Elasticsearch version (bin/elasticsearch --version):
6.5.2

Plugins installed: []
elasticsearch-prometheus-exporter

JVM version (java -version):
default docker version

OS version (uname -a if on a Unix-like system):
default docker version

Description of the problem including expected versus actual behavior:
Occasionally we see the cluster turn red. Looking at a thread dump I can see these threads running:
https://gist.github.com/johnskopis/bb3012a2f2b56304cc31d2861b6bfe0

Seems to me the management threadpool becomes full. Does this sound plausible?

This seems to be from monitoring using elasticsearch-prometheus-exporter.

Seems to be expensive to calculate completion stats:

https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-stats.html

Do the stats need to run in management TP?

Can it be less expensive?

Can the default change from all fields to no fields?

Any other ideas?

Thanks