Benchmark by db_bench

db_bench is in official rocksdb, many people are using db_bench.

To use db_bench of TerarkDB's rocksdb, you need a little extra work:

env LD_LIBRARY_PATH=/path/to/terark-zip-rocksdb-xxx/lib:$LD_LIBRARY_PATH LD_PRELOAD=libterark-zip-rocksdb-r.so ./db_bench --benchmarks=fillrandom,readrandom