set a specific shard id to force merge and clean commit logs.

[HowookJeong]

This is force merge about a specific shard of index using _routing.

When we use _routing, a specific shard increase a lot of segment files and shard size.

I think, it doesn't need to force merge all shard of index.

Thanks.

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[cla-checker-service]

❌ Author of the following commits did not sign a Contributor Agreement:
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[HowookJeong]

I already signed a Contributor Agreement.
Please_DocuSign_Individual_Contributor_Licen .pdf

[elasticmachine]

Pinging @elastic/es-core-features (Team:Core/Features)

[dakrone]

Thanks for opening this @HowookJeong. We did discuss this as a team, however, we decided that this is an edge case that we don't currently want to support. Doing this kind of force merging would make debugging segmentation issues harder and also integrating it into ILM would be very difficult. For now I am going to close this, but if there is enough interest in the future we can always revisit it.