index.xml

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    <title>A Blog on VR</title>
    <link>/</link>
    <description>Recent content in A Blog on VR</description>
    <generator>Hugo -- gohugo.io</generator>
    <language>en-US</language>
    <lastBuildDate>Mon, 16 May 2022 23:02:15 -0400</lastBuildDate><atom:link href="/index.xml" rel="self" type="application/rss+xml" />
    <item>
      <title>AWS Basics</title>
      <link>/cloud-native/aws/aws-basics/</link>
      <pubDate>Mon, 16 May 2022 23:02:15 -0400</pubDate>
      
      <guid>/cloud-native/aws/aws-basics/</guid>
      <description>AWS IAM  An AWS account is created with a root account which has admin privileges. IAM Group : is a collection of users who perform similar jobs on aws . IAM Policies can be attached to group IAM Policy: Provides permission to user to carry out allowed actions  can be Job Function or Aws Managed or Customer Managed   IAM Role : Allows aws services to securely access different services.</description>
    </item>
    
    <item>
      <title>Spring Framework</title>
      <link>/spring/spring-framework/</link>
      <pubDate>Sun, 14 Mar 2021 17:04:41 -0400</pubDate>
      
      <guid>/spring/spring-framework/</guid>
      <description>IOC Container IOC container find the beans, wire the bean and maintains the lifecycle of a bean. There are two types
 Beanfactory  Most basic container provided by spring    ApplicationContext  advanced version of IOC container I8n capabilities Provided webapplication context support support for AOP    </description>
    </item>
    
    <item>
      <title>Basics</title>
      <link>/things-i-learnt/scala/basics/</link>
      <pubDate>Sun, 27 Dec 2020 23:25:29 -0500</pubDate>
      
      <guid>/things-i-learnt/scala/basics/</guid>
      <description>Introduction An excerpt from wiki
 Scala is a general-purpose programming language providing support for both object-oriented programming and functional programming. The language has a strong static type system. Designed to be concise, many of Scala&amp;rsquo;s design decisions are aimed to address criticisms of Java.
  It is executed in a JVM. .scala file compiles to executable byte code by scala compiler. Byte Code is executed in JVM on different Operating systems</description>
    </item>
    
    <item>
      <title>AI/ML Services</title>
      <link>/cloud-native/gcp/gcp-aiml/</link>
      <pubDate>Mon, 20 Jul 2020 00:02:15 -0400</pubDate>
      
      <guid>/cloud-native/gcp/gcp-aiml/</guid>
      <description>GCP AI/ML Services AI Building Blocks  AI through simple REST calls    Sight
 Vision API : Derive insights from images Video API : content discovery and engaging video experiences    Conversation
 Dialogflow : to build virtual chat agents and conversational experiences Cloud Text-to-Speech API : to convert text to human like speech using Wavenet voices Cloud Speech-to-Text API : to convert speech to text    Language</description>
    </item>
    
    <item>
      <title>Mongo</title>
      <link>/things-i-learnt/mongo/</link>
      <pubDate>Sun, 28 Jun 2020 20:31:41 -0400</pubDate>
      
      <guid>/things-i-learnt/mongo/</guid>
      <description>Collection Name with “-” While getting started with MongoDB, I created my first collection with name “june-collection”. I did this directly using spring-data-mongodb library.
Mongo doesn’t restrict collection name with -, but while using mongo shell in windows, e.g. db.june-collection.deleteMany , the shell gives error saying “collection” is not recognized (the string after - in the collection name)
After some googling, found that collection name with “-” is not one of the best approaches.</description>
    </item>
    
    <item>
      <title>Basics</title>
      <link>/java-related/basics/</link>
      <pubDate>Sun, 28 Jun 2020 20:19:10 -0400</pubDate>
      
      <guid>/java-related/basics/</guid>
      <description>Java Java is a high level programming language. Main characteristics include
 robust secure platform/os independent object-oriented multi-threaded portable etc.  Java requires both compiler and interpretor to run.
The compiler converts the source code into byte code. The interpretor interprets this bytecode and excutes the application/logic. Since java is interpreted language, it is platform independent
Java Editions  Java Card : Smart card Edition, for chip cards Java ME : Micro Edition, for IOT devices, smart devices Java SE : Standard Edition Java MP : Micro Profile, a subset of Java EE with enough features to run microservices Java EE : Enterprise Edition  JVM Architecture Java Virtual Machine or JVM provides an environment to support execution of java bytecode.</description>
    </item>
    
    <item>
      <title>Internet</title>
      <link>/be-developer-roadmap/internet-basics/internet/</link>
      <pubDate>Sun, 07 Jun 2020 12:47:16 -0400</pubDate>
      
      <guid>/be-developer-roadmap/internet-basics/internet/</guid>
      <description>What is Internet? Internet is global network of billions of electronic devices and computer. It is possible to access almost any information, communicate wit anyone in world using internet.
How does Internet work? Internet is global network of physical cables/optical fibres which directly/indirectly connect all the electronice devices.</description>
    </item>
    
    <item>
      <title>Cloud Foundry</title>
      <link>/cloud-native/cf-cli/</link>
      <pubDate>Mon, 01 Jan 0001 00:00:00 +0000</pubDate>
      
      <guid>/cloud-native/cf-cli/</guid>
      <description>How to login to CF using cli : cf login -a &amp;lt;https://api.address&amp;gt; -u &amp;lt;username&amp;gt; -p &amp;lt;password&amp;gt;
 To bypass ssl validation during login : cf login -a &amp;lt;https://api.address&amp;gt; -u &amp;lt;username&amp;gt; -p &amp;lt;password&amp;gt; --skip-ssl-validation    For switching between space and organization :
cf target -s &amp;lt;space-name&amp;gt; cf target -o &amp;lt;organization-name&amp;gt;   To review current target configuration : cf target
  How to push an application to cf</description>
    </item>
    
    <item>
      <title>Kubernetes</title>
      <link>/cloud-native/k8s/basics/</link>
      <pubDate>Mon, 01 Jan 0001 00:00:00 +0000</pubDate>
      
      <guid>/cloud-native/k8s/basics/</guid>
      <description>What? Kubernetes is a container orchestration or container management tool. From K8s.io,
 Kubernetes is a portable, extensible, open-source platform for managing containerized workloads and services, that facilitates both declarative configuration and automation. It has a large, rapidly growing ecosystem. Kubernetes services, support, and tools are widely available.
 Why? Kubernetes helps in container management and provides with a framework to support multiple features of distributed, resilient and scalable system.</description>
    </item>
    
    <item>
      <title>PostgreSQL</title>
      <link>/things-i-learnt/postgresql/</link>
      <pubDate>Mon, 03 Aug 2020 00:16:39 -0400</pubDate>
      
      <guid>/things-i-learnt/postgresql/</guid>
      <description>Installation Steps to install postgreSql in Ubuntu 20.04
 sudo apt update - to refresh package index sudo apt install postgresql-contrib - to install postgresql alongwith additional tools and packages By default, a postgres user is created which can be used to manage postgres. sudo -i -u postgres psql to interact with postgres and \q to exit postgresql prompt createuser --interactive --password postgres-user to create new user createdb demo-db -O postgres-user to create a new db update the pg_hba.</description>
    </item>
    
    <item>
      <title>Java Memory Management</title>
      <link>/java-related/java-memory-management/</link>
      <pubDate>Sat, 04 Jul 2020 21:21:58 -0400</pubDate>
      
      <guid>/java-related/java-memory-management/</guid>
      <description>The Stack Memory  There can be multiple stacks In general in a stack data structure, as new elements are added the elements are pushed down in stack, while popping the first element is pushed out first. First in Last Out datastructure. Java store local variables of a class or method in stack, and are popped off the stack when it encounters end of function block or class block In general the variables stored in stack have very short lifetime.</description>
    </item>
    
    <item>
      <title>DNS</title>
      <link>/be-developer-roadmap/internet-basics/dns/</link>
      <pubDate>Sun, 07 Jun 2020 12:47:16 -0400</pubDate>
      
      <guid>/be-developer-roadmap/internet-basics/dns/</guid>
      <description>What is DNS and how it works? DNS : Domain Naming System All the electonice devices connected to internet communicate to each other via a sequence of numbers called ipaddresses. Since it&amp;rsquo;s difficult for humans to remember these IPAddresses, there is a central server which translates the requested resource name to an ip address. It&amp;rsquo;s like a phonebook with domain name and ipaddresses.
Types of DNS Servers  DNS Recursive servers  These are provided by ISP provider (internet providers), which assign an ipaddress to one&amp;rsquo;s machine.</description>
    </item>
    
    <item>
      <title>Java Garbage Collection</title>
      <link>/java-related/java-garbage-collection/</link>
      <pubDate>Sat, 04 Jul 2020 21:23:27 -0400</pubDate>
      
      <guid>/java-related/java-garbage-collection/</guid>
      <description>Java avoids memory leakage by
 running on a java virtual machine it adopts a garbage collection strategy: Any object which is not reachable from stack memory are eligible for garbage collection -System.gc() is a suggestion to JVM to run garbage collection, and not a gaurantee that all objects will be garbage collected. Usually it is not possible to have memory leaks from jvm to os, but sometimes there can be a soft leak.</description>
    </item>
    
    <item>
      <title>Browsers</title>
      <link>/be-developer-roadmap/internet-basics/browsers/</link>
      <pubDate>Sun, 07 Jun 2020 12:47:16 -0400</pubDate>
      
      <guid>/be-developer-roadmap/internet-basics/browsers/</guid>
      <description>What are browsers and how do they work? A browser is an application which helps user to view a website.
It mainly consists of
 User Interface [the UI of a browser which lets user enter a webaddress, refresh etc] Rendering Engine  The engine where DOM is converted to a webpage as we see it This layer is responsible for making all network requests, parse the html and request for more resources required   Browser Engine [Maintains communication between Browser UI and Rendering Engine] Network [To get data from various sources] Javascript Interpretor  It provides interpretor for javascript which is used to provide various interactive features on the webpage   Data Storage [for storing cache,cookies, history etc]  </description>
    </item>
    
    <item>
      <title>Elasticsearch Install Fest</title>
      <link>/things-i-learnt/elk-installation/</link>
      <pubDate>Mon, 01 Jan 0001 00:00:00 +0000</pubDate>
      
      <guid>/things-i-learnt/elk-installation/</guid>
      <description>How to Install Elasticsearch  install java jdk sudo yum install java-1.8.0-openjdk.x86_64 install elasticsearch 6.x  Download and install the public signing key rpm --import https://artifacts.elastic.co/GPG-KEY-elasticsearch Create a file elasticsearch.repo in /etc/yum.repos.d with content    [elasticsearch-6.x] name=Elasticsearch repository for 6.x packages baseurl=https://artifacts.elastic.co/packages/6.x/yum gpgcheck=1 gpgkey=https://artifacts.elastic.co/GPG-KEY-elasticsearch enabled=1 autorefresh=1 type=rpm-md  install elasticsearch using command sudo yum install elasticsearch  To setup auto start up at system reboot sudo systemctl daemon-reload sudo systemctl enable elasticsearch.</description>
    </item>
    
    <item>
      <title>Jit Compiler</title>
      <link>/java-related/jit-compiler/</link>
      <pubDate>Sun, 19 Jul 2020 23:55:40 -0400</pubDate>
      
      <guid>/java-related/jit-compiler/</guid>
      <description>How to find which methods are being compiled to native byte code by compiler.
 By running the class with flag *PrintCompilation * turned on.-XX:+PrintCompilation    There are two level of compiler in java C1 and C2
 On the basis of number of times a code block is used, it keeps on getting compiled at a more deeper tier. The first three level of compilation are done by C1 Compiler The C2 Compiler, compiles the code to native byte code as well places the code in code cache, hence even faster code execution.</description>
    </item>
    
    <item>
      <title>Http</title>
      <link>/be-developer-roadmap/internet-basics/http/</link>
      <pubDate>Sun, 07 Jun 2020 23:54:22 -0400</pubDate>
      
      <guid>/be-developer-roadmap/internet-basics/http/</guid>
      <description>What is HTTP? HyperText Transfer Protocol
 Client/Server model or request/response model Stateless a lot of application maintain state via session/cookie Application Layer internally uses TCP protocol. TCP defines how the data is read/decoded Client Action (GET, PUT/POST, DELETE, PATCH) Server Status Codes Headers  </description>
    </item>
    
    <item>
      <title>Influx DB</title>
      <link>/things-i-learnt/influx-db/</link>
      <pubDate>Mon, 01 Jan 0001 00:00:00 +0000</pubDate>
      
      <guid>/things-i-learnt/influx-db/</guid>
      <description>InfluxDB is a custom high-performance data store written specifically for time series data. It allows for high throughput ingest, compression and real-time querying of that same data.
Influx SQL    Action CLI Command     Launch Influx CLI influx   Create Database CREATE DATABASE databasename   Create User CREATE USER username WITH PASSWORD &amp;lsquo;userpassword&amp;rsquo; WITH privileges   Drop Series drop series from measurementname    Influx line protocol input : measurement,field name=field value,field name 1=field value 1SPACEtag name=tag value,tag name1 =tag value1SPACEtimestamp</description>
    </item>
    
    <item>
      <title>Java Collections</title>
      <link>/java-related/java-collections/</link>
      <pubDate>Sun, 02 Aug 2020 17:21:11 -0400</pubDate>
      
      <guid>/java-related/java-collections/</guid>
      <description>List Implementations  ArrayList  instantiated as array in memory with size of 10 elements    CopyOnWriteArrayList  Is thread safe version of Arraylist Is very costly in terms of ordinality Can be used when  application is multi-threaded multiple threads need to access the same list no. of iterations or reads are lot more than no. of writes/addition or deletion     AttributeList- Child of Arraylist, specific usage for Mbean LinkedList RoleList -Child of Arraylist RoleUnresolvedList - Child of Arraylist Stack Vector  Main Differences between arraylist and linkedlist  Arraylist holds references of object at each position.</description>
    </item>
    
    <item>
      <title>Windows Git Util</title>
      <link>/things-i-learnt/window-git-util/</link>
      <pubDate>Mon, 01 Jan 0001 00:00:00 +0000</pubDate>
      
      <guid>/things-i-learnt/window-git-util/</guid>
      <description>To run a git command on all folders in a directory in windows
@echo off set /p git_command=&amp;#34;Enter git command: &amp;#34; for /d %%i in (.\*) do (	echo +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ echo &amp;#34;%%i&amp;#34; cd &amp;#34;%%i&amp;#34; echo ----------------------------------------------- echo %git_command% %git_command% echo ----------------------------------------------- echo +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ cd.. ) </description>
    </item>
    
    <item>
      <title>Graalvm</title>
      <link>/java-related/graalvm/</link>
      <pubDate>Sun, 02 Aug 2020 17:22:16 -0400</pubDate>
      
      <guid>/java-related/graalvm/</guid>
      <description> An alternate JVM An alternate java compiler Provides a native compiler, hence application can run without JVM  Steps to Install
 wget https://github.com/graalvm/graalvm-ce-builds/releases/download/vm-20.1.0/graalvm-ce-java11-linux-amd64-20.1.0.tar.gz tar -xzvf graalvm-ce-java11-darwin-amd64-20.1.0.tar.gz Set GraalVM to Path sudo apt-get install gcc zlib1g-dev to install native image dependencies gu install native-image to install native image component native-image &amp;lt;class file&amp;gt; creates a native image with JVM packaged  Reference  https://www.graalvm.org/getting-started/  </description>
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    <item>
      <title>Important Links</title>
      <link>/things-i-learnt/exception-troubleshooting/</link>
      <pubDate>Mon, 01 Jan 0001 00:00:00 +0000</pubDate>
      
      <guid>/things-i-learnt/exception-troubleshooting/</guid>
      <description>SSLHandshakeException Exception: javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target Reason : jvm might need required certificates
Possible Solution : SO-Solution
 How to check for open ports in a unix machine  sudo netstat -tunlp  -t - Show TCP ports. -u - Show UDP ports. -n - Show numerical addresses instead of resolving hosts. -l - Show only listening ports. -p - Show the PID and name of the listener’s process.</description>
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