TiDB 4.0.12 Release Notes

Release date: April 2, 2021

TiDB version: 4.0.12

New Features

TiFlash
- Add tools to check the status of tiflash replica for online rolling updates

Improvements

TiDB
- Refine the output information of the EXPLAIN statement for the batch cop mode #23164
- Add the warning information for expressions that cannot be pushed to the storage layer in the output of the EXPLAIN statement #23020
- Migrate a part of the DDL package code from Execute/ExecRestricted to the safe API (2) #22935
- Migrate a part of the DDL package code from Execute/ExecRestricted to the safe API (1) #22929
- Add optimization-time and wait-TS-time into the slow log #22918
- Support querying partition_id from the infoschema.partitions table #22489
- Add last_plan_from_binding to help the users know whether a SQL statement's execution plan is matched with the hints in the binding #21430
- Scatter truncated tables without the pre-split option #22872
- Add three format specifiers for the str_to_date expression #22812
- Record the PREPARE execution failure as Failed Query OPM in the metrics monitor #22672
- Do not report errors for the PREPARE execution if tidb_snapshot is set #22641
TiKV
- Prevent a large number of reconnections in a short period of time #9879
- Optimize the write operations and Batch Get in the scenarios of many tombstones #9729
- Change the default value of leader-transfer-max-log-lag to 128 to increase the success rate of leader transfer #9605
PD
- Update the Region cache only when pending-peers or down-peers changes, which reduces the pressure of updating heartbeats #3471
- Prevent the Regions in split-cache from becoming the target of merge #3459
TiFlash
- Optimize the configuration file and remove useless items
- Reduce the size of TiFlash binary files
- Use an adaptive aggressive GC strategy to reduce memory usage
Tools
- TiCDC
  - Add a double confirmation when users create or resume the changefeed with the start-ts or checkpoint-ts 1 day before the current timestamp #1497
  - Add Grafana panels for the Old Value feature #1571
- Backup & Restore (BR)
  - Log the HTTP_PROXY and HTTPS_PROXY environmental variables #827
  - Improve the backup performance when there are many tables #745
  - Report errors if the service safe point check fails #826
  - Add the cluster_version and br_version information in backupmeta #803
  - Add retry for external storage errors to increase the success rate of backup #851
  - Reduce memory usage during backup #886
- TiDB Lightning
  - Check the TiDB cluster version before running TiDB Lightning to avoid unexpected errors #787
  - Fail fast when TiDB Lightning meets the cancel error #867
  - Add tikv-importer.engine-mem-cache-size and tikv-importer.local-writer-mem-cache-size configuration items to balance between memory usage and performance #866
  - Run batch split region in parallel for TiDB Lightning's Local-backend to increase the import speed #868
  - When using TiDB Lightning to import data from a S3 storage, TiDB Lightning no longer requires the s3:ListBucket permission #919
  - When resuming from a checkpoint, TiDB Lightning keeps using the original engine #924

Bug Fixes

TiDB
- Fix the issue that the get variable expression goes wrong when the session variable is hexadecimal literals#23372
- Fix the issue that wrong collation is used when creating the fast execution plan for the Enum or Set type #23292
- Fix the possible wrong result of the nullif expression when it is used with is-null #23279
- Fix the issue that the auto-analysis is triggered outside its time range #23219
- Fix the issue that the CAST function might ignore errors for the point get plan #23211
- Fix a bug that prevents SPM from taking effect when CurrentDB is empty #23209
- Fix the issue of possible wrong table filters for the IndexMerge plan #23165
- Fix the issue of unexpected NotNullFlag in the returning types of the NULL constant #23135
- Fix a bug that collation might not be handled by the text type #23092
- Fix the issue that the range partition might incorrectly handle the IN expression #23074
- Fix the issue that after marking a TiKV store as tombstone, starting new TiKV stores with different StoreIDs with the same IP address and port keeps returning the StoreNotMatch error #23071
- Do not adjust the INT type when it is NULL and compared with YEAR #22844
- Fix the issue of lost connection when loading data on tables with the auto_random column #22736
- Fix the issue of DDL hangover when the DDL operation meets panic in the cancelling path #23297
- Fix the wrong key range of index scan when comparing the YEAR column with NULL #23104
- Fix the issue that a successfully created view is failed to use #23083
TiKV
- Fix the issue that the IN expression does not properly handle unsigned/signed integers #9850
- Fix the issue that the ingest operation is not re-entrant #9779
- Fix the issue that the space is missed when converting JSON to string in TiKV coprocessor #9666
PD
- Fix a bug that the isolation level is wrong when the store lacks the label #3474
TiFlash
- Fix the issue of incorrect execution results when the default value of the binary type column contains leading or tailing zero bytes
- Fix a bug that TiFlash fails to synchronize schema if the name of the database contains special characters
- Fix the issue of incorrect results when handling the IN expression with decimal values
- Fix a bug that the metric for the opened file count shown in Grafana is high
- Fix a bug that TiFlash does not support the Timestamp literal
- Fix the potential not responding issue while handling the FROM_UNIXTIME expression
- Fix the issue of incorrect results when casting string as integer
- Fix a bug that the like function might return wrong results
Tools
- TiCDC
  - Fix a disorder issue of the resolved ts event #1464
  - Fix a data loss issue caused by wrong table scheduling due to the network problem #1508
  - Fix a bug of untimely release of resources after a processor is stopped #1547
  - Fix a bug that the transaction counter is not correctly updated, which might cause database connection leak #1524
  - Fix the issue that multiple owners can co-exist when PD has jitter, which might lead to table missing #1540
- Backup & Restore (BR)
  - Fix a bug that WalkDir for the s3 storage returns nil if the target path is bucket name #733
  - Fix a bug that the status port is not served with TLS #839
- TiDB Lightning
  - Fix the error that TiKV Importer might ignore that the file has already existed #848
  - Fix a bug that the TiDB Lightning might use the wrong timestamp and read the wrong data #850
  - Fix a bug that TiDB Lightning's unexpected exit might cause damaged checkpoint file #889
  - Fix the issue of possible data error that occurs because the cancel error is ignored #874