Summary:
For clean-up and in preparation for some other anticipated changes, including
* A new dynamically-scaling variant of HyperClockCache
* SecondaryCache support for HyperClockCache
This change does some refactoring for current and future code sharing and reusability. (Including follow-up on https://github.com/facebook/rocksdb/issues/10843)
## clock_cache.h
* TBD whether new variant will be a HyperClockCache or use some other name, so namespace is just clock_cache for the family of structures.
* A number of helper functions introduced and used.
* Pre-emptively split ClockHandle (shared among lock-free clock cache variants) and HandleImpl (specific to a kind of Table), and introduce template to plug new Table implementation into ClockCacheShard.
## clock_cache.cc
* Mostly using helper functions. Some things like `Rollback()` and `FreeDataMarkEmpty()` were not combined because `Rollback()` is Table-specific while `FreeDataMarkEmpty()` can be used with different table implementations.
* Performance testing indicated that despite more opportunities for parallelism, making a local copy of handle data for processing after marking an entry empty was slower than doing that processing before marking the entry empty (but after marking it "under construction"), thus avoiding a few words of copying data. At least for now, this answers the "TODO? Delay freeing?" questions (no).
Pull Request resolved: https://github.com/facebook/rocksdb/pull/10887
Test Plan:
fixed a unit testing gap; other minor test updates for refactoring
No functionality change
## Performance
Same setup as https://github.com/facebook/rocksdb/issues/10801:
Before: `readrandom [AVG 81 runs] : 627992 (± 5124) ops/sec`
After: `readrandom [AVG 81 runs] : 637512 (± 4866) ops/sec`
I've been getting some inconsistent results on restarts like the system is not being fair to the two processes, so I'm not sure there's such a real difference.
Reviewed By: anand1976
Differential Revision: D40959240
Pulled By: pdillinger
fbshipit-source-id: 0a8f3646b3bdb5bc7aaad60b26790b0779189949
Peter Dillinger
cc8c8f6958