Weekly update in TiDB

Last week, we landed 39 PRs in the TiDB repositories.

Added

• Add a session variable tidb_ddl_reorg_worker_cnt to control the number of the DDL organization workers
• Support parallel HASH aggregation and greatly improve the performance of the aggregation function
• Print explain results in a tree style
• Support the SHOW ERRORS statement and improve the SHOW WARNINGS statement

Fixed

• Make the INSERT IGNORE statement ignore BadNullError
• Fix a bug when only_full_group_by is set in SQL_MODE
• Fix the wrong results of avg(double)
• Make the CREATE TABLE IF NOT EXISTS LIKE statement work again
• Set the correct startHandle when some errors occur in adding indexes
• Fix a bug in pushing down TopN
• Fix the response result bug of COM_FIELD_LIST
• Fix a bug of the str_to_date() function
• Fix a bug of the INSERT statement when the field type is unsigned float/double

Improved

• Use the average error of the row count which is estimated by statistics to determine the pseudo column
• Use CorrelatedColumn to calculate range
• Make the frequency of updating the statistic metadata depend on the table size
• Refactor the execution framework of the aggregate functions
• Speed up the CreateTable operation
• Stop calling expression.Clone in the plan package except ResolveIndices
• Handle \N as NULL in LOAD DATA
• Avoid holding the Write lock for a long time
• Reduce the memory usage in the INSERT INTO SELECT statement
• Enhance the row count estimation when the correlated column exists
• Check the character set capitalization when creating a table
• Improve the accessPath for the unique key

Weekly update in TiKV and PD

Last week, we landed 25 PRs in the TiKV and PD repositories.

Added

• Support splitting a Region by key using tikv-ctl
• Provide PerfContext statistics in Coprocessor
• Fuzz decimals
• Collect thread state metrics

Fixed

• Fix the issue that the store runs out of space due to moving replicas
• Fix a bug in do_sub when the last nonzero digit is before the point
• Fix potential stale Read during merging
• Handle heartbeats of Regions with changed peers

Improved

• Return the UnknownSignature error for unimplemented signatures
• Remove Box<> around Cursor, Snapshot and Engine
• Upgrade Rust to the nightly-2018-06-14 version

New contributors (Thanks!)

TiDB:

• cityonsky
• mail2fish

Docs:

• yejiayu