TiDB 4.0.8 Release Notes

Release date: October 30, 2020

TiDB version: 4.0.8

New Features

• TiDB

  • Support the new aggregate function APPROX_PERCENTILE #20197

• TiFlash

  • Support pushing down CAST functions

• Tools

  • TiCDC

    • Support snapshot-level consistent replication #932

Improvements

• TiDB

  • Prioritize low-selectivity indexes in the greedy search procedure of Selectivity() #20154
  • Record more RPC runtime information in Coprocessor runtime statistics #19264
  • Speed up parsing the slow log to improve query performance #20556
  • Wait for timeout execution plans during the plan binding stage to record more debug information when the SQL optimizer is verifying potential new plans #20530
  • Add the execution retry time in the slow log and the slow query result #20495 #20494
  • Add the table_storage_stats system table #20431
  • Add the RPC runtime statistical information for the INSERT/UPDATE/REPLACE statement #20430
  • Add the operator information in the result of EXPLAIN FOR CONNECTION #20384
  • Adjust the TiDB error log to the DEBUG level for the client connection/disconnection activities #20321
  • Add monitoring metrics for Coprocessor Cache #20293
  • Add the runtime information of pessimistic lock keys #20199
  • Add two extra sections of time consumption information in the runtime information and trace span #20187
  • Add the runtime information of transaction commit in the slow log #20185
  • Disable the index merge join #20599
  • Add the ISO 8601 and timezone supports for temporal string literals #20670

• TiKV

  • Add the Fast-Tune panel page to assist performance diagnostics #8804
  • Add the security.redact-info-log configuration item, which redacts user data from logs #8746
  • Reformat the metafile of error codes #8877
  • Enable dynamically changing the pessimistic-txn.pipelined configuration #8853
  • Enable the memory profiling features by default #8801

• PD

  • Generate the metafile of errors #3090
  • Add the additional information for the operator #3009

• TiFlash

  • Add monitoring metrics of Raft logs
  • Add monitoring metrics of memory usage for cop tasks
  • Make the min/max index more accurate when data is deleted
  • Improve query performance in the case of a small data volume
  • Add the errors.toml file to support the standard error code

• Tools

  • Backup and Restore (BR)

    • Speed up the restore process by pipelining split and ingest #427
    • Support manually restoring PD schedulers #530
    • Use pause schedulers instead of remove schedulers #551

  • TiCDC

    • Print statistics in MySQL sink periodically #1023

  • Dumpling

    • Support dumpling data directly to S3 storages #155
    • Support dumping views #158
    • Support dumping the table that only contains generated columns #166

  • TiDB Lightning

    • Support multi-byte CSV delimiters and separators #406
    • Speed up the restore process by disabling some PD schedulers #408
    • Use the GC-TTL API for checksum GC safepoint in the v4.0 cluster to avoid the GC error #396

Bug Fixes

• TiDB

  • Fix the unexpected panic that occurs when using partitioned tables #20565
  • Fix the wrong result of outer join when filtering the outer side using index merge join #20427
  • Fix the issue that the NULL value is returned when converting data to the BIT type if the data is too long #20363
  • Fix the corrupted default value for the BIT type column #20340
  • Fix the overflow error that might occur when converting the BIT type to the INT64 type #20312
  • Fix the possible wrong result of the propagate column optimization for the hybrid type column #20297
  • Fix the panic that might occur when storing outdated plans from the plan cache #20246
  • Fix the bug that the returned result is mistakenly truncated if FROM_UNIXTIME and UNION ALL are used together #20240
  • Fix the issue that wrong results might be returned when the Enum type value is converted to the Float type #20235
  • Fix the possible panic of RegionStore.accessStore #20210
  • Fix the wrong result returned when sorting the maximum unsigned integer in BatchPointGet #20205
  • Fix the bug that the coercibilities of Enum and Set are wrong #20364
  • Fix an issue of ambiguous YEAR conversion #20292
  • Fix the issue of wrong reported result that occurs when the KV duration panel contains store0 #20260
  • Fix the issue that the Float type data is mistakenly inserted regardless of the out of range error #20252
  • Fix the bug that the generated column does not handle bad NULL values #20216
  • Fix the inaccurate error information for the YEAR type data that is out of range #20170
  • Fix the unexpected invalid auto-id error that might occur during the pessimistic transaction retry #20134
  • Fix the issue that the constraint is not checked when using ALTER TABLE to change the Enum/Set type #20046
  • Fix the wrong runtime information of cop tasks recorded when multiple operators are used for concurrency #19947
  • Fix the issue that read-only system variables cannot be explicitly selected as the session variables #19944
  • Fix the issue that the duplicate ORDER BY condition might cause sub-optimal execution plans #20333
  • Fix the issue that the generated metric profile might fail if the font size exceeds the maximum allowable value #20637

• TiKV

  • Fix the bug that the mutex conflict in encryption causes pd-worker to process heartbeats slowly #8869
  • Fix the issue that the memory profile is mistakenly generated #8790
  • Fix the failure to back up databases on GCS when the storage class is specified #8763
  • Fix the bug that a learner cannot find a leader when the Region is restarted or newly split #8864

• PD

  • Fix a bug that Key Visualizer of TiDB Dashboard might cause PD panic in some cases #3096
  • Fix the bug that PD might panic if a PD store is down for more than 10 minutes #3069

• TiFlash

  • Fix the issue of wrong timestamp in the log message
  • Fix the issue that during the multi-disk TiFlash deployment, the wrong capacity causes the creation of TiFlash replicas to fail
  • Fix the bug that TiFlash might throw errors about broken data files after restart
  • Fix the issue that broken files might be left on disk after TiFlash crashes
  • Fix the bug that it might take a long time to wait for index during learner reads if the proxy cannot catch up with the latest Raft lease information
  • Fix the bug that the proxy writes too much Region state information to the key-value engine while replaying the outdated Raft log

• Tools

  • Backup and Restore (BR)

    • Fix the send on closed channel panic during restore #559

  • TiCDC

    • Fix the unexpected exit caused by the failure to update the GC safepoint #979
    • Fix the issue that the task status is unexpectedly flushed because of the incorrect mod revision cache #1017
    • Fix the unexpected empty Maxwell messages #978

  • TiDB Lightning

    • Fix the issue of wrong column information #420
    • Fix the infinity loop that occurs when retrying to get Region information in the local mode #418