Memory hits as % of hit requests:       5min: 41.2%, 60min: 20.1%
         Disk hits as % of hit requests: 5min: 28.5%, 60min: 33.4%
         Storage Swap size:      90597584 KB
         Storage Swap capacity:  96.0% used,  4.0% free

96% of the cache full. That is 1% over the "high water" and 6% over the "low water" default settings. Assuming the cache_swap_high and cache_swap_low are still at those defaults your Squid will be a bit busy erasing ~6GB worth of ~23KB files from the disk. Could take a while, especially if the new arriving traffic is creating files faster than the erasures. The fact it got much above 90% is a sign that the traffic arriving _is_ faster than erase.


         Storage Mem size:       2076808 KB
         Storage Mem capacity:   100.0% used,  0.0% free
         Mean Object Size:       23.09 KB
         Requests given to unlinkd:      0
Median Service Times (seconds)  5 min    60 min:
         HTTP Requests (All):   0.04277  0.04047
         Cache Misses:          0.10281  0.09736
         Cache Hits:            0.00000  0.00000
         Near Hits:             0.04519  0.01955
         Not-Modified Replies:  0.00000  0.00000
         DNS Lookups:           0.03696  0.03696
         ICP Queries:           0.00000  0.00000
Resource usage for squid:
         UP Time:        623475.324 seconds
         CPU Time:       24039.848 seconds
         CPU Usage:      3.86%
         CPU Usage, 5 minute avg:        6.34%
         CPU Usage, 60 minute avg:       4.71%
         Process Data Segment Size via sbrk(): 3264060 KB
         Maximum Resident Size: 13229792 KB
         Page faults with physical i/o: 402
<snip>

Amos
--
Please be using
  Current Stable Squid 2.7.STABLE9 or 3.1.14
  Beta testers wanted for 3.2.0.9


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