Suggestions on RDS for MySQL Parameter Tuning

Sensitive Parameters

The following parameters can result in system security and stability issues if set improperly:

• lower_case_table_names

  Default value: 1

  Function: Controls whether table names stored on disks are case-sensitive when databases and tables are created. The value 1 indicates that table names are case-insensitive and are lowercase by default.

  

  RDS for MySQL 8.0 does not support modifications to this parameter.

  Impact: Changing this parameter value may cause primary/standby replication exceptions. Exercise caution when performing this operation.

  • If you want to change this parameter value from 1 to 0, change it on read replicas and reboot them first, and then repeat the operations on the primary DB instance.
  • If you want to change this parameter value from 0 to 1, change it on the primary DB instance and reboot it first, and then run SELECT @@GLOBAL.GTID_EXECUTED on read replicas. Wait until the result set is at least the same as the primary DB instance and then change this parameter value on read replicas and reboot them.
• innodb_flush_log_at_trx_commit

  Default value: 1

  Function: Controls the balance between strict ACID compliance for commit operations and higher performance. The default setting of 1 is required for full ACID compliance. Logs are written and flushed to disks at each transaction commit. If the value is set to 0, logs are written and flushed to disks once per second. If the value is set to 2, logs are written at each transaction commit and flushed to disks every two seconds.

  Impact: If this parameter is not set to 1, data security is not guaranteed. If the system fails, data may be lost.

  Recommended value for POC: 2

• sync_binlog

  Default value: 1

  Function: Controls how often the RDS for MySQL server synchronizes binary logs to the disk. The default setting of 1 requires synchronization of the binary log to the disk at each transaction commit. If the value is set to 0, synchronization of the binary log to the disk is not controlled by the RDS for MySQL server but relies on the OS to flush the binary log to the disk. This setting provides the best performance. However, if a power failure occurs or the OS crashes, all binary log information in binlog_cache will be lost.

  Impact: If this parameter is not set to 1, data security is not guaranteed. If the system fails, binary logs may be lost.

  Recommended value for POC: 1000

• innodb_large_prefix

  Default value: OFF

  Function: Specifies the maximum length of a single-column index in an InnoDB table.

  

  This parameter is available only for RDS for MySQL 5.6.

  Impact: Changing this parameter value during DDL execution may cause primary/standby replication exceptions. Exercise caution when performing this operation.

  • If you want to change this parameter value from OFF to ON, change it on read replicas first and then on the primary DB instance.
  • If you want to change this parameter value from ON to OFF, change it on the primary DB instance first and then on read replicas.
• innodb_buffer_pool_size

  Default value: Varies depending on the DB instance classes.

  Function: Specifies the size of the InnoDB buffer pool. The InnoDB buffer pool is used to cache table and index data. Increasing the value of this parameter reduces disk I/O.

  Impact: Setting this parameter to a large value may cause system breakdown. Exercise caution when changing this parameter value.

  Recommended value for POC: 70% to 75% of the memory for your DB instances with 32 GB memory or above

Performance Parameters

The following parameters can affect database performance:

• The values of innodb_spin_wait_delay and query_alloc_block_size are determined by the DB instance specifications. If you increase their values, database performance may be affected.
• The max_connections parameter sets the maximum number of clients allowed to connect concurrently. The default value of this parameter depends on the system architecture. System built-in connections occupy some connections specified by this parameter. To prevent concurrent connection conflicts, you are advised not to set this parameter to a value less than 30. This parameter cannot be set to a value smaller than the number of current connections.
• The default values of the following parameters are determined by the DB instance specifications: innodb_buffer_pool_size, max_connections, and back_log. These parameter values are default before being specified.
• The values of innodb_io_capacity_max and innodb_io_capacity are determined by the storage type. These parameter values are default before being specified.

Associated Parameters

• character_set_server: If you change the value of this parameter, the system changes the values of collation_server, character_set_database, and collation_database accordingly.

  The parameters character_set_server and collation_server are correlated with each other. The value of collation_server starts with the value of character_set_server. For example, if character_set_server is set to latin1, the value of collation_server starts with latin1.

• innodb_io_capacity: The value of this parameter must be less than or equal to the value of innodb_io_capacity_max. For example, if innodb_io_capacity_max is set to 2000, the maximum value of innodb_io_capacity is 2000.
• innodb_buffer_pool_size: The value of this parameter must be a multiple of the product of the value for innodb_buffer_pool_chunk_size and innodb_buffer_pool_instances. For example, if innodb_buffer_pool_chunk_size is 134217728 and innodb_buffer_pool_instances is 1, the value of innodb_buffer_pool_size must be a multiple of 134217728.

Constraints on Parameter Modification

• When the innodb_adaptive_hash_index and innodb_buffer_pool_size parameters are modified at the same time, the value of innodb_adaptive_hash_index will fail to be changed from OFF to ON.
• The value of innodb_buffer_pool_size must be an integer multiple of the product of innodb_buffer_pool_instances and innodb_buffer_pool_chunk_size.
• If innodb_buffer_pool_instances is set to 2, the value of innodb_buffer_pool_size must be greater than or equal to 1 (unit: GB).
• For MySQL 8.0, if the kernel version is earlier than 8.0.18, the value of max_prepared_stmt_count cannot exceed 1048576.

Other Parameters

• max_prepared_stmt_count: limits the upper limit of prepared statements. Too many prepared statements consume server memory resources. If this parameter is set to a small value, your DB instance may be vulnerable to the denial of service (DoS) attacks. You are advised to change this parameter value based on service requirements.
• The values of the following parameters will be adjusted based on kernel rules:
  • key_cache_age_threshold: automatically adjusted to a multiple of 100.
  • join_buffer_size and key_cache_block_size: automatically adjusted to multiples of 128.
  • query_cache_size, query_prealloc_size, innodb_log_buffer_size, max_allowed_packet, and thread_stack: automatically adjusted to multiples of 1024.
  • read_buffer_size, read_rnd_buffer_size, binlog_cache_size, and binlog_stmt_cache_size: automatically adjusted to multiples of 4096.
  • data_buffer_size, log_buffer_size, shared_pool_size, and temp_buffer_size: automatically adjusted to multiples of 1048576.
• binlog_format: set to row by default, indicating that binary logs are recorded as the modified data by row, including the data before and after modification. You are advised not to change the value of this parameter.
• log_timestamps: controls the time zone of timestamps in various logs, such as error logs and slow query logs. The default value is the system time zone and cannot be changed.
• skip_name_resolve: set to ON by default, indicating that the system skips domain name resolution and determines whether a connection can be set up based on the IP address in the whitelist.
• innodb_strict_mode: restricts the InnoDB check policy. The default value is OFF.
• binlog_rows_query_log_events: controls whether to write original SQL statements into binlogs. If this parameter is set to ON, database performance may deteriorate when a large amount of data is updated. Before you change the parameter value, consider the compatibility with tools such as Otter.