[Timestamp Pinning in Remote Store] Remote translog garbage collection changes

[sachinpkale]

Is your feature request related to a problem? Please describe

As part of shallow snapshot optimisations, we are introducing timestamp based implicit locking support. This feature will be called Timestamp Pinning in remote backed storage. When a timestamp is pinned, remote store garbage collectors will skip deleting data corresponding to the timestamp.

Describe the solution you'd like

As part of this solution, we need following changes to segment store garbage collection

• Each data node keeps an in-memory data structure remote_store_pinned_timestamps (this is updated regularly as part of [Timestamp Pinning in Remote Store] Scheduler to fetch pinned timestamp list from remote store #15062)
• If the last update time of remote_store_pinned_timestamps is > X mins, skip garbage collection.
• Fetch metadata files in sorted order (which generally is reverse-chronological order but not always)
• If timestamp of a metadata file md1 is > pinned_timestamp_a and the timestamp of next metadata file md2 <= pinned_timestamp_a add md2 to pinned_metadata_files
• Skip deletion of metadata files in pinned_metadata_files and corresponding data files

Related component

Storage:Remote

[sachinpkale]

We also need to handle garbage collection on index delete.