Summary:
…ons (#4676)"
This reverts commit b32d087dbb.
`MemoryAllocator` needs to be with `Cache`, since cache entry can
outlive DB and block based table. The cache needs to hold reference to
memory allocator when deleting cache entry.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4697
Differential Revision: D13133490
Pulled By: yiwu-arbug
fbshipit-source-id: 8ef7e8a51263bfd929f892fd062665ff4ce9ce5a
* Introduced `Memoryllocator`, which lets the user specify custom allocator for memory in block cache.
### Public API Change
* `NO_ITERATORS` is divided into two counters `NO_ITERATOR_CREATED` and `NO_ITERATOR_DELETE`. Both of them are only increasing now, just as other counters.
### New Features
* Introduced `Memoryllocator`, which lets the user specify custom memory allocator for block based table.
### Bug Fixes
* Fixed Get correctness bug in the presence of range tombstones where merge operands covered by a range tombstone always result in NotFound.