Punchlist for ZSTD Compression

[sarthakaggarwal97]

Is your feature request related to a problem? Please describe.
The issue entails the tasks that are essential to ensure robustness for ZSTD.

Describe the solution you'd like

• Long running tests to verify for any corruption or memory leaks
• Reindexing between different compression codecs
• Create a snapshot, delete an index, restore from snapshot
• Split/Shrink api since they modify segments to some extent
• Index Blocks
• Upgrade from the earliest version supported for version upgrade to 2.x (from os 1.0/es 7.9)
• Upgrade from the n-1 version
• Minor version upgrade with zstd and zstd no dict segments
• Force merge of segments with multiple compression mode into zstd
• Close an index, update the setting, test the indexing and search flows, snapshots, etc i.e. with multiple compression settings on different segments
• Move ZStd compression codecs to plugins from core (Optional)

Additional Context
#7908

[dblock]

#9476 (review)

This is a violation of semver, I propose we close this issue. Some of the checkboxes above do make a ton of sense though as standalone items.

[sarthakaggarwal97]

@dblock I agree with you. Most of these checkboxes were covered as a part of testing for #7908, let me know if we should create items for any specific checkbox so that we don't lose them. Thank you!

[dblock]

@dblock I agree with you. Most of these checkboxes were covered as a part of testing for #7908, let me know if we should create items for any specific checkbox so that we don't lose them. Thank you!

Yes, good idea. Up to you if you want to create the remaining ones as standalone features/issues and reference them back to here or rename this issue as something like "punchlist for zstd" :) I would keep the controversial ones like "move to plugin" here for now because they assume we move zstd back to being behind a feature flag/completely optional.