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(ITS#3832) slapd-read occasionally hangs while testing back-meta

Full_Name: Pierangelo Masarati
Version: HEAD
OS: Linux, Solaris 8
URL: ftp://ftp.openldap.org/incoming/
Submission from: (NULL) (
Submitted by: ando

It may occur (very rarely) that a client, usually slapd-read, hangs while
testing back-meta in test036.  The client appears to hang on ldap_bind_s().  The
funny thing is that the proxy server doesn't show any activity and, from the
logs, nothing about that connection appears.  As soon as I attach the slapd-read
process with gdb, the select() (or the poll()) in ldap_pvt_select() wakes up,
and the client terminates with a "serverUnavailable" error.  Nothing significant
appears from the trace of both processes (in slapd there's little to say: all
threads are idling).

Unfortunately I don't have a trace handy, but in case I can try to produce the
condition (it's rare, but it may definitely occur).  A similar behavior was
noted in back-meta when binding to the remote server under heavy load during
concurrency tests; I cured it by always performing asynchronous binds (back-ldap
already always used asynchronous binds) and by adopting some timeout/retry
policy when binding.

My point is that I'd like some advice about what direction to follow in
investigating the issue.  At the same time, I'm filing this problem as an ITS
because I want to keep track of it, since it keeps appearing, although very