Hi Florian,
the 4,700 logs/sec rate is from a specific CMA/DLS?
what is the incoming log-rate from other CMAs? the total rate to the MDS?
Is this the main & the problematic one, that keeps getting backlogged-up up to 1 hour of delay.
This is complex, it won't probably be fixed by trying to adjust the indexer threads.
It may, but it might require some tweaking and testing & there's no guarantees for improvement.
Your server is currently configured with eight (8) Pre-indexing & Index threads for each CMA.
you could try to reduce it to 4 (and then even 2) on the MDS level $INDEXERDIR via the .conf file, as was written above.
assuming you have many CMAs, which may interefere with each other.
but it's a guess. it may not help.
Your logs are probably either extremely heavy (high ratio of Threat logs) and/or some other underlying issue that requires a deeper TAC investigation, cause there's no apparent reason that your strong server wouldn't hold a ~5K logs/sec load for online log-indexing without any delay/backlog.
Run: SmartEventCollectLogs & send me the output for another attempt to help.
Also: with such an environment I can suggest adding a separate log-server/MLM.
Best open a TAC ticket.