Percona Server 引入 MyRocks

看到「MyRocks Engine: Things to Know Before You Start」這篇,才發現原來一月的時候 Percona Server 就已經將 MyRocks GA (General Availability) 了:「Percona Server for MySQL 5.7.20-19 Is Now Available」。

New Features:
Now MyRocks Storage Engine has General Availability status.


Now if you use Percona repositories, you can simply install MyRocks plugin and enable it with ps-admin --enable-rocksdb.

另外文章裡也提到了重要的差異 (在「What other differences should you be aware of?」這段),像是他並不是每個 table 都一個檔案,而是像早期 InnoDB 的作法,整個一包:

Let’s look at the directory layout. Right now, all tables and all databases are stored in a hidden .rocksdb directory inside mysqldir. The name and location can be changed, but still all tables from all databases are stored in just a series of .sst files. There is no per-table / per-database separation.

另外提到可以看到 Engine 的代碼是 ROCKSDB (從 ENGINE=ROCKSDB 那段看到的)。然後是 Isolation level 的支援度,只有 READ-COMMITTEDSERIALIZABLE,沒有 REPEATABLE-READ

Keep in mind that at this time MyRocks supports only READ-COMMITTED and SERIALIZABLE isolation levels. There is no REPEATABLE-READ isolation level and no gap locking like in InnoDB. In theory, RocksDB should support SNAPSHOT isolation level. However, there is no notion of SNAPSHOT isolation in MySQL so we have not implemented the special syntax to support this level. Please let us know if you would be interested in this.

然後 bulk load 在資料量超過記憶體大小時會有已知的 crash 問題:

For bulk loads, you may face problems trying to load large amounts of data into MyRocks (and unfortunately this might be the very first operation when you start playing with MyRocks as you try to LOAD DATA, INSERT INTO myrocks_table SELECT * FROM innodb_table or ALTER TABLE innodb_table ENGINE=ROCKSDB). If your table is big enough and you do not have enough memory, RocksDB crashes. As a workaround, you should set rocksdb_bulk_load=1 for the session where you load data.

然後目前沒有像 XtraBackup 的工具可以用,現階段如果要備份的話得透過傳統的方式來做 (mysqldump 或是 filesystem snapshot):

Right now there is no hot backup software like Percona XtraBackup to perform a hot backup of MyRocks tables (we are looking into this). At this time you can use mysqldump for logical backups, or use filesystem-level snapshots like LVM or ZFS.


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