executor: fix setting system variables to original values failed after auto analyze #37551
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executor/adapter.go
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| @@ -437,10 +437,12 @@ func (a *ExecStmt) Exec(ctx context.Context) (_ sqlexec.RecordSet, err error) { | |||
| sctx := a.Ctx | |||
| ctx = util.SetSessionID(ctx, sctx.GetSessionVars().ConnectionID) | |||
| if _, ok := a.Plan.(*plannercore.Analyze); ok && sctx.GetSessionVars().InRestrictedSQL { | |||
| oriStats, _ := sctx.GetSessionVars().GetSystemVar(variable.TiDBBuildStatsConcurrency) | |||
| oriStats, err := sctx.GetSessionVars().GetSessionOrGlobalSystemVar(variable.TiDBBuildStatsConcurrency) | |||
| terror.Log(err) | |||
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GetSystemVar returns empty values for both system variables in an internal session
I think we should try to avoid it, if it is not trivial to do so, we could use the default value as 'oriStats' here.
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It seems not trivial to use the global system variable value to initialize the session system variable for internal sessions because we need the first internal session to read the global system variable value from disk. The two quick-fix ways are:
- When
GetSystemVarreturns empty value, use the default value. - Use
GetSessionOrGlobalSystemVar(use the session system variable value if it exists, otherwise use the global system variable value).
Which ways do you prefer?
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I think to be default value is fine
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defaults are safer for internal sessions. Probably outside of the scope here, but we should even consider making internal sessions only use defaults unless a variable has a special flag saying it should apply to internal sessions.
Consider the case that the user changes the Txn Isolation, Optimistic/Pessimistic locking, change in lock wait timeout etc. These could affect how statements execute quite a lot, resulting in bugs.
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Changed to use default value. PTAL @xiongjiwei @morgo @bb7133
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What problem does this PR solve?
Issue Number: close #37410
Problem Summary:
What is changed and how it works?
When saving original values of
TiDBBuildStatsConcurrencyandTxnIsolationbefore auto analyze,GetSystemVarreturns empty values for both system variables in an internal session, which causes restoring original values after auto analyze failed. The pr usesGetSessionOrGlobalSystemVar, which would not return empty values, to replaceGetSystemVar.Check List
Tests
Trigger auto analyze and see no error log like #37410.
Side effects
Documentation
Release note
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