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    PolarDB:PolarDB for MySQL 8.0.2

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    PolarDB:PolarDB for MySQL 8.0.2

    Last Updated:Apr 11, 2024

    This topic describes the updates and features of PolarDB for MySQL 8.0.2.

    8.0.2.2.21

    Category

    Description

    Release date

    New feature and performance optimization

    • The speed of handling requests sent to establish a connection for the thread pool in low-concurrency scenarios is improved.

    • If the current SQL statement that is executed does not require the global consistency (high-performance mode) feature after the feature is enabled, hints can be used in the statement to disable the feature.

    • Correlated subqueries can be used in the Grouping clause and complex correlated subqueries can be eliminated.

    • The concurrency control and statement outline features can be enabled for a cluster of Multi-master Cluster (Database/Table) Edition. If the configurations of these features are added to or removed from a primary node of the cluster, the addition or removal operation is automatically synchronized to other primary nodes of the cluster.

    • Tair cache nodes can be added to a PolarDB for MySQL cluster to read data from the PolarDB for MySQL cluster.

    • The process for enabling the In-Memory Column Index (IMCI) feature is optimized to reduce the time required before the feature can be used.

    • The read performance of read-only nodes in scenarios where secondary indexes return the primary key of a table is improved.

    • The process for calculating transaction mask in IMCIs is optimized.

    2024-01-17

    Fixed issue

    • The following issue is fixed: When you upgrade a cluster, a concurrency control (CCL) rule that matches the DIGEST value may become invalid.

    • The following issue is fixed: Nodes crash due to backticks in the value of an input parameter when some built-in stored procedures are called.

    • The following issue is fixed: When the IMCI feature is used to query vectors, invalid sorting results are returned for descending sorting due to excessive NULL values in tables specified by the query statement.

    • The following issue is fixed: When read-only column store nodes start during the execution of DDL statements on tables for which IMCIs are created, column-oriented data failed to be restored.

    • The following issue is fixed: In some special scenarios, the elastic parallel query (ePQ) feature cannot be used in query statements that contain Recursive CTEs.

    • The following issue is fixed: When a database or table restoration task 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: When a database or table restoration task is initiated, the thread failed to exit due to exhausted disk space.

    • The following issue is fixed: When data structures are concurrently modified during the physical replication in X-Engine, read-only nodes are abnormal.

    • The following issue is fixed: A node in a cluster of X-Engine Edition cannot be upgraded from a read-only node to a synchronous secondary node.

    • The following issue is fixed: When the character set of the partition key in a partitioned table is modified, data is not repartitioned.

    • The following issue is fixed: When the IMCI feature is used to query a view that contains data of the BIT type, invalid query results are returned.

    • The following issue is fixed: A high latency occurs when data is written to tables in X-Engine in low concurrency scenarios.

    • The following issue is fixed: After you pull up a single-row subquery, the GROUP BY clause cannot identify the column involved in the subquery.

    • The following issue is fixed: After the subquery_to_derived feature is enabled in MySQL Community Edition, invalid results are returned.

    • The following issue is fixed: When you use the polar_abbrev_sort_key_size parameter to specify a sorting, operation, the memory was being corrupted.

    • The following issue is fixed: When an equivalent query is performed on a partitioned table whose primary key does not contain the partition key and the unique key (UK) is used for an index merge operation, only the data of the first partition is returned.

    8.0.2.2.20

    Category

    Description

    Release date

    New feature and performance optimization

    • For a cluster for which the statement outline feature is disabled, if the feature is enabled for the cluster after an upgrade, the cluster is not affected by character sets when it is matched against outlines.

    • The process for enabling the global consistency (high-performance mode) feature is optimized.

    • The INFORMATION_SCHEMA views of all read-only column store nodes can be accessed. By default, information about the nodes is aggregated for display.

    • 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.

    2023-12-20

    Fixed issue

    • The following issue is fixed: If a ROLLUP calculation is performed on a derived table, nodes crash due to the parallel scanning of the table.

    • The following issue is fixed: When you create an Object Storage Service (OSS) external table, nodes crash due to the invalid CONNECTION format that you specify.

    • The following issue is fixed: When a physical machine hosting a read-only node fails, the primary node cannot flush dirty pages in an efficient manner due to the continuity of its replication relationship with the read-only node in special cases.

    • The following issue is fixed: After a high-availability (HA) switchover between the primary and read-only nodes is performed, Auto-increment is rolled back due to table cache evictions caused by the excessive number of tables.

    • The following issue is fixed: When a table or an index in X-Engine is deleted, an extreme redo log time series is generated due to the concurrency with an occasional SwitchMemtable operation that is performed on the background, which results in the breakdown of read-only nodes.

    • The following issue is fixed: When a remote connection is forcibly closed, the internal connection object is leaked due to the abnormal execution of an ePQ.

    • The following issue is fixed: When ROLLUP statements are executed in parallel, invalid query results are returned due to the presence of the same constant column in the GROUP BY clause.

    • The following issue is fixed: ASSERT CRASH (assertion error) is triggered when all partitions of a partitioned table are pruned during partition pruning and RANGE INDEX is used to access global secondary indexes (GSIs) in the table.

    • The following issue is fixed: When cold data is archived in the ORC format, the archiving operation fails due to the presence of the fields of the BLOB type in the table.

    • The following issue is fixed: Limits are imposed on GSIs in parallel queries in scenarios such as Multi-Range Read (MRR) operations.

    8.0.2.2.19.1

    Category

    Description

    Release date

    Fixed issue

    To fix deadlock issues caused by a large amount of BLOB data, an official patch from MySQL 8.0.16 is introduced.

    2023-11-13

    8.0.2.2.19

    Category

    Description

    Release date

    New feature and performance optimization

    • The logic for switching read-only nodes to primary nodes is optimized.

    • The logic of the thread pool in processing new connections is optimized.

    • When a subquery is used as a UNION clause, the conditions can be pushed down to a derived table.

    • More equivalent conditions can be pushed down to a derived table.

    • Predicates that meet a specified condition can be pushed down to subqueries by the optimizer.

    • The cost model of accessing non-covered indexes for equality condition queries is optimized.

    • The opt_non_covering_key_cost parameter is added to specify whether to consider the initial positioning cost of secondary indexes.

    • The worst_seek_records_threshold parameter is added to specify whether to limit the maximum I/O cost of accessing non-covered indexes for equality condition queries during cost estimation.

    • The amount of memory consumed by the table object cache and the table definition cache is reduced.

    • Data lifecycle management (DLM) can be used to automatically archive the cold data of all tables partitioned by range.

    • The optimizer can select global secondary indexes of the partitioned table during a query that involves partition pruning.

    2023-10-30

    Fixed issue

    • The following issue is fixed: When the AccessKey pair of the Object Storage Server (OSS) server is corrupted, clusters cannot be started.

    • The following issue is fixed: In some scenarios, queries fail due to excessive memory usage of the GroupJoin operator.

    • The following issue is fixed: Some queries that contain OR predicates fail to be executed because the query plan cannot be bound to the correct columns.

    • The following issue is fixed: When a join operation is performed on the unsigned column and a signed column, the optimizer cannot accurately estimate the join selection rate.

    • The following issue is fixed: When a query is terminated by the scheduler, a database may be restarted.

    • The following issue is fixed: Read-only nodes that access the X-Engine cannot report version reference information, resulting in space reclamation failures.

    • The following issue is fixed: When a check point is loaded, the row ID fails to be rolled back in advance.

    • The following issue is fixed: The I/O performance of IMCIs is degraded in deferred materialization scenarios.

    • The following issue is fixed: If the optimizer fails to locate the appropriate partitions during partition pruning, an infinite loop may occur.

    8.0.2.2.18

    Category

    Description

    Release date

    Fixed issue

    The following issue is fixed: Nodes may crash if only keywords are specified but not the table schema and table name in the last rule when multiple concurrency control (CCL) rules are configured to delete the same type of SQL statements.

    2023-09-17

    8.0.2.2.17

    Category

    Description

    Release date

    New feature and performance optimization

    The speed of archiving cold data in the CSV format to OSS is improved.

    2023-08-23

    Fixed issue

    • The following issue is fixed: The Table definition has changed error is reported when the global consistency (high-performance mode) and multi-node elastic parallel query (ePQ) features are enabled.

    • The following issue is fixed: The number of scanned rows in an SQL statement may be inaccurate in scenarios where index condition pushdown is involved.

    • The following issue is fixed: Nodes crash when the phrase search mode is used for a full-text index.

    • The following issue is fixed: After the UNDO TRUNCATE statement is executed on the read/write node, if you use a read-only node to connect to the database and retrieve data, the read-only node may crash.

    8.0.2.2.16.1

    Category

    Description

    Release date

    Fixed issue

    • The following issue is fixed: Background threads consume a large number of CPU resources.

    • The following issue is fixed: When the AccessKey pair of the OSS server is corrupted, clusters cannot be started.

    2023-07-25

    8.0.2.2.16

    Category

    Description

    Release date

    New feature and performance optimization

    • An IMCI can be used to query data in a partition of a partitioned table.

    • The primary index of the InnoDB engine can be used to accelerate queries in IMCIs.

    • An IN subquery can be converted to a semi-join subquery when UPDATE or DELETE is performed on a table.

    • Scalar subqueries can be converted to derived tables in JOIN queries.

    • The Fast Query Cache feature is supported for partitioned tables that run the InnoDB engine.

    • An implicit auto-increment primary key is not automatically created when an OSS foreign table is being created.

    • A global secondary index can be created on a partitioned table whose UNIQUE CHECK IGNORE option is set to 1.

    • The innodb_polar_import_tablespace_strict_mode parameter is added. The default value is ON, which specifies that an error is returned if the table schema of a database or table that you want to restore contains full-text index.

    2023-07-23

    Fixed issue

    • The following issue is fixed: The JPPD optimization feature fails when a common table expression (CTE) contains a nested CTE and has multiple references.

    • The following issue is fixed: When you restore a database or table for a hybrid partitioned table, the restore operation fails.

    • The following issue is fixed: When the primary node is disabled and restarted, the secondary node does not trigger the reconnection mechanism.

    • The following issue is fixed: The fault recovery is interrupted at a low probability.

    • The following issue is fixed: Data is inserted into the wrong partition of tables that include the UNIQUE CHECK IGNORE attribute.

    8.0.2.2.15

    Category

    Description

    Release date

    New feature and performance optimization

    • Log transmission over the RDMA network is supported between the primary node and read-only nodes.

    • Partitioned tables and non-partitioned tables that contain auto-increment columns can be archived to OSS.

    • The federated query engine can push down the Order clause to the remote database for execution. Use the Order clause together with the Limit Offset clause to reduce network costs.

    • IMCIs can be created on a hybrid partitioned table that uses InnoDB and ORC.

    • The ALTER TABLE table_name CHANGE PARTITION partition_name ENGINE=CSV/ORC FORCE; syntax is added.

    • The performance of the thread pool in processing short-lived connections is improved.

    • The DLM feature can be used to archive the InnoDB partitions of a partitioned table to OSS.

    • You can add and remove InnoDB partitions in hybrid partitioned tables.

    2023-06-28

    Fixed issue

    • The following issue is fixed: When the disk is filled by temporary files generated by an IMCI query, the system cannot interrupt the query and clear the files in time.

    • The following issue is fixed: Parameters do not take effect when the stored procedure is repeatedly executed.

    • The following issue is fixed: Standard accounts can be used to delete sys.

    • The following issue is fixed: When slow query logs are concurrently recorded, the failure of internal counter in the thread pool may cause accumulated SQL requests.

    • The following issue is fixed: A node restarts unexpectedly when you restore a database or table for a partitioned table after high availability switchover is enabled.

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

    • The following issue is fixed: An error may occur when you execute the ALTER TABLE ... IMPORT TABLESPACE statement on a read/write node and perform a query operation on a read-only node at the same time.

    8.0.2.2.14

    Category

    Description

    Release date

    New feature and performance optimization

    • The primary key data slicing function call dbms_dts.show_parallel_ranges (<schema_name>, <table_name>, [<suggestion_ranges>]) is added.

    • You can create IMCIs on virtual columns.

    • You can use the recycle bin feature for tables with IMCIs.

    • The ALTER TABLE table_name CHANGE PARITION part_name ENGINE = 'csv'; command is added to archive partitions.

    • The row-level compression feature is added.

    • The OSS query capability is optimized. After the elastic parallel query feature is enabled, the system performs parallel queries when the value of loose_csv_max_oss_threads is greater than 1.

    • The error message that is reported when the format of an OSS foreign table file is invalid is optimized.

    • You can read data in the ORC format from OSS and write data in the ORC format to OSS.

    • The error message that is reported when misspelling happens.

    2023-05-24

    Fixed issue

    • The following issue is fixed: Replication delay occurs when the redo log of a wide table is returned from a read-only node.

    • The following issue is fixed: Nodes crash if you use the ORDER index to optimize a query in a hybrid partitioned table.

    • The following issue is fixed: Nodes crash if you truncate hybrid partitions.

    • The following issue is fixed: If you use the LIMIT OFFSET pushdown feature to optimize a query statement that contains window functions, the query result is incorrect.

    • The following issue is fixed: OSS cannot make parallel execution.

    • The following issue is fixed: OSS cannot read JSON files.

    • The following issue is fixed: The word "engine" is misspelled.

    • The following issue is fixed: When you read cold OSS data in the CSV format, you may read only the first object.

    • The following issue is fixed: Data that contains \n cannot be read after being archived by using DLM.

    • The following issue is fixed: After you archive cold data, some temporary files may remain on OSS.

    8.0.2.2.13

    Category

    Description

    Release date

    New feature and performance optimization

    • The memory usage is optimized when you scan tables in the recycle bin.

    • You can query global transaction identifiers (GTIDs) on read-only nodes.

    • You can add columns in seconds by creating IMCI data again.

    • The REGEXPR function is supported in IMCIs.

    • The IS NULL and IS NOT NULL conditions can be used to determine whether to use the IMCI pruner feature.

    • The parallel DDL feature can be used to create GSIs in parallel.

    • The Instant ADD COLUMN feature is supported on partitioned tables that have GSIs created.

    • The BNL, BKA, and MRR types are added for hint plans.

    • The by_expr_ignore_charset variable is added in SQL sharing. Differences in digests generated by the ORDER BY or GROUP BY clause in different character sets are eliminated after you set the by_expr_ignore_charset parameter to ON. However, when the parameter is set to ON, all digests generated in this mode are different from the digests generated before the parameter is set to ON.

    • The dbms_outln.add_optimizer_outline('schema', 'hints', 'query') API is provided in the statement outline feature to add optimizer hints.

    • You can switch a table that has global secondary indexes created to an interval range partitioned table, and create global secondary indexes on an interval range partitioned table.

    • The ALTER TABLE table_name CHANGE PARTITION partition_name ENGINE = 'csv'; command is added to archive all data of a specified partition in a partitioned table to OSS.

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

    • The non-blocking DDL feature supports the OPTIMIZE TABLE and TRUNCATE TABLE statements.

    2023-04-21

    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: When the engine_condition_pushdown parameter is set to true, tables that contain NULL fields are not pushed down correctly.

    • The following issue is fixed: The source file cannot be deleted from OSS when the ALTER TABLE engine = csv storage oss, force; command is executed.

    • The following issue is fixed: When you perform a check operation on an empty OSS foreign table, a database node crashes.

    8.0.2.2.12

    Category

    Description

    Release date

    New feature and performance optimization

    • The non-blocking DDL feature is added.

    • The SQL Trace feature is added.

    • The SQL detail feature is added.

    • The auto plan cache feature is added.

    • The IMCI feature is added.

    • If the index hints specified for a statement outline do not exist, only an alert is reported instead of an error.

    • Execution plans are displayed in the extended data of slow query logs.

    • The Innodb_scc_timeout_count parameter is added for the global consistency (high-performance mode) feature to record the number of timeouts that occur during a query.

    • The Innodb_scc_timeout_degrade_count parameter is added to record the number of events in which global consistency (high-performance mode) queries time out and are converted to asynchronous queries.

    • The adaptive digest length is supported, which indicates that the memory space calculated by the statement digest function is adaptive to the length of query statements.

    • The ccl_mode parameter is added for the CCL feature. This parameter indicates that if the access traffic of the PolarDB for MySQL database reaches a specified concurrency control threshold, requests sent to access the current cluster are denied.

    • The variables that start with an at sign (@) can be used as input values in built-in stored procedures.

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

    2023-03-20

    Fixed issue

    • The following issue is fixed: No error is reported when you add or remove a CCL rule or statement outline on a hot standby or read-only node.

    • The following issue is fixed: When a SHOW SLAVE HOSTS statement is executed on the primary node, the cluster crashes.

    8.0.2.2.11.1

    Category

    Description

    Release date

    New feature and performance optimization

    • If the value of the Schema_name parameter is empty in an SQL statement, and the digest value of the statement matches the digest value specified by a statement outline, the statement outline takes effect.

    • The loose_group_by_compatible_sorting parameter is added to specify whether to enable the GROUP BY sorting compatibility mode.

    2023-02-21

    Fixed issue

    The following issue is fixed: When you execute DDL statements on a partitioned table, an "illegal memory access" error message is returned.

    8.0.2.2.11

    Category

    Description

    Release date

    New feature and performance optimization

    • If a partition expression contains an auto-increment column, you can specify the value of the column and trigger partition pruning based on the specified value.

    • The without validation keyword can be added to the ADD PARTITION statement used to create a LIST DEFAULT HASH partitioned table to add list partitions.

    2023-02-20

    8.0.2.2.10

    Category

    Description

    Release date

    New feature and performance optimization

    • The without validation keyword can be added to switch a non-partitioned table to a partitioned table. Syntax: ALTER TABLE t1 partition by range(a) (partition p0 values less than (100), partition p1 values less than (200)) without validation.

    • Cost-based optimization allows the outer join conditions of a materialized derived table to be pushed down inside the derived table.

    • You can convert a predicate with an IN-List clause to a temporary table. This table can be semi-joined with a query in a FROM clause and uses the zero-copy method to avoid repeated materialization overheads.

    • HAVING conditions can be pushed down to WHERE conditions.

    • When the partition-level MDL feature is enabled, DDL statements can be executed on subpartitions and lock granularity is reduced. DDL statements only affect the involved partitions. DML statements executed on other partitions are not affected.

    2023-01-09

    Fixed issue

    • When TDE is enabled, the encryption operation on system tables is disabled. You are not allowed to encrypt system tables.

    • The timeout parameter related to the physical replication connection is modified to fix the issue of stuttering when the physical server crashes.

    8.0.2.2.9

    Category

    Description

    Release date

    New feature and performance optimization

    • A semicolon (;) at the end of an SQL statement in the query parameter of the dbms_ccl.add_ccl_digest_rule, dbms_outln.add_index_outline, or dbms_outln.add_optimizer_outline built-in stored procedure can be ignored.

    • The MEMBER keyword is changed to a non-reserved keyword.

    • The partial result cache feature is supported.

    • The join elimination feature of the optimizer can eliminate inner tables of left joins, including inner tables with multi-layer nested joins and semi-joins.

    • The federated query engine pushes all compatible conditions down to the remote server for execution and returns only the columns required in the query.

    • The federated query engine allows you to push down the Limit or Offset clause to the remote database for execution.

    2022-12-23

    Fixed issue

    The following issue is fixed: IF NOT EXISTS cannot be included in the statement that is used to create servers.

    8.0.2.2.8

    Category

    Description

    Release date

    New feature and performance optimization

    • Indexes can be created on some partitions of a partitioned table. You can create, delete, and rebuild indexes on the partitions of a partitioned table.

    • The REBUILD PARTITION and REORGANIZE PARTITION operations can be performed after partition-level MDL locks are created. This ensures that DDL operations performed on a partition do not affect DML operations on other partitions.

    • The usernames and passwords in the mysql.servers table are no longer stored and displayed in plaintext.

      Note

      The existing username and password of a server are not encrypted after the upgrade. You must manually delete the existing username and password and then recreate a username and password for the server.

    • The SELECT INTO OSSOUTFILE statement is added to export local tables on PolarFS to OSS.

    • The failover with hot standby feature is supported. For more information, see Overview.

    • The dynamic_partition_prune_enabled parameter is added to control partition pruning for dynamic partitions. After partition pruning is enabled in various scenarios in which a join query is performed on multiple partitioned tables, the system does not scan unnecessary partitions if the connection between partitions meets specified partition pruning conditions. This improves the query performance.

    • The partition-wise join feature can be used between partitioned tables and non-partitioned tables. This improves the efficiency of joins between partitioned tables and non-partitioned tables in queries that involve large volumes of data.

    • All types of UNION clauses are supported for Statement Outline.

    • The LIMIT OFFSET pushdown feature can be used when you access an independent partition in a partitioned table.

    2022-11-30

    Fixed issue

    • The following issue is fixed: The number of unique values of the GROUP BY field in the parallel optimizer is inaccurately estimated.

    • The following issue is fixed: Binary logs are generated when SQL statements are executed during hot upgrade.

    8.0.2.2.7

    Category

    Description

    Release date

    New feature and performance optimization

    • The ePQ feature supports cross-node parallel execution for data in OSS foreign tables.

    • Global secondary indexes are supported on partitioned tables.

    • Multi-stage ePQ is supported in queries that contain semi-join materialization (SJM) strategies.

    2022-10-25

    Fixed issue

    • The following issue is fixed: The ERROR 1028 (HY000): Sort aborted: Query execution was interrupted error is reported when a query execution is halted prematurely due to the use of the LIMIT 1 clause.

    • The following issue is fixed: Nodes do not respond when data is inserted into tables with implicit primary keys by using the Event Scheduler.

    • The following issue is fixed: Incorrect result sets of count(distinct ...) are returned for ePQ.

    • The following issue is fixed: If query conditions contain the DATE and DATETIME types, the result set of a parallel query may be incorrect.

    8.0.2.2.6.1

    Category

    Description

    Release date

    Fixed issue

    The following issue is fixed: Read-only nodes do not respond when the hash values of file names conflict.

    2022-09-17

    8.0.2.2.6

    Category

    Description

    Release date

    New feature and performance optimization

    • Thread pool optimization: When database transactions wait for metadata locks or row locks, additional threads can be generated in the thread pool to process new requests.

    • CCL is enhanced to support DDL throttling.

    • Temporary files can be asynchronously written to accelerate the process of reconstructing data in DDL statements.

    • The high concurrency performance of the thread pool is enhanced.

    • The oss_sts_token parameter is added to the statement for creating an OSS server to configure temporary credentials for OSS.

    2022-08-19

    Fixed issue

    The following issue is fixed: Errors are returned when both LIMIT OFFSET pushdown and MRR optimization are enabled.

    8.0.2.2.5.1

    Category

    Description

    Release date

    New feature and performance optimization

    • Hybrid partitioned tables can be created. For more information, see Create a hybrid partitioned table.

    • In-memory temporary tables can be customized on read-only nodes. Only the MEMORY and MyISAM engines are supported.

    • The ReadableProto feature is supported. The Protobuf protocol is used to read the information serialized and stored in the BLOB-typed field on the database.

    • Optimized DDL sorting: Two-way merging is changed to multiple-way merging to reduce I/O operations and improve the performance of creating indexes by executing DDL statements.

    • The oss_prefix parameter is added to the statement for creating an OSS server to configure the OSS file path.

    2022-07-22

    Fixed issue

    • The following issue is fixed: group_by_implicit_sorting concurrent execution results are unordered when you select indexes for group by columns.

    • The following issue is fixed: cost and rows errors occur when you execute the EXPLAIN FORMAT=TREE statement to view the Hash Join results.

    • The issue that causes high latency when physical replication is performed during a time period of low workloads in the cluster is fixed.

    • 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.

    • The following issue is fixed: A database fails to respond due to an excessive number of log records that are generated after you use the Instant ADD COLUMN feature and then roll back an update operation.

    8.0.2.2.4

    Category

    Description

    Release date

    New feature and performance optimization

    The FEDERATED storage engine is supported. You can create and use FEDERATED tables.

    2022-05-31

    Fixed issue

    • The following issue is fixed: When a skip scan is performed on an index that is prefixed with multiple sets of data, the results of the skip scan may be incorrect.

    • The following issue is fixed: When a skip scan is performed and some data in the database is marked as deleted, the results of the skip scan may be incorrect.

    • The following issue is fixed: The fast query cache feature blocks the synchronization of redo logs when the read-only node obtains the metadata lock (MDL).

    8.0.2.2.3

    Category

    Description

    Release date

    Fixed issue

    The issue that causes incorrect results when an index is used for GROUP BY operations is fixed.

    2022-04-19

    8.0.2.2.2

    Category

    Description

    Release date

    New feature and performance optimization

    • The parallel query feature supports parallel SQL execution on multiple nodes. In a single query, some or all of the workers can be allocated to and executed on remote nodes to effectively use the computing resources of multiple nodes in the cluster. The following descriptions provide details:

      • The parallel query feature can overcome the performance bottleneck of a single node and accelerate analytical queries such as big queries.

      • Queries are allocated to idle nodes to accelerate executions and improve resource usage.

      • You can create a computing resource pool that contains multiple cluster groups to achieve high elasticity.

    • The restrict_on_limit_without_order switch that is used to control the limit parallel query without the ORDER BY clause is added to the parallel_query_switch parallel query parameter.

    • Conditions can be pushed down to materialized derived tables.

    2022-03-31

    8.0.2.2.1

    Category

    Description

    Release date

    New feature and performance optimization

    2022-03-15

    Fixed issue

    • The following issue is fixed: A large number of undo logs are accumulated because the history list cannot be removed.

    • The following issue is fixed: A partitioned table cannot be created by executing the CREATE TABLE .. LIKE.. LIST DEFAULT HASH statement.

    • The following issue is fixed: A partitioned table that includes the UNIQUE CHECK IGNORE attribute cannot be displayed in the system table mysql.tables.

    8.0.2.2.0

    Category

    Description

    Release date

    New feature and performance optimization

    • The parallel query capability is improved. The linear acceleration capability is greatly enhanced and the multi-phase parallel computing capability is introduced. For more information, see Overview.

    • The capabilities for partitioned tables are enhanced. More partitioned table types and interval partitioning are supported. For more information, see Partitioned tables.

    • Subquery decorrelation is supported.

    • When PolarProxy is connected, you can use the stored procedure to define sensitive fields and tag the metadata of sensitive field values.

    • The status variable Online_altered_partition is added to count the number of online ALTER TABLE ADD PARTITION and ALTER TABLE DROP PARTITION operations.

    • Transaction resumable uploads are supported for the database kernel. Uncommitted transactions can be read by read-only nodes for the database kernel.

    2022-01-12

    Fixed issue

    • The SELECT FOR UPDATE WAIT N and SELECT FOR SHARE WAIT N statements are supported. N specifies the number of seconds during which a row remains locked. The timeout applies only to locking a single row. To lock multiple rows for a query, the system detects the timeout only based on a single row instead of multiple rows. If the lockout time exceeds the specified N value, the system returns a similar lockout timeout error: Lock wait timeout exceeded; try restarting transaction.

    • The following issue is fixed: The optimizer fails to choose a better path to the range of an index for some GROUP BY statements.

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

    • The size of database cache can be modified.

    • This prevents unnecessary traversal of partitioned table partitions and improve query efficiency.

    • The issue of failed DDL operations on encrypted tables is fixed.

    • master_key_id_mutex is optimized to ensure that DDL operations can be executed in parallel.

    • The following issue is fixed: A read-only node fails to respond when the node replays logs in high concurrency scenarios.

    • The following issue is fixed: A read-only node stops responding due to m_recv_bits.is_set(fold) when physical replication is being performed on the node in high concurrency scenarios.

    8.0.2.1.4.1

    Category

    Description

    Release date

    New feature and performance optimization

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

    2021-10-26

    Fixed issue

    The size of database cache can be modified.

    8.0.2.1.4

    Category

    Description

    Release date

    New feature and performance optimization

    The Index Hints feature of MySQL 8.0.20 is supported.

    2020-12-01

    Fixed issue

    • The stability issue of parallel hash joins is fixed.

    • The following issue is fixed: The estimated number of rows for each index key in statistics is miscalculated.

    • The following issue is fixed: An error occurs in processing empty data when shared temporary tables are scanned in parallel.

    • The following issue is fixed: An error occurs when you use the REGEXP_REPLACE function provided by PolarDB to process data.

    • The following issue is fixed: An unexpected exit occurs when a complex query contains subquery constants.

    • The following issue is fixed: A filesort operation returns invalid data.

    8.0.2.1.3

    Category

    Description

    Release date

    New feature 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.

    2020-10-26

    Fixed issue

    • The following issue is fixed: The displayed number of parallel partitions in a parallel execution plan is inaccurate.

    • The following issue is fixed: An unexpected exit occurs when parallel subqueries are run.

    • The following issue is fixed: Multiple worker threads cannot return random results when the RAND() function is used in parallel queries.

    8.0.2.1.2

    Category

    Description

    Release date

    New feature and performance optimization

    PolarDB supports the latest volcano iterator executor for parallel queries.

    2020-09-27

    8.0.2.1.1

    Category

    Description

    Release date

    New feature and performance optimization

    The write performance of clusters is optimized.

    2020-08-26

    Fixed issue

    The memory leak issue is fixed.

    8.0.2.1.0

    Category

    Description

    Release date

    New feature and performance optimization

    • The EXPLAIN statement can be executed to query the information about a parallel execution plan. After you specify FORMAT=TREE in the EXPLAIN statement, the execution plan is displayed in the tree format.

    • Hash joins are supported in 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 statistics about performance metrics of PolarDB for MySQL clusters. To collect performance metrics, you can query the PERF_STATISTICS in-memory table. For more information, see Performance Agent.

    • The warm buffer pool feature is supported. When an instance restarts after an unexpected exit or an upgrade, the data in the buffer pool is not cleared. This significantly accelerates the restart process and allows you to maintain the same level of system performance after the restart.

    2020-07-22