fix(runaway): ensure DistSQLContext's checker is synchronized with session variables (#61907)

[ti-chi-bot]

This is an automated cherry-pick of #61907

What problem does this PR solve?

Issue Number: close #61899.

What changed and how does it work?

Update GetDistSQLCtx to check and align the RunawayChecker in the cached DistSQL context with the session's current value.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

Prepare:

create table t1(a int, b int);
insert into t1 value(rand()*1000, rand()*1000); x 44600

mysql> select count(*) from t1;
+----------+
| count(*) |
+----------+
|    44600 |
+----------+
1 row in set (0.01 sec)

mysql> CREATE RESOURCE GROUP IF NOT EXISTS rg1 RU_PER_SEC = 100 QUERY_LIMIT=(RU=10, ACTION=KILL);
Query OK, 0 rows affected (0.06 sec)

mysql> SET RESOURCE GROUP rg1;
Query OK, 0 rows affected (0.00 sec)

Before:

mysql> explain analyze select * from t1 where b > 36;
ERROR 8253 (HY000): Query execution was interrupted, identified as runaway query [RequestUnit = RRU:13.419626, WRU:0.000000, WaitDuration:0s(10)]

mysql> explain analyze select min(a)+10 from t1 where a < 639;
ERROR 8253 (HY000): Query execution was interrupted, identified as runaway query [RequestUnit = RRU:38.330615, WRU:0.000000, WaitDuration:0s(10)]

mysql> explain analyze select * from t1 where b > (select min(a)+3 from t1 where a < 452);
+--------------------------+----------+---------+-----------+---------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------+----------+------+
| id                       | estRows  | actRows | task      | access object | execution info                                                                                                                                                                                                                                                                                                                                                                                                                            | operator info                                    | memory   | disk |
+--------------------------+----------+---------+-----------+---------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------+----------+------+
| TableReader_36           | 18466.67 | 44437   | root      |               | time:217.3ms, loops:46, RU:78.809008, cop_task: {num: 9, max: 121.4ms, min: 572.6µs, avg: 24.1ms, p95: 121.4ms, max_proc_keys: 17376, p95_proc_keys: 17376, tot_proc: 25.1ms, tot_wait: 370.2µs, copr_cache_hit_ratio: 0.00, build_task_duration: 8.17µs, max_distsql_concurrency: 1}, rpc_info:{Cop:{num_rpc:9, total_time:217.1ms}}                                                                                                     | data:Selection_35                                | 414.5 KB | N/A  |
| └─Selection_35           | 18466.67 | 44437   | cop[tikv] |               | tikv_task:{proc max:8ms, min:0s, avg: 2.78ms, p80:6ms, p95:8ms, iters:79, tasks:9}, scan_detail: {total_process_keys: 44600, total_process_keys_size: 1906316, total_keys: 44609, get_snapshot_time: 199µs, rocksdb: {key_skipped_count: 44600, block: {cache_hit_count: 93}}}, time_detail: {total_process_time: 25.1ms, total_suspend_time: 45.2µs, total_wait_time: 370.2µs, total_kv_read_wall_time: 25ms, tikv_wall_time: 26.2ms}    | gt(test.t1.b, 3)                                 | N/A      | N/A  |
|   └─TableFullScan_34     | 55400.00 | 44600   | cop[tikv] | table:t1      | tikv_task:{proc max:8ms, min:0s, avg: 2.78ms, p80:6ms, p95:8ms, iters:79, tasks:9}                                                                                                                                                                                                                                                                                                                                                        | keep order:false, stats:partial[b:unInitialized] | N/A      | N/A  |
+--------------------------+----------+---------+-----------+---------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------+----------+------+
3 rows in set (0.24 sec)

After:

mysql> explain analyze select min(a)+10 from t1 where a < 639;
ERROR 8253 (HY000): Query execution was interrupted, identified as runaway query [RequestUnit = RRU:29.563074, WRU:0.000000, WaitDuration:0s(10)]

mysql> explain analyze select * from t1 where b > 36;
ERROR 8253 (HY000): Query execution was interrupted, identified as runaway query [RequestUnit = RRU:10.572321, WRU:0.000000, WaitDuration:0s(10)]

mysql> explain analyze select * from t1 where b > (select min(a)+3 from t1 where a < 452);
ERROR 8253 (HY000): Query execution was interrupted, identified as runaway query [RequestUnit = RRU:30.184085, WRU:0.000000, WaitDuration:0s(10)]

Release note

Fixed an issue where the evaluating of non-correlated subqueries could cause runaway configuration to become invalid.

[codecov]

Codecov Report

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Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.5     #62220   +/-   ##
================================================
  Coverage               ?   57.7295%           
================================================
  Files                  ?       1771           
  Lines                  ?     631476           
  Branches               ?          0           
================================================
  Hits                   ?     364548           
  Misses                 ?     242299           
  Partials               ?      24629           

Flag	Coverage Δ
integration	38.4083% <100.0000%> (?)
unit	72.6658% <100.0000%> (?)

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Components	Coverage Δ
dumpling	52.9278% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	63.2038% <0.0000%> (?)

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[LGTM Timeline notifier]

Timeline:

• 2025-07-04 09:08:28.12417971 +0000 UTC m=+1645160.847358696: ☑️ agreed by JmPotato.
• 2025-07-08 06:53:30.321115961 +0000 UTC m=+1982663.044294943: ☑️ agreed by rleungx.

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