[Dovecot] dovecot performance

[Giorgenes Gelatti]

The master process exec's the mail process (imap or pop3) after fork.

gpg

2008/8/15 Sebastien Tandel <sebastien.tandel at corp.terra.com.br>:
> Hi,
>
>
>>> It is well known that preforking is a good pratice if you want to
>>> achieve a higher performance.
>>> When I was asked about it I readily answered: "of course it does". For
>>> my surprise later, i doesn't.
>>
>> With fork latencies in the range of 500 to 1500 microseconds (on Pentium
>> 900 MHz-class hardware!) on most modern kernels[1] I wonder whether this
>> "good practice" isn't on the verge of voodoo ;-)
>
> OK, it measures the fork instruction. But fork is using a copy-on-write
> mechanism ... It means that *none* of the parent's memory pages are copied.
> Each page is simply *shared* by *all* the child /until/ a modification is
> made to it.Therefore this test obviously does not take into account time
> taken when modifying data. And I strongly suspect that dovecot is not only
> doing read-only access to memory when running. :-/
>
> P.S. : I'm not saying though it is mandatory to have such a mechanism in
> dovecot ;)
>
>
> Regards,
> Sebastien
>
>> (Of course, in a http server, where you might expect thousands of
>> connects per second, this is another story -- which is mitigated by HTTP
>> 1.1, when properly streaming several requests per connection).
>>
>> - ----------------
>> [1] <http://bulk.fefe.de/scalability/>, search "The fork benchmark"
>>
>> Regards
>> - -- tomás
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>
>