concurrency problems with "set=" directive

["Y. Zoolinski" <yzoolinski@lavache.com>]

The problem appeared when I wanted to migrate my directory from openLdap 
2.0.27 (redhat 7.X) to openLdap 2.0.27 (redhat 9).
When I run requests on concurrency, results becomes wrong, that means 
that instead of finding 5 results (for example) it gonna return me 0 and 
somethimes 1 or 2 rows.
I run concurrency by starting two shell scripts (on 2 différent 
machines) executing loop on ldapsearch 1000 times.

My directory contains users and lists of people. I want to allow users 
to see people only if they have "myattribut" set to "yes" so I'm using 
directive "Set=" in my acl to filter output :

-- slapd.conf --
...
attributetype ( 1.1.2.4.6 NAME ( 'myattribut' ) SUP name )
...
access to dn.regex="ou=level2,o=level1$"
   by set="user/myattribut & [yes]" read
...

In my slapd.conf, I've tried several config by playing with 
"concurrency", "threads", "cachesize", "dbcachesize" but none solves my 
problem.

Remarque on the case "concurrency 1" and "threads 1" : whereas in the 
others context the problem appears as soon as I start my second shell 
script, in this particular case, the concurrency problem appears later, 
after many hundreds of requests.

Just another point, after the result be corrupted, it stays as is even 
if I start only one shell script.

Have you any idea ?

Thanks and Regards