EXTTODO by Claudio Jeker <jeker@n-r-g.com> and 
Andre Oppermann <opi@nrg4u.com>
(c) 1998,1999,2000,2001,2002 Internet Business Solutions Ltd.

The EXTTODO patch is a part of the qmail-ldap patch.
This patches for qmail come with NO WARRANTY.

These patches are under the BSD license.

RELEASE: 5. Jan. 2003

EXTTODO:
======================

TOC:
 WHAT DOES IT DO
 INSTALL
 CONFIG FILES
 SETUP
 BIG PICTURE

NEWS:
 
 This is the first release of the EXTTODO patch.

================================================================================

WHAT DOES IT DO

 The exttodo patch addresses a problem known as the silly qmail (queue)
 problem. This problem is found only on system with high injection rates.

 qmail with a big local and remote concurrency could deliver a tremendous 
 amount of messages but normally this can not be achieved because qmail-send
 becomes a bottleneck on those high volumes servers.
 qmail-send preprocesses all new messages before distributing them for local
 or remote delivering. In one run qmail-send does one todo run but has the 
 ability to close multiple jobs. Because of this layout qmail-send can not 
 feed all the new available (local/remote) delivery slots and therefor it is 
 not possible to achieve the maximum throughput.
 This would be a minor problem if one qmail-send run could be done in extreme
 short time but because of many file system calls (fsync and (un)link) a todo
 run is expensive and throttles the throughput.

 The exttodo patch tries to solve the problem by moving the todo routine into 
 an external program. This reduces the run time in qmail-send.

 exttodo adds a new program to qmail called qmail-todo. qmail-todo prepares
 incoming messages for local and remote delivering (by creating info/<messid>
 local/<messid> and remote/<messid> and removing todo/<messid>). See also
 INTERNALS. As next qmail-todo transmits the <messid> to qmail-send which will
 add this message into the priority queue which schedules the message for 
 delivery. 

INSTALL

 To enable the exttodo patch you need to define EXTERNAL_TODO while compiling
 qmail(-ldap) this can be done with the -D flag of cc (e.g. cc -DEXTERNAL_TODO).

 NOTE: the exttodo patch can also be used on qmail systems without the 
 qmail-ldap patch.
 
================================================================================

CONFIG FILES

 No additional control files are used or needed.

================================================================================

SETUP

 qmail-todo will be started by qmail-start and therefor no additional setup
 is needed.

 To verify that exttodo is running just check if qmail-todo is running.

================================================================================

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|
                           +-------+

Communication between qmail-send and qmail-todo

todo -> send:
   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.
   L<string>\0
          Dump string to the logger without adding additional \n or similar.
send -> todo:
   H      Got a SIGHUP reread ~/control/locals and ~/control/virtualdomains
   X      Quit ASAP.

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