Re: [squid-users] Multiple Squid Instances

On 24/08/11 21:46, viswanathan sekar wrote:
> Hi All,
>
> I had an argument with my friends telling them that mulitple squid
> instances in multi-core processors will give better performance with
> iptables load balancing.
> Some of my friends disagreed with me telling single squid instance
> will give same performance.
>
> I am really confused,
>
> which will give better performacne from the above two?
>
> Is squid IO bound or CPU bound ?

Both.

  - instances using cache_dir tend to be disk I/O bound
  - instances using only memory caching tend to be network I/O bound
  - instances doing much ACL filtering tend to be CPU bound

With >2 cores you can mix these types to get better overall performance
in one area or another.

As for iptables;

  So far I have had two people indicating a nice req/sec increase using:
a single instance, single core utilized, identical config, only changing
2 vs 1 http_port receiving traffic. We don't know why precisely, I do
know that two ports means Squid does two accept() per cycle of FD checking.
  (I forget what the actual increase % mentioned was, no strict
measurements were taken though).

NOTE: iptables is just a way of presenting client with one port and
using this effect for two ports in the background. Same effect was seen
with other non-iptables methods of spreading the load over two ports
(round-robin DNS in the one case of that. I expect PAC selection of an
instance port would work too).

   Nice project in there if someone wants to research its reliability
and measure the actual gain/loss metrics.

NP: Squid makes _extreme_ demands of the disks. If there is anything
getting in between or trying to utilize them for other purposes
(including RAID) the disk I/O performance is degraded. Sometimes a lot.

Amos

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