Re: [SM-USERS] Threaded Sorting

[Jonathan A. <jo...@sq...>]

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Hi R.,
On Monday, January 16, 2006, R. wrote:
> Jonathan Angliss wrote:
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>> Hi R.,
>> On Monday, January 16, 2006, R. wrote:
>>> Hello.
>>> In conf.pl General Options I have the choice of
>>> 10. Allow server thread sort    : true
>>> 11. Allow server-side sorting   : true
>>
>>> what is the difference between these two settings?
>>
>> server-side sorting makes the IMAP server do the sorting based on
>> criteria we provide. Server side thread allows the server to build a
>> thread for us. Depending on your IMAP server, that might be by
>> subject, or references (a header combination of In-Reply-To and
>> References), or both. If you look at the headers for this email, you
>> should see a References header which allows the IMAP server to build a
>> thread of messages like a tree.
>>
>>> The problem is, when I have a big mailbox with f.e. 50000 mails and I
>>> choose "Threaded View" my apache runs amok. I takes 5 minutes with 98
>>> Percent CPU to perform this task.
>>
>> Youch... your IMAP server has to read all 50,000 emails and read the
>> headers to build the thread for us.  That's a bit of a task on its
>> own.  This ultimately ends up generating a load of data (see [1] for
>> details).

> No, well, its my apache on a different computer than Cyrus which has the
> heavy load, not the Cyrus sever itself.

Doesn't really matter. Apache goes into a loop while waiting for data
to return from the IMAP server, which after a while can cause an
increased CPU usage. UW-IMAP has a similar issue when listing
/home/$username if you have a large amount of files, or symlinks to
other locations. UW-IMAP uses a bit of memory, while Apache consume
all the resources while waiting for a loop to finish.

> The Cyrus server takes very low CP time. But my Cyrus Server doesn't
> work as expected. I run it in a XEN environment, XEN Vers. 2 which
> has no glibc and things like indexing the database doesn't work at
> all. I am going to upgrade to XEN Vers. 3 in a few weeks and hope I
> have a fully functional Cyrus.

> But when the Cyrus server does no indexing and (thats what I guess)
> doesn't sort the mails then Squirrelmail on the apache does the
> sorting? Could that be the reason for Apache's heavy CPU usage?

Not really.  SquirrelMail knows nothing of the lack of indexing or any
issues on the IMAP side regarding the storage of mail.  If Cyrus has
an issue with indexing, then server side sorting should be disabled on
the server by default to stop it being an issue, however I don't think
that is the cause of your CPU spikes by Apache as SquirrelMail doesn't
get told "hey, my indexes are bad, why don't you do the work".  If
that was really the case, you'd find it'd error out with something
like:

  "Exceeded maximum execution time of 30 seconds"

Or something to that affect.

> Besides, can I use othr criteria than the date of the mails like
> number of mails in the Mailbox?

Unfortunately it doesn't appear to be the case based on the criteria
for the SEARCH functions in IMAP.  The best I can suggest is a date
based search, limiting the view, but then you're forcing yourself into
only being able to see a certain range of emails.

- --
Jonathan Angliss
<jo...@sq...>
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