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.

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