This topic describes the updates and features of the PolarDB for MySQL database kernel.

The following figure shows the position of the PolarDB database engine in the PolarDB architecture.

1

For more information about the architecture and features of PolarDB, see Architecture.

Features of the PolarDB database kernel

Feature 5.6 5.7 8.0
Parallel DDL Not supported. Not supported. Supported. The version of the kernel must be 8.0.1.1.7 or later.
Fast Query Cache Not supported. Not supported. Supported. The version of the kernel must be 8.0.1.1.5 or later.
Statement Outline Not supported. Supported. The minor version of the kernel must be 5.7.1.0.2 or later. Supported. The minor version of the kernel must be 8.0.1.1.1 or later.
ROLLUP Not supported. Not supported. Supported. The version of the kernel must be 8.0.1.1.0 or later.
Recycle bin Not supported. Not supported. Supported. The version of the kernel must be 8.0.1.1.2 or later.
Transparent Data Encryption (TDE) Supported. The version of the kernel must be 5.6.1.0.21 or later. Supported. The version of the kernel must be 5.7.1.0.3 or later. Supported. The version of the kernel must be 8.0.1.1.1 or later.
Parallel query Parallel query Not supported. Not supported. Supported. The version of the kernel must be 8.0.1.0.5 or later.
Hash joins in parallel queries Not supported. Not supported. Supported. The version of the kernel must be 8.0.2.1.0 or later.
Perform semijoins in parallel Not supported. Not supported. Supported. The version of the kernel must be 8.0.1.1.2 or later.
Parallel Hint Not supported. Not supported. Supported. The version of the kernel must be 8.0.1.0.5 or later.
High concurrency optimization Statement Concurrency Control Supported. The version of the kernel must be 20200616 or later. Not supported. Supported. The version of the kernel must be 8.0.1.1.7 or later.
Inventory Hint Not supported. Not supported. Supported. The version of the kernel must be 8.0.1.1.1 or later.
Statement Queue Supported. The version of the kernel must be 20200616 or later. Not supported. Supported. The version of the kernel must be 8.0.1.1.1 or later.
Hot row optimization applicable to flash sales Supported. The version of the kernel must be 20200601 or later. Not supported. Supported. The version of the kernel must be 8.0.1.1.10 or later.
The thread pool feature Supported. The version of the kernel must be 20200423 or later. Not supported. Supported. The version of the kernel must be 8.0.1.1.1 or later.

Query the kernel version

  • For PolarDB for MySQL 8.0, execute the following statements to query the kernel version:
    • If your cluster is created after February 5, 2020, execute the following statement:
      show variables like "%polardb_version%";
    • If your cluster is created on or before February 5, 2020, execute the following statement:
      show variables like '%rds_release_date%';

    To view the time when the cluster is created, log on to the PolarDB console, find the cluster, and then click the cluster ID. On the Overview page, you can view the value of the Created At parameter.

    Creation time
  • For PolarDB for MySQL 5.6, execute the following statement to query the kernel version:
    show variables like '%rds_release_date%';
Note For more information about the version of the PolarDB database kernel, see Version of the PolarDB database kernel.

PolarDB for MySQL 8.0 release notes

PolarDB for MySQL 8.0 supports the following versions.

Minor version Revision version Release date Minor MySQL version that is fully compatible with PolarDB for MySQL Release overview
8.0.2.x

In public preview

8.0.2.1.4 20201201 8.0.18 The Index Hints feature of MySQL 8.0.20 is supported. For more information, see Index Hints.
8.0.2.1.3 20201026 8.0.18
  • The cost estimation model for hash joins is improved.
  • Parallel hash joins are supported. The build phase and the probe phase can be executed in parallel.
8.0.2.1.2 20200927 8.0.18 The latest volcano iterator executor is supported.
8.0.2.1.1 20200826 8.0.18 Some known bugs are fixed.
8.0.2.1.0 20200722 8.0.18
8.0.1.x 8.0.1.1.10 20210112 8.0.13
  • The implicit sorting feature of Group By is supported.
  • The hot row optimization feature is supported. For more information, see Hot row optimization.
  • The physical replication optimization feature of data definition language (DDL) operations is supported. For more information, see DDL physical replication optimization.
8.0.1.1.9 20201218 8.0.13 The SPM and PLAN keywords are removed.
8.0.1.1.8 20201209 8.0.13
  • The multi-plan mode is supported in the execution plan manager.
  • The rds_ap_threshold system variable is added to block the requests that cause the system to scan an excessive number of records. These requests are evaluated by the optimizer.
  • The efficiency of writing dirty pages to disks on the primary node is improved.
  • A multi-shard writing mechanism for redo logs is supported.
8.0.1.1.7 20201116 8.0.13
  • The parallel scanning efficiency of driven tables in scenarios such as Join queries is improved.
  • Remaining binary logs can be cleared when the binary logging feature is disabled.
  • Interrupted physical replications of secondary nodes can be automatically detected and then resumed.
  • The efficiency of the switchover between the primary node and read-only nodes is improved.
  • Quick startup is supported for clusters that contain a large number of tables. This way, table data files can be rapidly scanned.
8.0.1.1.6 20200921 8.0.13
  • The compatibility between the SQL plan manager (SPM) and parallel queries is improved.
  • The merge sort efficiency of parallel queries is improved.
  • The computations of DELETE operations can be pushed down.
  • The Commit Timestamp (CTS) feature of PolarDB is supported.
8.0.1.1.5 20200819 8.0.13
  • A feature is added to determine whether the primary node immediately applies the checkpoint policy when it establishes a replication relationship with read-only nodes.
  • Simple range queries are supported and computations can be pushed down.
8.0.1.1.4 20200704 8.0.13
  • DDL statements can be executed in parallel. This improves the efficiency of executing the DDL statements.
  • The length of each queue for the simulated asynchronous I/O (AIO) can be dynamically adjusted.
  • The cache coherence is supported for a full-text search (FTS).
8.0.1.1.3 20200529 8.0.13 The parallel query feature is improved.
8.0.1.1.2 20200409 8.0.13
  • The recycle bin feature is supported. This prevents data loss that is caused by unintended DROP operations. For more information, see Recycle bin.
  • The negative impact of the operations that are performed on temporary tables on performance is reduced.
  • The parallel query feature is improved.
8.0.1.1.1 20200328 8.0.13
  • The thread pool feature is supported. For more information, see Thread pool.
  • Global database networks (GDNs) are supported. For more information, see Global database networks.
  • The parallel query feature is improved.
8.0.1.1.0 20200205 8.0.13
  • The cost estimation model for parallel queries is improved.
  • The thread scheduling capabilities of parallel query executors are enhanced.
8.0.1.0.6 20200101 8.0.13 Some known bugs are fixed.
8.0.1.0.5 20191203 8.0.13 Diagnosis information about the execution plans of parallel queries is added. This ensures that the execution plans are easy to read.
  • 8.0.2.1.4(20201201)
    Category Description
    New features and performance optimization The Index Hints feature of MySQL 8.0.20 is supported.
    Bug fixes The stability issue in parallel queries is fixed.
    The following bug is fixed: The estimated number of rows for each index key in statistics is miscalculated.
    The following bug is fixed: An error occurs in processing empty data when shared temporary tables are scanned in parallel.
    The following bug is fixed: An error occurs when you use the official REGEXP_REPLACE function to process data.
    The following bug is fixed: A breakdown occurs when a complex query contains subquery constants.
    The following bug is fixed: The filesort returns invalid data.
  • 8.0.2.1.3(20201026)
    Category Description
    New features and performance optimization The cost estimation model for hash joins is improved.
    Parallel hash joins are supported. The build phase and the probe phase can be executed in parallel.
    Bug fixes The following bug is fixed: A wrong number of parallel partitions in a parallel execution plan is displayed.
    The following bug is fixed: An exceptional breakdown occurs for parallel subqueries.
    The following bug is fixed: Multiple worker threads cannot generate random results when the RAND() function is used in parallel queries.
  • 8.0.2.1.2(20200927)
    Category Description
    New features and performance optimization PolarDB supports the latest volcano iterator executor for parallel queries.
  • 8.0.2.1.1(20200826)
    Category Description
    New features and performance optimization The write performance of clusters is optimized.
    Bug fixes The memory leak bug is fixed.
  • 8.0.2.1.0(20200722)
    Category Description
    New features and performance optimization The EXPLAIN statement returns a parallel plan. You can specify FORMAT=TREE to view a parallel execution plan tree.
    Hash joins are supported for parallel queries. The performance of join operations that do not use indexes is improved. For more information, see Hash joins in parallel queries.
    The Resource Manager feature is added to monitor CPU and memory resources. For more information, see Resource Manager.
    The Performance Agent feature is added to collect the statistics about the performance metrics of PolarDB for MySQL instances. To obtain the performance metric data, you can directly query the PERF_STATISTICS in-memory table. For more information, see Performance Agent.
    The warm buffer pool feature is supported. When a PolarDB for MySQL instance restarts after a breakdown or an upgrade, data in the buffer pool remains available. This significantly accelerates the restart process, and ensures that the performance is not compromised after the restart.
  • 8.0.1.1.10(20210112)
    Category Description
    New features and performance optimization The implicit sorting feature of Group By is supported. This feature works in the same way as in PolarDB for MySQL 5.7.
    Parallel queries can be disabled if a BLOB field exists.
    The cache information about statement concurrency control can be automatically updated on read-only nodes.
    The hot row optimization feature is supported. For more information, see Hot row optimization.
    The physical replication optimization feature of DDL operations is supported. For more information, see DDL physical replication optimization.
    Quick reverse traversal is supported if computations are pushed down.
    Bug fixes The following bug is fixed: The system tables are lost when a read-only node is promoted to the primary node.
    The following bug is fixed: An excessive number of scanned rows are evaluated when range queries are used after the parallel query feature is enabled.
    The following bug is fixed: The results of aggregate queries are of the integral type if the field type is BIT.
    The following bug is fixed: The SELECT DISTINCT queries return invalid results after enumerated fields are used.
    The following bug is fixed: An exception occurs in the results of parallel queries that use the EXISTS condition.
    The following bug is fixed: Read-only nodes fail to restart in some cases.
    The following bug is fixed: An exception occurs in table information in the data dictionary when a read-only node executes DDL statements. This is because the table for which DDL statements are being executed is re-opened when a foreign key association table is opened.
    The following bug is fixed: The full-text index query fails due to the improper setting of a node restart flag after a primary/secondary switchover.
    The following bug is fixed: The log application threads on read-only nodes are blocked due to a metadata lock (MDL).
    The following bug is fixed: The new primary node becomes unavailable after a primary/secondary switchover because the released memory is reused.
    The following bug is fixed: All nodes become unavailable due to the polar.info data error.
    The following bug is fixed: An auto-increment column exception occurs in partitioned tables.
    The following bug is fixed: An data error occurs when redo logs on the primary node are overwritten.
    The following bug is fixed: The primary node is unavailable when it is waiting for an MDL.
    The bug related to the use of transparent data encryption (TDE) is fixed.
    The following bug is fixed: The cluster becomes unavailable when you execute the LOCK TABLE statement and enable the recycle bin feature.
    The following bug is fixed: A deadlock occurs when DDL statements are executed on the primary node.
    The following bug is fixed: The thread pool and the connection control fail to take effect at the same time.
  • 8.0.1.1.9(20201218)
    Category Description
    New features and performance optimization The SPM and PLAN keywords are removed. This prevents issues that you cannot manage the tables whose names contain these two words.
  • 8.0.1.1.8(20201209)
    Category Description
    New features and performance optimization The multi-plan mode is supported in the execution plan manager.
    The rds_ap_threshold system variable is added to block the requests that cause the system to scan an excessive number of records. These requests are evaluated by the optimizer.
    The efficiency of writing dirty pages to disks on the primary node is improved.
    A multi-shard writing mechanism for redo logs is supported.
    Bug fixes The following bug is fixed: The MDL key null pointer occurs during parallel queries.
    The following bug is fixed: A query fails when you create a parallel thread cache.
    The following bug is fixed: An error is returned when multi-range read (MRR) is used in parallel queries.
  • 8.0.1.1.7(20201116)
    Category Description
    New features and performance optimization The parallel scanning efficiency of driven tables in scenarios such as Join queries is improved.
    Remaining binary logs can be cleared when the binary logging feature is disabled.
    Interrupted physical replications of secondary nodes can be automatically detected and then resumed. This prevents long-term interruptions of physical replications.
    The efficiency of the switchover between the primary node and read-only nodes is improved.
    Quick startup is supported for clusters that contain a large number of tables. This way, table data files can be rapidly scanned.
    Bug fixes The following bug is fixed: A cluster breakdown may occur when you obtain the type of trx->wait_lock.
    The following bug is fixed: The number of AIO threads reaches an upper limit when a multi-queue simulated AIO is enabled.
    The following bug is fixed: A query cannot be directly closed if a query initialization failure occurs when you query indexes.
    The following bug is fixed: The Next Page of the current cursor points to a page that does not exist when a secondary node is in the split merge operation (SMO).
    The following bug is fixed: Read-only nodes read logs that have been overwritten by the primary node.
    The following bug is fixed: The system fails to clear redo log files because the timestamp intervals in the redo logs are large.
    The following bug is fixed: The table cache information in the related cache is not cleared when MDLs are released.
  • 8.0.1.1.6(20200921)
    Category Description
    New features and performance optimization The compatibility between the SPM and parallel queries is improved.
    The merge sort efficiency of parallel queries is improved.
    The computations of DELETE operations can be pushed down.
    The CTS feature of PolarDB is supported.
    Bug fixes
    The following bug is fixed: The description of pq_optimize_switch is wrong.
    The following bug is fixed: Subqueries cannot be stably executed.
  • 8.0.1.1.5(20200819)
    Category Description
    New features and performance optimization A feature is added to determine whether the primary node immediately applies the checkpoint policy when it establishes a replication relationship with read-only nodes.
    Simple range queries are supported and computations can be pushed down.
    The polar file system (PFS) adds the pfs_remount feature. This feature fixes the issue that files in PFS fail to be mounted when the files are open.
    The performance bottlenecks caused by forcible pauses of parse threads on read-only nodes are removed. The efficiency of data synchronization between the primary node and read-only nodes during physical replication is improved.
    The performance of Early Lock Release (ELR) is improved in multi-connection scenarios. The cluster performance in multi-connection scenarios is improved by 10 times.
    Bug fixes The following bug is fixed: Read-only nodes become unavailable after they fail to connect to the primary node.
    The following bug is fixed: After a full-text index is used and DDL statements are executed, a read-only node becomes unavailable after a primary/secondary switchover.
    The following bug is fixed: Binary logs cannot be purged after the UNDO TRUNCATE command is run.
    The following bug is fixed: Statistics are inconsistent between the primary node and read-only nodes.
  • 8.0.1.1.4(20200704)
    Category Description
    New features and performance optimization DDL statements can be executed in parallel. This improves the efficiency of executing the DDL statements.
    The length of each queue for the simulated AIO can be dynamically adjusted.
    The cache coherence is supported for FTS.
    A WHERE condition supports subqueries that include aggregate functions. If the subqueries support index scans, these subqueries can also be executed in parallel.
    The lock mode can be checked for temporary tables and standard tables.
    Bug fixes The following bug is fixed: Instances become unavailable because some DDL statements are being replicated when the primary node serves as a read-only node.
    The following bug is fixed: The performance is deteriorated because thread pools are enabled.
    The following bug is fixed: Deadlocks occur because binary logs are purged.
    Several bugs that are related to a memory leak are fixed.
    Several bugs that occur in high availability scenarios are fixed.
  • 8.0.1.1.3(20200529)
    Category Description
    New features and performance optimization Security is enhanced. For example, password management is improved.
    The performance of parallel queries is improved in the following scenarios:
    • The performance of parallel queries is improved in the scenarios where GROUP BY, UNION, and SELECT COUNT(*) FROM <table> are executed.
    • Shared InnoDB temporary tables are used for execution plans in parallel subqueries.
    • The views, derived tables, and temporary tables are used in execution plans.
    • Temporary tables can be defined for parallel queries. However, take note of the following limits:
      • If you do not specify conditions in the SELECT COUNT(*) statement to query data in temporary tables, parallel queries are not supported.
      • Parallel queries are not supported for temporary tables for which the Memory Engine is used.
    A new version of the audit log format is supported. In this format, information about virtual IP addresses (VIPs) is added.
    The rate of idle space to total space on index pages can be managed. This reduces latch contention and the probability of performing structure modification operations (SMOs), and improves write performance.
    The simulated AIO among multiple queues is supported. This improves dirty page flushing and write performance.
    Buffer pool pages can be excluded from core files. This reduces the sizes of the core files and prevents impacts on online services.
    Bug fixes The following bug is fixed: If the upper memory limit of TempTable is reached, the TempTable storage engine in the original logic misreports an out-of-memory error instead of moving data from memory to disks.
    The following bug is fixed: Instances become unavailable when the sort buffer size is set to a small value and ORDER BY is used in InnoDB FTS.
    The following bug is fixed: If a temporary table contains duplicate column names, the requested fields fail to be found.
    The following bug is fixed: In parallel queries, when the MAX or MIN function is used in conjunction with GROUP BY and a loose index scan is used, the statement is still being executed after the query is killed.
    Several bugs that are related to failovers are fixed.
    Several bugs that are related to parallel queries are fixed.
    The following bug is fixed: If you run the SHOW BINARY LOGS command, transactions may not be committed.
  • 8.0.1.1.2(20200409)
    Category Description
    New features and performance optimization The method of optimizing sorting based on string prefixes is supported. That is, column values are first sorted based on string prefixes. If the string prefixes are the same, the column values are sorted based on the full length of the strings. When columns of the CHAR and VARCHAR data types are sorted, you can specify the most different prefix length for the column values to accelerate the comparison process. This reduces sorting time.
    Parallel queries are supported in the following scenarios:
    • Parallel queries are supported for the estimation model of Range Cost.
    • Parallel queries are supported for temporary tables.
    • Parallel queries can be performed based on the semi-join materialization strategies: lookup and scan.
    Three types of session state trackers are added. The PolarDB intelligent proxy can use these session state trackers for connection maintenance. After the trackers are enabled, you can track the changes of user variables in sessions, creation and deletion of temporary tables, and the prepare and dealloction operations in SQL statements.
    The performance of dropping an adaptive hash index (AHI) is optimized when DDL statements are executed. This reduces the impact of DDL statements on instance performance.
    The recycle bin feature is added to prevent data loss that is caused by unintended deletion operations.
    The performance of truncating temporary tablespaces in large buffer pools is improved. This reduces the impact of temporary table operations on the instance performance.
    Bug fixes The following bug is fixed: If aggregate functions are nested in the IF function, the bug occurs when the ROLLUP function is executed.
    The bug that occurs when the values of the BLOB data type are sorted is fixed.
    The specific bug that occurs when the PREPARE statement that includes aggregate functions is executed in parallel queries is fixed.
    Several bugs that are related to parallel queries are fixed.
    The following bug is fixed: Excessive redo logs may be cleared.
    Bugs that are related to the redo logs of read-only nodes are fixed.
  • 8.0.1.1.1(20200328)
    Category Description
    New features and performance optimization Parallel queries are supported when subqueries contain the ROLLUP statement.
    The statement concurrency control feature is supported.
    The POLARDB_INDEX hint is added.
    The sync latency between the primary node and read-only nodes is reduced.
    The thread pool feature is supported. For more information, see Thread pool.
    The keyring_rds plug-in for transparent data encryption (TDE) is supported.
    GDNs are supported. For more information, see Global database networks.
    The lock-free transaction system is optimized and the read and write performance is improved.
    Bug fixes Several bugs that are related to parallel queries are fixed.
    The following bug is fixed: The value 0 is returned for the statistics in online DDL operations.
    The file system in user mode is optimized to accelerate instance startup.
    The following bug is fixed: Instances may become unavailable if innodb_flush_method is set to all_o_direct.
    The following bug is fixed: Instances may become unavailable if you release a lock after a transaction is committed.
    The following bug is fixed: User requests may be blocked when slow query logs are truncated.
    The following bug is fixed: Instances may become unavailable because of the compressed pages on read-only nodes.
    The following bug is fixed: Replication connections may be accidentally killed in thread pools.
  • 8.0.1.1.0(20200205)
    Category Description
    New features and performance optimization The parallel query feature is improved, and the parallel computing of the ROLLUP function that is used for enterprise-level analysis is supported.
    The capabilities of the estimation model of the optimizer are improved. For example, the selectivity of the filters is enhanced, and the cost estimation model is improved for parallel queries. A parallel or serial execution plan can be more appropriately selected for the executed SQL statements based on the selectivity.
    The parallel worker threads of the worker threads that are allocated based on the first in, first out (FIFO) mode are managed in a unified manner. This prevents a large number of parallel queries from exhausting system resources.
    Bug fixes Memory-related bugs in parallel queries are fixed.
    Bugs that are related to instability in parallel queries are fixed.
  • 8.0.1.0.6(20200101)
    Category Description
    Bug fixes The following bug is fixed: The binary log index file is not closed after the primary node serves as a read-only node.
    The following bug is fixed: Instances become unavailable when read-only nodes access undo log pages that have been purged.
    The following bug is fixed: Background threads access tablespace pages that do not exist if a read-only node serves as the primary node during a primary/secondary switchover.
    The following bug is fixed: When instances are shut down, log threads exit but redo logs are still being written. In this case, the instances become unavailable.
  • 8.0.1.0.5(20191203)
    Category Description
    New features and performance optimization The optimizer trace allows you to trace information about parallel queries. For example, you can use the optimizer trace tool to analyze the reason why a parallel query is used or not used.
    Hints are added for parallel queries. You can add hints to SQL statements to explicitly enable parallelism and specify the degree of parallelism.
    Parallel scans are supported if you execute the INSERT... SELECT statement when the isolation level is READ COMMITTED. You can execute the INSERT... SELECT statement to insert the imported data into another table.
    Bug fixes Several bugs that are related to parallel queries are fixed.
    The following bug is fixed: Instances become unavailable when a read-only node is promoted to the primary node during a primary/secondary switchover.
    The following bug is fixed: Errors are reported because some DDL statements are executed during a primary/secondary switchover.
    The following bug is fixed: An error message "too many connection error" is reported if the maximum number of connections that are supported by locks is reached.

PolarDB for MySQL 5.7 release notes

The following table describes the versions and the features that are supported by PolarDB for MySQL 5.7.

Release date Revision version MySQL minor version that is fully compatible Description
20201117 5.7.1.0.4 5.7.28 Fixes several known issues.
20201021 5.7.1.0.3 5.7.28
20200828 5.7.1.0.2 5.7.28 Fixes several known issues.
20200730 5.7.1.0.1 5.7.28 Fixes several known issues.
  • 5.7.1.0.5 (20201222)
    Category Description
    Fixed issues Fixes the issue that read-only nodes crash when you query data from read-only nodes after the key of the primary node is modified.
    Fixes the issue that read-only nodes crash when you analyze partition tables on read-only nodes.
    Fixes the issue that the new primary node crashes due to tablespace inconsistency after a failover.
  • 5.7.1.0.3 (20201021)
    Category Description
    New features and optimized performance Supports TDE.
    Fixed issues Fixes the issue that statistics are inconsistent between the primary node and read-only nodes.
    Fixes the issue that an error is returned when you execute the SHOW PROCESSLIST statement.
  • 5.7.1.0.2 (20200828)
    Category Description
    Fixed issues Fixes the issue that .IDB files cannot be created after a migration from ApsaraDB RDS for MySQL 5.7.
    You cannot run CF_STATUS_COMMAND commands during a failover process. This ensures the success of the failover.
    Fixes the issue that the primary node is unavailable due to the page contention that is caused by background updates for statistics thread and the truncate operation.
  • 5.7.1.0.1 (20200730)
    Category Description
    Fixed issues Fixes the issue that maxscale is unavailable due to the missing code of specific PolarDB dedicated commands.
    Fixes the issue that the cluster that you create from the cluster recycle bin is unavailable because no tablespace can be found.
    Fixes the issue that the unmout PFS file crashes if one or more files are still open when you run the promote replica command.

PolarDB for MySQL 5.6 release notes

The following table describes the versions and features that are supported by PolarDB for MySQL 5.6.

Version Release date MySQL minor version with full compatibility Released feature
5.6.1.0.22 Not published 5.6.16 Directory indexes are supported in polar file system (PFS). This improves the performance of the cluster that has a large number of tables.
5.6.1.0.21 20201112 5.6.16 The transparent data encryption (TDE) and Restore data of specific databases and tables features are supported.
5.6.1.0.20 20201027 5.6.16 The efficiency of physical replications in some scenarios is improved.
20200831 20200922 5.6.16 Polar file system (PFS) supports local disks and writable snapshots. The performance of PFS is optimized.
20200616 20200701 5.6.16 The statement queue feature is supported. For more information, see Statement Queue.
20200601 20200605 5.6.16 The statement concurrency control feature is supported to improve concurrency performance. For more information, see Statement Concurrency Control.
20200507 20200513 5.6.16 The performance bottlenecks that are caused by internal data structures are removed. The simulated I/O system is optimized.
  • 5.6 (5.6.1.0.22)
    Category Description
    New features and optimized performance Directory indexes are supported in polar file system (PFS). This improves the performance of the cluster that has a large number of tables.
    Fixed issues The issue that the cluster becomes unavailable after a failover between primary node and read-only nodes due to invalid node roles in specific cases is fixed.
    The issue that read-only nodes crash due to the uninitialized statement queue is fixed.
    The issue that new system tables are not initialized after a failover between the primary node and read-only nodes is fixed.
    The issue that the thread pool and connection control features are enabled at the same time is fixed.
    The issue that a cluster becomes unavailable due to duplicate IDs in the full-text index is fixed.
    The issue that you cannot query data from read-only nodes in some cases is fixed.
    The issue that the replication is interrupted when the log replication thread accidentally exits is fixed.
  • 5.6 (5.6.1.0.21)
    Category Description
    New features and optimized performance The statement queue feature is supported. For more information, see Restore data of specific databases and tables.
    The transparent data encryption (TDE) feature is supported.
    PFS allows you to mount multiple disks to restore individual tables.
    Resource occupation that is caused by the Adaptive Hash Index (AHI) lock during physical replications is optimized.
    Fixed issues The issue that the out of memory (OOM) error occurs when you use DYNAMIC RANGE and INDEX MERGE in SELECT statements is fixed.
    The issue that a cluster crashes when you create or delete an account in some cases is fixed.
    The issue that standby nodes cannot be reconnected in some cases is fixed.
    The issue that the cluster fails to start when a failover error occurs is fixed.
    The issue that the state of the Binlog thread is invalid in some cases is fixed.
  • 5.6 (5.6.1.0.20)
    Category Description
    New features and optimized performance The efficiency of physical replications in some scenarios is improved.
    Fixed issues The issue that a cluster crashes when you run the CREATE TABLE... SELECT command in some cases is fixed.
    The issue that the OOM error occurs in the stored procedure due to the excessive use of derived tables is fixed.
    The issue that the restore time is invalid or the restore operation fails is fixed. This issue occurs when you want to restore data to a specific point in time.
    The issue that a large number of logs about PFS exceptions are reported is fixed.
    The issue that tables are lost when you perform DDL operations is fixed. This issue occurs after the foreign key check is disabled.
    The issue that read-only nodes crash when you truncate multiple temporary tables is fixed.
  • 5.6 (20200831)
    Category Description
    New features and optimized performance PFS supports local disks and writable snapshots. The performance of PFS is optimized.
    Fixed issues The issue that the cluster crashes due to the uninitialized statement queue is fixed.
    The issue that a large amount of storage is consumed by the corefile is fixed.
    The issue that statistics are inconsistent between the primary node and read-only nodes is fixed.
    The issue that other read-only nodes cannot connect to the new primary node after a read-only node is specified as the primary node is fixed.
    The issue that statistics are inconsistent between the primary node and read-only nodes is fixed.
  • 5.6 (20200616)
    Category Description
    New features and optimized performance The statement queue feature is supported. For more information, see Statement Queue.
    The replication delay between the primary node and read-only nodes is reduced.
    The metadata lock can be replicated when you execute the LOCK TABLE statement.
    Fixed issues The metadata lock issue that occurs during data replication is fixed.
    The issue that a full-text search (FTS) index is created in the system table is fixed.
    The issues that are related to the updates and performance optimization of hot rows are fixed.
  • 5.6 (20200601)
    Category Description
    New features and optimized performance 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 Statement Concurrency Control.
    Fixed issues The issue that the write performance is reduced due to the issues of thread pools is fixed.
  • 5.6 (20200507)
    Category Description
    New features and optimized performance 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 AIO model is optimized.
    Fixed issues The issue that the performance is reduced due to the BoolFlag data type is fixed.
    The issue that instances become unavailable when the pfs_umount table is not closed is fixed.

Version upgrades

  • Upgrade DB versions and minor versions

    PolarDB does not allow you to upgrade the DB versions and the minor versions in a direct way. For example, you cannot upgrade PolarDB for MySQL 5.6 to PolarDB for MySQL 8.0 or upgrade the minor version of PolarDB for MySQL from 8.0.1 to 8.0.2 in a direct way. However, you can use Data Transmission Service (DTS) to migrate or synchronize data from the cluster of the source version to the cluster of the destination version. For more information about how to migrate or synchronize data, see Overview of data migration or synchronization solutions.

  • Upgrade revision versions

    For more information about how to upgrade revision versions, see Upgrade the revision version.