tidb_stats_load_sync_wait Parameter does not take effect

[Chad20N13]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

set global tidb_stats_load_sync_wait=30000;

2. What did you expect to see? (Required)

execute SQL need to wait 30 seconds

3. What did you see instead (Required)

SQL return result in 3 seconds, and report a warning : sync load stats timeout

4. What is your TiDB version? (Required)

MySQL [lifedata]> select tidb_version();
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tidb_version() |
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Release Version: v7.5.0
Edition: Community
Git Commit Hash: 069631e
Git Branch: heads/refs/tags/v7.5.0
UTC Build Time: 2023-11-24 08:50:14
GoVersion: go1.21.3
Race Enabled: false
Check Table Before Drop: false
Store: tikv |
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)

[Chad20N13]

[Chad20N13]

[jiyfhust]

Is sql hint max_execution_time or session/global variable max_execution_time set a small value?
It looks will choose the smallest value as the actual waitTime.

waitTime := min(syncWait, hintMaxExecutionTime, sessMaxExecutionTime)

tidb/pkg/planner/core/plan_stats.go

Line 112 in 9bad202

waitTime := min(syncWait, hintMaxExecutionTime, sessMaxExecutionTime)

[jiyfhust]

There maybe a bug, not very sure about yet:

syncWait := plan.SCtx().GetSessionVars().StatsLoadSyncWait * time.Millisecond.Nanoseconds()

infact StatsLoadSyncWait is ms unit.

and MaxExecutionTime is ms unit too.

However Compare syncWait with MaxExecutionTime is not right, is it?

Not sure if #50915 can close it.

[jiyfhust]

There maybe a bug, not very sure about yet:

syncWait := plan.SCtx().GetSessionVars().StatsLoadSyncWait * time.Millisecond.Nanoseconds()

infact StatsLoadSyncWait is ms unit.

and MaxExecutionTime is ms unit too.

However Compare syncWait with MaxExecutionTime is not right, is it?

Not sure if #50915 can close it.

@hawkingrei PTAL

tidb/pkg/planner/core/plan_stats.go

Line 41 in 9bad202

syncWait := plan.SCtx().GetSessionVars().StatsLoadSyncWait * time.Millisecond.Nanoseconds()

tidb/pkg/planner/core/plan_stats.go

Line 112 in 9bad202

waitTime := min(syncWait, hintMaxExecutionTime, sessMaxExecutionTime)

[Chad20N13]

max_execution_time is 86400000

[Chad20N13]

[jiyfhust]

max_execution_time is 86400000

There maybe a bug, not very sure about yet:

syncWait := plan.SCtx().GetSessionVars().StatsLoadSyncWait * time.Millisecond.Nanoseconds()

infact StatsLoadSyncWait is ms unit.

and MaxExecutionTime is ms unit too.

However Compare syncWait with MaxExecutionTime is not right, is it?

Not sure if #50915 can close it.

The syncWait will be 86400000Nanoseconds, that is 86.4ms。Then reported timeout error.
The total time is 3.02s, is it a slow query even there is no need to load stats？

[Chad20N13]

tidb_stats_load_sync_wait is 30000
max_execution_time is 86400000

max_execution_time
Scope: SESSION | GLOBAL
Persists to cluster: Yes
Applies to hint SET_VAR: Yes
Type: Integer
Default value: 0
Range: [0, 2147483647]
Unit: Milliseconds
The maximum execution time of a statement. The default value is unlimited (zero).

I do not know the logic or time unit of these two parameters, please analyze the problem in detail .

[jiyfhust]

/severity moderate