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  What is cache penetration, cache breakdown and cache avalanche?

When designing and developing highly available system, cache is an very important consideration. It is useful to cache some frequently accessed data so that they can be accessed quickly and also cache can protect the downstream system like DB from being hit too often.  To provide better cache design in large systems, some problems may need to be considered first. In this post, we will talk about some frequently discussed cache problems and mitigation plans. Cache penetration Cache penetrati...

   SYSTEM DESIGN,CACHE PENETRATION,CACHE BREAKDOWN,CACHE AVALANCHE     2020-04-10 08:43:00

  Resolve git issue git@github.com: Permission denied (publickey)

Sometimes when clone a remote repository from github.com, you may see below error. D:\Project\Playground\GitBisect>git clone git@github.com:bradleyboy/bisectercise.git Cloning into 'bisectercise'... git@github.com: Permission denied (publickey). fatal: Could not read from remote repository. Please make sure you have the correct access rights and the repository exists. The issue occurs when there is no key on your machine which is associated with your github account. To fix the issue, please ...

   GIT,GITHUB,PERMISSION DENIED,PUBLIC KEY     2019-07-12 10:10:49

  Generate first N prime numbers

Recently I am taking an online course named "Startup Engineering" on coursera. There is one assignment which is to use NodeJS to write a program to generate the first 100 prime numbers. This may be very easy for many people. Here I just want to share with you the code to generate not only the first 100 prime numbers. but also any number of prime numbers. Below is the code snippet: //Helper class to generate prime numbers var PrimeProcessor=(function(){ var primeArray=[]; functio...

   Algorithm,Prime number,NodeJS,coursera,JavaScript     2013-06-29 22:08:22

  Where Have You Installed Your Python Packages?

Preface I am writing this article because I recently noticed in the Python community that there are several frequently asked questions: Why does running the command after installing pip result in a "executable not found" error? Why does importing a module result in a "ModuleNotFound" error? Why can I run my code in PyCharm, but it doesn't work in the command prompt? Rather than just providing solutions, it is better to teach people how to fish. To address these types of issues, you need to und...

   PYTHON,PATH,PATH_PREFIX,PACKAGE LOCATION     2023-12-17 01:03:45

  ConcurrentHashMap vs Collections.synchronizedMap()

ConcurrentHashMap and Collections.synchronizedMap() both provide thread-safe operations of collections of data. They are used in multithreaded programs to provide both thread safety and performance improvements. In many cases, we can use either of them. But the realization of thread safety is different for these two implementations. ConcurrentHashMap will create an HashEntry[] array internally to store the elements passed in from a Map, while Collections.synchronizedMap() will return a Synchroni...

   ConcurrentHashMap,Collections.synchronizedMap     2014-09-18 05:04:59

  FTP active mode and passive mode

1. What's active mode and passive mode a. FTP has two ports to control: Port 20 is for data transfer Port 21 is for control or establish TCP connection b. The process of active connection Note: C represents Client and S represents Server S opens port 20 and 21 C connects to port 21 of S with a random port, this port can be between 1024 and 65536, it sends port+x to server at the same time to specify C(X)->S(21) When S receives the command, it will sends back ACK, S(21)->C(X) S will set ...

   FTP,Active mode,Passive mode     2013-04-01 07:01:25

  A trick of building multithreaded application on Solaris

Firstly, Let’s see a simple multithreaded application: #include <stdio.h> #include <pthread.h> #include <errno.h> void *thread1_func(void *p_arg) { errno = 0; sleep(3); errno = 1; printf("%s exit, errno is %d\n", (char*)p_arg, errno); } void *thread2_func(void *p_arg) { errno = 0; sleep(5); printf("%s exit, errno is %d\n", (char*)p_arg, errno); } int main(void) { pthread_t t1, t2; ...

   C, Solaris     2014-10-14 02:59:40

  File upload in PHP

File is a special kind of form data, when being uploaded to the server through HTTP POST request, PHP will create a $_FILES global array, the relevant file information will be stored in this global array. We will illustrate file upload with some code snippets using PHP and look into the internal work mechanism. Lastly will talk about file upload security. File upload In order for users to upload files in client side, we have to provide a form on the user interface. Since the uploaded file is a s...

   File upload,PHP     2012-11-30 22:01:28

  Why cannot compare double values directly for equality?

A question in PHP: Get some value from the database and use floatval() to convert it to floatint point value, then compare it with another value which is also converted to floating point value with floatval(). These two values are the same when using var_dump() to output, the two outputs are float(8.87), they are the same. But when comparing them for equality, the result is weird., they are not equal. Why?To analyze this question, we need to start with PHP data types. PHP uses weak types. In PHP...

   PHP,floating, precision,compare,equality     2012-06-27 09:01:36

  What and what not to log while debugging

Log is a critical part of an application. It serves as an eye to the programmer on how the application is working while debugging. Especially for applications running on production environment, if the application encounters problem and the problem cannot be reproduced on other environments, log will be extremely useful. While log is essential, but developers have to log smartly. Because if don't put log smartly, you may not get what you want while debugging or you may get too many...

   PROGRAMMING,DEBUG,LOG,SUPPORT     2016-03-14 08:09:03

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