Differences Between MyRocks Variants

MyRocks is available in

• Facebook's (FB) MySQL branch (originally based on MySQL 5.6)
• MariaDB (from 10.2 and 10.3)
• Percona Server from 5.7

This page lists differences between these variants.

RocksDB Data Location

FB and Percona store RocksdDB files in $datadir/.rocksdb. MariaDB puts them in $datadir/#rocksdb. This is more friendly for packaging and OS scripts.

Compression Algorithms

• FB's branch doesn't provide binaries. One needs to compile it with appropriate compression libraries.

• In MariaDB, available compression algorithms can be seen in the rocksdb_supported_compression_types variable. From MariaDB 10.7, algorithms can be installed as a plugin. In earlier versions, the set of supported compression algorithms depends on the platform.
  • On Ubuntu 16.04 (current LTS) it is Snappy,Zlib,LZ4,LZ4HC .
  • On CentOS 7.4 it is Snappy,Zlib.
  • In the bintar tarball it is Snappy,Zlib.
• Percona Server supports: Zlib, ZSTD, LZ4 (the default), LZ4HC. Unsupported algorithms: Snappy, BZip2, XPress.

RocksDB Version Information

• FB's branch provides the rocksdb_git_hash *status* variable.
• MariaDB provides the @@rocksdb_git_hash *system* variable.
• Percona Server doesn't provide either.

RocksDB Version

• Facebook's branch uses RocksDB 5.10.0 (the version number can be found in include/rocksdb/version.h)

commit ba295cda29daee3ffe58549542804efdfd969784
Author: Andrew Kryczka <andrewkr@fb.com>
Date:   Fri Jan 12 11:03:55 2018 -0800

• MariaDB currently uses 5.8.0

commit 9a970c81af9807071bd690f4c808c5045866291a
Author: Yi Wu <yiwu@fb.com>
Date:   Wed Sep 13 17:21:35 2017 -0700

• Percona Server uses 5.8.0

commit ab0542f5ec6e7c7e405267eaa2e2a603a77d570b
Author: Maysam Yabandeh <myabandeh@fb.com>
Date:   Fri Sep 29 07:55:22 2017 -0700

Binlog Position in information_schema.rocksdb_global_info

• FB branch provides information_schema.rocksdb_global_info type=BINLOG, NAME={FILE, POS, GTID}.
• Percona Server doesn't provide it.
• MariaDB doesn't provide it.

One use of that information is to take the output of myrocks_hotbackup and make it a new master.

Gap Lock Detector

• FB branch has a "Gap Lock Detector" feature. It is at the SQL layer. It can be controlled with gap_lock_XXX variables and is disabled by default (gap-lock-raise-error=false, gap-lock-write-lock=false).

• Percona Server has gap lock checking ON but doesn't seem to have any way to control it? Queries that use Gap Lock on MyRocks fail with an error like this:

insert into tbl2 select * from tbl1;
ERROR 1105 (HY000): Using Gap Lock without full unique key in multi-table or multi-statement transactions
is not allowed. You need to either rewrite queries to use all unique key columns in WHERE equal conditions,
or rewrite to single-table, single-statement transaction.  Query: insert into tbl2 select * from tbl1

• MariaDB doesn't include the Gap Lock Detector.

Generated Columns

• Both MariaDB and Percona Server support generated columns, but neither one supports them for the MyRocks storage engine (attempts to create a table will produce an error).

• Invisible columns in MariaDB 10.3 are supported (as they are an SQL layer feature).

rpl_skip_tx_api

Facebook's branch has a performance feature for replication slaves, rpl_skip_tx_api. It is not available in MariaDB or in Percona Server.

Details

The above comparison was made using

• FB/MySQL 5.6.35
• Percona Server 5.7.20-19-log
• MariaDB 10.2.13 (MyRocks is beta)