I have a cluster with 8 nodes and all the nodes almost always show a heap usage in the high 70%. I never seem to see a "pretty jigsaw" pattern in the heap usage.
All the nodes are in individual systems that have 64GB of RAM. The nodes are given 24GB of RAM. So they should have plenty of space.
I've looked at fielddata size and it is almost always less than 1GB. I've cleared it several times (through both restarting the node and running the clear cache command).
We have 2446 indices (we have several indices that are daily rollovers and have data back for almost 1 year). Most of the indices have 4 shards plus a backup. The total number of shards is 17745.
Is heap usage supposed to be always high? How do I find out what is using heap usage?