Maildir: Linux Kernel Mailing List with 367918 mails, total of 1,9GB.

NOTE: The total times are heavily affected by disk I/O. In these tests the
index files are cached in memory by OS. The files themselves are mostly
uncached (I flushed the cache by reading another 2GB file 3 times).

System: 1GHz AMD Athlon CPU, 1GB RAM, 120GB IDE disk,
Linux 2.4.21, XFS filesystem


DOVECOT 0.99.11
---------------

 - NOTE: Debugging enabled, disabling it might give slightly lower user CPU
   times

1) select mailbox for the first time

   2.85s user 2.20s system 55% cpu 9.035 total

2) select mailbox for second time

   0.01s user 0.02s system 127% cpu 0.024 total

3) resync cur/ directory (touch cur, select mailbox)

   2.91s user 0.55s system 77% cpu 4.483 total

4) "uid thread references us-ascii all" for the first time

   67.27s user 41.25s system 27% cpu 6:30.85 total

5) "uid thread references us-ascii all" for the second time (uses indexes)

   30.39s user 0.25s system 95% cpu 32.055 total

6) "uid sort (date) us-ascii all" (uses indexes that threading created)

   22.88s user 0.13s system 99% cpu 23.048 total

7) "uid sort (subject) us-ascii all" (uses indexes that threading created)

   38.41s user 0.15s system 99% cpu 38.708 total

size of created index file:

       4636252 .imap.index
     121513984 .imap.index.cache

8) cache file compression

   4.21s user 1.42s system 26% cpu 21.270 total

     113536000 .imap.index.cache

   Compression had only minimal effect on performance. Compression isn't
   usually done until 30% of file consists of old data for expunged messages.


COURIER 1.72
------------

1) select mailbox for the first time

   4.93s user 0.51s system 80% cpu 6.762 total
   - slightly faster since it doesn't have to write 21MB of index files

2) select mailbox for second time

   - courier doesn't have a indexes so this is equilevant to 3)

3) resync cur/ directory (touch cur, select mailbox)

   12.91s user 0.42s system 100% cpu 13.324 total
   - oops, slower than generating the uids first time. slow hashes or
     something..

4) "uid thread references us-ascii all" for the first time

   606.94s user 69.56s system 64% cpu 17:22.02 total
   - that's 10x slower in user CPU. Over 2.5x slower in total time.

5) "uid thread references us-ascii all" for the second time

   - courier doesn't have indexes, so this is equilevant to 4)

6) "uid sort (date) us-ascii all"

   442.58s user 55.11s system 61% cpu 13:28.79 total
   - courier doesn't have indexes, so it has to open all mail files.

7) "uid sort (subject) us-ascii all"

   444.13s user 56.82s system 59% cpu 14:03.14 total
   - courier doesn't have indexes, so it has to open all mail files