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pingcap
executor, util: fix UnionScan Next() skip reading data when passed chunk capacity is 0
What problem does this PR solve?
Issue Number: close #36903
Problem Summary:
What is changed and how it works?
In the old UnionScan executor code, if an empty chk is passed to UnionScan.Next(chk) , the UnionScan executor will not read any data.
This bug could be trigger in select pkey from t_vwvgdc where 0 <> 0 union select pkey from t_vwvgdc;
The union first children return empty chunk, and the chunk is reused for the second children (union scan) to read data.
mysql> explain select pkey from t_vwvgdc where 0 <> 0 union select pkey from t_vwvgdc;
+------------------------------+---------+-----------+----------------+-------------------------------------------------------+
| id | estRows | task | access object | operator info |
+------------------------------+---------+-----------+----------------+-------------------------------------------------------+
| HashAgg_13 | 24.20 | root | | group by:Column#7, funcs:firstrow(Column#7)->Column#7 |
| └─Union_14 | 29.00 | root | | |
| ├─TableDual_16 | 0.00 | root | | rows:0 |
| └─UnionScan_18 | 29.00 | root | | |
| └─TableReader_20 | 29.00 | root | | data:TableFullScan_19 |
| └─TableFullScan_19 | 29.00 | cop[tikv] | table:t_vwvgdc | keep order:false, stats:pseudo |
+------------------------------+---------+-----------+----------------+-------------------------------------------------------+
6 rows in set (0.00 sec)
Now I change req.GrowAndReset(us.maxChunkSize) to ensure capacity > 0 for the req.
Check List
Tests
- [ ] Unit test
- [ ] Integration test
- [ ] Manual test (add detailed scripts or steps below)
- [ ] No code
Side effects
- [ ] Performance regression: Consumes more CPU
- [ ] Performance regression: Consumes more Memory
- [ ] Breaking backward compatibility
Documentation
- [ ] Affects user behaviors
- [ ] Contains syntax changes
- [ ] Contains variable changes
- [ ] Contains experimental features
- [ ] Changes MySQL compatibility
Release note
Please refer to Release Notes Language Style Guide to write a quality release note.
Fix a bug that UnionScan's Next() function skips reading data when the passed chunk's capacity is 0
[REVIEW NOTIFICATION]
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- qw4990
- xhebox
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Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/b56e0ff76bb0363def99fd04899e99729bd7c231
This pull request has been accepted and is ready to merge.
TiDB MergeCI notify
🔴 Bad News! New failing [1] after this pr merged. These new failed integration tests seem to be caused by the current PR, please try to fix these new failed integration tests, thanks!
| CI Name | Result | Duration | Compare with Parent commit |
|---|---|---|---|
| idc-jenkins-ci/integration-cdc-test | 🟥 | 3 min 51 sec | New failing |
| idc-jenkins-ci-tidb/tics-test | 🟢 all 1 tests passed | 23 min | Existing passed |
| idc-jenkins-ci-tidb/integration-common-test | 🟢 all 17 tests passed | 15 min | Existing passed |
| idc-jenkins-ci-tidb/common-test | 🟢 all 11 tests passed | 14 min | Existing passed |
| idc-jenkins-ci-tidb/sqllogic-test-2 | 🟢 all 28 tests passed | 7 min 46 sec | Existing passed |
| idc-jenkins-ci-tidb/integration-ddl-test | 🟢 all 6 tests passed | 7 min 19 sec | Existing passed |
| idc-jenkins-ci-tidb/sqllogic-test-1 | 🟢 all 26 tests passed | 5 min 59 sec | Existing passed |
| idc-jenkins-ci-tidb/mybatis-test | 🟢 all 1 tests passed | 4 min 36 sec | Existing passed |
| idc-jenkins-ci-tidb/integration-compatibility-test | 🟢 all 1 tests passed | 3 min 33 sec | Existing passed |
| idc-jenkins-ci-tidb/plugin-test | 🟢 build success, plugin test success | 4min | Existing passed |