From b2872189409f32b537c58103c295f84d515d8ddb Mon Sep 17 00:00:00 2001
From: Xiaochao Dong <the.xcdong@gmail.com>
Date: Thu, 4 May 2023 15:27:51 +0800
Subject: [PATCH] Avoid expensive log.Valuer evaluation for disallowed levels
 (#6322)

Signed-off-by: Xiaochao Dong (@damnever) <the.xcdong@gmail.com>
---
 CHANGELOG.md               |  1 +
 pkg/logging/logger.go      |  5 ++++-
 pkg/logging/logger_test.go | 19 +++++++++++++++++++
 3 files changed, 24 insertions(+), 1 deletion(-)
 create mode 100644 pkg/logging/logger_test.go

diff --git a/CHANGELOG.md b/CHANGELOG.md
index a08c755f21f..a95be6c8805 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -42,6 +42,7 @@ We use *breaking :warning:* to mark changes that are not backward compatible (re
 - [#6071](https://github.com/thanos-io/thanos/pull/6071) Query Frontend: *breaking :warning:* Add experimental native histogram support for which we updated and aligned with the [Prometheus common](https://github.com/prometheus/common) model, which is used for caching so a cache reset required.
 - [#6163](https://github.com/thanos-io/thanos/pull/6163) Receiver: changed max backoff from 30s to 5s for forwarding requests. Can be configured with `--receive-forward-max-backoff`.
 - [#6327](https://github.com/thanos-io/thanos/pull/6327) *: *breaking :warning:* Use histograms instead of summaries for instrumented handlers.
+- [#6322](https://github.com/thanos-io/thanos/pull/6322) Logging: Avoid expensive log.Valuer evaluation for disallowed levels.
 
 ### Removed
 
diff --git a/pkg/logging/logger.go b/pkg/logging/logger.go
index b711607b479..cca8853da58 100644
--- a/pkg/logging/logger.go
+++ b/pkg/logging/logger.go
@@ -46,11 +46,14 @@ func NewLogger(logLevel, logFormat, debugName string) log.Logger {
 		logger = log.NewJSONLogger(log.NewSyncWriter(os.Stderr))
 	}
 
+	// Sort the logger chain to avoid expensive log.Valuer evaluation for disallowed level.
+	// Ref: https://github.com/go-kit/log/issues/14#issuecomment-945038252
+	logger = log.With(logger, "ts", log.DefaultTimestampUTC, "caller", log.Caller(5))
 	logger = level.NewFilter(logger, lvl)
 
 	if debugName != "" {
 		logger = log.With(logger, "name", debugName)
 	}
 
-	return log.With(logger, "ts", log.DefaultTimestampUTC, "caller", log.DefaultCaller)
+	return logger
 }
diff --git a/pkg/logging/logger_test.go b/pkg/logging/logger_test.go
new file mode 100644
index 00000000000..2e4eb3f73fa
--- /dev/null
+++ b/pkg/logging/logger_test.go
@@ -0,0 +1,19 @@
+// Copyright (c) The Thanos Authors.
+// Licensed under the Apache License 2.0.
+
+package logging
+
+import (
+	"testing"
+
+	"github.com/go-kit/log/level"
+)
+
+func BenchmarkDisallowedLogLevels(b *testing.B) {
+	logger := NewLogger("warn", "logfmt", "benchmark")
+
+	for i := 0; i < b.N; i++ {
+		level.Info(logger).Log("hello", "world", "number", i)
+		level.Debug(logger).Log("hello", "world", "number", i)
+	}
+}