We've got, again, a little mystery here. Our main text collection is suddenly running at a snail's pace since Monday very early in the morning, the monitoring graph for response time went up. This is not unusual for Solr so the JVM's were all restarted, it always solves a sluggish collection, not this time. They were restarted yesterday as well, but no change. The VM's Solr is running on were rebooted today, also no change.

Not all queries are slow all the time, a random query is just slow sometimes, or sometime most of the times. All 6 replica's are sometimes slow.

We also took a good look at our monitoring, JVM heap was normal, IO was normal, CPU was normal until the first restart. CPU usage is since the first restart erratic but not worryingly off the charts, just not 'normal' as usual.

No changes were made to the collection for days before it became sluggish.

CPU sampling with VisualVM is not helpful either, nothing really stands out, especially when i compare it to another cluster that is still healthy. GC is also normal.

So, any ideas out here?

Many thanks,