Benchmarking RocksDB

To benchmark RocksDB outside of CockroachDB, use upstream's db_bench tool.

To build it, run:

$ git clone https://github.com/facebook/rocksdb.git
$ cd rocksdb
$ make -jNCPUS db_bench DEBUG_LEVEL=0

If you see an error about needing to install "gflags", you need to install https://github.com/gflags/gflags. On Debian, sudo apt-get install libgflags-dev; on macOS, brew install gflags. Then make clean. RocksDB won't relink against gflags unless you do a make clean first.

To create a database with 1000 range tombstones, for example:

$ ./db_bench -benchmarks=fillrandom -write_buffer_size=67108864 -level0_file_num_compaction_trigger=4 -max_background_compactions=32 -level0_slowdown_writes_trigger=8 -level0_stop_writes_trigger=12 -num_levels=4 -min_level_to_compress=2 -compression_type=zlib -compression_ratio=0.5 -block_size=16384 -open_files=10000 -target_file_size_base=1048576 -max_bytes_for_level_base=268435456 -writes_per_range_tombstone=50000 -range_tombstone_width=50000 -max_num_range_tombstones=1000 -num=50000000 -db=/tmp/SOMENAME

It's not clear how many of these options are actually required, but they were lifted wholesale from an upstream PR with benchmarking instructions.

You can then run benchmarks against the generated database:

./db_bench -benchmarks=readrandom -readonly -use_existing_db=true -open_files=10000 -num=50000000 -reads=1000000 -cache_size=1073741824 -threads=32 -db=/tmp/SOMENAME

Make sure -use_existing_db=true is specified. The default creates a blank empty database in the database folder, even if one already exists.