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MySQL semi-sync settings
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MySQL semi-sync settings

MySQL semi-sync settings affect the performance of the database cluster. When you create a MySQL semi-sync database cluster, the values for all settings are set automatically. The values are chosen to ensure high cluster performance, they vary depending on the cluster configuration and MySQL semi-sync version.

If the automatic values are not suitable for your tasks, set your own values when creating a cluster or change settings in an already created cluster.

For your information

We recommend that you change the settings only when necessary — incorrect values can degrade cluster performance. When you scale the cluster, the values of some settings are automatically replaced with valid values.

View a list of settings

See the detailed description of settings in official MySQL documentation.

You can view the list of settings available for change at create cluster or change settings.

If you have changed settings, you can see a list of all changes.

  1. In Control Panel, go to Cloud PlatformDatabases.
  2. Open the cluster page → Settings tab.
  3. The DBMS Settings block displays the previously changed settings — name and value.

Change settings

For your information

Changing some parameters in the settings entails rebooting the databases in the cluster — the cluster may be unavailable during this time. These settings depend on the MySQL semi-sync version — see their list.

  1. In Control Panel, go to Cloud PlatformDatabases.
  2. Open the cluster page → Settings tab.
  3. In the DBMS Settings block, click Change and specify the new values.
  4. Click Save.

List of settings that require a reboot

  • innodb_adaptive_hash_index_parts;
  • innodb_autoinc_lock_mode;
  • innodb_buffer_pool_instances;
  • innodb_buffer_pool_pool_load_at_startup;
  • innodb_commit_concurrency;
  • innodb_flush_method;
  • innodb_ft_cache_size;
  • innodb_ft_max_token_size;
  • innodb_ft_min_token_size;
  • innodb_ft_total_cache_size;
  • innodb_ft_sort_pll_degree;
  • innodb_log_buffer_size (except MySQL sync 8);
  • innodb_log_file_size;
  • innodb_page_cleaners;
  • innodb_purge_threads;
  • innodb_read_io_threads;
  • innodb_rollback_on_timeout;
  • innodb_sort_buffer_size;
  • innodb_sync_array_size;
  • innodb_write_io_threads;
  • max_digest_length;
  • table_open_cache_instances;
  • thread_pool_size;
  • thread_stack.

Settings when scaling a cluster

Any DBMS parameter has limits of acceptable values. When cluster scaling (configuration change), the values of some settings are automatically changed to valid values so that the cluster can run.

When the cluster is scaled and goes to ACTIVE status, you can set the new values — change settings.

A list of settings that change values when the cluster is scaled:

innodb_buffer_pool_size, innodb_log_file_size, innodb_buffer_pool_instances, thread_pool_size, max_heap_table_size, tmp_table_size, temptable_max_ram


MySQL semi-sync uses utf8mb4 as the encoding (CHARSET).

The sorting algorithm (COLLATION) is used as a sorting algorithm:

  • in MySQL semi-sync 5.7 — utf8mb4_general_ci
  • in MySQL semi-sync 8 — utf8mb4_0900_ai_ci

You can change the CHARSET and COLLATION values when creating objects.