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releases/readme: add the release notes for TiDB 2.0 (#449)
* releases/readme: add the release notes for 2.0 * releases: address comments
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,155 @@ | ||
| --- | ||
| title: TiDB 2.0 Release Notes | ||
| category: Releases | ||
| --- | ||
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| # TiDB 2.0 Release Notes | ||
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| On April 27, 2018, TiDB 2.0 GA is released! Compared with TiDB 1.0, this release has great improvement in MySQL compatibility, SQL optimizer, executor, and stability. | ||
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| ## TiDB | ||
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| - SQL Optimizer | ||
| - Use more compact data structure to reduce the memory usage of statistics information | ||
| - Speed up loading statistics information when starting a tidb-server process | ||
| - Support updating statistics information dynamically [experimental] | ||
| - Optimize the cost model to provide more accurate query cost evaluation | ||
| - Use `Count-Min Sketch` to estimate the cost of point queries more accurately | ||
| - Support analyzing more complex conditions to make full use of indexes | ||
| - Support manually specifying the `Join` order using the `STRAIGHT_JOIN` syntax | ||
| - Use the Stream Aggregation operator when the `GROUP BY` clause is empty to improve the performance | ||
| - Support using indexes for the `MAX/MIN` function | ||
| - Optimize the processing algorithms for correlated subqueries to support decorrelating more types of correlated subqueries and transform them to `Left Outer Join` | ||
| - Extend `IndexLookupJoin` to be used in matching the index prefix | ||
| - SQL Execution Engine | ||
| - Refactor all operators using the Chunk architecture, improve the execution performance of analytical queries, and reduce memory usage. There is a significant improvement in the TPC-H benchmark result. | ||
| - Support the Streaming Aggregation operators pushdown | ||
| - Optimize the `Insert Into Ignore` statement to improve the performance by over 10 times | ||
| - Optimize the `Insert On Duplicate Key Update` statement to improve the performance by over 10 times | ||
| - Optimize `Load Data` to improve the performance by over 10 times | ||
| - Push down more data types and functions to TiKV | ||
| - Support computing the memory usage of physical operators, and specifying the processing behavior in the configuration file and system variables when the memory usage exceeds the threshold | ||
| - Support limiting the memory usage by a single SQL statement to reduce the risk of OOM | ||
| - Support using implicit RowID in CRUD operations | ||
| - Improve the performance of point queries | ||
| - Server | ||
| - Support the Proxy Protocol | ||
| - Add more monitoring metrics and refine the log | ||
| - Support validating the configuration files | ||
| - Support obtaining the information of TiDB parameters through HTTP API | ||
| - Resolve Lock in the Batch mode to speed up garbage collection | ||
| - Support multi-threaded garbage collection | ||
| - Support TLS | ||
| - Compatibility | ||
| - Support more MySQL syntaxes | ||
| - Support modifying the `lower_case_table_names` system variable in the configuration file to support the OGG data synchronization tool | ||
| - Improve compatibility with the Navicat management tool | ||
| - Support displaying the table creating time in `Information_Schema` | ||
| - Fix the issue that the return types of some functions/expressions differ from MySQL | ||
| - Improve compatibility with JDBC | ||
| - Support more SQL Modes | ||
| - DDL | ||
| - Optimize the `Add Index` operation to greatly improve the execution speed in some scenarios | ||
| - Attach a lower priority to the `Add Index` operation to reduce the impact on online business | ||
| - Output more detailed status information of the DDL jobs in `Admin Show DDL Jobs` | ||
| - Support querying the original statements of currently running DDL jobs using `Admin Show DDL Job Queries JobID` | ||
| - Support recovering the index data using `Admin Recover Index` for disaster recovery | ||
| - Support modifying Table Options using the `Alter` statement | ||
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| ## PD | ||
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| - Support `Region Merge`, to merge empty Regions after deleting data [experimental] | ||
| - Support `Raft Learner` [experimental] | ||
| - Optimize the scheduler | ||
| - Make the scheduler to adapt to different Region sizes | ||
| - Improve the priority and speed of restoring data during TiKV outage | ||
| - Speed up data transferring when removing a TiKV node | ||
| - Optimize the scheduling policies to prevent the disks from becoming full when the space of TiKV nodes is insufficient | ||
| - Improve the scheduling efficiency of the balance-leader scheduler | ||
| - Reduce the scheduling overhead of the balance-region scheduler | ||
| - Optimize the execution efficiency of the the hot-region scheduler | ||
| - Operations interface and configuration | ||
| - Support TLS | ||
| - Support prioritizing the PD leaders | ||
| - Support configuring the scheduling policies based on labels | ||
| - Support configuring stores with a specific label not to schedule the Raft leader | ||
| - Support splitting Region manually to handle the hotspot in a single Region | ||
| - Support scattering a specified Region to manually adjust Region distribution in some cases | ||
| - Add check rules for configuration parameters and improve validity check of the configuration items | ||
| - Debugging interface | ||
| - Add the `Drop Region` debugging interface | ||
| - Add the interfaces to enumerate the health status of each PD | ||
| - Statistics | ||
| - Add statistics about abnormal Regions | ||
| - Add statistics about Region isolation level | ||
| - Add scheduling related metrics | ||
| - Performance | ||
| - Keep the PD leader and the etcd leader together in the same node to improve write performance | ||
| - Optimize the performance of Region heartbeat | ||
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| ## TiKV | ||
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| - Features | ||
| - Protect critical configuration from incorrect modification | ||
| - Support `Region Merge` [experimental] | ||
| - Add the `Raw DeleteRange` API | ||
| - Add the `GetMetric` API | ||
| - Add `Raw Batch Put`, `Raw Batch Get`, `Raw Batch Delete` and `Raw Batch Scan` | ||
| - Add Column Family options for the RawKV API and support executing operation on a specific Column Family | ||
| - Support Streaming and Streaming Aggregation in Coprocessor | ||
| - Support configuring the request timeout of Coprocessor | ||
| - Carry timestamps with Region heartbeats | ||
| - Support modifying some RocksDB parameters online, such as `block-cache-size` | ||
| - Support configuring the behavior of Coprocessor when it encounters some warnings or errors | ||
| - Support starting in the importing data mode to reduce write amplification during the data importing process | ||
| - Support manually splitting Region in halves | ||
| - Improve the data recovery tool `tikv-ctl` | ||
| - Return more statistics in Coprocessor to guide the behavior of TiDB | ||
| - Support the `ImportSST` API to import SST files [experimental] | ||
| - Add the TiKV Importer binary to integrate with TiDB Lightning to import data quickly [experimental] | ||
| - Performance | ||
| - Optimize read performance using `ReadPool` and increase the `raw_get/get/batch_get` by 30% | ||
| - Improve metrics performance | ||
| - Inform PD immediately once the Raft snapshot process is completed to speed up balancing | ||
| - Solve performance jitter caused by RocksDB flushing | ||
| - Optimize the space reclaiming mechanism after deleting data | ||
| - Speed up garbage cleaning while starting the server | ||
| - Reduce the I/O overhead during replica migration using `DeleteFilesInRanges` | ||
| - Stability | ||
| - Fix the issue that gRPC call does not get returned when the PD leader switches | ||
| - Fix the issue that it is slow to offline nodes caused by snapshots | ||
| - Limit the temporary space usage consumed by migrating replicas | ||
| - Report the Regions that cannot elect a leader for a long time | ||
| - Update the Region size information in time according to compaction events | ||
| - Limit the size of scan lock to avoid request timeout | ||
| - Limit the memory usage when receiving snapshots to avoid OOM | ||
| - Increase the speed of CI test | ||
| - Fix the OOM issue caused by too many snapshots | ||
| - Configure `keepalive` of gRPC | ||
| - Fix the OOM issue caused by an increase of the Region number | ||
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| ## TiSpark | ||
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| TiSpark uses a separate version number. The current TiSpark version is 1.0 GA. The components of TiSpark 1.0 provide distributed computing of TiDB data using Apache Spark. | ||
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| - Provide a gRPC communication framework to read data from TiKV | ||
| - Provide encoding and decoding of TiKV component data and communication protocol | ||
| - Provide calculation pushdown, which includes: | ||
| - Aggregate pushdown | ||
| - Predicate pushdown | ||
| - TopN pushdown | ||
| - Limit pushdown | ||
| - Provide index related support | ||
| - Transform predicate into Region key range or secondary index | ||
| - Optimize `Index Only` queries | ||
| - Optimize table scan when runtime index degenerates | ||
| - Provide cost-based optimization | ||
| - Support statistics | ||
| - Select index | ||
| - Estimate broadcast table cost | ||
| - Provide support for multiple Spark interfaces | ||
| - Support Spark Shell | ||
| - Support ThriftServer/JDBC | ||
| - Support Spark-SQL interaction | ||
| - Support PySpark Shell | ||
| - Support SparkR |
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