MyRocks Performance Troubleshooting

A guide to diagnosing and resolving performance issues in MyRocks using status variables, `SHOW ENGINE ROCKSDB STATUS`, and RocksDB performance context.

MyRocks exposes its performance metrics through several interfaces:

• Status variables

• SHOW ENGINE ROCKSDB STATUS

• RocksDB's perf context

the contents slightly overlap, but each source has its own unique information, so be sure to check all three.

Status Variables

Check the output of

SHOW STATUS LIKE 'Rocksdb%'

See MyRocks Status Variables for more information.

SHOW ENGINE ROCKSDB STATUS

This produces a lot of information.

One particularly interesting part is compaction statistics. It shows the amount of data on each SST level and other details:

*************************** 4. row ***************************  Type: CF_COMPACTION  Name: default Status:  ** Compaction Stats [default] ** Level Files Size Score Read(GB) Rn(GB) Rnp1(GB) Write(GB) Wnew(GB) Moved(GB) W-Amp Rd(MB/s) Wr(MB/s) Comp(sec) Comp(cnt) Avg(sec) KeyIn KeyDrop ----------------------------------------------------------------------------------------------------------------------------------------------------------  L0 3/0 30.16 MB 1.0 0.0 0.0 0.0 11.9 11.9 0.0 1.0 0.0 76.6 159 632 0.251 0 0  L1 5/0 247.54 MB 1.0 0.7 0.2 0.5 0.5 0.0 11.6 2.6 58.5 44.1 12 4 2.926 30M 10M  L2 112/0 2.41 GB 1.0 0.6 0.0 0.6 0.5 -0.1 11.4 43.4 55.2 45.9 11 1 10.827 21M 3588K  L3 466/0 8.91 GB 0.4 0.0 0.0 0.0 0.0 0.0 8.9 0.0 0.0 0.0 0 0 0.000 0 0  Sum 586/0 11.59 GB 0.0 1.3 0.2 1.0 12.8 11.8 32.0 1.1 7.1 72.6 181 637 0.284 52M 13M  Int 0/0 0.00 KB 0.0 0.9 0.1 0.8 0.8 0.0 0.1 20.5 48.4 45.3 19 6 3.133 33M 3588K

Performance Context

RocksDB has an internal mechanism called "perf context". The counter values are exposed through two tables:

• INFORMATION_SCHEMA.ROCKSDB_PERF_CONTEXT_GLOBAL - global counters

• INFORMATION_SCHEMA.ROCKSDB_PERF_CONTEXT - Per-table/partition counters

By default statistics are NOT collected. One needs to set rocksdb_perf_context_level to some value (e.g. 3) to enable collection.

_{This page is licensed: CC BY-SA / Gnu FDL}