Summary:
This PR does two things:
1. Adds a new table property `newest_key_time`
2. Uses this property to improve TTL and temperature change compaction.
### Context
The current `creation_time` table property should really be named `oldest_ancestor_time`. For flush output files, this is the oldest key time in the file. For compaction output files, this is the minimum among all oldest key times in the input files.
The problem with using the oldest ancestor time for TTL compaction is that we may end up dropping files earlier than we should. What we really want is the newest (i.e. "youngest") key time. Right now we take a roundabout way to estimate this value -- we take the value of the _oldest_ key time for the _next_ (newer) SST file. This is also why the current code has checks for `index >= 1`.
Our new property `newest_key_time` is set to the file creation time during flushes, and the max over all input files for compactions.
There were some additional smaller changes that I had to make for testing purposes:
- Refactoring the mock table reader to support specifying my own table properties
- Refactoring out a test utility method `GetLevelFileMetadatas` that would otherwise be copy/pasted in 3 places
Credit to cbi42 for the problem explanation and proposed solution
### Testing
- Added a dedicated unit test to my `newest_key_time` logic in isolation (i.e. are we populating the property on flush and compaction)
- Updated the existing unit tests (for TTL/temperate change compaction), which were comprehensive enough to break when I first made my code changes. I removed the test setup code which set the file metadata `oldest_ancestor_time`, so we know we are actually only using the new table property instead.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/13083
Reviewed By: cbi42
Differential Revision: D65298604
Pulled By: archang19
fbshipit-source-id: 898ef91b692ab33f5129a2a16b64ecadd4c32432
