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• Optimizing MySQL -

  - by Josh

  I've been researching how to optimize MySQL a bit, but I still have a few questions. MySQL Primer Results http://pastie.org/private/lzjukl8wacxfjbjhge6vw Based on this, the first problem seems to be that the max_connections limit is too low. I had a similar problem with Apache initially, the max connection limit was set to 100, and the web server would frequently lock up and take an excruciatingly long time to deliver pages. Raising the connection limit to 512 fixed this issue, and I read that raising the connection limit on MySQL to match this was considered good practice. Being that MySQL has actually been "locking up" recently as well (connections have been refused entirely for a few minutes at a time at random intervals) I'm assuming this is the main cause of the issue. However, as far as table cache goes, I'm not sure what I should set this as. I've read that setting this too high can hinder performance further, so should I raise this to right around 551, 560, 600, or do something else? Lastly, as far as raising the join_buffer_size value goes, this doesn't even seem to be included in Debian's my.cnf file by default. Assuming there's not much I can do about adding indexes, should I look into raising this? Any suggested values? Any suggestions in general here would be appreciated as well. Edit: Here's the number of open tables the MySQL server is reporting. I believe this value is related to my question (Opened_tables: 22574)

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• Is there ever a reason to use C++ in a Mac-only application?

  - by Emil Eriksson

  Is there ever a reason to use C++ in a Mac-only application? I not talking about integrating external libraries which are C++, what I mean is using C++ because of any advantages in a particular application. While the UI code must be written in Obj-C, what about logic code? Because of the dynamic nature of Objective-C, C++ method calls tend to be ever so slightly faster but does this have any effect in any imaginable real life scenario? For example, would it make sense to use C++ over Objective-C for simulating large particle systems where some methods would need to be called over and over in short time? I can also see some cases where C++ has a more appropriate "feel". For example when doing graphics, it's nice to have vector and matrix types with appropriate operator overloads and methods. This, to me, seems like it would be a bit clunkier to implement in Objective-C. Also, Objective-C objects can never be treated plain old data structures in the same manner as C++ types since Objective-C objects always have an isa-pointer. Wouldn't it make sense to use C++ instead in something like this? Does anyone have a real life example of a situation where C++ was chosen for some parts of an application? Does Apple use any C++ except for the kernel? (I don't want to start a flame war here, both languages have their merits and I use both equally though in different applications.)

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• What are the consequences of immutable classes with references to mutable classes?

  - by glenviewjeff

  I've recently begun adopting the best practice of designing my classes to be immutable per Effective Java [Bloch2008]. I have a series of interrelated questions about degrees of mutability and their consequences. I have run into situations where a (Java) class I implemented is only "internally immutable" because it uses references to other mutable classes. In this case, the class under development appears from the external environment to have state. Do any of the benefits (see below) of immutable classes hold true even by only "internally immutable" classes? Is there an accepted term for the aforementioned "internal mutability"? Wikipedia's immutable object page uses the unsourced term "deep immutability" to describe an object whose references are also immutable. Is the distinction between mutability and side-effect-ness/state important? Josh Bloch lists the following benefits of immutable classes: are simple to construct, test, and use are automatically thread-safe and have no synchronization issues do not need a copy constructor do not need an implementation of clone allow hashCode to use lazy initialization, and to cache its return value do not need to be copied defensively when used as a field make good Map keys and Set elements (these objects must not change state while in the collection) have their class invariant established once upon construction, and it never needs to be checked again always have "failure atomicity" (a term used by Joshua Bloch) : if an immutable object throws an exception, it's never left in an undesirable or indeterminate state

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• What's a good, quick algorithms refresh?

  - by Casey Patton

  I have programming interviews coming up in a couple weeks. I took an algorithms class a while ago but likely forgot some key concepts. I'm looking for something like a very short book (< 100 pages) on algorithms to get back up to speed. Sorting algorithms, data structures, and any other essentials should be included. It doesn't have to be a book...just looking for a great way to get caught up in about a week. What's the best tool for a quick algorithms intro or refresher?

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• alternative to environment variables

  - by tonyl7126

  The amount of servers and the complexity of our application is growing and we now have servers in different regions (hosted on AWS). Certain database operations require low latency so we have stuck a database in each region (which is basically a user cache) to keep the network latency low. The way the application server currently knows which user cache/database to make its call to depends on an environemnt variable set in it. This has been working fine, but it seems hacky and not optimal. Is there any way for this to be done automatically? I was considering using a package like fping and pinging each database when the app server reloads (or caching it the first time) and using the corresponding latencies to decide which database has the lowest latency for each app server. Not sure if this is the best idea though.

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• How to write a very basic compiler [closed]

  - by Ali

  Possible Duplicate: Best Online resources to learn about Compilers? What would be the best way to learn about compilers, and executable formats? Advanced compilers like gcc compile codes into machine readable files according to the language in which the code has been written (e.g. C, C++, etc). In fact, they interpret the meaning of each codes according to library and functions of the corresponding languages. Correct me if I'm wrong. I wish to better understand compilers by writing a very basic compiler (probably in C) to compile a static file (e.g. Hello World in a text file). I tried some tutorials and books, but all of them are for practical cases. They deal with compiling dynamic codes with meanings connected with the corresponding language. How can I write a basic compiler to convert a static text into a machine readable file? The next step will be introducing variables into the compiler; imagine that we want to write a compiler which compile only some functions of a language. Introducing practical tutorials and resources is highly appreciated :-)

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• Moving from windows to linux

  - by rincewind

  I need to reconcile these 2 facts: I don't feel comfortable working on Linux; I need to develop software for Linux. Some background: I have a 10+ years of programming experience on Windows (almost exclusively C/C++, but some .NET as well), I was a user of FreeBSD at home for about 3 years or so (then had to go back to Windows), and I've never had much luck with Linux. And now I have to develop software for Linux. I need a plan. On Windows, you can get away with just knowing a programming language, an API you're coding against, your IDE (VisualStudio) and some very basic tools for troubleshooting (Depends, ProcessExplorer, DebugView, WinDbg). Everything else comes naturally. On Linux, it's a very different story. How the hell would I know what DLL (sorry, Shared Object) would load, if I link to it from Firefox plugin? What's the Linux equivalent of inserting __asm int 3/DebugBreak() in the source and running the program, and then letting the OS call a debugger? Why the hell release builds use something, called appLoader, while debug builds work somehow different? Worst of all: how to provision Linux development environment? So, taking into account that hatred is usually associated with not knowing enough, what would you recommend? I'm ok with Emacs and GCC. I need to educate myself as a Linux admin/user, and I need to learn proper troubleshooting tools (strace is cool, btw), equivalents to the ones I mentioned above. Do I need to do Linux From Scratch? Or do I need to just read some books (I've read "UNIX programming enviornment" by Kernighan and "Advanced Programming..." by Stevens, but I need to learn something more practical)? Or do I need to have some Linux distro on my home computer?

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• Multi-lingual error messages and error numbers

  - by Jon Hopkins

  So we're looking at the possibility of porting our software to support multiple languages and one of the areas we're going to have to deal with is error messages and other notifications. These obviously have to be reported to the users in their own language. Our team (largely) only speak English and even if we were all multi-lingual we're looking at selling to a wide range of countries and could never expect to have a reasonable number of people speaking all languages (we're a small company). The obvious way to get round the language issue when errors or other messages we may get asked about which are being reported is error numbers which would be consistent across language. While these are going to exist in the backend (if only as key on the error message), I'd really rather not throw them at users if we don't have to but I don't have any other solution. Anyone have any useful suggestions for alternatives?

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• Theoretically bug-free programs

  - by user2443423

  I have read lot of articles which state that code can't be bug-free, and they are talking about these theorems: Halting problem Gödel's incompleteness theorem Rice's theorem Actually Rice's theorem looks like an implication of the halting problem and the halting problem is in close relationship with Gödel's incompleteness theorem. Does this imply that every program will have at least one unintended behavior? Or does it mean that it's not possible to write code to verify it? What about recursive checking? Let's assume that I have two programs. Both of them have bugs, but they don't share the same bug. What will happen if I run them concurrently? And of course most of discussions talked about Turing machines. What about linear-bounded automation (real computers)?

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• What's the best practice for async APIs that return futures on Scala?

  - by Maurício Linhares

  I have started a project to write an async PostgreSQL driver on Scala and to be async, I need to accept callbacks and use futures, but then accepting a callback and a future makes the code cumbersome because you always have to send a callback even if it is useless. Here's a test: "insert a row in the database" in { withHandler { (handler, future) => future.get(5, TimeUnit.SECONDS) handler.sendQuery( this.create ){ query => }.get( 5, TimeUnit.SECONDS ) handler.sendQuery( this.insert ){ query => }.get( 5, TimeUnit.SECONDS ).rowsAffected === 1 } } Sending the empty callback is horrible but I couldn't find a way to make it optional or anything like that, so right now I don't have a lot of ideas on how this external API should look like. It could be something like: handler.sendQuery( this.create ).addListener { query => println(query) } But then again, I'm not sure how people are organizing API's in this regard. Providing examples in other projects would also be great.

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• What are the basic features of an email module in a common web application?

  - by Coral Doe

  When developing an email module, what are the features to have in mind, besides actual email sending? I am talking about an email module that notifies users of events and periodically sends reports. The only other feature I have in mind is maintaining grey/black lists for users that do illegal operations in the system or any other things that may lead to email/domain/IP banning. Is there an etiquette for developing email modules? Are there some references of requirements for such modules?

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• How to avoid code duplication for a system which has logic that may change year wise?

  - by aravind

  What would be the way to design a system which has logic that may change year wise? There is an application which conducts online exams. There are five questions for a particular subject. The questions may (or may not) change year wise. As per my current design, the questions in database are stored year wise. There are some year specific code logic as well. In order to enable the application for another year, the year specific database records and code will be copied or duplicated. How to avoid this code duplication?

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• Should I use Ruby version 1.8.7 or 1.9.2 to start developing Rails apps?

  - by BeachRunnerJoe

  Hello. I'm diving into RoR and I see that the current version of Rails (3.0.5) works with both 1.8.7 and 1.9.2. Currently, I have both versions of Ruby installed using RVM, but I'm wondering which version I should be using as I dive into Rails and start developing apps. I suppose I'd prefer to use the newest version (1.9.2), but I don't know the technologies well enough to know pros/cons of using either. Thanks so much!

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• What's better than outputdebugstring for windows debugging?

  - by Peter Turner

  So, before I came to my current place of employment, the windows OutputDebugString function was completely unheard of, everyone was adding debug messages to string lists and saving them to file or doing showmessage popups (not very useful for debugging drawing issues). Now everybody (all 6 of us) is like "What can I say about this OutputDebugString?" and I'm like, "with much power comes much responsibility." I kind of feel as though I've passed a silent but deadly code smell to my colleagues. Ideally we wouldn't have bugs to debug right? Ideally we'd have over 0% code coverage, eh? So as far as petty debugging is concerned (not complete rewriting of a 3 million line Delphi behemoth) what's a better way to use debug running code than just adding OutputDebugString all over?

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• Internal Mutation of Persistent Data Structures

  - by Greg Ros

  To clarify, when I mean use the terms persistent and immutable on a data structure, I mean that: The state of the data structure remains unchanged for its lifetime. It always holds the same data, and the same operations always produce the same results. The data structure allows Add, Remove, and similar methods that return new objects of its kind, modified as instructed, that may or may not share some of the data of the original object. However, while a data structure may seem to the user as persistent, it may do other things under the hood. To be sure, all data structures are, internally, at least somewhere, based on mutable storage. If I were to base a persistent vector on an array, and copy it whenever Add is invoked, it would still be persistent, as long as I modify only locally created arrays. However, sometimes, you can greatly increase performance by mutating a data structure under the hood. In more, say, insidious, dangerous, and destructive ways. Ways that might leave the abstraction untouched, not letting the user know anything has changed about the data structure, but being critical in the implementation level. For example, let's say that we have a class called ArrayVector implemented using an array. Whenever you invoke Add, you get a ArrayVector build on top of a newly allocated array that has an additional item. A sequence of such updates will involve n array copies and allocations. Here is an illustration: However, let's say we implement a lazy mechanism that stores all sorts of updates -- such as Add, Set, and others in a queue. In this case, each update requires constant time (adding an item to a queue), and no array allocation is involved. When a user tries to get an item in the array, all the queued modifications are applied under the hood, requiring a single array allocation and copy (since we know exactly what data the final array will hold, and how big it will be). Future get operations will be performed on an empty cache, so they will take a single operation. But in order to implement this, we need to 'switch' or mutate the internal array to the new one, and empty the cache -- a very dangerous action. However, considering that in many circumstances (most updates are going to occur in sequence, after all), this can save a lot of time and memory, it might be worth it -- you will need to ensure exclusive access to the internal state, of course. This isn't a question about the efficacy of such a data structure. It's a more general question. Is it ever acceptable to mutate the internal state of a supposedly persistent or immutable object in destructive and dangerous ways? Does performance justify it? Would you still be able to call it immutable? Oh, and could you implement this sort of laziness without mutating the data structure in the specified fashion?

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• Are project managers useful in Scrum?

  - by Martin Wickman

  There are three roles defined in Scrum: Team, Product Owner and Scrum Master. There is no project manager, instead the project manager job is spread across the three roles. For instance: The Scrum Master: Responsible for the process. Removes impediments. The Product Owner: Manages and prioritizes the list of work to be done to maximize ROI. Represents all interested parties (customers, stakeholders). The Team: Self manage its work by estimating and distributing it among themselves. Responsible for meeting their own commitments. So in Scrum, there is no longer a single person responsible for project success. There is no command-and-control structure in place. That seems to baffle a lot of people, specifically those not used to agile methods, and of course, PM's. I'm really interested in this and what your experiences are, as I think this is one of the things that can make or break a Scrum implementation. Do you agree with Scrum that a project manager is not needed? Do you think such a role is still required? Why?

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• Which is better : Storing/retrieving images on/from SQL server or in a directory on server

  - by Pankaj Upadhyay

  I am working on a project in Asp.net MVC and need to work with images. There is an SQL database with a Product table. Every product in the table will have it's own image. I have two ways to do this : 1) Save the image in a web directory and store the URL on database. 2) Store the image in SQL itself in binary format and then retrieve it. Which is a better approach ? Mind you, I have no idea how second method works :-P . I will only learn this if there are merits to the second method

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• Is there any reason not to go directly from client-side Javascript to a database?

  - by Chris Smith

  So, let's say I'm going to build a Stack Exchange clone and I decide to use something like CouchDB as my backend store. If I use their built-in authentication and database-level authorization, is there any reason not to allow the client-side Javascript to write directly to the publicly available CouchDB server? Since this is basically a CRUD application and the business logic consists of "Only the author can edit their post" I don't see much of a need to have a layer between the client-side stuff and the database. I would simply use validation on the CouchDB side to make sure someone isn't putting in garbage data and make sure that permissions are set properly so that users can only read their own _user data. The rendering would be done client-side by something like AngularJS. In essence you could just have a CouchDB server and a bunch of "static" pages and you're good to go. You wouldn't need any kind of server-side processing, just something that could serve up the HTML pages. Opening my database up to the world seems wrong, but in this scenario I can't think of why as long as permissions are set properly. It goes against my instinct as a web developer, but I can't think of a good reason. So, why is this a bad idea? EDIT: Looks like there is a similar discussion here: Writing Web "server less" applications EDIT: Awesome discussion so far, and I appreciate everyone's feedback! I feel like I should add a few generic assumptions instead of calling out CouchDB and AngularJS specifically. So let's assume that: The database can authenticate users directly from its hidden store All database communication would happen over SSL Data validation can (but maybe shouldn't?) be handled by the database The only authorization we care about other than admin functions is someone only being allowed to edit their own post We're perfectly fine with everyone being able to read all data (EXCEPT user records which may contain password hashes) Administrative functions would be restricted by database authorization No one can add themselves to an administrator role The database is relatively easy to scale There is little to no true business logic; this is a basic CRUD app

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• Resources for popular domain models

  - by Songo

  I have come across many situations where I had to build a system for a library or a clinic or other popular domains. The thing is a domain model for a library was probably done 1000 times already with different level of details of course. Here is an example. Is there a popular website or community where one can find ready made domain models for popular systems? The whole purpose I'm trying to achieve is to quickly get a grasp of the domain I'm modeling and customize it to my needs. Re-inventing the wheel seems really absurd when the same system might have been modeled properly previously. Note I know Google might sound like the perfect source, but there is a repository out there that people can post there models, so that others can share them.

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• If I define a property to prototype appears in the constructor of object, why?

  - by Eduard Florinescu

  I took the example from this question modified a bit: What is the point of the prototype method? function employee(name,jobtitle,born) { this.name=name; this.jobtitle=jobtitle; this.born=born; this.status="single" } employee.prototype.salary=10000000; var fred=new employee("Fred Flintstone","Caveman",1970); console.log(fred.salary); fred.salary=20000; console.log(fred.salary) And the output in console is this: What is the difference salary is in constructor but I still can access it with fred.salary, how can I see if is in constructor from code, status is still employee property how can I tell for example if name is the one of employee or has been touch by initialization? Why is salary in constructor, when name,jobtitle,born where "touched" by employee("Fred Flintstone","Caveman",1970); «constructor»?

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• Why there is perception that VB.NET is good for small to medium size application and not for enterprise class project?

  - by Gens

  I love VB.NET very much. Coding VB.NET with Visual Studio is just like typing messages. Smooth, fast and simple. Any error will be notified instantly. The OO capability of VB.NET is good enough. But often in any .Net languages discussion, there is perception that VB.NET is good for small to medium size application and not for large scale project? Why there is such perception? Or am I missing anything regarding to VB.NET?

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• Why doesn't the Visual Studio C compiler like this? [migrated]

  - by justin

  The following code compiles fine on Linux using gcc -std=c99 but gets the following errors on the Visual Studio 2010 C compiler: Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 16.00.40219.01 for 80x86 Copyright (C) Microsoft Corporation. All rights reserved. fib.c fib.c(42) : error C2057: expected constant expression fib.c(42) : error C2466: cannot allocate an array of constant size 0 fib.c(42) : error C2133: 'num' : unknown size The user inputs the amount of Fibonacci numbers to generate. I'm curious as to why the Microsoft compiler doesn't like this code. http://pastebin.com/z0uEa2zw

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• How to use the unit of work and repository patterns in a service oriented enviroment

  - by A. Karimi

  I've created an application framework using the unit of work and repository patterns for it's data layer. Data consumer layers such as presentation depend on the data layer design. For example a CRUD abstract form has a dependency to a repository (IRepository). This architecture works like a charm in client/server environments (Ex. a WPF application and a SQL Server). But I'm looking for a good pattern to change or reuse this architecture for a service oriented environment. Of course I have some ideas: Idea 1: The "Adapter" design pattern Keep the current architecture and create a new unit of work and repository implementation which can work with a service instead of the ORM. Data layer consumers are loosely coupled to the data layer so it's possible but the problem is about the unit of work; I have to create a context which tracks the objects state at the client side and sends the changes to the server side on calling the "Commit" (Something that I think the RIA has done for Silverlight). Here the diagram: ----------- CLIENT----------- | ------------------ SERVER ---------------------- [ UI ] -> [ UoW/Repository ] ---> [ Web Services ] -> [ UoW/Repository ] -> [DB] Idea 2: Add another layer Add another layer (let say "local services" or "data provider"), then put it between the data layer (unit of work and repository) and the data consumer layers (like UI). Then I have to rewrite the consumer classes (CRUD and other classes which are dependent to IRepository) to depend on another interface. And the diagram: ----------------- CLIENT ------------------ | ------------------- SERVER --------------------- [ UI ] -> [ Local Services/Data Provider ] ---> [ Web Services ] -> [ UoW/Repository ] -> [DB] Please note that I have the local services layer on the current architecture but it doesn't expose the data layer functionality. In another word the UI layer can communicate with both of the data and local services layers whereas the local services layer also uses the data layer. | | | | | | | | ---> | Local Services | ---> | | | UI | | | | Data | | | | | | | ----------------------------> | |

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• What is meant by Scope of a variable?

  - by Appy

  I think of the scope of a variable as - "The scope of a particular variable is the range within a program's source code in which that variable is recognized by the compiler". That statement is from "Scope and Lifetime of Variables in C++", which I read many months ago. Recently I came across this in LeMoyne-Owen College courses: What exactly is the difference between the scope of variables in C# and (C99, C++, Java) when However a variable still must be declared before it can be used

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• Licensing Options for a dead project

  - by Russell Durham

  I'm currently working on a project where the original author informally told me that he didn't want to publish the source. Since then, the original author has gone leaving me to be the sole developer on the project. I've tried to contact him several times about making the project open source so that I can have other developers assist me but he is not responding to any communications. I'm not planning on trying to make money of the software, I just want a general license that allows me to put the code on GitHub or BitBucket so that other people in the community can assist me with the development. Can I do this since he is gone and not responding to any form of communication? Is there a time period I need to wait? I know what I asking for is legal advice, I just have no idea where to start looking to find the answer so I decided to start here.

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