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  How Query Optimizer Works in RDBMS

In a previous post, we discussed how the various relational operators are implemented in relational database systems. If you have read that post, you probably still remember that there are a few alternative implementations for every operator. Thus, how should RDBMS determine which algorithm (or implementation) to use? Obviously, to optimize the performance for any query, RDBMS has to select the correct the algorithm based on the query. It would not be desirable to always use the same algori...

   DATABASE,DATABASE DESIGN,DATABASE OPTIMIZATION     2019-04-20 07:26:32

  Check whether a remote server port is open on Linux

As a system administrator or network engineer or application developer, there is a need to check whether a port on remote server is open so that you can tell whether the service under check is running or not. In this post, we would cover a few methods to check whether a remote server port is open or not on Linux. telnet telnet is the most frequently used command on both Windows and Linux to check port. The simple usage for this command is  telnet [host] [port] When the port is open, the o...

   LINUX,TELNET,PORT,NC,NMAP     2017-12-23 11:45:20

  HeartBleed: Inside the heart, what causes the bleeding?

Just after a few weeks since Apple's famous goto fail bug, there is one bug in OpenSSL which catches the attention from the world again. The bug is named HeartBleed, found in OpenSSL library, a famous open source library supporting lots of  SSL/TLS communication among server/client applications. The reason why this bug catches the attentions from the world is it affects almost all sites which are using the affected OpenSSL library, these includes many applications like Nginx server, some v...

   OpenSSL,HeartBleed     2014-04-09 05:47:30

  Go channel explained

In Go, a channel is a type of concurrent data structure that allows two or more goroutines (Go's term for lightweight threads) to communicate with each other. Channels provide a way for goroutines to send and receive values, and they are an essential part of Go's concurrency model. Here's a simple example that demonstrates how to use channels in Go: package main import ( "fmt" ) func main() { // Create a new channel with the `make` function ch := make(chan int) // Start a new ...

   GOLANG,CHANNEL     2022-12-10 22:24:26

  jsonSerialize() in extended class

Since PHP 5.4.0, there is a convenient interface JsonSerializable which can be used to indicate that a PHP object can be serialized to JSON object. It has only one method which should be implemented by any class which implements this interface. The method is named jsonSerialize(). It's really easy to serialize an object to JSON object. Here is one example: <?php class ArrayValue implements JsonSerializable { public function __construct(array $array) { $this->array = $array; ...

   JSON,jsonSerialize,Inheritance,extends     2014-07-26 05:54:00

  Read white space with scanf()

Usually, when we want to enter string with white spaces in C, we need to call gets() or fgets(0 method. We usually will not use scanf(0 or fscanf() because they cannot accept white spaces when scan user inputs.   But when we specify the format in scanf() function, we may read strings with white space. the code section below illustrate this: #include <stdio.h>   int main(int argc,char **argv){        char name[30];      fprintf(stdout,"Please en...

   C,scanf,white space, string format     2011-09-26 11:45:43

  Understanding an interesting JavaScript map function question

With the evolvement of JavaScript, lots of new features have been added this old but robust language.  Among them are lots of functional programming language related functions like map, filter, each etc. In this post, we will cover one function map and its interesting behavior. Before dive into the details, let first take an example, do you know the output of below function call? ['1', '7', '11'].map(parseInt) You may think that it's easy and the output would be [1, 7, 11] Can you try to ru...

   JAVASCRIPT,MAP,FUNCTIONAL PROGRAMMING     2019-06-14 08:34:46

  Understand this in JavaScript

In JavaScript, this is always pointing to the owner of a function or a method. Function Let's check out function first. function introduce() {      alert("Hello, I am Laruence\r\n"); } For this function, what does this point to? In JavaScript, a global function's owner is the current page, i.e, the window object. Because its a method of the window object if we define a global function. Now you should know the this will point to the window object in the above function. ...

   JavaScript,this,event,call     2013-04-03 04:10:03

  A strange behavior of printing struct with nested struct in GoLang

Normally when trying to print a struct , we would use %v to show all data of the struct. It will print the default format for each field in the struct. %v the value in a default format when printing structs, the plus flag (%+v) adds field names But recently we observed a strange behavior when printing a struct with nested struct which has a String() string implemented, the %v format prints an 'unexpected' output per our understanding.   Let's see the example snippet first. pa...

   PROGRAMMING,GOLANG     2018-10-29 09:59:49

  Different types of keystore in Java -- JCEKS

JCEKS stands for Java Cryptography Extension KeyStore and it is an alternative keystore format for the Java platform. Storing keys in a KeyStore can be a measure to prevent your encryption keys from being exposed. Java KeyStores securely contain individual certificates and keys that can be referenced by an alias for use in a Java program. The process of storing and loading different entries in JCEKS is similar to what JKS does. So please refer to the article Different types of keystore in Java -...

   Java,KeyStore,JCEKS,Tutorial     2015-01-05 00:30:56

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