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    PolarDB:Release notes for PolarDB for MySQL 5.6

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    PolarDB:Release notes for PolarDB for MySQL 5.6

    Last Updated:Sep 11, 2025

    This topic provides the release notes for PolarDB for MySQL 5.6.

    5.6.1.0.46.1

    Category

    Description

    Release date

    Fixed issues

    • Fixed a rare issue where the background purge process could corrupt a secondary index during a transaction rollback.

    2025-08-28

    5.6.1.0.46

    Category

    Description

    Release date

    Fixed issues

    • Fixed a potential crash on read-only nodes caused by an uninitialized Hist_View.

    • Fixed a potential cluster crash that occurred when updating a NULL value to an empty string in tables that use the REDUNDANT row format and contain columns added with second-level precision.

    • Fixed an issue where a database and table restoration job was interrupted if the database or table name in the job parameters contained uppercase letters.

    • Fixed an issue where BackQuery queries returned an error if consistent read was not ensured.

    • Fixed an issue where recording `IMPORT TABLE` restore SQL statements to the binary log could interrupt downstream binary log dump replication.

    2025-06-18

    5.6.1.0.45

    Category

    Description

    Release date

    Fixed issues

    • Fixed a system variable compatibility issue where setting a flagset type variable, such as optimizer_switch, with duplicate entries no longer causes an error.

    • Fixed an issue where a read-only node would continuously fail to provide services after reconnecting to the RW node.

    2025-01-20

    5.6.1.0.44

    Category

    Description

    Release date

    Performance optimizations

    • Optimized the performance stability of the file system when table files are frequently created and deleted during DDL operations.

    2024-10-18

    Fixed issues

    • Fixed a crash that could occur when a read-only node with the RO No Sync feature enabled was promoted to an RW node through a high availability (HA) switchover.

    • Fixed an issue where user threads on a read-only node waited too long for a free page when the buffer pool reached its capacity limit.

    • Fixed a conflict between the advanced transaction splitting feature of the proxy and the Fast Query Cache feature that affected result sets.

    • Fixed an issue where the auto-increment value could roll back to 0 after all data in a table was cleared.

    5.6.1.0.43

    Category

    Description

    Release date

    New features and performance optimizations

    • Added the preemptive DDL feature to resolve metadata lock (MDL) acquisition failures during DDL synchronization.

    • Optimized the page read performance of read-only nodes on the distributed file system (PolarFileSystem).

    • Optimized thread priorities in the distributed file system (PolarFileSystem) to ensure timely processing of transaction requests and improve DDL performance in PolarDB for MySQL.

    • The Fast Query Cache feature now includes information about the number of returned rows. SQL Explorer and Audit can display the number of rows returned by queries that hit the cache.

    2024-07-08

    Fixed issues

    • Fixed an issue where system O&M access affected the status metrics of slow SQL statements.

    • Fixed an issue where the result set was incorrect when a function was used in the HAVING clause.

    5.6.1.0.42

    Category

    Description

    Release date

    Fixed issues

    • Added a mechanism to reload the latest auto-increment value by running `flush table` when an auto-increment rollback occurs. This avoids the need to restart the RW node or run `ALTER TABLE`, reducing the impact.

    • Fixed an auto-increment duplicate key issue that occurred when an insert statement was executed on a partitioned table after a DDL statement modified its partitions.

    • Fixed a potential crash of the RW node triggered by a DDL statement when logical read-ahead was enabled.

    2024-04-24

    5.6.1.0.41

    Category

    Description

    Release date

    New features and performance optimizations

    Optimized the database and table restoration feature. For example, the restoration speed is increased and task rollback on failure is supported.

    2024-01-05

    Fixed issues

    • Fixed an issue where abnormal checkpoints occurred during an undo truncate process.

    • Fixed an issue where dirty page flushing on the RW node was blocked because the RW node did not terminate its replication relationship with a read-only node whose physical server had failed.

    • Fixed an issue where the standby node lost the physical replication reconnection mechanism after a Degrade operation was performed on the RW node.

    • Fixed an issue where the migration link was interrupted due to a PolarDB cluster restart during a one-click upgrade from ApsaraDB RDS for MySQL to PolarDB for MySQL.

    • Fixed an issue where adding a new read-only (RO) node failed because the registration offset of the RO node was too low during the new database and table restoration process.

    • Fixed an error that occurred when performing a DDL operation on a table in the discarded state.

    5.6.1.0.40

    Category

    Description

    Release date

    New features and performance optimizations

    • Supports an SQL blacklist feature by setting the Concurrency_count parameter in the concurrency_control system table to 0.

    • Added the innodb_polar_import_tablespace_strict_mode parameter. The default value is ON. When this parameter is on, an error is reported if the table schema contains a full-text index during a database and table restoration operation.

    2023-09-07

    Fixed issues

    • Fixed an issue where a read-only (RO) node would crash if you connected to the database through the RO node to read data after an undo truncate operation was completed on the read/write (RW) node.

    • Fixed an issue where the HA process was stuck when an HA switchover was performed to promote an RO node to an RW node.

    5.6.1.0.39.1

    Category

    Description

    Release date

    Fixed issues

    Fixed an issue where SQL latency increased due to excessive pressure on the local disk after audit logging was enabled.

    2023-08-02

    5.6.1.0.39

    Category

    Description

    Release date

    New features and performance optimizations

    • The digest value of an SQL statement is no longer calculated when the statement is executed without an added Statement Outline.

    • Supports recording DDL and LOCK TABLE statements to system tables.

    • Added the innodb_polar_import_tablespace_strict_mode parameter. The default value is ON. When this parameter is on, an error is reported if the table schema contains a full-text index during a database and table restoration operation.

    • Added the Innodb_trx_history_list_len monitoring metric to view the length of the undo history list.

    • Optimized the internal lock granularity of PolarFS, significantly improving performance in some high-payload scenarios.

    2023-07-11

    Fixed issues

    • Fixed an issue where the secondary node did not trigger the reconnection mechanism when the primary node was shut down and restarted.

    • Fixed an issue where a regular user could delete the performance_schema database.

    • Fixed a potential error that occurred when running a query on an RO node while an ALTER TABLE ... IMPORT TABLESPACE operation was running on the RW node.

    • Fixed an issue where the checkpoint LSN did not advance as expected.

    • Fixed a replication delay issue that occurred when replaying redo logs of a wide table on an RO node.

    • Fixed an issue where a large value for the group_concat_max_len parameter caused an arithmetic overflow, leading to an incorrect result from the GROUP_CONCAT function.

    5.6.1.0.38.1

    Category

    Description

    Release date

    Fixed issues

    Fixed an issue where an abnormal internal counter in the thread pool could cause a backlog of SQL requests during concurrent recording of Redis Slow Log.

    2023-06-14

    5.6.1.0.38

    Category

    Description

    Release date

    New features and performance optimizations

    Supports changing passwords for high-privilege accounts using the SET PASSWORD command.

    2023-04-24

    Fixed issues

    • Fixed a read timeout that occurred when establishing physical replication on a read-only node, which prevented database connection.

    • Fixed an issue where undo logs could not be recycled after the undo log recycling feature was enabled.

    • Fixed an issue where querying information_schema caused a subsequent drop in the cache hit rate due to table cache pollution.

    5.6.1.0.37

    Category

    Description

    Release date

    New features and performance optimizations

    Thread pool optimizations:

    • You can use the thread_pool_high_priority_users parameter to configure a list of high-priority users. The thread pool prioritizes allocating threads to meet the needs of high-priority users.

    • Added a slow query timeout mechanism. The thread pool ignores the number of threads in a slow query state when calculating the total number of threads. This ensures the total number of threads is no longer limited by the number of slow query threads.

    2023-03-16

    5.6.1.0.36

    Category

    Description

    Release date

    New features and performance optimizations

    • Supports the statement outline feature.

    • Adjusted the timeout parameters for physical replication connections to prevent connection issues when the physical server of the RW node fails.

    2023-01-06

    5.6.1.0.35.1

    Category

    Description

    Release date

    New features and performance optimizations

    • Optimized the low limit in `order by limit` scenarios to select a better execution plan based on execution cost. A control switch, loose_low_limit_check_enabled, is added to choose whether to use the low limit optimization method. The default value is ON.

    • In `order by limit` scenarios, a control switch, loose_prefer_ordering_index, is added to control the optimization method for the ordering index. The default value is ON, which prioritizes sorting optimization using the `order by` column index.

    2022-10-27

    5.6.1.0.35

    Category

    Description

    Release date

    New features and performance optimizations

    Optimized the memory overhead of accessing `information_schema.tables`.

    2022-10-14

    5.6.1.0.34

    Category

    Description

    Release date

    New features and performance optimizations

    Supports the DDL read-ahead feature to improve the efficiency of index creation.

    2022-07-13

    Fixed issues

    Fixed an issue where the LRU List cleanup was blocked, preventing page release, in scenarios with excessive dirty pages in the Buffer Pool and slow dirty page flushing.

    5.6.1.0.32

    Category

    Description

    Release date

    New features and performance optimizations

    Supports the hot replica feature to further optimize HA efficiency.

    2022-03-15

    Fixed issues

    Fixed an issue where running the show engine innodb status command displayed full deadlock information when innodb_show_verbose_deadlock was set to ON (the default value).

    5.6.1.0.30

    Category

    Description

    Release date

    Fixed issues

    • Fixed unstable statistics information for partitioned tables.

    • Fixed a number length encoding error when the message length is 251.

    2021-11-10

    5.6.1.0.29

    Category

    Description

    Release date

    New features and performance optimizations

    • The database kernel supports resumable transaction transmission.

    • Supports Fast Query Cache. For more information, see Fast Query Cache.

    2021-09-09

    Fixed issues

    Accelerated redo log application on read-only nodes and secondary clusters to improve the synchronization efficiency of the primary node.

    5.6.1.0.28

    Category

    Description

    Release date

    New features and performance optimizations

    Added the polar_replica_work_on_nonblock_mdl_mode parameter. When this parameter is enabled, uncommitted transactions with RU/RC isolation levels on read-only nodes no longer block DDL operations on the primary node. Also, the transactional properties of table definitions are no longer guaranteed on read-only nodes.

    2021-07-23

    Fixed issues

    Optimized the loading speed of tablespace metadata. For database instances with over a million table files, this significantly shortens the recovery time after a primary node crash and the startup time for secondary nodes.

    5.6.1.0.27

    Category

    Description

    Release date

    Fixed issues

    • Optimized the `truncate polar logs lsn` command on standby nodes to use 4 KB alignment when deleting files.

    • Changed KICKOUT to a non-reserved keyword.

    • Adjusted the policy for whether to immediately trigger a checkpoint when a read-only node first registers with the primary node. A checkpoint may not be triggered if the LSN difference is less than a specific threshold.

    • The `load polar logs` command now supports adding conditional statements.

    • Fixed an issue with duplicate auto-increment values.

    2021-06-01

    5.6.1.0.26

    Category

    Description

    Release date

    Fixed issues

    • Fixed a potential connection failure when running `FLUSH PRIVILEGES` or `FLUSH GRANT` commands for batch authorization.

    • Fixed incorrect partitioned table estimations caused by the premature termination of the estimation logic in some cases.

    • Fixed incorrect results from `SHOW PROCESSLIST` in some scenarios.

    • Fixed an issue where creating or deleting a temporary table in a stored procedure could cause the cluster to become unavailable when the session_track_temporary_tables system variable was enabled.

    2021-03-19

    5.6.1.0.25

    Category

    Description

    Release date

    New features and performance optimizations

    Optimized the database-level and table-level restoration feature to improve data restoration speed.

    2021-02-05

    Fixed issues

    • Fixed an issue where a read-only node became unavailable after reading a truncated undo page.

    • Fixed an issue where changing the primary zone might fail on a cluster that had already performed a primary/secondary failover.

    5.6.1.0.24

    Category

    Description

    Release date

    New features and performance optimizations

    • Optimized the PolarDB engine initialization process to shorten the engine startup time in large-table scenarios.

    • You can now view the Kernel Version of the cluster on the Basic Information page.

    • The default value of the innodb_adaptive_hash_index parameter is changed from ON to OFF.

    2021-01-22

    Fixed issues

    • Fixed an issue where Undo Log could not be truncated during migration from RDS to PolarDB.

    • Fixed an issue where new system tables could not be added.

    • Fixed an issue where the primary node became unavailable during database and table restoration.

    • Fixed incorrect sorting when query results were of the DECIMAL type.

    • Fixed several issues that could cause the MySQL service process to crash in special circumstances.

    5.6.1.0.23

    Category

    Description

    Release date

    Fixed issues

    Fixed memory leaks on read-only nodes.

    2021-01-04

    5.6.1.0.22

    Category

    Description

    Release date

    New features and performance optimizations

    PFS now supports directory indexing to improve cluster performance in scenarios with a massive number of tables.

    2020-12-25

    Fixed issues

    • Fixed an issue where the cluster became unavailable due to incorrect node roles after a primary/secondary failover in some cases.

    • Fixed a crash on read-only nodes caused by an uninitialized Statement Queue.

    • Fixed an issue where new system tables were not initialized after a primary/secondary failover.

    • Fixed an issue where the thread pool and Connection Control features were enabled simultaneously.

    • Fixed an issue where the cluster became unavailable due to duplicate IDs in the full-text index.

    • Fixed query failures on read-only nodes in some cases.

    • Fixed a replication interruption caused by an abnormal exit of the log replication thread.

    5.6.1.0.21

    Category

    Description

    Release date

    New features and performance optimizations

    2020-11-12

    Fixed issues

    • Fixed an out-of-memory (OOM) issue that occurred when using DYNAMIC RANGE AND INDEX MERGE in SELECT statements.

    • Fixed a cluster crash that occurred when creating or deleting an account in some cases.

    • Fixed an issue where STANDBY nodes could not be reconnected in some cases.

    • Fixed an issue where a cluster failed to start when an exception occurred during a primary/secondary failover.

    • Fixed an issue where the binary log thread was in an incorrect state in some cases.

    5.6.1.0.20

    Category

    Description

    Release date

    New features and performance optimizations

    Improved the efficiency of physical replication in some cases.

    2020-10-27

    Fixed issues

    • Fixed a cluster crash that could occur when executing the CREATE TABLE... SELECT command.

    • Fixed a memory leak in a stored procedure caused by excessive use of derived tables.

    • Fixed an issue where data was not restored to the correct point in time or the restore job failed during a point-in-time restore.

    • Fixed an issue with excessive output of PolarFS exception logs.

    • Fixed table loss when performing DDL operations after foreign key checks were disabled.

    • Fixed a crash on read-only nodes when truncating multiple temporary tables at the same time.

    20200831

    Category

    Description

    Release date

    New features and performance optimizations

    PFS supports local disks, mounting writable snapshots, and performance optimizations.

    2020-09-22

    Fixed issues

    • Fixed a cluster crash that could occur when using the Statement Queue feature in some cases.

    • Fixed an issue where Corefiles occupied too much space.

    • Fixed inconsistent statistics information between the primary node and read-only nodes.

    • Fixed an issue where other read-only nodes could not connect to the new primary node after a read-only node was promoted to primary.

    • Fixed inconsistent full-text index caches between the primary node and read-only nodes.

    20200616

    Category

    Description

    Release date

    New features and performance optimizations

    • Supports the Statement Queue feature. For more information, see Statement Queue.

    • Optimized the replication delay between RO and RW nodes.

    • Supports replicating the MDL lock for `LOCK TABLE`.

    2020-07-01

    Fixed issues

    • Fixed issues in MDL lock replication.

    • Fixed an issue where an FTS INDEX was created on a system table.

    • Fixed some issues with hot spot update optimization.

    20200601

    Category

    Description

    Release date

    New features and performance optimizations

    2020-06-05

    Fixed issues

    Fixed a write performance degradation issue caused by the thread pool.

    20200507

    Category

    Description

    Release date

    New features and performance optimizations

    • Added a concurrency control feature.

    • Added a parameter to control the free space on index pages.

    • Optimized Simulate AIO.

    2020-05-13

    Fixed issues

    • Fixed a performance degradation issue caused by the bool flag class.

    • Fixed an issue where the cluster became unavailable because the `pfs_umount` table was not closed.