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    PolarDB:PolarDB for MySQL 5.7 kernel parameter release notes

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    PolarDB:PolarDB for MySQL 5.7 kernel parameter release notes

    Last Updated:Nov 11, 2025

    This topic provides the release notes for kernel parameters in PolarDB for MySQL 5.7.

    2025.10.21

    Category

    Parameter

    Level

    Description

    New

    loose_innodb_btr_cur_fine_history_length

    Global

    When the length of history_list exceeds this threshold, the priority for the Purge thread to acquire an Index lock is increased.

    Valid values: 10000 to 4294967295.

    Default value: 100000.

    Note

    This parameter is available only for MySQL 5.7 with a minor version of 5.7.1.0.36 or later.

    Modified

    default_time_zone

    Global

    Sets the specified time zone name. The range of valid values for the time zone parameter is expanded.

    innodb_lru_scan_depth

    Global

    Adjusts the LRU dirty page flushing threshold. You can now adjust the parameter value in the console.

    Valid values: 100 to 1099511627776.

    Note

    • The default value and valid range of the parameter are dynamically adjusted based on the node specifications of the cluster.

    • Changes to this parameter take effect immediately. You do not need to restart the cluster.

    loose_max_execution_time

    Global

    Controls the execution duration of query statements. The default value is changed to 86400000.

    Valid values: 0 to 4294967295.

    Default value: 86400000.

    Unit: milliseconds.

    Note

    Changes to this parameter take effect immediately. You do not need to restart the cluster.

    default_tmp_storage_engine

    Global/Session

    Specifies the default storage engine for explicitly created temporary tables. The range of valid values for read-only (RO) nodes and standby nodes is expanded to include InnoDB.

    Valid values:

    • InnoDB

    • MyISAM

    • MEMORY

    Default value: MyISAM.

    Note

    • The valid range of this parameter can be modified only for MySQL 5.7 with a minor version of 5.7.1.0.36 or later.

    • Changes to this parameter take effect immediately. You do not need to restart the cluster.

    polar_dump_connection

    Global

    Sets the number of parallel connections for a dump. You can now adjust the parameter value in the console.

    Valid values: 1 to 32.

    Default value: 1.

    Note

    • This parameter can be modified only for MySQL 5.7 with a minor version of 5.7.1.0.35 or later.

    • Changes to this parameter take effect immediately. You do not need to restart the cluster.

    2025.10.21

    Category

    Parameter

    Level

    Description

    New

    loose_innodb_fast_log_write

    Global

    Specifies whether to accelerate log writing when you use a high-performance parameter template or when the innodb_flush_log_at_trx_commit=0 parameter is set to 0.

    • OFF (default): Indicates a shutdown.

    • ON indicates an enabled state.

    Note

    This parameter is available only for database engines of MySQL 5.7 whose minor version is 5.7.1.0.37 or later.

    2025.07.03

    Category

    Parameter

    Level

    Description

    New

    loose_sql_big_selects

    Session

    Specifies whether to allow large-scale SELECT queries.

    Valid values:

    • OFF (default): Shutdown.

    • ON: The feature is enabled.

    Note

    • The default value of this parameter depends on the value of the max_join_size parameter when you connect to the PolarDB cluster. If max_join_size is 18446744073709551615, the default value of this parameter is ON. Otherwise, the default value is OFF.

    • If you manually modify the value of this parameter, the new value is retained.

    2025.05.07

    Category

    Parameter

    Level

    Description

    Modified

    innodb_buffer_pool_size

    Global

    You can flexibly adjust the Buffer Pool Size parameter in the console.

    The buffer size of the InnoDB engine.

    Valid values: {DBNodeClassMemory × 1/4} to {DBNodeClassMemory × 4/5}. Unit: bytes.

    Note

    The default value varies based on node specifications. For more information, see Parameter settings.

    2025.04.02

    Category

    Parameter

    Level

    Description

    New

    loose_join_buffer_size

    Session

    Specifies the buffer size for full joins.

    Valid values: 128 to 67108864. Default value: 524288. Unit: bytes.

    Modified

    table_open_cache

    Global

    The table_open_cache parameter is now visible. You can modify this parameter for each node.

    Valid values: 1 to 524288. Default value: 16384. Unit: bytes.

    2025.03.20

    Category

    Parameter

    Level

    Description

    New

    loose_innodb_slave_log_apply_worker

    Global

    Lets you flexibly adjust the number of Apply threads in the console to improve the replication performance of secondary nodes.

    Valid values: 1 to 64. Default value: 8.

    2025.03.13

    Category

    Parameter

    Level

    Description

    Modified

    loose_innodb_ro_read_no_sync_enable

    Global

    The RO No Sync parameter is now visible. Enabling this parameter significantly improves the page I/O read performance of read-only nodes.

    • OFF (default): Disables this feature.

    • ON: Enables this feature.

    Note

    • This parameter is available only for database engines of MySQL 5.7 whose minor version is 5.7.1.0.36 or later.

    • Changes to this parameter take effect immediately. You do not need to restart the cluster.

    2025.02.12

    Category

    Parameter

    Level

    Description

    New

    loose_polar_performance_schema

    Global

    Specifies whether to enable the Polar Performance Schema feature.

    Valid values:

    • ON: Enables the Polar Performance Schema feature.

    • OFF (default): Disables the Polar Performance Schema feature.

    Note

    This parameter is available only for database engines of MySQL 5.7 whose minor version is 5.7.1.0.35 or later.

    Modified

    loose_opt_outline_enabled

    Global

    This parameter can now be dynamically modified in the console.

    A switch for the statement outline feature. Valid values:

    • ON (default): Enables the statement outline feature.

    • OFF: Disables the statement outline feature.

    Note

    This parameter is available only for database engines of MySQL 5.7 whose minor version is 5.7.1.0.3 or later.

    innodb_open_files

    Global

    The configurable range for this parameter is modified.

    Valid values: 11 to 500000. Default value: 20000.

    innodb_online_alter_log_max_size

    Global

    The maximum size of a log file during online index creation.

    Valid values: 65536 to 1099511627775. Default value: 107374182400. Unit: bytes.

    Note

    Changes to this parameter take effect immediately. You do not need to restart the cluster.

    2025.01.16

    Category

    Parameter

    Level

    Description

    New

    loose_innodb_buffer_pool_instances

    Global

    Specifies the number of buffer pool instances.

    Valid values: 1 to 64. Default value: 8.

    2025.01.10

    Category

    Parameter

    Level

    Description

    New

    loose_max_digest_length

    Global

    Specifies the maximum length of digest text in the performance schema table.

    Valid values: 0 to 1048576. Default value: 1024. Unit: bytes.

    Note

    This parameter is available only for database engines of MySQL 5.7 whose minor version is 5.7.1.0.35 or later.

    2024.12.26

    Category

    Parameter

    Level

    Description

    Modified

    loose_explicit_defaults_for_timestamp

    Session

    Controls how default values for timestamp columns are handled.

    • OFF (default): Disables this feature.

    • ON: Enables this feature.

    Note

    • This parameter is available only for database engines of MySQL 5.7 whose minor version is 5.7.1.0.36 or later.

    • Changes to this parameter take effect immediately. You do not need to restart the cluster.

    2024.12.19

    Category

    Parameter

    Level

    Description

    Modified

    loose_innodb_flush_pages_using_space_id

    Global

    The default value of this parameter is changed from OFF to ON.

    Attempts to flush or remove pages by space ID.

    Note

    Changes to this parameter take effect immediately. You do not need to restart the cluster.

    2024.09.26

    Category

    Parameter

    Level

    Description

    New

    loose_innodb_polar_page_track

    Global

    Specifies whether to enable optimization for global consistency (high-performance mode).

    • OFF (default): Disables this feature.

    • ON: Enables this feature.

    Note

    • This parameter is available only for database engines of MySQL 5.7 whose minor version is 5.7.1.0.35 or later.

    • Changes to this parameter take effect immediately. You do not need to restart the cluster.

    Modified

    loose_innodb_purge_batch_size

    Global

    The default value of the parameter is adjusted based on the instance specifications to improve CPU utilization.

    2024.09.05

    Category

    Parameter

    Level

    Description

    New

    loose_innodb_blob_prepare_pages

    Global

    Specifies whether to enable allocation and write optimization for large object (BLOB) pages.

    • OFF (default): Disables this feature.

    • ON: Enables this feature.

    Note

    • This parameter is available only for database engines of MySQL 5.7 whose minor version is 5.7.1.0.35 or later.

    • Changes to this parameter take effect immediately. You do not need to restart the cluster.

    loose_innodb_blob_prepare_max_extern_size

    Global

    Specifies the maximum size for a large object (BLOB) when BLOB write optimization is enabled.

    Valid values: 8192 to 536870912. Default value: 409600. Unit: bytes.

    Note

    • This parameter is available only for database engines of MySQL 5.7 whose minor version is 5.7.1.0.35 or later.

    • Changes to this parameter take effect immediately. You do not need to restart the cluster.

    Category

    Parameter

    Level

    Description

    Modified

    default_time_zone

    Global/Session

    Set default_time_zone to a time zone name. The range of supported time zones is expanded. Valid values:

    • PRC

    • Asia/Jakarta

    • Europe/Berlin

    • Asia/Tokyo

    • US/Pacific

    • US/Eastern

    • Europe/London

    • Australia/Sydney

    • Asia/Manila

    • Asia/Bangkok

    • Asia/Seoul

    • America/Los_Angeles

    • America/Vancouver

    • Asia/Singapore

    • Singapore

    • Canada/Atlantic

    • Canada/Central

    • Canada/East-Saskatchewan

    • Canada/Eastern

    • Canada/Mountain

    • Canada/Newfoundland

    • Canada/Pacific

    • Canada/Saskatchewan

    • Canada/Yukon

    2024.08.15

    Category

    Parameter

    Level

    Description

    New

    loose_polar_support_mdl_sync_preemption

    Global/Session

    Specifies whether to enable preemptive DDL.

    • OFF (default): Disables this feature.

    • ON: Enables this feature.

    Note

    This parameter is available only for database engines of MySQL 5.7 whose minor version is 5.7.1.0.34 or later.

    loose_polar_mdl_sync_preempt_after_wait_second

    Global

    Specifies a timeout period for a blocked metadata lock (MDL) synchronization. If the MDL is not acquired before the timeout, the system starts to preempt the thread.

    Valid values: 1 to 31536000. Default value: 10. Unit: seconds.

    Modified

    default_time_zone

    Global/Session

    Set default_time_zone to a time zone name. The range of supported time zones is expanded. Valid values:

    • PRC

    • Asia/Jakarta

    • Europe/Berlin

    • Asia/Tokyo

    • US/Pacific

    • US/Eastern

    • Europe/London

    • Australia/Sydney

    • Asia/Manila

    • Asia/Bangkok

    • Asia/Seoul

    • America/Los_Angeles

    • Asia/Singapore

    • Singapore

    • Canada/Atlantic

    • Canada/Central

    • Canada/East-Saskatchewan

    • Canada/Eastern

    • Canada/Mountain

    • Canada/Newfoundland

    • Canada/Pacific

    • Canada/Saskatchewan

    • Canada/Yukon

    2024.07.19

    Category

    Parameter

    Level

    Description

    Modified

    default_time_zone

    Global

    Set default_time_zone to a time zone name. The range of supported time zones is expanded. Valid values:

    • PRC

    • Asia/Jakarta

    • Europe/Berlin

    • Asia/Tokyo

    • US/Pacific

    • US/Eastern

    • Europe/London

    • Australia/Sydney

    • Asia/Manila

    • Asia/Bangkok

    • Asia/Seoul

    2024.07.04

    Category

    Parameter

    Level

    Description

    New

    loose_sync_gtids_to_replica

    Global

    Specifies whether to synchronize global transaction identifiers (GTIDs) to read-only nodes in real time.

    • OFF (default): Disables this feature.

    • ON: Enables this feature.

    Note

    This parameter is available only for database engines of MySQL 5.7 whose minor version is 5.7.1.0.27 or later.

    2024.06.24

    Category

    Parameter

    Level

    Description

    Modified

    innodb_purge_threads

    Global

    The parameter value is adjusted based on the instance specifications. For example, if the instance has 4 cores, the parameter value is 4. If the instance has 8 cores, the parameter value is 8.

    Valid values: 4 to 32.

    innodb_purge_batch_size

    Global

    The default value of the parameter is changed to 1000.

    2024.06.21

    Category

    Parameter

    Level

    Description

    Modified

    loose_rds_audit_max_sql_size

    Global

    The maximum length of a single SQL statement in an audit log is increased to 1048576.

    2024.03.29

    Category

    Parameter

    Level

    Description

    New

    loose_innodb_buffer_pool_resize_cancel

    Global

    Specifies whether to automatically cancel a blocked buffer pool scale-in operation during Serverless auto-scaling. Valid values:

    • OFF (default): Does not automatically cancel a blocked buffer pool scale-in operation during Serverless auto-scaling.

    • ON: Automatically cancels a blocked buffer pool scale-in operation during Serverless auto-scaling.

    init_connect

    Global

    The SQL statement that is automatically executed when a new connection is established. Valid values:

    • '' (default)

    • 'set names utf8mb4'

    • 'set names utf8'

    • 'set default_collation_for_utf8mb4=utf8mb4_general_ci'

    • 'set default_collation_for_utf8mb4=utf8mb4_general_ci;set names utf8mb4'

    • 'set names utf8mb4 collate utf8mb4_general_ci'

    • 'set names utf8mb4 COLLATE utf8mb4_bin'

    • 'set names utf8mb4 collate utf8mb4_unicode_ci'

    2024.03.22

    Category

    Parameter

    Level

    Description

    Modified

    innodb_open_files

    Global

    The maximum value of the innodb_open_files parameter is changed to 81920.

    2024.02.21

    Category

    Parameter

    Level

    Description

    Modified

    loose_thread_pool_enabled

    Global

    For new clusters, the default value of the loose_thread_pool_enabled parameter is ON. This means the thread pool is enabled by default for new clusters.

    2023.12.25

    Category

    Parameter

    Level

    Description

    Modified

    loose_innodb_primary_flush_max_lsn_lag

    Global/Session

    The default value of the loose_innodb_primary_flush_max_lsn_lag parameter is changed to GREATEST(1073741824, {DBNodeClassMemory × 9/100}).

    2023.12.18

    Category

    Parameter

    Level

    Description

    New

    max_connections

    Global/Session

    The maximum number of connections to the database.

    Valid values: 1 to 200000. Default value: 2312.

    max_user_connections

    Global/Session

    The maximum number of connections for a single user.

    Valid values: 10 to 200000. Default value: 1800.

    innodb_buffer_pool_size

    Global/Session

    The buffer size of the InnoDB engine.

    Valid values: {DBNodeClassMemory × 1/4} to {DBNodeClassMemory × 4/5}. Default value: 3328 MB. Unit: bytes.

    2023.12.12

    Category

    Parameter

    Level

    Description

    New

    block_encryption_mode

    Global

    Sets the mode used for encryption and decryption operations by the AES_ENCRYPT and AES_DECRYPT functions. Valid values:

    • aes-128-ecb (default)

    • aes-192-ecb

    • aes-256-ecb

    • aes-128-cbc

    • aes-192-cbc

    • aes-256-cbc

    2023.12.06

    Category

    Parameter

    Level

    Description

    New

    loose_innodb_log_io_threads

    Global

    The number of I/O threads for redo logs in the InnoDB engine.

    Valid values: 1 to 64. Default value: 4.

    2023.11.21

    Category

    Parameter

    Level

    Description

    New

    loose_polarfs_cache_enabled

    Global

    A switch for the PFS CACHE optimization feature. Valid values:

    • OFF (default): Disables the PFS CACHE optimization feature.

    • ON: Enables the PFS CACHE optimization feature.

    sync_binlog

    Global

    Sets the frequency at which binary logging is written. Valid values: 0 to 4294967295. Default value: 1.

    2023.11.09

    Category

    Parameter

    Level

    Description

    New

    loose_innodb_purge_blob_read_ahead

    Global

    Specifies whether to enable the BLOB read-ahead feature during a purge operation. Valid values:

    • OFF (default): The BLOB read-ahead feature is disabled during a purge operation.

    • ON: The BLOB read-ahead feature is enabled during a purge operation.

    loose_innodb_persist_replica_enable

    Global

    Controls whether read-only nodes remain available when the read/write node is unavailable. Valid values:

    • OFF (default): Read-only nodes are unavailable when the read/write node is unavailable.

    • ON: Read-only nodes remain available as much as possible when the read/write node is unavailable.

    2023.10.25

    Category

    Parameter

    Level

    Description

    New

    loose_innodb_serverless_replica_pcu_min_ratio

    Global

    Sets the specification ratio between RO nodes and RW nodes in a serverless cluster.

    Valid values: 0.00 to 1.00. Default value: 0.5.

    2023.08.09

    Category

    Parameter

    Level

    Description

    New

    innodb_ft_server_stopword_table

    Global/Session

    Sets the stop words for the full-text index.

    loose_kill_idle_transaction_timeout

    Global

    The timeout period for a transaction in the idle state. After the timeout period, the connection is automatically disconnected.

    Valid values: 0 to 31536000. Default value: 0. Unit: seconds.

    Modified

    loose_thread_pool_size

    Global

    The valid range of this parameter is changed to DBNodeClassCPU to DBNodeClassCPU × 10.

    2023.07.14

    Category

    Parameter

    Level

    Description

    New

    loose_innodb_csn_slot_recycle_pct

    Global

    The CTS log recycle rate for PolarTrans.

    Valid values: 0 to 99. Default value: 1. Unit: percent.

    2023.07.10

    Category

    Parameter

    Level

    Description

    Modified

    loose_innodb_replica_share_log

    Global

    The default value of this parameter is changed to OFF.

    2023.06.28

    Category

    Parameter

    Level

    Description

    New

    sort_buffer_size

    Global/Session

    The size of the buffer allocated for sorting operations in each session.

    Valid values: 32768 to 4294967295. Default value: 1024 KB. Unit: bytes.

    2023.05.30

    Category

    Parameter

    Level

    Description

    New

    loose_opt_show_specific_table_with_ignore_wild_one

    Global/Session

    A switch for performance control of the SHOW TABLES statement. Valid values:

    • OFF (default): Disables performance control for the SHOW TABLES statement.

    • ON: When you use the SHOW TABLES statement and specify a table name, only the definition file of the specified table is opened. The underscore character does not match any character. For example, in the SHOW TABLES FROM test LIKE "t_1"; statement, only the table named t_1 is matched.

    loose_opt_show_specific_table

    Global/Session

    A switch for performance control of the SHOW TABLES statement. Valid values:

    • OFF (default): Disables performance control for the SHOW TABLES statement.

    • ON: When you use the SHOW TABLES statement and specify a table name, only the definition file of the specified table is opened.

    2023.05.22

    Category

    Parameter

    Level

    Description

    New

    lower_case_table_names

    Global/Session

    Specifies whether table names are case-sensitive. Valid values:

    • 1 (default): Table names are stored in lowercase and comparisons are not case-sensitive.

    • 0: Table names are stored as specified and comparisons are case-sensitive.

    • 2: Table names are stored as specified, but comparisons are not case-sensitive.

    2023.04.13

    Category

    Parameter

    Level

    Description

    New

    loose_innodb_polar_scc_max_waiters_inside

    Global

    The maximum number of threads that can wait for the transaction resolution of a read-only node to be replayed to the target CSN.

    Valid values: 0 to 4294967295. Default value: 0.

    Modified

    innodb_undo_log_truncate

    Global

    Lets you enable or disable the undo log recycling feature in the console. Valid values:

    • ON (default): Enables the undo log recycling feature.

    • OFF: Disables the undo log recycling feature.

    loose_innodb_polar_scc_wait_timeout

    Global

    Lets you set the wait time for the transaction resolution of a read-only node to be replayed to the target CSN.

    Valid values: 0 to 1000000. Default value: 100. Unit: milliseconds.

    loose_innodb_polar_scc_timeout_degrade

    Global

    Lets you configure whether to allow reading historical data after the transaction resolution replay of a read-only node to the target CSN times out. Valid values:

    • OFF (default): Does not allow reading historical data after a timeout.

    • ON: Allows reading historical data after a timeout.

    2023.03.23

    Category

    Parameter

    Level

    Description

    New

    loose_foreign_key_checks

    Global/Session

    Specifies whether to check foreign key constraints. Valid values:

    • ON (default): Checks foreign key constraints.

    • OFF: Does not check foreign key constraints.

    Modified

    loose_max_execution_time

    Global/Session

    • Before modification: The max_execution_time parameter must be set to the same value for different nodes.

    • After modification: The max_execution_time parameter can be set to different values for different nodes.

    2022.10.24

    Category

    Parameter

    Level

    Description

    Modified

    loose_innodb_logical_read_ahead_threads

    Global

    The default number of threads for logical read-ahead is adjusted.

    2022.10.14

    Category

    Parameter

    Level

    Description

    Modified

    loose_optimizer_switch

    Global

    Stricter regex expressions are added to block input in an invalid format.

    2022.09.16

    Category

    Parameter

    Level

    Description

    New

    loose_innodb_polar_parallel_merge_ways

    Global

    Sets the number of ways for merge sort during index creation.

    Valid values: 2 to 16. Default value: 2.