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    PolarDB:PolarDB for MySQL 5.6

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    PolarDB:PolarDB for MySQL 5.6

    Last Updated:Sep 14, 2024

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

    5.6.1.0.43

    Category

    Description

    Release date

    New feature and feature optimization

    • The preemptible data definition language (DDL) feature is added to address metadata lock (MDL) acquisition failures during DDL synchronization.

    • The page read performance of read-only nodes on the PolarFileSystem (PFS) is enhanced.

    • The thread priorities in the PFS are optimized, which ensures the timely processing of transaction requests and improves the performance of DDL operations in PolarDB for MySQL.

    • The fast query cache feature includes information about the number of rows returned for each query. SQL Explorer and Audit can display the exact number of rows returned for queries that hit the cache.

    2024-07-08

    Fixed issue

    • The following issue is fixed: System maintenance activities have an impact on the metrics used to monitor the performance of slow SQL queries.

    • The following issue is fixed: The result set is incorrect when a function is used in the HAVING clause.

    5.6.1.0.42

    Category

    Description

    Release date

    Fixed issue

    • After an Autoinc rollback occurs, the most recent value of the autoincrement field can be restored by using the FLUSH TABLE statement. This method eliminates the need to restart the primary node or perform an ALTER TABLE operation and minimizes the impact on system performance.

    • The following issue is fixed: The auto-increment duplicate key issue occurs when an insert statement is executed on a partitioned table shortly after DDL statements are executed to modify the partitions.

    • The following issue is fixed: The primary node may crash during the execution of a DDL statement after logical prefetching is enabled.

    2024-04-24

    5.6.1.0.41

    Category

    Description

    Release date

    New feature and feature optimization

    The database and table restoration feature is optimized. For example, databases and tables can be restored more quickly, and failed tasks can be rolled back.

    2024-01-05

    Fixed issue

    • The following issue is fixed: Abnormal checkpoints occur after an UNDO TRUNCATE statement is executed.

    • The following issue is fixed: When the physical machine of a read-only node fails, the primary node does not terminate the data replication under special circumstances. As a result, the primary node cannot flush data.

    • The following issue is fixed: After you perform a degrade operation on an primary node, the physical replications on the standby nodes cannot be reconnected.

    • The following issue is fixed: When you upgrade an ApsaraDB RDS for MySQL instance to a PolarDB for MySQL cluster, the migration link is interrupted due to the restart of the cluster.

    • The following issue is fixed: When a database or table restoration is initiated, the read-only node fails to be added because the redo log on the primary node is cleared.

    • The following issue is fixed: An error is returned when you execute a DDL statement on a table in the discarded state.

    5.6.1.0.40

    Category

    Description

    Release date

    New feature and feature optimization

    • The Concurrency_count parameter in the concurrency_control system table can be set to 0 to implement an SQL blacklist.

    • The innodb_polar_import_tablespace_strict_mode parameter is added. The default value of this parameter is ON, which indicates that an error is reported when a table whose schema contains full-text indexes is restored.

    2023-09-07

    Fixed issue

    • The following issue is fixed: After an UNDO TRUNCATE statement is executed on a primary node and you use a read-only node to connect to a database, the read-only node crashes.

    • The following issue is fixed: When a high-availability (HA) switchover is performed to switch a read-only node to the primary node, the HA switchover process gets stuck.

    5.6.1.0.39.1

    Category

    Description

    Release date

    Fixed issue

    The following issue is fixed: The latency in SQL statement execution increases due to the excessive workload of the on-premises disk after the audit log feature is enabled.

    2023-08-02

    5.6.1.0.39

    Category

    Description

    Release date

    New feature and feature optimization

    • If the statement outline is not added, the digest of the SQL statement is not calculated when the SQL statement is executed.

    • DDL and LOCK TABLE statements can be recorded to system tables.

    • The innodb_polar_import_tablespace_strict_mode parameter is added. The default value of this parameter is ON, which indicates that an error is reported when a table whose schema contains full-text indexes is restored.

    • The Innodb_trx_history_list_len metric is added to monitor the length of the undo history list.

    • The lock granularity of PolarFileSystem is optimized to significantly improve performance in some high-load scenarios.

    2023-07-11

    Fixed issue

    • The following issue is fixed: A secondary node cannot be reconnected when the primary node is disabled and then is restarted.

    • The following issue is fixed: A regular user can delete the performance_schema database.

    • The following issue is fixed: An error is reported when ALTER TABLE ... IMPORT TABLESPACE is executed on the read/write node and read-only nodes are queried.

    • The following issue is fixed: The checkpoint LSN is not pushed down as expected.

    • The following issue is fixed: Replication latency occurs when the redo logs of a wide table are replayed on read-only nodes.

    • The following issue is fixed: When a large value is specified for the group_concat_max_len parameter, an arithmetic overflow occurs, which causes an invalid result of the GROUP_CONCAT function.

    5.6.1.0.38.1

    Category

    Description

    Release date

    Fixed issue

    The following issue is fixed: When slow query logs are concurrently recorded, a large number of SQL requests are piled up due to the abnormality of internal counter in the thread pool.

    2023-06-14

    5.6.1.0.38

    Category

    Description

    Release date

    New feature and feature optimization

    The SET PASSWORD command can be used to modify the password of a privileged account.

    2023-04-24

    Fixed issue

    • The following issue is fixed: A read timeout error occurs and the database cannot be connected when physical replication is established on a read-only node.

    • The following issue is fixed: Undo logs cannot be recycled after the undo log recycling feature is enabled.

    • The following issue is fixed: When the information_schema database is queried, the cache hit ratio decreases due to table cache pollution.

    5.6.1.0.37

    Category

    Description

    Release date

    New feature and feature optimization

    Thread pool optimizations:

    • You can use the thread_pool_high_priority_users parameter to configure a list of high-priority users. The thread pool preferentially allocates threads to requests from high-priority users.

    • The timeout mechanism for slow queries is added. When the thread pool counts the overall number of threads, the number of threads in the slow query state is ignored, so that the overall number of threads is not limited by the number of slow query threads.

    2023-03-16

    5.6.1.0.36

    Category

    Description

    Release date

    New feature and feature optimization

    • The statement outline feature is supported.

    • The timeout parameter related to the physical replication connection is modified to prevent issues in the case that the physical machine where the primary node is deployed fails.

    2023-01-06

    5.6.1.0.35.1

    Category

    Description

    Release date

    New feature and feature optimization

    • The low limit in the ORDER BY LIMIT clause is optimized to select a better execution plan based on the execution cost. The loose_low_limit_check_enabled parameter is added to specify whether to use the low limit optimization mode. Default value: ON.

    • The loose_prefer_ordering_index parameter is added to specify whether to use the ORDER BY column index to optimize sorting performance. The default value of this parameter is ON, which indicates that the ORDER BY column index is preferred for sorting optimization.

    2022-10-27

    5.6.1.0.35

    Category

    Description

    Release date

    New feature and feature optimization

    The memory overheads for accessing information_schema.tables are reduced.

    2022-10-14

    5.6.1.0.34

    Category

    Description

    Release date

    New feature and feature optimization

    The read-ahead mechanism for DDL statements is supported, which improves the efficiency of index creation.

    2022-07-13

    Fixed issue

    The following issue is fixed: When a large number of dirty pages exist in the buffer pool and page buffer pool flushing is slow, the least used page cannot be evicted.

    5.6.1.0.32

    Category

    Description

    Release date

    New feature and feature optimization

    The hot standby node feature is supported to further optimize high availability efficiency.

    2022-03-15

    Fixed issue

    The following issue is fixed: If the innodb_show_verbose_deadlock parameter is set to the default value ON, the information of all deadlocks is displayed when the show engine innodb status command is run.

    5.6.1.0.30

    Category

    Description

    Release date

    Fixed issue

    • The following issue is fixed: The statistics gathered for partitioned tables are inconsistent.

    • The following issue is fixed: When the packet length is 251 bytes, a length encoding error occurs.

    2021-11-10

    5.6.1.0.29

    Category

    Description

    Release date

    New feature and feature optimization

    • Transaction-based resumable transfer is supported for the database engine.

    • The fast query cache feature is supported. For more information, see Fast query cache.

    2021-09-09

    Fixed issue

    The process of loading redo logs is accelerated for the read-only nodes and the secondary cluster, which improves the synchronization efficiency of the primary node.

    5.6.1.0.28

    Category

    Description

    Release date

    New feature and feature optimization

    The polar_replica_work_on_nonblock_mdl_mode parameter is added. If this parameter is set to on, the uncommitted transactions that use the READ UNCOMMITTED or READ COMMITTED isolation level on read-only nodes no longer block DDL operations on the primary node. In addition, atomicity, consistency, isolation, and durability (ACID) is no longer ensured for the operations of creating tables on the read-only nodes.

    2021-07-23

    Fixed issue

    The speed at which the tablespace metadata is loaded is increased. For an instance that contains millions of tables, this can significantly reduce the time required to restore a failed primary node and the time required to start a read-only node.

    5.6.1.0.27

    Category

    Description

    Release date

    Fixed issue

    • 4K alignment is used when you run the truncate polar logs lsn command to delete files on read-only nodes.

    • KICKOUT is used as a non-reserved keyword.

    • The policy that specifies whether a checkpoint is immediately triggered when a read-only node is attached to the primary node for the first time is adjusted. The new policy specifies that the checkpoint is not triggered if the log sequence number (LSN) difference is less than a specified threshold.

    • Conditional statements can be added in the load polar logs statement.

    • The following issue is fixed: Duplicate entries exist for the auto-increment field.

    2021-06-01

    5.6.1.0.26

    Category

    Description

    Release date

    Fixed issue

    • The following issue is fixed: The connection fails when you run the FLUSH PRIVILEGES or FLUSH GRANT command that is used to authorize multiple users at a time.

    • The following issue is fixed: An incorrect estimation result is returned in some cases because the estimation of partitioned tables is aborted.

    • The following issue is fixed: The SHOW PROCESSLIST statement in some scenarios returns an invalid result.

    • The following issue is fixed: If the session_track_temporary_tables system variable is enabled for a cluster, the cluster becomes unavailable when temporary tables are created or deleted during a storage procedure.

    2021-03-19

    5.6.1.0.25

    Category

    Description

    Release date

    New feature and feature optimization

    The database-level data recovery feature and the table-level data recovery feature are optimized. This way, data can be recovered in a more efficient manner.

    2021-02-05

    Fixed issue

    • The following issue is fixed: Read-only nodes become unavailable after the nodes read truncated undo pages.

    • The following issue is fixed: The primary zone cannot be changed for a cluster that has performed a failover.

    5.6.1.0.24

    Category

    Description

    Release date

    New feature and feature optimization

    • The process for initializing the PolarDB engine is optimized. The amount of time required to initialize the engine is reduced in large table scenarios.

    • The Kernel Version of a PolarDB cluster is displayed on the Basic Information page of the cluster in the PolarDB console.

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

    2021-01-22

    Fixed issue

    • The following issue is fixed: Undo logs cannot be truncated when data is being migrated from an ApsaraDB RDS instance to a PolarDB cluster.

    • The following issue is fixed: System tables cannot be added.

    • The following issue is fixed: The primary node becomes unavailable when databases or tables are being restored.

    • The following issue is fixed: The returned decimal numbers are not correctly sorted.

    • The following issue is fixed: The MySQL service process breaks down in some scenarios.

    5.6.1.0.23

    Category

    Description

    Release date

    Fixed issue

    The following issue is fixed: Memory leaks occur on read-only nodes.

    2021-01-04

    5.6.1.0.22

    Category

    Description

    Release date

    New feature and feature optimization

    The directory indexing feature is supported by Polar file system (PFS). This improves cluster performance in scenarios in which a large number of tables are stored in the cluster.

    2020-12-25

    Fixed issue

    • The following issue is fixed: A cluster becomes unavailable due to invalid node roles after a failover between the primary node and a read-only node is performed in some cases.

    • The following issue is fixed: Read-only nodes crash because the statement queue feature is not initialized.

    • The following issue is fixed: New system tables are not initialized after a failover between the primary node and a read-only node.

    • The following issue is fixed: The other feature is automatically enabled when the thread pool or connection control feature is enabled.

    • The following issue is fixed: A cluster becomes unavailable due to duplicate IDs in the full-text index.

    • The following issue is fixed: Queries cannot be executed on a read-only node in some cases.

    • The following issue is fixed: The replication process is interrupted when the log replication thread unexpectedly exits.

    5.6.1.0.21

    Category

    Description

    Release date

    New feature and feature optimization

    2020-11-12

    Fixed issue

    • The following issue is fixed: The out of memory (OOM) error occurs when you use DYNAMIC RANGE and INDEX MERGE in SELECT statements.

    • The following issue is fixed: A cluster crashes when you create or delete an account in some cases.

    • The following issue is fixed: Read-only nodes cannot be reconnected in some cases.

    • The following issue is fixed: A cluster fails to start when a failover error occurs.

    • The following issue is fixed: The Binlog thread is not in the expected state in some cases.

    5.6.1.0.20

    Category

    Description

    Release date

    New feature and feature optimization

    Physical replication can be performed in a more efficient manner in some scenarios.

    2020-10-27

    Fixed issue

    • The following issue is fixed: A cluster crashes when you execute the CREATE TABLE... SELECT statement.

    • The following issue is fixed: Memory leaks occur in the stored procedure due to the excessive use of derived tables.

    • The following issue is fixed: The data is not restored to the specified point in time or fails to be restored.

    • The following issue is fixed: A large number of PolarFileSystem exception logs are reported.

    • The following issue is fixed: After the foreign key check is disabled, tables are lost when you perform DDL operations.

    • The following issue is fixed: Read-only nodes crash when you truncate multiple temporary tables at the same time.

    20200831

    Category

    Description

    Release date

    New feature and feature optimization

    Local disks and writable snapshots that are created for the disks attached to an instance are supported by PolarFileSystem. The performance of PFS is optimized.

    2020-09-22

    Fixed issue

    • The following issue is fixed: The cluster crashes when you use the statement queue feature in some cases.

    • The following issue is fixed: A large amount of storage resources is being consumed by the core files.

    • The following issue is fixed: Statistics are inconsistent between the primary node and read-only nodes.

    • The following issue is fixed: After a read-only node is specified as the primary node, the other read-only nodes cannot connect to the new primary node.

    • The following issue is fixed: The full-text index cache that is allocated to implement sharing between the primary node and read-only nodes is inconsistent.

    20200616

    Category

    Description

    Release date

    New feature and feature optimization

    • The statement queue feature is supported. For more information, see Statement queue.

    • The replication latency between the primary node and read-only nodes is reduced.

    • The metadata lock can be replicated when you execute the LOCK TABLE statement.

    2020-07-01

    Fixed issue

    • The metadata lock issue that occurs during data replication is fixed.

    • The following issue is fixed: A full-text search index is created in the system table.

    • The issues that are related to the updates and performance optimization of hot rows are fixed.

    20200601

    Category

    Description

    Release date

    New feature and feature optimization

    • Hot rows can be updated, and the performance of hot rows can be optimized. For more information, see Hot row optimization.

    • The statement concurrency control feature is supported. For more information, see Concurrency control.

    2020-06-05

    Fixed issue

    The following issue is fixed: The write performance is reduced due to issues in thread pools.

    20200507

    Category

    Description

    Release date

    New feature and feature optimization

    • The statement concurrency control feature is added.

    • A parameter is added to manage the ratio of idle space to total space on index pages.

    • The simulated asynchronous I/O model is optimized.

    2020-05-13

    Fixed issue

    • The following issue is fixed: The performance is degraded because the data of the Boolean flag data type exists.

    • The following issue is fixed: Clusters become unavailable because the pfs_umount table is not closed.