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From Bill Stoddard <b...@wstoddard.com>
Subject Re: mod_cache performance
Date Tue, 03 Aug 2004 19:27:10 GMT
Mathihalli, Madhusudan wrote:
> 
> : -----Original Message-----
> : From: Bill Stoddard [mailto:bill@wstoddard.com] 
> [SNIP]
> : > 
> : > Here's some comparative numbers to chew on.
> : > 
> : > One client and one server on 100Mbps network (cheapy 
> : 100Base-T switch);
> : > 50 simulated users hitting 7 URLs 100 times with flood 
> : (35,000 requests).
> : > 
> : > mod_disk_cache: Requests: 35000 Time: 40.91 Req/Sec: 856.78
> : > mod_mem_cache:  Requests: 35000 Time: 54.90 Req/Sec: 637.81
> : > no cache:       Requests: 35000 Time: 54.86 Req/Sec: 638.81
> : > squid:          Requests: 35000 Time: 105.35 Req/Sec: 332.25
> : > 
> : > mod_disk_cache completely filled out the network at ~50% CPU usage.
> : >    [Can't push through more than ~8MB/sec (~64Mb/sec) without GigE.]
> : > mod_mem_cache filled up the CPU but not the network
> : >    [Poor scaling characteristics.  It goes to 100% CPU with 
> : just 5 users!]
> : 
> : mod_mem_cache is broken then. It used to kick the pants off 
> : of 'no cache' and mod_disk_cache.
> 
> .. Well, doesn't it depend upon the size of the data set. With 'ab', I
> guess that's possible that mod_mem_cache can beat mod_disk_cache - but
> with a dataset like SPECweb99, I'd really doubt if it can really do it.
> 
> BTW, I wonder how mem_cache can significantly out-perform no-cache
> scenario - 'cause a good file system should buffer cache the
> most-accessed files, and there should be minimal perf. difference.
> 
> -Madhu

It depends almost entirely on the expense of the file open. On Windows, opening a file for
i/o is hideously 
expensive, so a simple memory cache works well on Windows. Caching open file descriptors (and
using 
TransmitFile) works even better.

Bill



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