1.2 sendmail Versions Covered

1.2 sendmail Versions Covered

This book discusses issues involved in performance tuning several different versions of sendmail, not just the most recent release. This choice was made for several reasons. First, not every organization feels that it can use the most up-to-date version of sendmail at its site. These organizations will still find valuable information in this book. Second, some organizations have elected not to use sendmail because of historical problems that may not affect more recent versions. If someone has had a bad experience in the past with sendmail performance, it's entirely possible that the reasons for the problem no longer exist in the code. In such a case, I want to give the reader the full opportunity to understand what might have happened and why it might no longer present a problem. Third, by the standards of most Internet applications, sendmail is a very old program. That is, sendmail in some form has been in operation for more than 20 years. The program itself is now older than some people charged with installing and maintaining it. The sendmail Mail Transfer Agent (MTA) has a lengthy history, and despite most of the code having been rewritten, often several times since then, good programmers don't like to break compatibility with older behavior. As a consequence, the way sendmail works now owes a great deal to evolutionary changes in the code over a long period of time. Some of the ways in which sendmail chooses to implement certain features might seem strange, and understanding its history can help lead to understanding about why things are as they are.

Historically, sendmail adds new features or changes its behavior only when the middle number in its version changes. That is, its behavior should be expected to change between versions 8.9.3 and 8.10.0, but should remain relatively stable between versions 8.11.5 and 8.11.6. Revisions that alter the rightmost number typically represent bug fixes or possibly refinements or minor tunings in the operation of sendmail. Recently, each of the changes associated with the advancement of the middle release number has largely been associated with a single theme. The changes between versions 8.8 and 8.9 centered on spam control. The Open Source release of version 8.10 added a large number of smaller features to the MTA; a partial list of these features has been documented [SA99]. Version 8.11 added cryptographic support to the Open Source release of sendmail. The focus of sendmail version 8.12 is most relevant to this book, as its advances occurred primarily in the realm of performance. Although by no means was every new feature in successive sendmail versions associated with that release's theme, many were. In any case, email administrators running sendmail who are concerned with performance would be well advised to try to install the latest version of sendmail, especially if they are currently working with some revision of 8.11 or earlier.

Just for reference, we can test the CPU-bound server described earlier in this chapter to measure the benefit of upgrading to sendmail 8.12 from version 8.11. Using the most generic sendmail.cf file appropriate for each version of sendmail, queueing and then delivering one approximately 1KB message to the mailbox of one of 50 randomly selected users on that machine, we get a throughput of 221 messages/second using sendmail 8.11.6, and 242 messages/second using sendmail 8.12.2. This difference represents a performance gain of about 11%. The server was CPU bound during this test, so it just measures improvements in the efficiency of the code. This improvement is quite modest, but it can be obtained "for free." As we will see, we can make additional changes to a sendmail 8.12 configuration file that will improve these numbers further.



sendmail Performance Tuning
sendmail Performance Tuning
ISBN: 0321115708
EAN: 2147483647
Year: 2005
Pages: 67

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