faster delivery of cyrus imap -- writev() takes 1.2 sec!

[Su Li]

Hi,

I tried to make Cyrus imap deliver mail faster, by changing
--with-duplicated-db to skiplist and disabled notification. It didn't work.
I am sending email from my testing tool. I run 4 of them, each trying to
send one email to mail server with a delay of 20 msec. It seems the Cyrus
imap can only process 1 email per second.

My configuration for imap is:

./configure --with-auth=unix --without-krb4 --without-ucdsnmp
--with-bdb-incdir=/usr/local/BerkeleyDB.4.0/include
--with-bdb-libdir=/usr/local/BerkeleyDB.4.0/lib --with-dblib=berkeley
--with-dbpath=/usr/local/BerkeleyDB.4.0 --with-lock=fcntl
--with-mboxlist-db=skiplist --with-seen-db=skiplist  --without-notify
--disable-sieve --enable-fulldirhash --with-idle=no
--with-duplicate-db=skiplist

I run "strace -T -p pid", in which pid is pid of lmtpd. The following line
catches my eyes. 

writev(11, [{"\0\0\0018(\"Sat, 7 Sep 2002 22:12:14 -"..., 316},
{"\0\0\0Q(\"TEXT\" \"PLAIN\" (\"CHARSET\" {"..., 88}, {"\0\0\0E(\"TEXT\"
\"PLAIN\" (\"CHARSET\" {"..., 76},
{"\0\0\0000\0\0\0\2\0\0\0\0\0\0\2Y\0\0\2Y\0\0\0000\377\377"..., 52},
{"\0\0\0\0", 4}, {"\0\0\0*loadtest <loadtest1586 at web9."..., 48},
{"\0\0\0!<loadtest1586 at web9.swlab.rim"..., 40}, {"\0\0\0\0", 4},
{"\0\0\0\0", 4}, {"\0\0\0\3NIL\0", 8}], 10) = 640 <1.207524>

It takes 1.2 sec to do writev() for each email! I search through the code in
/imap/messages.c. It looks like the following function is doing the writing:

/*
 * Write the BODY (if 'newformat' is zero) or BODYSTRUCTURE
 * (if 'newformat' is nonzero) for 'body' to 'ibuf'.
 */
static void
message_write_body(ibuf, body, newformat)

I wonder why writev() takes so long to do the writing? In the mean time I
don't found error messages about locking. I guess it is not
"duplicate_check" who is take so long. It there any thing to don with my
configurations, or sendmail's configuration? 

Thanks a lot.


Su

Research In Motion
(519)888-7465 ext 3041