Return to p5 CVS log

Up to [CSRG BSD Unix] / 43BSDReno / share / doc / ucs / mmdf

Annotation of 43BSDReno/share/doc/ucs/mmdf/p5, revision 1.1.1.1

1.1       root        1: .SH
                      2: Deliver
                      3: .PP
                      4: The \fBdeliver\fR process changed little until late 1984,
                      5: when a dead-host caching facility and advanced retry mechanisms
                      6: were added to \fBdeliver\fR.
                      7: Until then, the major changes to \fBdeliver\fR were
                      8: bug fixes and changes to enhance error recovery.
                      9: Most notably, the mechanism to return mail was made much more persistent.
                     10: In MMDFI, if a message could not be returned to the sender, it
                     11: was ``dropped on the floor''.  This is not acceptable.
                     12: The new mechanism first tries to return to the sender; if that fails,
                     13: an attempt is made to send the message to the local ``Postmaster''
                     14: address.  If this too fails, then \fBdeliver\fR tries to write the message
                     15: into a ``dead letter'' file
                     16: (usually /usr/mmdf/lock/home/DeadLetters).
                     17: The last resort is to scream loudly into the log files.
                     18: .PP
                     19: The recent changes to \fBdeliver\fR are
                     20: designed to reduce \fBdeliver\fR's load
                     21: on a system that handles a large amount of mail.
                     22: The first change is to move the dead-host caching function out
                     23: of the channels (currently only SMTP) and into \fBdeliver\fR.  This has
                     24: two advantages.
                     25: First, \fBdeliver\fR no longer has to hand every address to
                     26: the channel to find out that the host is dead.  This was expensive, since
                     27: communications between \fBdeliver\fR and the channel
                     28: are interactive using pipes
                     29: and thus involved a great deal of context-switching and pipe I/O.
                     30: Second, the dead-host caching is now a generally available facility that
                     31: can be used by any channel without duplication of code.
                     32: .PP
                     33: The second change is to add a mechanism for storing the retry history
                     34: for each dead host on each channel including retry count and last retry
                     35: time.
                     36: From this information it is possible to implement intelligent
                     37: retry strategies using exponential backoff and maximal retry times.
                     38: This greatly reduces the overhead caused by recalcitrant hosts
                     39: that are unavailable over a long period of time.
                     40: The retry history change is conditionally compiled
                     41: into deliver since it can,
                     42: by design, use quite a bit of memory if there are a lot of dead
                     43: hosts or pending messages (or both!).
                     44: Machines with a relatively limited address space may not
                     45: be able to use this feature.

This archive runs on limited infrastructure. Preserving old code on modern bandwidth. Automated agents are requested to crawl responsibly.