TiDB doesn't log any slow log if log.level >= "error"

[youjiali1995]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. Deploy a nightly cluster with config below:

[log]
level = "error"
slow-threshold = 0

2. Execute any query.
3. See whether there is the tidb_slow_query.log file.

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

slow logs show.

3. What did you see instead (Required)

No slow logs.

4. What is your TiDB version? (Required)

[v5.1-v5.3], nightly

[youjiali1995]

Introduced by #23534 which uses the same config of the server logger to initialize the slow query logger:
https://github.com/pingcap/tidb/pull/23534/files#diff-800042943fbf571b5e1b46f93f2ebab487a70873fd3c9708b00b39b9d59ce278R20.

The slow query logger uses default config before https://github.com/pingcap/tidb/pull/23534/files#diff-163bbfde1f383898e507b5ca82bd6bec58809a82f6b8352d991f50962f7f472aL277-L285 and it uses Debug or Warn to log:

tidb/executor/adapter.go

Lines 1028 to 1031 in e97e8c0

	if costTime < threshold {
	logutil.SlowQueryLogger.Debug(sessVars.SlowLogFormat(slowItems))
	} else {
	logutil.SlowQueryLogger.Warn(sessVars.SlowLogFormat(slowItems))

[youjiali1995]

We can use the default value of level to init the slow query logger here:

tidb/util/logutil/slow_query_logger.go

Line 34 in dfd7157

sqConfig := cfg.Config

Slow query logger can always use Warn() to log slow query because it determines whether to log by execution duration, not by log level:

tidb/executor/adapter.go

Lines 1028 to 1031 in dfd7157

	if costTime < threshold {
	logutil.SlowQueryLogger.Debug(sessVars.SlowLogFormat(slowItems))
	} else {
	logutil.SlowQueryLogger.Warn(sessVars.SlowLogFormat(slowItems))

If so, we can add a test case here to check the level of slow query logger is always less than warn level:

tidb/util/logutil/log_test.go

Line 117 in dfd7157

func TestSlowQueryLoggerCreation(t *testing.T) {

@TonsnakeLin

[github-actions]

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