We recently upgraded one of our Elastic Search servers from Oracle Linux 6.9 to 7.4. After the upgrade the server has over 1 million open files allocated to the ElasticSearch process. I am using version 5.2 of Elastic. The cluster has 228 indexes and 710 shards.
I compared this with another server that was not upgraded (still on Linux 6.9). That server has about 16,000 open files for the ElasticSearch process. That server is also running version 5.2 of Elastic. The cluster has 385 indexes and 1,221 shards.
Has anyone experienced this issue? Any reason for the large number of open files?