[Dovecot] Possible sort optimization (?)

[Michael M Slusarz]

Maybe this is just noise... but I can reproduce this fairly reliably.

Mailbox with 21,000+ messages

This query:

a UID SORT RETURN (ALL COUNT) (DATE) UTF-8 SUBJECT "foo"

is always about 10 percent slower than this split query (I've done  
this 4-5 times, and the numbers are similar):

a UID SEARCH RETURN (SAVE) CHARSET UTF-8 SUBJECT "foo"
b UID SORT RETURN (ALL COUNT) (DATE) UTF-8 UID $

(The particular query I used matched 5 messages out of the 21,000+)


My not-very-scientific benchmarking process:

1.) Stop dovecot process
2.) Delete all dovecot index files for that mailbox
3.) Flush linux paging cache (sync && echo 3 > /proc/sys/vm/drop_caches)
4.) Restart dovecot
5.) Access dovecot via command-line (PREAUTH)
6.) SELECT mailbox
7.) Issue command(s)


Could be a potential area for performance improvement or could simply  
be lazy benchmarking.

michael