[Dovecot] Indexing Performance Question (was tpop3d vs dovecot)

Nate nm_list at visp.net
Thu Feb 1 19:31:49 UTC 2007

At 10:50 PM 1/31/2007, FiL wrote:
>10 minutes to read 748Mb? Kinda slow, isn't it ?
>For me reading 2Gb mailbox (not maildir) takes MUCH less time than 
>that (around 20 sec).
>It should be within 40secs to read the whole maildir.

I whole-heartedly agree, that is slow; however, not necessarily any 
problem with dovecot.  More a filesystem issue.  Because it's not 1 
large synchronous file, the disk has to seek like crazy to read each 
file.  Here's some testing to show it's normal:

I looped through all the files and cat them to /dev/null.  This is 
independent of dovecot.  This is reading the entire contents of every 
file to /dev/null.  I don't know why or if dovecot would have to do 
that to build an index, should be able to get away with the first 100 
lines max I'd think.

[root at test cur]# time for x in `ls` ; do cat $x > /dev/null ; done
real    15m28.568s
user    0m20.993s
sys     1m27.609s

Now if I copy the contents of cur/ to another directory (on an 
otherwise idle machine), so it's all written synchronously on the 
disk, the results change dramatically.  (a reboot is performed to 
clear all cache after the copy)
[root at test testspool]# time for x in `ls` ; do cat $x > /dev/null ; done
real    2m15.945s
user    0m20.493s
sys     1m10.796s

Finally, to simulate a mbox like you mention I tar all the files to 1 
large file, reboot, and cat the new tarfile to /dev/null.
[root at test natetest]# time cat cur.tar >/dev/null
real    0m15.162s
user    0m0.044s
sys     0m1.024s

What's sad with these tests is it takes 2m15s to read all the data in 
71570 individual files, and only 15s to do it in 1 file.  Granted 
there's a bit of overhead from the shell script looping, but not 
*that* much!  I wonder how these tests would go on a different file 
system.  I'm currently using reiserfs.

- Nate  

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