[Dovecot] Something other than dotlock for uidlist locking?

James Berry james at jberry.us
Wed Aug 9 03:43:27 EEST 2006

Hi Timo, (By the way, this seems to relate to a performance issue on  
Mac OS X with HFS+).

On Aug 28, 2005, at 12:30 PM, Timo Sirainen wrote:
> On Thu, 2005-08-25 at 10:26 -0700, James Berry wrote:
>> If I read the code correctly, only dotlocks are supported for locking
>> of dovecot-uidlist. And I don't see any settings in the config file
>> for it.
>> As it turns out, dotlocks are very slow on my system, due to their
>> implementation via hardlinks.
>> Would it be possible to support other locking mechanisms for locking
>> of the uidlist file?
> They are locked only when they are modified, and the modification  
> works
> by creating a new file and renaming it over the dovecot-uidlist file.
> Is it only hardlinks that are problematic? It shouldn't be too  
> difficult
> to change the dotlock code to rely on working O_EXCL instead of
> hardlinks.
> Hmm. Actually I just did that in CVS. I guess I should also put out  
> some
> setting to enable it in config file. For now you could just change  
> this:
> 	ret = set->use_excl_lock ?
> 		try_create_lock_excl(&lock_info, write_pid) :
> 		try_create_lock_hardlink(&lock_info, write_pid);
> to
> 	ret = try_create_lock_excl(&lock_info, write_pid);
> and see if it works faster.

Well, a year later I finally got around to trying this out. On a Mac  
system. And guess what? It seems much, much snappier. Sorry about the  
delay in testing it. One of the symptoms I've been seeing on the  
server is that performance gradually degrades over time, even if  
dovecot is restarted. The problem seems better after a server  
restart, which clears out an area on disk which tracks unlinked and  
hardlinked files. I believe this option will fix that performance issue.

Any chance of getting a configuration option for this?


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