Summary:
introduce the class WBWIMemTable that implements ReadOnlyMemTable interface with data stored in a WriteBatchWithIndex object.
This PR implements the main read path: Get, MultiGet and Iterator. It only supports Put, Delete and SingleDelete operations for now. All the keys in the WBWIMemTable will be assigned a global sequence number through WBWIMemTable::SetGlobalSequenceNumber().
Planned follow up PRs:
- Create WBWIMemTable with a transaction's WBWI and ingest it into a DB during Transaction::Commit()
- Support for Merge. This will be more complicated since we can have multiple updates with the same user key for Merge.
- Support for other operations like WideColumn and other ReadOnlyMemTable methods.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/13123
Test Plan: * A mini-stress test for the read path is added as a new unit test
Reviewed By: jowlyzhang
Differential Revision: D65633419
Pulled By: cbi42
fbshipit-source-id: 0684fe47260b41f51ca39c300eb72ca5bc9c5a3b
