I am working on a single node cluster that currently has about 700 indexes each with 5 shards. I am seeing slow starts of the Elasticsearch node (up to 4m30s). I have found the following parameter in documentation:
I see it's default value is 4 allowing for 4 concurrent threads to recover primaries from disk. I bumped this up to a higher number and I am getting way better node restart times (starting now in about 1m30s with setting value equal to 128). I am completely winging it on the number of threads here and playing with numbers from 16 to as high as 256 (although I noticed that for my example once I reach a certain number of threads I no longer gain any significant improvement).
Is there any maximum number recommendation for this parameter (maybe cores on server?). I wonder why 4 is the default?
Also, is there any other configuration parameter you know about that might help speed up the node restart?