Summary: With `table_options.cache_index_and_filter_blocks = true`, index and filter blocks are stored in block cache. Then people are curious how much of the block cache total size is used by indexes and bloom filters. It will be nice we have a way to report that. It can help people tune performance and plan for optimized hardware setting. We add several enum values for db Statistics. BLOCK_CACHE_INDEX/FILTER_BYTES_INSERT - BLOCK_CACHE_INDEX/FILTER_BYTES_ERASE = current INDEX/FILTER total block size in bytes.
Test Plan:
write a test case called `DBBlockCacheTest.IndexAndFilterBlocksStats`. The result is:
```
[gzh@dev9927.prn1 ~/local/rocksdb] make db_block_cache_test -j64 && ./db_block_cache_test --gtest_filter=DBBlockCacheTest.IndexAndFilterBlocksStats
Makefile:101: Warning: Compiling in debug mode. Don't use the resulting binary in production
GEN util/build_version.cc
make: `db_block_cache_test' is up to date.
Note: Google Test filter = DBBlockCacheTest.IndexAndFilterBlocksStats
[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from DBBlockCacheTest
[ RUN ] DBBlockCacheTest.IndexAndFilterBlocksStats
[ OK ] DBBlockCacheTest.IndexAndFilterBlocksStats (689 ms)
[----------] 1 test from DBBlockCacheTest (689 ms total)
[----------] Global test environment tear-down
[==========] 1 test from 1 test case ran. (689 ms total)
[ PASSED ] 1 test.
```
Reviewers: IslamAbdelRahman, andrewkr, sdong
Reviewed By: sdong
Subscribers: andrewkr, dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D58677
Aaron Gao