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diff --git a/usr.sbin/sendmail/contrib/xla/README b/usr.sbin/sendmail/contrib/xla/README deleted file mode 100644 index a72fd03..0000000 --- a/usr.sbin/sendmail/contrib/xla/README +++ /dev/null @@ -1,207 +0,0 @@ - XLA - Extended Load Average design for Sendmail R6 - -------------------------------------------------- - - Christophe Wolfhugel - Herve Schauer Consultants - wolf@grasp.insa-lyon.fr, wolf@hsc-sec.fr - - -WARNING: this extension is supplied as a contribution to Sendmail. -Should you have trouble, questions, please contact me directly, and -*not* the Sendmail development team. - - -ABSTRACT - -Sendmail currently furnishes a limitation mecanism which is based on -the system load average, when available. Experience has prooven that -this was not sufficiant for some particular situations, for example -if you have slow and/or overloaded links. This can easily cause both -system and network congestions with Sendmail having to handle a large -number of simultaneous sessions on the same overloaded link, causing -most of the SMTP sessions to timeout after a long time. The system -load average is also generally too slow to react when your system -gets a burst of incoming or outgoing SMTP sessions which on some -stations can easily cause system unavailabilities. - -The extended load average module has been designed in order to furnish -a way of limitation the load generated by Sendmail to both your -system and your network. This design can be used either alone or as -complementary to the system load average if your system supports it. - -Limitation is based on the number of incoming/outgoing SMTP sessions, -and remote hosts are classified in classes. The system administrator -will define a maximum number of incoming SMTP sessions as well as -a maximum total (incoming + outgoing) sessions for each class of -hosts. A class can be either an individual machine or a network. - -When the limit is reached for a given class, all incoming SMTP -connections will be politely refused. When the limit is reached for -all classes, the SMTP connections will be refused by the system -(which one could consider as less politely :)). -On outgoing mail, messages will be queued for delayed processing. - -The extended load average parameters are given in the Sendmail -configuration file, and when not present, Sendmail behaves the -usual way. - - -COMPILATION - -Copy the xla.c module in the src sub-directory, edit the Makefile -in order to define XLA (-DXLA). Also add the xla.[co] module name -in the list of files so that it gets compiled. - -Regenerate sendmail by removing all objects, or at least those -containing references to XLA (this list may vary, so use grep to -get the module list). This will generate a new sendmail executable -containing the xla code. - -Debugging level 59 has been assigned to this module and when used -it provides some output (sendmail -d59.x). Please check the source -code to see which levels are supported. - - -CONFIGURATION - -The extended average uses a new set of configuration lines in the -sendmail.cf file. All newly introduced line begin with the letter L -(capital L). - -Before detailling the syntax, first an example (this can be placed -at any section of the sendmail.cf file, note that the order is -important). Fields are separated by (one or more) tabs/spaces. - -# File name used to store the counters -L/etc/sendmail.la -# Classes definition -# Lname #queue #reject -L*.insa-lyon.fr 8 3 -L*.univ-lyon1.fr 6 4 -L* 15 16 - -The first line defines the working file which will be used in order -to have the occurences of Sendmail read and update the counters. The -format of this file is described in the "Design" section. -This line is mandatory and the specified file must be absolute (ie -begin with a slash). - -Then you can specify one or more classes. The last class (*) is also -mandatory and should be in last position as the first match will stop -the search and if there is no match the behavior of Sendmail is unknown. - -Each class has three fields separated by one or more tabs/spaces. - -L{mask} {queue_#} {refuse_#} - -The {mask} is a simple mask. It can be either an explicit host name -(like grasp.insa-lyon.fr) or a mask starting with "*." or just "*". -No other variants are allowed. - -Lgrasp.insa-lyon.fr will match exactely any session to/from this host. - -L*.insa-lyon.fr will match any session to/from any machine in the - insa-lyon.fr domain as well as from the machine - named "insa-lyon.fr" if it exists. - -L* will match any session, and thus should also be - last in the list to act as a catchup line. - -The {queue_#} is the maximum number of SMTP sessions in the given class -for both incoming and outgoing messages. The {refuse_#} indicates when -to refuse incoming messages for this class. The interaction between -those counters is somewhat subtle. It seems logical that a standard -configuration has {queue_#} >= {refuse_#}, and in fact in most -configurations they can be equal (that's why what I use in my environment). -Thus, this is not mandatory. If {queue_#} < {refuse_#} outgoing messages -will be lower priority than incoming messages and once a class gets loaded -the outgoing messages are blocked first. - -I use very low values in some situations, for example I have a customer -connected to the Internet via a 9600 bps line, they also have internal -users sending burst of messages (10, 20 small messages coming in just -one or two seconds). Both situations were unsupportable. The line is -too slow to handle many simultaneous connections and the mail server -does not have the ressources to handle such a heavy load (it's a 12 Megs -Sun 3 also doing Usenet news). - -I have defined following section in the configuration file, and experience -shows the benefits for everyone. Fake domain for the example: customer.fr. - -L/etc/sendmail.la -L*.customer.fr 8 8 -L* 3 3 - -This means that there might not be more than 8 simultaneous SMTP sessions -between the mail server and any other internal host. This is to protect -the station from heavy loads like users (or applications !) sending -several tenths of messages in just a few seconds). -No more than 3 SMTP sessions are authorized with any other host, this is -to save the load of the slow 9600 line to the Internet. - -Drawback is that is you have 3 * 2 Megs sessions established from/to the -outside, all your mail will be held until one slot gets available, on -a 9600 bps line just make your counts, il blocks your line during over -one hour. - - -DESIGN - -Sendmail will analyze the "L" lines in the configuration file during -startup (or read the initialized structure from the frozen file). -When started in daemon mode (and only there), any existing working file -will be cleared and a new one is created. Each class gets a record in -the sendmail.la work file. The size of this record is a short integer -(generally two bytes) and represents the count of active sessions in -the given class. Read/Write operations in this file are done in -one operation (as anyway the size is far below one disk sector). The -file is locked with Sendmail's lockfile() function priori to any -access. - -Handling incoming SMTP sessions. - -There is interaction is two points in the Sendmail source code. First -on the listen system call: if all slots in all classes are in use, -a listen(0) is done so that the system rejects any incoming SMTP session. -This avois to fork and then reject the connexion. - -If there are some free slots, nothing better than accepting the -connection, then forking can be done. The child process then checks if -the adequate class is full or not. If full, it rejects the connection -with a "421 Too many sessions" diagnostic to the sender (which should -then appear when the remote users do a mailq). If the treshold {reject_#} -is not reached, the connection is accepted and the counter is sendmail.la -is updated. - -Handling outgoing SMTP sessions. - -As soon as Sendmail needs to connect to a distant host, the adequate class -is checked against {queue_#} and if no slots are available, the message is -queued for further processing. - -Sendmail's connection caching. - -Sendmail-R6 introduces a new design: connection caching, ie several SMTP -sessions can be opened at the same time. This could cause some problems -when sending mail, as after having a few connections opened, all slots -could be in use and generate a partial delivery of the message. In -order to deal with this, xla.c uses following design "for a given -sendmail process, only the first connection in a given class is counted". -This can be done because sendmail does not do parralel message sending -on the different channels. - -End of connection. - -As soon as a connection is closed, the counters will be automatically -updated. - - - -Please look at the code to understand of all this works. Comments, -suggestions, questions welcome. - - - - Christophe Wolfhugel - Herve Schauer Consultants - Paris, France - May 23, 1993 |
