When sendmail
is installed with near-default
settings, it provides excellent email services for most machines. But
when installed to service high loads, high volumes, or high rates,
special tuning becomes a requirement.
There are a few new items in V8.13 that affect performance tuning. They are described in other chapters but referenced here. In this chapter, we augment some of the knowledge imparted in the third edition of the sendmail book.
The RequiresDirfsync
option (Section 24.1.12
[V8.13]) turns off
the REQUIRES_DIR_FSYNC
(3.4.47[3ed]) compile-time
macro’s setting at
runtime. Turning off directory fsyncs
increases
performance—but at (possibly) increased risk.
The existing SuperSafe
option (24.9.107[3ed])
now accepts a new
PostMilter
setting that delays
fsync
( )ing the df
file
until after all Milters have reviewed the message. This improves
performance when a great deal of email is rejected by Milters that
review the message body.
The Timeout.queuereturn.dsn
(Section 24.1.15[V8.13])
and
Timeout.queuewarn.dsn
(Section 24.1.16
[V8.13]) options
have been added. Use them to lower bounce timeouts, and thereby to
create less congested queues and increase performance.
Some sites have developed delivery agents that receive messages using
SMTP over standard input/output. Such delivery agents use the
P=[LPC]
equate (20.5.11[3ed]) to achieve this
effect. Beginning
with V8.13,
sendmail
enables connection caching
(24.7.5[3ed]) for such delivery agents,
thereby increasing delivery performance.
Although this is not a V8.13 improvement, you can safely increase the performance of your queue disks under Solaris 7 and above, and other operating systems by mounting them with the following mount(1) options:
logging,noatime
Here, the logging
causes transactions (such as
creating and deleting files) to be stored in a log before they are
applied to the disk. Once a transaction is logged, it can be applied
to the underlying disk layout later. This speeds up disk I/O and can
help a machine to reboot faster.
The noatime
prevents inodes from being updated
each time a file is read. This eliminates a disk write that has no
significant value. The speed increase will be most noticeable when
many queued files are being retried in parallel.
One or the other of these mount
(1) options may
not be available with your operating system. See your online
documentation to find out which you can use.
3.17.28.48