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authorJannis Hoffmann <jannis@fehcom.de>2024-07-09 11:44:11 +0200
committerJannis Hoffmann <jannis@fehcom.de>2024-07-09 11:44:11 +0200
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+.TH s/qmail: qmail-todo 8
+.SH NAME
+qmail-todo \- schedule state change of message for delivery
+.SH SYNOPSIS
+.B qmail-todo
+.SH DESCRIPTION
+.B s/qmail
+with a high local and remote concurrency number
+is able to deliver a tremendous amount of messages (throughput).
+Depending on the provided resources however,
+often this can not be achieved since
+.B qmail-send
+becomes a bottleneck on delivery.
+
+.B qmail-send
+preprocesses all new messages before deploying them for
+.I local
+or for
+.I remote
+delivering. In a particulur run,
+.B qmail-send
+does one 'todo' processing, but has the ability to close multiple jobs.
+Due to this layout, potentially
+.B qmail-send
+can not feed all the new available (local/remote) delivery slots
+and therefore, it is not possible to achieve the maximum throughput.
+
+This is a minor problem, given
+.B qmail-send
+is able to complete this in short time; but due to
+many file system calls (fsync and (un)link) a 'todo'
+run is expensive and throttles the throughput.
+
+.B qmail-todo
+solves this 'silly qmail (queue) problem'
+which is apparent only on system with high injection rates,
+delegating the scheduling of 'todo' runs to a dedicated process.
+
+.SH "COMMUNICATION"
+.B qmail-todo
+interfaces with
+.B qmail-send
+on file descriptors \fI[1,8]\fR on sending
+and \fI[7,0]\fR for receiving.
+.B qmail-todo
+communicates with
+.B qmail-clean
+on file descriptors \fI[2,0]\fR for sending
+and \fI[3,1]\fR for receiving.
+
+.B qmail-todo
+and
+.B qmail-send
+share an extended and peristent message exchange format:
+
+.EX
+D[LRB]<mesgid>\0
+ Start delivery for new message with id <messid>.
+ The character L, R or B defines the type
+ of delivery: Local, Remote, or Both, respectively.
+.EE
+
+.EX
+L<string>\0
+ Dump string to the logger without adding additional
+ '\\n' or similar.
+.EE
+
+.B qmail-todo
+sends "\\0" terminated messages, whereas
+.B qmail-send
+just sends one character to
+.BR qmail-todo .
+
+.SH "BIG PICTURE"
+.EX
+ +-------+ +-------+
+ | clean | | clean |
+ +--0-1--+ +--0-1--+ +-----------+
+ trigger ^ | ^ | +->0,1 lspawn |
+ | | v | v / +-----------+
+ +-------+ v +--2-3--+ +--5-6--+ /
+ | | | | 0<--7 1,2<-+
+ | queue |--+--| todo | | send |
+ | | | | 1-->8 3,4<-+
+ +-------+ +-------+ +---0---+ \\
+ | \\ +-----------+
+ v +->0,1 rspwan |
+ +---0---+ +-----------+
+ | logger|
+ +-------+
+.EE
+
+.SH "EXIT CODES"
+.B qmail-todo
+exits
+.I 0
+if the messages have been processed successfully.
+It exits
+.I 1
+in case there is a communication problem with
+.BR qmail-send .
+The exit code
+.I 111
+together with a diagnostic message is facilitated by
+.B qmail-todo
+in case it failes reading the required control files.
+
+.SH "DIAGNOSTICS"
+.B qmail-todo
+provides additional diagnostic messages to
+.B qmail-send
+to be displayed in the logs. In particular, in
+case of problems creating and (un)linking files.
+
+.SH "CREDITS"
+.B qmail-todo
+included in
+.B s/qmail
+has been created by Andre Oppermann (http://www.nrg4u.com)
+as part of this LDAP patch for
+.BR qmail .
+This man-page uses parts of his EXTERNAL discription.
+
+
+.SH "SEE ALSO"
+qmail-send(8),
+qmail-queue(8).