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  File System vs Core Data: the image cache test

Code for this project is on GitHub While doing a full re-write of Droplr's iOS app for the 2.0 launch, I couldn't find any good file/image caches out there had a particular feature I really wanted: extending item expiration whenever it's touched. I set out to write my own — which wasn't that much of a challenge — but somewhere along the process I had this crazy idea that perhaps (SQLite-backed) Core Data would be a much better tool for the job: No mismatch between cache index ...

   File system.Image cache,Multimedia     2012-02-01 08:52:02

  A turing machine in 133 bytes of javascript

Multiply turing machine The fact it took me 20 lines of javascript to implement a nondeterministic turing machine simulatorlast week kept me up at night. All weekend. Too much code for something so simple and I kept having this gut feeling implementing a basic version shouldn’t take more than 140 bytes. Sunday afternoon I sat down for about an ...

   Turing machine,JavaScript,Simple code     2011-11-28 09:27:28

  Java Cipher encryption/decryption example

In Java, Cipher is the API for doing data encryption/decryption. Many cryptographic algorithms such as AES, DES, RC4 etc can be specified when creating Cipher instance. The Cipher instance calls the underlying algorithm specific implementation to do the actual encryption/decryption.  Before doing the encryption/decryption, a key needs to be created and it will be used to do the encryption/decryption. A sample program for performing all these is : import java.security.Key; import javax.cryp...

   Java, Java Security, Cipher, Example, Sample     2015-08-14 07:07:10

  About short URL and its implementation

IntroductionURL shortening is a kind of technique to convert a long URL to a short URL. There are many companies now providing this kind of service, we now take Google's URL shortener service http://goo.gl/ as an example.First we navigate to http://goo.gl/, then we enter a random URL into the text field, here we use http://www.url-to-be-shortened.com as the input, it will return us an shortened URL : http://goo.gl/ZSVMM. URL ParsingWhen we type http://goo.gl/ZSVMM in browser address bar, the DNS...

       2012-07-02 07:15:09

  Redis Cluster and Common Partition Techniques in Distributed Cache

In this post, I will discuss a few common partition techniques in distributed cache. Especially, I will elaborate on my understanding on the use of Redis Cluster. Please understand that at the time of writing, the latest version of Redis is 4.0.10. Many articles on the same topic have a different idea from this post. This is mainly because, those articles are probably outdated. In particular, they may refer to the Redis Cluster implementation in Redis 3. Redis Cluster has been improved...

   REDIS,DISTRIBUTED CACHE,CLOUD COMPUTING     2019-01-17 08:10:37

  The Book That Every Programmer Should Read

No, it’s not Knuth’s “The Art of Programming”. I’m talking about quite an easy-to-read (compared to TAoP) book, which, in fact, does not require any engineering or mathematical background from the reader.I am talking about C. Petzold’s “CODE”. It is a truly remarkable book about how computers work. Let me explain why I think this book is so awesome.The book starts from the very beginning, from explaining what code is, bringi...

   Programmer,Book,Must read,CODE,C. Petzold     2011-10-31 10:43:58

  The biggest iOS 5 bug you've never heard of

There is a huge bug when Group Messaging is disabled in iOS 5. I'm shocked Apple hasn't fixed this yet. Today a friend sent out a text message blast, announcing they got a new phone number. Shortly after, I got text messages from three random people I don't know. I was confused how these people got my number, but then I realized they were replies intended for my friend who sent out the text blast. If you've ever used the Group Messaging feature,...

   iOS5,Bug,Group Messaging     2011-12-10 06:04:39

  FTP Must Die

The File Transfer Protocol (FTP) is specified in RFC 959, published in October 1985. The attempt in this specification is to satisfy the diverse needs of users of maxi-hosts, mini-hosts, personal workstations, and TACs, with a simple, and easily implemented protocol design.That's from the introduction. Does anyone here know what a TAC is? I don't. I had to look it up, since the acronym wasn't even expanded in the RFC. It took three tries in Google, and I finally found it in some obscur...

   FTP,Future,Death,Trend,Protocol     2012-02-06 08:13:36

  Understanding How is Data Stored in RDBMS

We all know that DBMS (database management system) is used to store (a massive amount of) data. However, have you ever wondered how is data stored in DBMS? In this post, we will focus on data storage in RDBMS, the most traditional relational database systems. Physical Storage Data can be stored in many different kinds of medium or devices, from the fastest but costy registers to the slow but cheap hard drives, or even magnetic tapes. Nowadays, IaaS providers such as AWS...

   RDBMS,DATABASE     2019-02-04 09:25:36

  The Cognitive Benefits Of Chewing Gum

Why do people chew gum? If an anthropologist from Mars ever visited a typical supermarket, they’d be confounded by those shelves near the checkout aisle that display dozens of flavored gum options. Chewing without eating seems like such a ridiculous habit, the oral equivalent of running on a treadmill. And yet, people have been chewing gum for thousands of years, ever since the ancient Greeks began popping wads of mastic tree resin in their mouth to sweeten the breath. Socrates pr...

   Pressure,Gum,Release,Benefits     2011-11-30 11:37:26

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