[BUG] OpenSearchMergePolicy should not allow segment merge if enough amount of space is not available for the segment merge to go through

[RS146BIJAY]

Describe the bug
Currently, OpenSearch allows segment merge to go through even though not enough amount of space is available. This can cause available space on the node to drop below flood stage mark (even though OpenSearch has applied blocks on cluster), even causing available space on the node to reach to 0. This can cause FSHealthService checks to fail for this node, ultimately causing these nodes to be removed from cluster.

Expected behavior
OpenSearchMergePolicy should not allow segment merge if enough amount of space is not available for the segment merge to go through

[anasalkouz]

Hi @RS146BIJAY, thanks for reporting the issue, I am surprised that this validation is not there. Seems to me as a basic validation for the segment merge process. Are you actively working on this?

[RS146BIJAY]

@anasalkouz Yes we are actively working on all this issue (all included under the parent META issue)