docs: add heap profiling tutorial

documentation/memory/step1/using_heap_profiler.md

@@ -1,24 +1,88 @@
 # Using Heap Profiler
 
-## Heap Profiler
+To debug a memory issue we need to be able to see how much space our specific type of objects take, and what variables retain them to get garbage collected. For the effective debugging we also need to know the allocation pattern of our variables over time.
+
+The heap profiler acts on top of V8 towards to bring snapshots of memory over time. In this document, we will cover the memory profiling using:
+
+1. Allocation Timeline
+2. Sampling Heap Profiler
+
+Unlike heap dump that was cover in the [step 2](../step2/using_heap_snapshot.md), the idea of using real-time profiling is to understand allocations in a given time frame.
+
+## Heap Profiler - Allocation Timeline
 
 Heap Profiler is similar to the Sampling Heap Profiler, except it will track every allocation. It has
 higher overhead than the Sampling Heap Profiler so it’s not recommended to use in production.
 
+> You can use [@mmarchini/observe](https://www.npmjs.com/package/@mmarchini/observe) to do it programmatically.
+
 ### How To
 
-// TODO
+Start the application:
+
+```console
+node --inspect index.js
+```
+
+> `--inspect-brk` is an better choice for scripts.
+
+Connect to the dev-tools instance and then:
+
+- Select `memory` tab
+- Select `Allocation instrumentation timeline`
+- Start profiling
+
+![image](https://user-images.githubusercontent.com/26234614/136712329-ac9fc581-af2b-4a94-8849-b959ebea0a59.png)
+
+After it, the heap profiling is running, it is strongly recommended to run samples in order to identify memory issues, for this example, we will use `Apache Benchmark` to produce load in the application.
+
+> In this example, we are assuming the heap profiling under web application.
+
+```console
+ab -n 1000 -c 5 http://localhost:3000
+```
+
+Hence, press stop button when the load expected is complete
+
+![image](https://user-images.githubusercontent.com/26234614/136714198-867632e0-2417-4336-9e6c-828fcf5be6b7.png)
+
+Then look at the snapshot data towards to memory allocation.
+
+![image](https://user-images.githubusercontent.com/26234614/136846720-65bf7073-eddc-4afd-9753-e21ef75e0243.png)
+
+Check the [usefull links](#usefull-links) section for futher information about memory terminology.
 
 ## Sampling Heap Profiler
 
 Sampling Heap Profiler tracks memory allocation pattern and reserved space over time. As it’s
 sampling based it has a low enough overhead to use it in production systems.
 
+> You can use the module [`heap-profiler`](https://www.npmjs.com/package/heap-profile) to do it programmatically.
+
 ### How To
 
-// TODO
+Start the application:
+
+```console
+node --inspect index.js
+```
+
+> `--inspect-brk` is an better choice for scripts.
+
+Connect to the dev-tools instance and then:
+
+- Select `memory` tab
+- Select `Allocation sampling`
+- Start profiling
+
+![image](https://user-images.githubusercontent.com/26234614/136847038-1cb6dfd4-26d4-4e2a-8dd1-8d74c2151360.png)
+
+Produce some load and stop the profiler. It will generate a summary with allocation based in the stacktrace, you can lookup to the functions with more heap allocations in a timespan, see the example below:
+
+![image](https://user-images.githubusercontent.com/26234614/136849337-1dd4c46e-b479-48a8-a995-422bb3f17f56.png)
 
 ## Useful Links
 
-- https://developers.google.com/web/tools/chrome-devtools/memory-problems/allocation-profiler
-_ https://github.com/v8/sampling-heap-profiler
+- https://developer.chrome.com/docs/devtools/memory-problems/memory-101/
+- https://github.com/v8/sampling-heap-profiler
+- https://developer.chrome.com/docs/devtools/memory-problems/allocation-profiler/