mdbox / selecting folder accesses hundrets of others

[Florian Lohoff]

On Sat, May 08, 2021 at 08:57:07AM -0400, Coy Hile wrote:
> >> Dovecot: 2.3.4
> >> Hi,
> >> i am debugging a problem where after a force-resync removed all cache
> >> files (All files are 44 byte). Trying to open a folder takes literally minutes
> >> (Huge mailbox - 220K folder, 45GByte compressed storage)
> 
> I don’t have an answer for you, unfortunately, as you all exercise
> your mail system far more thanI do.
> 
> Taking a wild guess, I’d think that having a large number of folders
> has potential to be more of an issue than having a large amount of
> mail in fewer folders. Operating under that assumption, is it possible
> to bound the problem? (Hypothetically say 128k folders were good, more
> than that and something went out to lunch or something similar.)
> 
> I am, however, watching this with interest.

The point is: If this is not a bug/misbehaviour caused by this specific
mailbox and you have for larger installation an average of 10
folders per mailbox you have an up to 10 fold iop amplification for
certain operations.

So it could be relevant for all sorts of larger installation. It may not 
be these extremes with 220k folders. This just puts the issue right
in front of your face because its that extreme thats its noticeable.

Flo
-- 
Florian Lohoff                                                     f at zz.de
  Any sufficiently advanced technology is indistinguishable from magic.
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