System Bottlenecks

[Spicer, Kevin]

Errol Neal wrote:
>> The best I/O improvement is by making sure you've got plenty of RAM
>> and putting the MailScanner work directory in tmpfs (not either of
>> the mail queues though!)
> 
> Also, if one is to use the tmpfs, how large should the file system be?
> 

number of MailScanner children * batch size (no of messages) * average mail size * margin of error

tmpfs resizes automatically, but obviously you don't want to run out of RAM and start swapping.

Heres a silly example...

5 children * batchsize 100 * average_size 200k [which is silly, who has many messages that size] * margin of error say 5 (cautious)
= 488M

And thats using stupidly large numbers!, the real figures are probably an order of magnitude or two (but allow for peaks - what happens when every mail has an attachment, like some virus storms we've had).  A cautious mind would probably spec 1G of ram (but 512M would probably be okay) with that batch size.  In the real world though its often worth decreasing the batch size to improve performance (which reduces the memory requirement).



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