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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

  How to find which process a file is being written by in Linux?

Some people ask a file is being written by one process and they want to check this process, but they cannot find the process even with sof. This question is very common and there are many solutions, here we introduce a straightforward method. In Linux, each file will be stored on one device and of course there will be a relative inode, then we can use vfs.write to know who is writing the inode on one specified device continuously. Luckily there is inodewatch.stp in the installation package of s...

   Linux,process,file write     2013-03-16 21:44:35

  Some tricks on PHP session

1. Session timeout problem There is a nuance we found with session timing out although the user is still active in the session.  The problem has to do with never modifying the session variable. The GC will clear the session data files based on their last modification time.  Thus if you never modify the session, you simply read from it, then the GC will eventually clean up. To prevent this you need to ensure that your session is modified within the GC delete time.  You can accomp...

   PHP,Session,Timeout,Solution,Various domain     2015-03-13 07:05:37

  How to choose a jQuery plug-in?

jQuery plug-in provides a good way to save time and simplify the development, programmers don't need to write each component from scratch. However, the plug-in will also be a destabilizing factor in your code library. A plug-in saves countless development time, but a poor quality plug-in will cost more than the actual time to write your own component from scratch. Luckily, usually you have many pls to choose from, but even if you have only one plug-in, you also need to know whether it's worth us...

   jQuery, plug-in     2012-10-27 03:51:40

  Some famous article aggregators

Blogs are still very important places for people sharing their thoughts about something although some social media platforms have replaced some of these capabilities. As a blog writer, how can you let others know what you are thinking about? Besides your friends and social media platforms, there are some article aggregators around us which can help us promote our articles. Other than some aggregators like Google News, readers can submit articles to these sites themselves What are some famous art...

   News aggregator,Reddit,Digg,Hacker News     2013-08-12 03:34:37

  Be careful about nil check on interface in GoLang

nil check is frequently seen in GoLang code especially for error check since GoLang's special error handling convention. In most cases, nil check is straight forward, but in interface case, it's a bit different and special care needs to be taken. Take a look at below code snippet and guess what the output will be. package main import ( "bytes" "fmt" "io" ) func check(w io.Writer) { if w != nil { fmt.Println("w is not nil") } fmt.Printf("w is %+v\n", w) } func main() { var b *bytes.B...

   INTERFACE,GOLANG,NIL CHECK,NIL TYPE,NIL VALUE     2019-04-06 07:47:07

  Signature sign/verification demo in Java

Digital signature is commonly used in areas where data authentication and integrity are required. It is extremely important to have signature while transferring sensitive data from one peer to other peers through network since there might be malicious applications or man-in-the-middle attacks which may alter the data along the way. Java provides some APIs to generate and verify digital signature. One important class is Signature.  When generating the signature, a private key needs to be pa...

   SECURITY,JAVA,SIGNATURE     2015-11-21 09:48:12

  Recover deleted file in Linux EXT3 file system

Environment : CentOS 5.3 x86_64, /dev/sdb1 is the data segment /data0. EXT3 file system. Problem : /data0/tcsql/cankao/phpcws-1.5.0/httpcws.cpp is deleted mistakenly and httpcws.cpp is not backed up. It will take much time to rewrite this program again. So we must recover it back. debugfs is feasible in EXT2 file system, but in EXT3 file system, it's not very useful. There is one open source software called ext3grep which can help us recover deleted file in EXT3 file system. The recovery steps a...

   Linux,EXT3,File recovery     2013-08-16 07:06:45

  New Features to Look Out for in Xcode 9

When we say Xcode, we mean a designing toolset which is completely packed with features. Using this Xcode, developers can create applications for platforms such as the Apple TV, the iPad, Apple Watch, and the iPhones and even for the Macintosh. The development system for Xcode has a mixture of features. These are called the instrument analysis tool, simulators, and the ever important OS frameworks which are present in the package in a variety of form of tvOS SDKs, iOS SDKs, watchOS SDKs, and the...

   XCODE,IPHONE,XCODE9     2017-09-26 06:31:30

  Remote form submission

Remote form submission is way of submitting HTML forms from local to a particular remote server. This is used by many advertisers, spammers or even hackers to submit bad data to other websites in order to get what they want. They can write some automation scripts to help them do spamming. How can people do remote form submission and how to prevent this kind of attacks? Since a website can be accessed by almost every one, so one can save a local copy of a HTML form of a website through File->S...

   PHP,Security,Remote form submission     2013-07-14 01:04:49

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