Re: (ITS#7013) OpenLDAP freezes and doesn't respond

[hyc@symas.com]

cgrosjean@janua.fr wrote:
> Full_Name: Cyril Grosjean
> Version: 2.4.26
> OS: Red Hat Enterprise Linux Server release 5.4 (Tikanga)
> URL: ftp://ftp.openldap.org/incoming/
> Submission from: (NULL) (82.66.198.206)
>
>
> My OpenLDAP server freezes, after a few requests, and I can't understand why.
> I have a few LDAP clients (ldapsearch, a custom Java app. and
> ApacheDirectoryStudio), running from different systems, either locally on the
> OpenLDAP server, or on another OpenLDAP server, or on a remote workstation, and
> none manages to get an answer from OpenLDAP. The connection is established but
> each client gets stuck waiting for any result.
>
> We can reproduce the freeze, after a few requests coming from the custom Java
> application. The problem doesn't occur if we don't use that application.
>
>
> The last time, it occured only a few minutes after the OpenLDAP daemon was
> restarted, under very low load.
> I use OpenLDAP 2.4.26, over Red Hat Enterprise Linux Server release 5.4
> (Tikanga), Kernel version 2.6.18-164.el5, amd64 architecture over VMWare.
> I also use BDB 4.8.30, and OpenLDAP's been compiled with the following options:
>
> ./configure --prefix=/opt/openldap-2.4.26 --enable-dynamic=yes
> --enable-dynlist=yes --enable-memberof=yes --enable-ppolicy=yes
> --enable-accesslog=yes --enable-sssvlv=yes
>
> I noticed only 60 to 70 established connections on port 389 (according to
> netstat) when the freeze occurs.
>
> The OpenLDAP server is set in syncrepl mirror mode replication, and the other
> OpenLDAP server (only used as a hot stand-by) works fine (but doesn't receive
> any load). However, one can reproduce the problem with replication disabled.

Looks like you have a thread blocked trying to modify a record, while all the 
other writer threads are blocked waiting for that writer to complete. The 
output of db_stat -CA would help to indicate why the writer is blocked.

It also looks like you've configured your replication with mirrormode and 
delta-syncrepl. This combination is not yet supported in OpenLDAP, certainly 
not in 2.4.26. It may be supported in 2.4.27, depending on how our ongoing 
testing turns out.

-- 
   -- Howard Chu
   CTO, Symas Corp.           http://www.symas.com
   Director, Highland Sun     http://highlandsun.com/hyc/
   Chief Architect, OpenLDAP  http://www.openldap.org/project/