MyRocks tuning for better false positive rate

With MyRocks, you can control the size of the bloom filter bitmap with the column family parameter memtable_prefix_bloom_size_ratio. For good performance, the filter blocks are cached in the RocksDB block cache and normally stay there since they are accessed frequently.

The filter_policy variable controls the number of bits per key in the column family settings. By default, 10 bits are used per key which yields less than 1% of false positives.

Bloom Filter factors

1. Size of the bitmap
2. Number of keys in the list
3. Number of bits set to “1” for each key value

The number of false positives would be low, but 1GB is a lot of memory. In most cases a bitmap of a few hundred bytes is sufficient.

List of all of key concepts