Mailboxes with slow access

ellie timoney ellie at
Sun Jan 20 20:33:40 EST 2019

Hi Miguel,

On Sat, Jan 19, 2019, at 8:20 AM, Miguel Mucio Santos Moreira wrote:
> Hi folks!
> I've had a problem with some huge mailboxes, with a lot of folders and
> subfolders. Problably thousand of folders.> The access on these mailboxes is too slow, if you change from INBOX to
> another folder called CYRUS, even if CYRUS folder has just 4 messages
> for example the access is slow.
This sounds like you don't have enough RAM to hold the metadata for
these mailboxes in memory, and so the system is swapping while
accessing them.
You could find the imapd process that is servicing this connection and
look at its virtual memory size, and compare that to the amount of
physical RAM in your system, to see whether this is the case.
Or, if you post up the size of these mailboxes' cyrus.header,
cyrus.index, cyrus.annotations, cyrus.cache (...) files and the size of
their [user].conversations file (if you have conversations enabled),
then maybe someone will be able to suggest a RAM size that would
support this.
You mention being in a murder environment -- I'm not sure if you will
need to increase the RAM on just the backend for these mailboxes, or the
frontends as well.  Maybe someone running a large murder can chime in
with how they provision their servers?
Sorry I don't have specific numbers for you, but hopefully this points
you in the right direction!
> I was trying to find out  anything on internet about this issue and I
> read that a parameter maxword on imapd.conf  could be the solution.> Nowadays in our cyrus-imap murder all backend servers and
> frontend servers have the maxword parameter set to default value
> which is 128kb.> Based on that information, I'd like to know if I increase this
> parameter to a high value like 1Mb for instance it could fix the issue
> about slow access and which considerations about memory, disk and cpu
> resources I must take care if I set up this value in my environment.> Another question is, this value must be setting in all backends and
> frontends servers?
imapd.conf(5) says:
>           maxword: 131072
>               Maximum size of a single word for the parser.  Default
>               128k
This setting won't have any effect on performance at all.  It's just an
upper limit for the IMAP parser -- if some IMAP client tries to send a
single word that is longer than this, the imapd process serving their
connection will exit immediately with a "word too long" error rather
than trying to keep parsing.  Normal traffic won't hit this limit, it's
just protecting itself from (possibly malicious) garbage.  The default
should be never need changing really.
Hope this helps,

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