s/qmail:

Section: Misc. Reference Manual Pages (qmail-todo)
Updated: 8
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NAME

qmail-todo - schedule state change of message for delivery

SYNOPSIS

qmail-todo

DESCRIPTION

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 qmail-send becomes a bottleneck on delivery.

qmail-send preprocesses all new messages before deploying them for local or for remote delivering. In a particulur run, qmail-send does one 'todo' processing, but has the ability to close multiple jobs. Due to this layout, potentially 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 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.

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.

COMMUNICATION

qmail-todo interfaces with qmail-send on file descriptors [1,8] on sending and [7,0] for receiving. qmail-todo communicates with qmail-clean on file descriptors [2,0] for sending and [3,1] for receiving.

qmail-todo and qmail-send share an extended and peristent message exchange format:

D[LRB]<mesgid>
  Start delivery for new message with id <messid>.
  The character L, R or B defines the type
  of delivery: Local, Remote, or Both, respectively.

L<string>
Dump string to the logger without adding additional
'\n' or similar.

qmail-todo sends "\0" terminated messages, whereas qmail-send just sends one character to qmail-todo.

BIG PICTURE

               +-------+   +-------+
               | 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|
                           +-------+

EXIT CODES

qmail-todo exits 0 if the messages have been processed successfully. It exits 1 in case there is a communication problem with qmail-send. The exit code 111 together with a diagnostic message is facilitated by qmail-todo in case it failes reading the required control files.

DIAGNOSTICS

qmail-todo provides additional diagnostic messages to qmail-send to be displayed in the logs. In particular, in case of problems creating and (un)linking files.

CREDITS

qmail-todo included in s/qmail has been created by Andre Oppermann (http://www.nrg4u.com) as part of this LDAP patch for qmail. This man-page uses parts of his EXTERNAL discription.

This document was created by man2html, using the manual pages.
Time: 16:40:05 GMT, September 13, 2025