Does anyone allow unlimited or extremely large quotas?

[David Carter]

On Fri, 19 Nov 2010, Michel Sébastien wrote:

>> On a 32 bit architecture: we had one folder with over a million messages
>> which was causing processes to run out of virtual memory trying to map
>> the cache file in.  This wouldn't be a problem with a 64 bit userland.
>
> very impressive to have so much messages in one folder therefor in one 
> partition!.

We have hit this limit once, and so far only once, as well.

A user was sorting their email archive (thousands of messages) generating 
copies to the Trash mailbox. They repeated this exercise multiple times.

Each time that the user reached hit their quota limit (several GBytes), 
they emptied the Trash folder. Consequently the live mailbox itself never 
contained huge numbers of messages. However delayed expunge means that a 
lot of wreckage was left behind: hundreds of thousands of messages.

Easily fixed by a reconstruct which discarded the obsolete information.

> Is mmap still efficient ? map a gigabit file should cost a lot of I/O 
> and a relatively long reponse time to just access the records of the 
> most recent emails.

The mmap() itself has very little cost.

It would only become a problem if something actually tried to read all of 
the cache entries, causing the data to be paged in from disk.

-- 
David Carter                             Email: David.Carter at ucs.cam.ac.uk
University Computing Service,            Phone: (01223) 334502
New Museums Site, Pembroke Street,       Fax:   (01223) 334679
Cambridge UK. CB2 3QH.