CPU overhead from JOIN::join_free is about 2X larger with MyRocks than with InnoDB #1485
Description
I am looking at flamegraphs from sysbench with a cached database and 1 client. A common problem I see is that the percentage of samples that JOIN::join_free and its callees accounts for is ~2X larger in MyRocks than in InnoDB with simple microbenchmarks.
From the range-covered-pk.range100 microbenchmark (covered range query of PK index) the percentage of samples is 0.90% for InnoDB and 2.18% for MyRocks
JOIN::join_free from InnoDB:
0.90% JOIN::join_free
0.72% mysql_unlock_read_tables
0.70% unlock_external
0.68% handler::ha_external_lock
0.62% ha_innobase::external_lock
0.50% innobase_commit
And from MyRocks
2.18% JOIN::join_free
1.22% JOIN::cleanup
1.15% cleanup_table
1.09% ha_rocksdb::index_end
... destructors - some MyRocks and many more RocksDB class instances
0.88% mysql_unlock_read_tables
0.85% unlock_external
0.81% handler::ha_external_lock
0.75% ha_rocksdb::external_lock
0.70% Rdb_transaction::commit
0.66% Rdb_transaction_impl::rollback
...
Flamegraphs
