--On Tuesday, November 3, 2020 6:41 PM +0100 Simone Piccardi piccardi@truelite.it wrote:
The problem manifests itself without periodicity and looking on the number of connection before it we could not see any usage peak. We tried to strace slapd threads during the problem, and they seem blocked on a mutex waiting for the one running at 100% (in a single CPU, user time). I'm attaching a top results during one of these events.
If you can attach to the process while this is occurring, I'd suggest obtaining a full GDB backtrace to see what the different slapd threads are doing at that time. Also, what mutex specifically is slapd waiting on?
From the behaviour I was suspecting (just a wild and uninformated guess) some indexing issue, blocking all access.
We tried to change tool-threads to 4 because I found it cited in some example as related to threads used for indexing, but the change has no effect. Re-reading last version of man-page, if I understand it correctly, it's effective only for slapadd etc.
Correct, this has setting has zero to do with a running slapd process. It only affects how many threads are used by slapadd & slapindex while doing indexing during offline operations. Additionally any value above 2 has no impact with back-mdb (it'll just be set back to 2).
So a first question is: there is any other configuration parameter about indexing that I can try?
If you really believe that this is indexing related, you should be able to tell this from the slapd logs at "stats" logging, where you would see a specific search taking a significant amount of time. However that generally does not lead to a system that's paused as searches shouldn't trigger a mutex issue like what you're describing.
Is this on RHEL7 or later? If you have both "stats" and "sync" logging enabled (the recommended setting for replicating nodes), what does the slapd log show is happening at this time?
Regards, Quanah
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Quanah Gibson-Mount Product Architect Symas Corporation Packaged, certified, and supported LDAP solutions powered by OpenLDAP: http://www.symas.com