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For merge, whenever a new disk component is added for an index (due to flush or merge), the corresponding merge policy would be notified. The merge policy checks the existing disk components for an index, and if it decides some disk components need to be merged, it would submit the merge request to the LSMIOOperationScheduler. By default, the merge request is sent for each index independently. However, currently we have a CorrelatedPrefixPolicy which only checks the disk components of the primary index, and sends a corresponding merge request for all secondary indexes together when the primary index needs to be merged.

Correlated Merge Policy

Proposed Solution