On 21/11/2011 6:06 p.m., Benjamin wrote:
Hi Amos,
Really your support is grateful to us.You always help us to
understanding of squid and its work pattern.Thanks for your kind support.
On 21/11/2011 1:33 a.m., benjamin fernandis wrote:
Hi All,
I configured squid box to get good cache performance and for that i
set cache_mem and object size in cache.
cat /etc/squid/squid.conf | grep cache_mem
cache_mem 6144 MB
cat /etc/squid/squid.conf | grep -i maximum_object_size_in_memory
maximum_object_size_in_memory 1 MB
And whenever i check memory usage at OS level while squid is serving
to traffic. it shows me
free -mto
total used free shared buffers
cached
Mem: 7995 345 7650 0
30 78
Swap: 8999 0 8999
Total: 16995 345 16650
So as per my squid setup i set 6GB , So why free -mto showing me that
only 345 mb is used and 7650 mb is free.
As per my understanding , if i assign 6GB RAM to squid then 6GB will
be deducted from my actual memory and then OS has that remaining
amount of memory.
My perception is right ?
Yes your understanding is generally correct.
There is one circumstance I can think of when the OS might show lower
than cache_mem usage. That is when memory pooling control has been
disabled when building Squid. In that case Squid will not
pre-allocate any memory for use.
If suppose memory pooling control has been disabled in that case, does
squid will not have full control on memory utilization or suppose i
assign 6 GB ram to squid, so does squid use 6gb ram for caching ?
Memory pooling control is mandatory to enable in squid while we are
talking for memory utilization or work flow of squid ?
No. Squid will continue to operate as normal and will allocate the 6GB
cache_mem eventually, it just means the OS is aware of how much
cache_mem area has (or not) been used at any given time. And squid will
continuously be allocating/deallocating memory blocks. You can see the
churn in the cachemgr memory allocation report.
The benefits of pooling is speed of avoiding allocating new blocks of
RAM. We have not had any actual speed measurements in many years to get
actual numbers. But when I tested it casually about Mar this year the
default malloc library most OS supply was still slower than pools. For
higher speed you will be needing some modern library like talloc which
seemed as good or better than pools (though no numbers means that may be
an illusion). The other allocator libraries competing with talloc are
also very close.
What is the purpose of --enable-async-io option in squid?
To enable Asynchrnous I/O (AIO) for threaded read/write to disks.
This is required for AUFS.
Yes, i am using AUFS.
i read on internet that it enable more performance while using more
thread with that option
Yes. Up to the amount of AIO threads your disk controller can work
with efficiently. There is a point at which the threads become too
many for the controller and things get slow again. I'm not personally
aware what that upper limit is.
i installed squid rpm which i got from my os distro.i used fedora 15
64 bit.But i can't find that option in squid -v command.so i guess
that is not included while installing squid from rpm.
So --enable-async-io is mandatory while we r using AUFS or while we
are talking for performance how many thread is idle for squid. On
internet i see 128 thread configuration at many blogs.
Suppose --enable-async-io is not enabled with squid so in that case
what is default thread for AUFS?
Well, its equivalent to "--with-aufs-threads=N_THREADS --with-pthreads
--enable-storeio=ufs,aufs", so they may have set those individually
instead. Or just using the default of 16 per cache_dir.
Amos
