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TDSQL-C for MySQL
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    Use Limits

    Last updated: 2023-07-13 11:05:59
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      This document describes the TDSQL-C for MySQL use limits that you must follow to ensure the stable and secure operation of your cluster.

      Engine Limits

      TDSQL-C for MySQL only supports the InnoDB engine.

      Naming Limits

      Limit
      Description
      Cluster name
      The length must be less than 60 characters.
      It can contain letters, digits, hyphens, underscores, and dots.
      Read-write/read-only instance name
      The length must be less than 60 characters.
      It can contain letters, digits, hyphens, underscores, and dots.
      Account name
      The length ranges from 1 to 16 characters.
      It must be a combination of letters, digits and special characters, which must start with a letter and end with a letter or digit.
      The special symbols are underscores and dots.
      It cannot be the same as an existing account name.
      Database name
      The length can be up to 60 characters.
      It must be a combination of lowercase letters, digits, hyphens, and underscores.
      It must start with a letter and end with a letter or digit.
      It cannot be the same as an existing database name and cannot be changed after creation.

      Quota Limits

      Quota
      Limit
      Read-only instance
      A cluster can have 0–15 read-only instances.
      Tag
      Tag keys must be unique. There can be up to 20 tags. A tag can be bound to up to 50 instances at a time.
      Free tier of backup space
      TDSQL-C for MySQL backup space currently is free of charge. In the future, a free tier of backup space will be set based on the storage space selected during cluster purchase, and any excessive usage will incur fees.
      Backup retention period
      Backups can be retained for 7 (default) to 1,830 days.
      Log retention period
      Logs can be retained for 7 (default) to 1,830 days.
      Project
      A project is defined on a cluster basis, and multiple instances in the same cluster belong to the same project.

      Operation Limits

      Limit
      Description
      Kernel version upgrade
      Cluster switch will be required after version upgrade is completed (that is, the database may be disconnected for seconds). We recommend that you use applications configured with automatic reconnection feature and conduct the switch during the instance maintenance time.
      If the number of tables in a single instance exceeds one million, upgrade may fail and database monitoring may be affected. Make sure that the number of tables in a single instance is below one million.
      The kernel minor version cannot be downgraded once upgraded.
      Failover
      When the source node fails, TDSQL-C for MySQL will switch to a replica node. As a disconnection for less than 30 seconds will occur during the switch, make sure that your business has an automatic reconnection mechanism.
      Network switch
      Switching the network may cause all of the instance's private IPs to change. The system will automatically assign new IPs, so you need to modify the instance IPs on the client promptly.
      The original IPs will expire after 24 hours by default. The expiration time can be customized during the network switch. If it is set to zero, the original IPs will be repossessed immediately after the network switch.
      When switching the network, you can only select a new VPC and subnet in the same region and AZ where the instance resides.
      Storage space
      There is a limit on the storage space of each pay-as-you-go or serverless compute instance. For more information, see Product Specifications and Compute Unit.
      The storage space in the monthly subscription billing mode is as purchased.
      The compute instance specification has a storage upper limit. If you need more storage space, upgrade the specification.
      Data recovery
      We recommend that you back up important data to avoid data loss before restoring data. You can do so through rollback or cluster cloning.
      Configuration adjustment
      TDSQL-C for MySQL supports fast in-place configuration upgrade or downgrade, and a momentary disconnection may occur in special cases. Make sure that your business has an automatic reconnection mechanism. We recommend that you perform this operation during off-peak hours.

      Keywords/Reserved Words Limits

      A keyword refers to a word that has a meaning in a SQL statement. A reserved word refers to a certain word in a keyword (such as SELECT, DELETE, and BIGINT) that is reserved in the corresponding version of the database. These reserved words/keywords require special processing (such as by adding quotation marks) before they can be used as identifiers like table name and column name; otherwise, errors will occur. In contrast, non-reserved words/keywords can be directly used as identifiers.
      The keywords and reserved words in TDSQL-C for MySQL are basically the same as those in MySQL as listed in Keywords and Reserved Words.
      In addition, TDSQL-C for MySQL has the following additional reserved words and keywords:
      CLUSTER
      THREADPOOL_SYM
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