Greetings,

I am observing a rather strange issue in the following setup:

* 1 OpenLDAP master server (2.4.31)

* 4 OpenLDAP slave servers (2.4.40)

* The OpenLDAP slaves do forward any update attempt to the master using the chain overlay / proxyauthz (mainly to update the pwdFailureTime attribute for ppolicy)

If I try to shut the master down (for maintenance let's say), the slaves behave properly, then begin to deadlock one after each other after a few minutes (by deadlock I mean no log output anymore, and any ldapwhoami / ldapsearch request connects and then times out)

On the attached image, I monitored at the same time one of the slaves using collectd, to keep an eye on cn=monitor data (the period between 15:24:30 and 15:26:00 has been extrapolated by Grafana, no data is available at this time since cn=monitor access also deadlocks)

I can see that backload / pending threads and waiters seem to increase gradually until the server gets unresponsive.

I found nothing on the ML (except https://www.openldap.org/lists/openldap-technical/200912/msg00112.html) or searching for clues, Is this predictable behavior or and obvious misconfiguration, or it is an interesting occastion to dig a bit deeper ?

Thanks in advance,