What are the Bottlenecks in lmtpd

[ram]

I see that sometimes on my cyrus server , when mail is being delivered
by postfix. lmtpd takes too long to deliver 

But strangely enough this happens only "some" times .. and any other
time things are working fine. The number of mails received & downloaded
per hour are much the same throughout the day (working hours). And this
server does nothing else except running cyrus +postfix and mysql for
authentication

I want to analyse what are the possible bottlenecks for lmtpd whenever
it goes slow 

I have a feeling that the creations of files in /var/spool/imap/stage./
and moving them is taking most of the time 

Is there any way I can pinpoint what is going wrong. 



Thanks
Ram