1) List the key components in a Hadoop version2 worker node that may be seen if you type “jps” command while a MapReduce job is being processed?

Data Node Without HA

Data Node With HA

  • Zookeeper
  • Journal Node
  • Data node
  • MRAppMaster

2) List the KEY processes you would see if type “jps” on a Hadoop v2 Master node?

In NameNode Without HA

  •      Namenode

IN Namenode with HA
  • Zookeeper
  • Zookeeper Fail Over controller
  • Journal Node
  • NameNode

3) What are some of the “generations” that a JVM (Java Virtual Machine) heap memory is broken in to?

JVM Generations:

In Java, we don't explicitly allocate and deallocate memory in the code. The GC finds those unreferenced objects and removes them. According to an article by Sangmin Lee[1], the GC was designed by following the two hypotheses below.
  • Most objects soon become unreachable.
  • References from old objects to young objects only exist in small numbers.
Therefore, the memory heap is broken into different segments, Java calls them as generations.

Young Generation: All new objects are allocated in Young Generation. When this area is full, GC removes unreachable objects from it. This is called "minor garbage collection" or "minor GC".

Old Generation: When objects survived from Young Generation, they are moved to Old Generation or Tenured Generation. Old Generation has bigger size and GC removes objects less frequently from it. When GC removes objects from Old Generation, it is called "major garbage collection" or "major GC".

Permanent Generation: Permanent Generation contains metadata of classes and methods, so it is also known as "method area". It does not store objects survived from Old Generation. The GC occurs in this area is also considered as "major GC". Some places call a GC as "full GC" if it performs on Permanent Generation.

You may notice the Young Generation is divided into a Eden space and two Survivor Spaces. They are used to determine the age of objects and whether to move them to Old Generation.

4) What is a "stop the world" event in Java Garbage collection process?

It means the JVM stops running the application for a GC execution.  During the stop-the-world time, every thread will stop their tasks until the GC thread complete its task.

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5) What packets are exchanged during TCP 3-way handshake?

The Three-Way Handshake:

TCP utilizes a number of flags, or 1-bit boolean fields, in its header to control the state of a connection. The three we're most interested in here are:
  • SYN - (Synchronize) Initiates a connection
  • FIN - (Final) Cleanly terminates a connection
  • ACK - Acknowledges received data
As we'll see, a packet can have multiple flags set.

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