Summary:
Note: This PR is the 3rd PR of a bigger PR stack (https://github.com/facebook/rocksdb/issues/9073) and depends on the second PR (https://github.com/facebook/rocksdb/pull/9071). **See changes from this PR only 00447324d0**
Context:
pdillinger brought up a good [point](https://github.com/facebook/rocksdb/pull/9073#discussion_r741478309) about lacking RAII support for per cache reservation in `CacheReservationManager` when reviewing https://github.com/facebook/rocksdb/pull/9073.
To summarize the discussion, the current API `CacheReservationManager::UpdateCacheReservation()` requires callers to explicitly calculate and pass in a correct`new_mem_used` to release a cache reservation (if they don't want to rely on the clean-up during `CacheReservationManager`'s destruction - such as they want to release it earlier).
While this implementation has convenience in some use-case such as `WriteBufferManager`, where [reservation](https://github.com/facebook/rocksdb/blob/main/memtable/write_buffer_manager.cc#L69-L91) and [release](https://github.com/facebook/rocksdb/blob/main/memtable/write_buffer_manager.cc#L109-L129) amounts do not necessarily correspond symmetrically and thus a flexible `new_mem_used` inputing is needed, it can be prone to caller's calculation error as well as cause a mass of codes in releasing cache in other use-case such as filter construction, where reservation and release amounts do correspond symmetrically and many code paths requiring a cache release, as [pointed](https://github.com/facebook/rocksdb/pull/9073#discussion_r741478309) out by pdillinger.
Therefore we decided to provide a new API in `CacheReservationManager` to update reservation with better RAII support for per cache reservation, using a handle to manage the life time of that particular cache reservation.
- Added a new class `CacheReservationHandle`
- Added a new API `CacheReservationManager::MakeCacheReservation()` that outputs a `CacheReservationHandle` for managing the reservation
- Updated class comments to clarify two different cache reservation methods
Tests:
- Passing new tests
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9130
Reviewed By: pdillinger
Differential Revision: D32199446
Pulled By: hx235
fbshipit-source-id: 1cba7c636e5ecfb55b0c1e0c2d218cc9b5b30b4e
2fbe32b0c1