On Mon, 24 May 2004, Sasa Stupar wrote:

> Davide,
> I have been looking arround about mail formats and found out interesting 
> info on http://www.washington.edu/imap/documentation/formats.txt.html .
> 
> Just a part of it what is very interesting:
> --------------
> There's a general reason why file/message formats are a bad idea.
>   Just about every filesystem in existance serializes file creation and
>   deletions because these manipulate the free space map.  This turns out
>   to be an enormous problem when you start creating/deleting more than a
>   few messages per second; you spend all your time thrashing in the
>   filesystem.
> 
>        It is also extremely slow to do a text search through a
>   file/message format mailbox.  All of those open()s and close()s really
>   add up to major filesystem thrashing.
> -------------

They serialize per directory entry eventually, that's why XMail uses a 
split spool. About the mailbox, what the heck does it matter for a single 
mailbox? At which rate a *single* mailbox can receive messages? Shooting 
awesomely high, 1 per second, with the dentry lock held for maybe 3 
milliseconds. OTOH mbox is crap, since it is a single huge file with no 
index structure, that needs complete rewriting each time you remove 
messages.



- Davide

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