common/config_opts: New default 20 bits/key bloom filters for RocksDB.

Signed-off-by: Mark Nelson <mnelson@redhat.com>

src/common/config_opts.h

@@ -983,15 +983,14 @@ OPTION(rocksdb_collect_compaction_stats, OPT_BOOL, false) //For rocksdb, this be
 OPTION(rocksdb_collect_extended_stats, OPT_BOOL, false) //For rocksdb, this behavior will be an overhead of 5%~10%, collected only rocksdb_perf is enabled.
 OPTION(rocksdb_collect_memory_stats, OPT_BOOL, false) //For rocksdb, this behavior will be an overhead of 5%~10%, collected only rocksdb_perf is enabled.
 OPTION(rocksdb_enable_rmrange, OPT_BOOL, false) // see https://github.com/facebook/rocksdb/blob/master/include/rocksdb/db.h#L253
-OPTION(rocksdb_bloom_bits_per_key, OPT_INT, 0) // number of bits per key to use for the bloom filter
+OPTION(rocksdb_bloom_bits_per_key, OPT_INT, 20) // number of bits per key to use for the bloom filter
 OPTION(rocksdb_cache_index_and_filter_blocks, OPT_BOOL, true) // put indexes and filters in block cache instead of always loading with open SST files.
 OPTION(rocksdb_cache_index_and_filter_blocks_with_high_priority, OPT_BOOL, true) // Index and filters have high priority in the block cache
 OPTION(rocksdb_pin_l0_filter_and_index_blocks_in_cache, OPT_BOOL, true) // Pin Level 0 indexes and filters in block cache.
 OPTION(rocksdb_index_type, OPT_STR, "two_level") // Type of index for SST files: binary_search, hash_search, two_level
 OPTION(rocksdb_partition_filters, OPT_BOOL, true) // Use partitioned filters.  See https://github.com/facebook/rocksdb/wiki/Partitioned-Index-Filters
 OPTION(rocksdb_metadata_block_size, OPT_U64, 4096) // Block size for index partions.  0 = rocksdb default
 
-
 // rocksdb options that will be used for omap(if omap_backend is rocksdb)
 OPTION(filestore_rocksdb_options, OPT_STR, "")
 // rocksdb options that will be used in monstore