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Last updated: 2022-06-13 15:37:15

    TXRocks is a transactional storage engine developed by Tencent's TXSQL team based on RocksDB. It saves more storage space and has a lower write amplification.

    Product Overview

    By leveraging the LSM tree storage structure of RocksDB, the TXRocks transactional storage engine not only reduces wastes caused by InnoDB's half-full pages and fragments, but also uses the compact storage format. Therefore, it has a performance comparable to that of InnoDB but requires only a half or even smaller storage space. It is more suitable for businesses with a large data volume and high requirements for the transactional read/write performance.

    Prerequisites

    The database version must be MySQL 5.7 or 8.0 in two-node architecture.

    Purchasing TencentDB for MySQL Instance (with RocksDB Engine)

    You can select RocksDB as the engine when purchasing an instance on the TencentDB for MySQL purchase page. For more information on other parameters, see Creating MySQL Instance.

    Note:

    RocksDB is a key-value storage engine, with efficient writing and high compression. Currently, only TencentDB for MySQL 5.7 and 8.0 instances can use the RocksDB engine.

    Creating RocksDB Table

    If RocksDB is selected as the default engine during instance creation, it will be the default engine used for table creation. You can run the following command to view the default engine:

    show variables like '%default_storage_engine%';
    


    If the default engine is RocksDB, you cannot specify a storage engine in table creation statements:

    After a table is created, its data will be stored in RocksDB and can be used in the same way as in InnoDB.

    Engine Feature Limits

    TXRocks has certain limits on engine features as detailed below:

    CategoryFeatureTXRocks Limit
    DDLOnline DDLNot supported. For example, `ALTER TABLE ... ALOGRITHM=INSTANT` is not supported. Only the `COPY` algorithm is supported for partition management operations.
    SQL Foreign keyNot supported.
    Partitioned tableNot supported.
    Generated columnNot supported.
    Explicit DEFAULT expressionNot supported. For example, `CREATE TABLE t1(c1 FLOAT DEFAULT(RAND()))ENGINE=ROCKSDB` will fail, with the error `'Specited storage engine' is not supported for default value expressions` reported.
    Encrypted tableNot supported.
    Index Spatial indexThe spatial index and spatial data types such as `GEOMETRY` and `POINT` are not supported.
    Full-text indexNot supported.
    Multi-valued indexNot supported.
    Replication Group replicationNot supported.
    Binlog formatOnly the `ROW` format is supported, while `STMT` and `MIXED` formats are not.
    Clone pluginNot supported.
    Transportable tablespaceNot supported.
    Transaction and lock LOCK NOWAIT and SKIP LOCKEDNot supported.
    Gap lockNot supported.
    SavepointNot supported.
    Partial LOB field updateNot supported.
    XA transactionNot recommended.

    Parameter Description

    Note:

    When creating a TencentDB for MySQL instance, you can select RocksDB as the default storage engine. You can also customize the parameter template to suit your needs by following the parameter descriptions below.

    MySQL 5.7 parameter list

    Parameter Restart Required Default Value Value Range/Valid Values Description
    rocksdb_use_direct_io_for_flush_and_compaction Yes ON ON/OFF Whether to use DIO during compaction.
    rocksdb_flush_log_at_trx_commit No 1 0/1/2 Controls when to write logs to the disk.
    It is similar to innodb_flush_log_at_trx_commit and indicates whether transactions need to be synced when being committed.
  • 0: Transactions are not synced when being committed.
  • 1: Transactions are synced when being committed.
  • 2: Transactions are synced once every second.
  • rocksdb_lock_wait_timeout No 1 1–1073741824 Lock wait timeout period in seconds.
    rocksdb_deadlock_detect No ON ON/OFF Whether to enable deadlock detection. After it is enabled, all deadlock information will be recorded in mysqld error logs.
    rocksdb_manual_wal_flush Yes ON ON/OFF If the total size of WAL files exceeds rocksdb_max_total_wal_size, RocksDB will forcibly flush the column family to the disk to ensure that the oldest WAL file can be deleted.

    MySQL 8.0 parameter list

    Parameter Restart Required Default Value Value Range/Valid Values Description
    rocksdb_flush_log_at_trx_commit No 1 0/1/2 Controls when to write logs to the disk.
    It is similar to innodb_flush_log_at_trx_commit and indicates whether transactions need to be synced when being committed.
  • 0: Transactions are not synced when being committed.
  • 1: Transactions are synced when being committed.
  • 2: Transactions are synced once every second.
  • rocksdb_lock_wait_timeout No 1 1–1073741824 Lock wait timeout period in seconds.
    rocksdb_merge_buf_size No 524288(=512K) 100–18446744073709551615 Size of the merge sort buffer used during secondary index creation.
    rocksdb_merge_combine_read_size No 8388608 (=8M) 524288(=512K)–18446744073709551615 Size of the memory used by k-way merge during secondary index creation.
    rocksdb_deadlock_detect No ON ON/OFF Whether to enable deadlock detection.
    rocksdb_manual_wal_flush Yes ON ON/OFF If the total size of WAL files exceeds rocksdb_max_total_wal_size, RocksDB will forcibly flush the column family to the disk to ensure that the oldest WAL file can be deleted.

    RocksDB Monitoring Metrics

    RocksDB monitoring metrics are as listed below:

    Metric Description
    rocksdb_bytes_read Data read from disk
    rocksdb_bytes_written Data written to disk
    rocksdb_block_cache_bytes_read Blocks read
    rocksdb_block_cache_bytes_write Blocks written
    rocksdb_wal_log_capacity Data written to WAL log
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