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TencentDB for MySQL
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    Instructions

    Last updated: 2024-07-22 12:50:43
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      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 on a 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:
      Category
      Feature
      TXRocks Limit
      DDL
      Online DDL
      Not supported. For example, `ALTER TABLE ... ALOGRITHM=INSTANT` is not supported. Only the `COPY` algorithm is supported for partition management operations.
      SQL
      Foreign key
      Not supported.
      Partitioned table
      Not supported.
      Generated column
      Not supported.
      Explicit DEFAULT expression
      Not 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 table
      Not supported.
      Index
      Spatial index
      The spatial index and spatial data types such as `GEOMETRY` and `POINT` are not supported.
      Full-text index
      Not supported.
      Multi-valued index
      Not supported.
      Replication
      Group replication
      Not supported.
      Binlog format
      Only the `ROW` format is supported, while `STMT` and `MIXED` formats are not.
      Clone plugin
      Not supported.
      Transportable tablespace
      Not supported.
      Transaction and lock
      LOCK NOWAIT and SKIP LOCKED
      Not supported.
      Gap lock
      Not supported.
      Savepoint
      Not supported.
      Partial LOB field update
      Not supported.
      XA transaction
      Not 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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