Merging changes synced from https://github.com/MicrosoftDocs/visualstudio-docs-pr (branch live)

Author: ghogen

docs/profiling/perf-insights-string-concatenation.md

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+---
+title: Performance insights for string concatenations
+description: Learn how to improve performance for string concatenations.
+ms.date: 7/20/2022
+ms.topic: reference
+author: mikejo5000
+ms.author: mikejo
+manager: jmartens
+ms.technology: vs-ide-debug
+ms.workload: 
+  - multiple
+---
+
+# Use StringBuilder for concatenations
+
+This article describes performance insights for string concatenations.
+
+## Cause
+
+Calls to System.String.Concat are a significant proportion of the profiling data. Consider using the <xref:System.Text.StringBuilder> class to construct strings from multiple segments.
+
+## Performance insight description
+
+A <xref:System.String> object is immutable. Therefore, any modification to the string creates a new string object and the garbage collection of the original. This behavior is the same whether you call String.Concat explicitly or use the string concatenation operators such as + or +=. Program performance can decrease if these methods are frequently called, such as when characters are added to a string in a tight loop.
+
+The StringBuilder class is a mutable object, and, unlike System.String, most of the methods on StringBuilder that modify an instance of this class return a reference to that same instance. You can insert characters or append text to a StringBuilder instance, and remove or replace characters in the instance without the need for allocating a new instance and deleting the original instance.
+
+## How to investigate a warning
+
+In the CPU Usage tool, click **View source code** to go to the [call tree](../profiling/cpu-usage.md#BKMK_Call_tree_structure) and source line highlighting view showing where the most amount of time is spent in string concatenations. If the problem is occurring in multiple locations within the application, navigate to the caller/callee view to see each call location.

docs/profiling/toc.yml

@@ -32,8 +32,14 @@
     href: analyze-database.md
   - name: Events Viewer
     href: events-viewer.md
-  - name: CPU usage
-    href: cpu-usage.md
+  - name: CPU Usage
+    items:
+    - name: CPU usage
+      href: cpu-usage.md
+    - name: Performance insights
+      items:
+      - name: String concatenation
+        href: perf-insights-string-concatenation.md
   - name: File IO
     href: use-file-io.md    
   - name: Memory usage