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From Paul Marquis <pmarq...@iname.com>
Subject apache-api/6793: Apache unneccesarily respawns child pipe processes
Date Fri, 03 Nov 2000 17:11:03 GMT

>Number:         6793
>Category:       apache-api
>Synopsis:       Apache unneccesarily respawns child pipe processes
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    apache
>State:          open
>Class:          sw-bug
>Submitter-Id:   apache
>Arrival-Date:   Fri Nov 03 09:20:01 PST 2000
>Originator:     pmarquis@iname.com
>Release:        <= 1.3.14
Linux c194.clearway.com 2.2.15pre3 #3 Sat Jan 29 18:02:45 CET 2000 ppc unknown
Linux c178.clearway.com 2.2.14-5.0 #1 Tue Mar 7 21:07:39 EST 2000 i686 unknown
When Apache is compiled with Reliable Piped Logs on UNIX, which appears to
be the default, the caretaker process polls child processes that are log
handlers for writability using select() to determine if the process is dead.
If it determines the process is dead, it kills and restarts it. Unfortunately,
select() will return a failure simply when the pipe is full and the child
just hasn't had a chance to read it.  Child log handlers will be unnecessarily

This problem is exacerbated on Linux where select() will return failure on
pipes well before the pipe is full -- a single byte will cause this situation.
This is a "feature" of select() on Linux.

Dean Gaudet has suggested a fix, and I include the text of a message from the
Apache Development mailing list below:


the test for write in the other_child code is flawed logic... the pipe
could be unwriteable just simply because it's full.  apache shouldn't nuke
the logger for that...

my suggestion is to just get rid of the writeable test.  if a server
blocks up because the logger is blocked it'll be obvious from the
scoreboard, and the fix will be to kill the logger manually.

as it is currently, this feature is more a liability than a feature :)

(i obviously never tested it well enough under load.)
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