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• PHP frameworks - should I use them?

  - by 30secondstosam

  First of all let me explain who I am: I am a PHP Developer working for a company developing their CMS which handles online stores, data feeds and other content like blogs. I have been programming for 6 years and 4 of those have been in PHP. (I used to be a C# developer). My question is regarding PHP frameworks. I see so many jobs asking for zend, cakephp and other MVC types of frameworks. However, even as an experienced developer I have never used a PHP framework. Should I start learning? If so where do I even start as there are so many. I am about to re-write so much of my work's CMS and I'm wondering whether I could help myself a lot by using a framework. What do people think? Considering I will be re-writing a lot of the online store stuff... I am experienced in OO and I have used the .NET framework in the past. Thanks in advance for the replies.

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• How to REALLY start thinking in terms of objects?

  - by Mr Grieves

  I work with a team of developers who all have several years of experience with languages such as C# and Java. Most of them are young enough to have been shown OOP as a standard way to develop software in university and are very comfortable with concepts such as inheritance, abstraction, encapsulation and polymorphism. Yet, many of them, and I have to include myself, still tend to create classes which are meant to be used in a very functional fashion. The resulting software is often several smaller classes which correctly represent business objects which get passed through larger classes which only supply ways to modify and use those objects (functions). Large complex difficult-to-maintain classes named Manager are usually the result of such behaviour. I can see two theoretical reasons why people might write this type of code: It's easy to start thinking of everything in terms of the database Deep down, for me, a computer handling a web request feels more like a functional operation than an object oriented operation when you think about Request Handlers, Threads, Processes, CPU Cores and CPU operations... I want source code which is easy to read and easy to modify. I have seen excellent examples of OO code which meet these objectives. How can I start writing code like this? How I can I really start thinking in an object oriented fashion? How can I share such a mentality with my colleagues?

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• Copy-and-Pasted Test Code: How Bad is This?

  - by joshin4colours

  My current job is mostly writing GUI test code for various applications that we work on. However, I find that I tend to copy and paste a lot of code within tests. The reason for this is that the areas I'm testing tend to be similar enough to need repetition but not quite similar enough to encapsulate code into methods or objects. I find that when I try to use classes or methods more extensively, tests become more cumbersome to maintain and sometimes outright difficult to write in the first place. Instead, I usually copy a big chunk of test code from one section and paste it to another, and make any minor changes I need. I don't use more structured ways of coding, such as using more OO-principles or functions. Do other coders feel this way when writing test code? Obviously I want to follow DRY and YAGNI principles, but I find that test code (automated test code for GUI testing anyway) can make these principles tough to follow. Or do I just need more coding practice and a better overall system of doing things? EDIT: The tool I'm using is SilkTest, which is in a proprietary language called 4Test. As well, these tests are mostly for Windows desktop applications, but I also have tested web apps using this setup as well.

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• Object construction design

  - by James

  I recently started to use c# to interface with a database, and there was one part of the process that appeared odd to me. When creating a SqlCommand, the method I was lead to took the form: SqlCommand myCommand = new SqlCommand("Command String", myConnection); Coming from a Java background, I was expecting something more similar to SqlCommand myCommand = myConnection.createCommand("Command String"); I am asking, in terms of design, what is the difference between the two? The phrase "single responsibility" has been used to suggest that a connection should not be responsible for creating SqlCommands, but I would also say that, in my mind, the difference between the two is partly a mental one of the difference between a connection executing a command and a command acting on a connection, the latter of which seems less like what I have been lead to believe OOP should be. There is also a part of me wondering if the two should be completely separate, and should only come together in some sort of connection.execute(command) method. Can anyone help clear up these differences? Are any of these methods "more correct" than the others from an OO point of view? (P.S. the fact that c# is used is completely irrelevant. It just highlighted to me that different approaches were used)

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• Algorithms or patterns for a linked question and answer cost calculator

  - by kmc

  I've been asked to build an online calculator in PHP (and the Laravel framework). It will take the answers to a series of questions to estimate the cost of a home extension. For example, a couple of questions may be: What is the lie of your property? Flat, slightly inclined, heavily inclined. (these suggestive values could have specific values in the underlying calculator like, 0 degrees, 5 degrees, 10 degrees. What is your current flooring system? Wooden, or concrete? These would then impact the results of other questions. Once the size of the extension has been input, the lie of the land will affect how much site works will cost, and how much rubbish collection will cost. The second question will impact the cost of the extensions flooring, as stumping and laying floorboards is a different cost to laying foundations and a concrete slab. It will also influence what heating and cooling systems are available in the calculator. So it's VERY interlinked. The answer to any question can influence the options of other questions, and the end result. I'm having trouble figuring out an approach to this that will allow new options and questions to be plugged in at a later stage without having things too coupled. The Observer pattern, or Laravel's events may be handy, but currently the sheer breadth of the calculator has me struggling to gather my thoughts and see a sensible implementation. Are there any patterns or OO approaches that may help? Thanks!

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• Advice on choosing a book to read

  - by Kioshiki

  I would like to ask for some recommendations on useful books to read. Initially I had intended on posting quite a long description of my current issue and asking for advice. But I realised that I didn’t have a clear idea of what I wanted to ask. One thing that is clear to me is that my knowledge in various areas needs improving and reading is one method of doing that. Though choosing the right book to read seems like a task in itself when there are so many books out there. I am a programmer but I also deal with analysis, design & testing. So I am not sure what type of book to read. One option might be to work through two books at the same time. I had thought maybe one about design or practices and another of a more technical focus. Recently I came across one book that I thought might be useful to read: http://xunitpatterns.com/index.html It seems like an interesting book, but the comments I read on amazon.co.uk show that the book is probably longer than it needs to be. Has anyone read it and can comment on this? Another book that I already own and would probably be a good one to finish reading is this: http://www.amazon.co.uk/Code-Complete-Practical-Handbook-Construction/dp/0735619670/ref=sr_1_1?ie=UTF8&qid=1309438553&sr=8-1 Has anyone else read this who can comment on its usefulness? Beyond these two I currently have no clear idea of what to read. I have thought about reading a book related to OO design or the GOF design patterns. But I wonder if I am worrying too much about the process and practices and not focusing on the actual work. I would be very grateful for any suggestions or comments. Many Thanks, Kioshiki

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• How to justify rewriting/revamping legacy software in a business case?

  - by sxthomson

  I work for a great little software company which makes good revenue from our main software package. The problem for me is that it's almost unmaintainable. It's written in Delphi 7 (has upgraded versions over time) and has been worked on by a lot of developers over the past 20 or so years. The software lacks any meaningful architecture - there's no object orientation whatsoever, horrible amounts of cyclical dependencies and an over-reliance on global variables to name just a few things. Another huge thing for me is Delphi 7 does NOT support 64-bit. The problem here for me is that my management team don't care about technical things, they want to know why they should care. Obviously that's expected, so what I'm asking here is for some guidance, or tales, or pitfalls about this kind of thing. There's a few things I would love to include, namely for me, the length of time taken to debug/write a feature in "legacy" code, versus coherent, well structured OO code. Does anyone know of any blog posts or the like where this is talked about? For us in the company this is a huge reason. Despite being decent developers we feel like writing a new feature is just piling more rubbish on top. On top of that, even for me who has a decent level of understanding of the code, changing things is infuriating - a small change can have a ridiculous domino effect. Anyone have any experiences they'd like to share?

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• Why grep -i is so slow? How to do it faster for ASCII?

  - by Vi.

  $ time lzop -d < tvtropes-index.lzo | egrep -B 5 '[Dd][eE][sS][cC][eE][nN][dD] ?[Ff][rR][oO][mM]' real 0m0.438s $ time lzop -d < tvtropes-index.lzo | egrep -B 5 'descend ?from' -i real 0m11.294s Both search insensitively. why -i so slow? How to make fast grep -i without entering things [iI][nN] [tT][hH][iI][sS] [wW][aA][Yy]? For example, perl -ne 'print if /descend ?from/i' works fast, but '-B 5' is not as trivial to implement as in grep (as well as other options).

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• How should I start refactoring my mostly-procedural C++ application?

  - by oob

  We have a program written in C++ that is mostly procedural, but we do use some C++ containers from the standard library (vector, map, list, etc). We are constantly making changes to this code, so I wouldn't call it a stagnant piece of legacy code that we can just wrap up. There are a lot of issues with this code making it harder and harder for us to make changes, but I see the three biggest issues being: Many of the functions do more (way more) than one thing We violate the DRY principle left and right We have global variables and global state up the wazoo. I was thinking we should attack areas 1 and 2 first. Along the way, we can "de-globalize" our smaller functions from the bottom up by passing in information that is currently global as parameters to the lower level functions from the higher level functions and then concentrate on figuring out how to removing the need for global variables as much as possible. I just finished reading Code Complete 2 and The Pragmatic Programmer, and I learned a lot, but I am feeling overwhelmed. I would like to implement unit testing, change from a procedural to OO approach, automate testing, use a better logging system, fully validate all input, implement better error handling and many other things, but I know if we start all this at once, we would screw ourselves. I am thinking the three I listed are the most important to start with. Any suggestions are welcome. We are a team of two programmers mostly with experience with in-house scripting. It is going to be hard to justify taking the time to refactor, especially if we can't bill the time to a client. Believe it or not, this project has been successful enough to keep us busy full time and also keep several consultants busy using it for client work.

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• What are some techniques I can use to refactor Object Oriented code into Functional code?

  - by tieTYT

  I've spent about 20-40 hours developing part of a game using JavaScript and HTML5 canvas. When I started I had no idea what I was doing. So it started as a proof of concept and is coming along nicely now, but it has no automated tests. The game is starting to become complex enough that it could benefit from some automated testing, but it seems tough to do because the code depends on mutating global state. I'd like to refactor the whole thing using Underscore.js, a functional programming library for JavaScript. Part of me thinks I should just start from scratch using a Functional Programming style and testing. But, I think refactoring the imperative code into declarative code might be a better learning experience and a safer way to get to my current state of functionality. Problem is, I know what I want my code to look like in the end, but I don't know how to turn my current code into it. I'm hoping some people here could give me some tips a la the Refactoring book and Working Effectively With Legacy Code. For example, as a first step I'm thinking about "banning" global state. Take every function that uses a global variable and pass it in as a parameter instead. Next step may be to "ban" mutation, and to always return a new object. Any advice would be appreciated. I've never taken OO code and refactored it into Functional code before.

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• Are there legitimate reasons for returning exception objects instead of throwing them?

  - by stakx

  This question is intended to apply to any OO programming language that supports exception handling; I am using C# for illustrative purposes only. Exceptions are usually intended to be raised when an problem arises that the code cannot immediately handle, and then to be caught in a catch clause in a different location (usually an outer stack frame). Q: Are there any legitimate situations where exceptions are not thrown and caught, but simply returned from a method and then passed around as error objects? This question came up for me because .NET 4's System.IObserver<T>.OnError method suggests just that: exceptions being passed around as error objects. Let's look at another scenario, validation. Let's say I am following conventional wisdom, and that I am therefore distinguishing between an error object type IValidationError and a separate exception type ValidationException that is used to report unexpected errors: partial interface IValidationError { } abstract partial class ValidationException : System.Exception { public abstract IValidationError[] ValidationErrors { get; } } (The System.Component.DataAnnotations namespace does something quite similar.) These types could be employed as follows: partial interface IFoo { } // an immutable type partial interface IFooBuilder // mutable counterpart to prepare instances of above type { bool IsValid(out IValidationError[] validationErrors); // true if no validation error occurs IFoo Build(); // throws ValidationException if !IsValid(…) } Now I am wondering, could I not simplify the above to this: partial class ValidationError : System.Exception { } // = IValidationError + ValidationException partial interface IFoo { } // (unchanged) partial interface IFooBuilder { bool IsValid(out ValidationError[] validationErrors); IFoo Build(); // may throw ValidationError or sth. like AggregateException<ValidationError> } Q: What are the advantages and disadvantages of these two differing approaches?

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• Design in "mixed" languages: object oriented design or functional programming?

  - by dema80

  In the past few years, the languages I like to use are becoming more and more "functional". I now use languages that are a sort of "hybrid": C#, F#, Scala. I like to design my application using classes that correspond to the domain objects, and use functional features where this makes coding easier, more coincise and safer (especially when operating on collections or when passing functions). However the two worlds "clash" when coming to design patterns. The specific example I faced recently is the Observer pattern. I want a producer to notify some other code (the "consumers/observers", say a DB storage, a logger, and so on) when an item is created or changed. I initially did it "functionally" like this: producer.foo(item => { updateItemInDb(item); insertLog(item) }) // calls the function passed as argument as an item is processed But I'm now wondering if I should use a more "OO" approach: interface IItemObserver { onNotify(Item) } class DBObserver : IItemObserver ... class LogObserver: IItemObserver ... producer.addObserver(new DBObserver) producer.addObserver(new LogObserver) producer.foo() //calls observer in a loop Which are the pro and con of the two approach? I once heard a FP guru say that design patterns are there only because of the limitations of the language, and that's why there are so few in functional languages. Maybe this could be an example of it? EDIT: In my particular scenario I don't need it, but.. how would you implement removal and addition of "observers" in the functional way? (I.e. how would you implement all the functionalities in the pattern?) Just passing a new function, for example?

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• Align paragraph at the bottom of page (or at the bottom of the end of section)

  - by danihp

  I need to align a paragraph at bottom of last page of a section. I'm looking for a workaround of foot page because OO has repagination problems when I use foot notes. Someone know how can I align a paragraph at the bottom of last page of a section (or at the bottom of a pate) without foot notes? I need some think like: [page XX XXX XXX XXXX X XX X XX X XX XX XXX XXX XXXX X XX X XX X XX XX X. YYY Y YY Y YY Y YYYYY Y. ] Where YYY is the bottom aligned paragraph. Notice that I can enclose paragraph into table, ... but not as foot note.

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• Why is 'grep -i' so slow? How to do it faster for ASCII?

  - by Vi.

  Consider: $ time lzop -d < tvtropes-index.lzo | egrep -B 5 '[Dd][eE][sS][cC][eE][nN][dD] ?[Ff][rR][oO][mM]' real 0m0.438s $ time lzop -d < tvtropes-index.lzo | egrep -B 5 'descend ?from' -i real 0m11.294s Both search case insensitively. Why is the -i version so slow? How do I make grep -i fast without entering things like [iI][nN] [tT][hH][iI][sS] [wW][aA][Yy]? For example, perl -ne 'print if /descend ?from/i' works fast, but '-B 5' is not as trivial to implement as in grep (as well as other options).

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• Are small amounts of functional programming understandable by non-FP people?

  - by kd35a

  Case: I'm working at a company, writing an application in Python that is handling a lot of data in arrays. I'm the only developer of this program at the moment, but it will probably be used/modified/extended in the future (1-3 years) by some other programmer, at this moment unknown to me. I will probably not be there directly to help then, but maybe give some support via email if I have time for it. So, as a developer who has learned functional programming (Haskell), I tend to solve, for example, filtering like this: filtered = filter(lambda item: included(item.time, dur), measures) The rest of the code is OO, it's just some small cases where I want to solve it like this, because it is much simpler and more beautiful according to me. Question: Is it OK today to write code like this? How does a developer that hasn't written/learned FP react to code like this? Is it readable? Modifiable? Should I write documentation like explaining to a child what the line does? # Filter out the items from measures for which included(item.time, dur) != True I have asked my boss, and he just says "FP is black magic, but if it works and is the most efficient solution, then it's OK to use it." What is your opinion on this? As a non-FP programmer, how do you react to the code? Is the code "googable" so you can understand what it does? I would love feedback on this :) Edit: I marked phant0m's post as answer, because he gives good advice on how to write the code in a more readable way, and still keep the advantages. But I would also like to recommend superM's post because of his viewpoint as a non-FP programmer.

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• Need Directions to become a programmer [closed]

  - by Omin

  Before youguys go on about how there are many types of programmers, please read through the post. Long term goal: Develop my own software (company) Short term goal: Get a job that involves coding/programming Current status: Support Analyst (at a software company but does not involve any programming) with 40k salary, 3rd year computer engineering student I had everything figured out. I'm going to develop a 2D scrolling game for iphone or android, publish the app, sell a bunch, and then apply at a studios as a software developer. And then something hit me. I think I need to get a job that involes programming to learn as much as I can in the shortest time possible. So I got a phone interview at a fast growing start up software company, passed that no problem, but then had to take an online technical assessment. That failed miserably. I thought that if I could just present myself, show that I am hard working, positive attitude, eager to make self improvements, type of a guy, I could get the job. I was wrong. And now, I am lost. Im thinking of staying with my job until I find a new one as a programmer. I will be working, self studying, and trying to make this happen without finishing university. I forgot to mention that the online technical assessment was based on data structures/algorithms, OO design, runtime complexity. I was hoping that I could get some guidence. Should I be focusing on app development or study computer science fundamentals? I have a list of books I can be going through: Learning C# O'Reilly (I got interested in C# because of Unity3D and Mono), C# 5.0 in a Nutshell, Head First Design Patterns, Code Complete, Introduction to Algorithms, Programming Interviews Exposed, Cracking the Coding Interview, The Google Resume.

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• Are there any good resources for refactoring existing C# code to use LINQ while keeping your tests passing?

  - by Paddyslacker

  I've been teaching myself a little LINQ and an exercise I thought would be useful was to take my existing Project Euler C# code, which I built using Test Driven Development and gradually convert it to LINQ. I realise that LINQ is not always the best solution for all of the Project Euler problems, but I don't want to get into that here. I'm wondering whether or not it's feasible to refactor "traditional" OO C# code to use LINQ and functional programming syntax whilst keeping all of your tests passing. I can't find a way to make the tiny steps I'm used to making using TDD when converting to LINQ and this is a roadblock for me. I seem to have to make large changes to come up with a single function that I then replace whole chunks of my code with. I realise I could write this from scratch in LINQ, but in the real world, I'd like to be able to replace parts of my existing C# code to take advantage of LINQ where appropriate. Has anyone been successful with this approach? What resources did you find useful for refactoring existing C# code to use LINQ whilst taking a Test Driven Development approach?

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• In OpenOffice Spreadsheet, how can I set the default Date format?

  - by Joe Casadonte

  I'm using OO 3.1.1 on Ubuntu 9.10 (in case that matters to the answer). I like my dates to appear as YYYY-MM-DD. I can't think of a time when I want to see a date in any other format, so I'm constantly changing how dates look. That's manageable, though annoying. What's gotten me to the point of posting is that when I edit a cell with a date value, I have to edit it in the format MM/DD/YYYY, which is really, really annoying, as I'm usually mucking with the day (or possibly the month), and very seldom the year. So there's lots of cursor or mouse use, wasting my time. So is there a way that I can change how dates are edited, or at least the default display format? Thanks!

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• Has the emerging generation of programmers got the wrong idea about design patterns? [closed]

  - by MattDavey

  Over the years I've noticed a shift in attitude towards design patterns, particularly amongst the emerging generation of developers. There seems to be a notion these days that design patterns are silver bullets that instantly cure any problem, a proliferating idea that advancing as a software engineer simply means learning and applying more and more patterns. When confronted with a problem, developers no longer strive to truly understand the issue and design a solution - instead they simply pick a design pattern which seems to be a close fit, and try to brute-force it. You can see evidence of this by the many, many questions on Stack Overflow that begin with the phrase "what pattern should I use to...". I fall into a slightly more mature category of developers (5-10 years experience) and I have a very different viewpoint on patterns - simply as a communication tool to enhance clarity. I find this perspective of design patterns being lego bricks (collected like pokemon cards) a little disconcerting. Will developers lose this attitude as they gain more experience in software engineering? Or could these notions perhaps steer the direction of our craft in years to come? Did the older generation of developers have any similar concerns about us? (perhaps about OO design or similar...). if so, how did we turn out?

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• CLSF & CLK 2013 Trip Report by Jeff Liu

  - by jamesmorris

  This is a contributed post from Jeff Liu, lead XFS developer for the Oracle mainline Linux kernel team. Recently, I attended both the China Linux Storage and Filesystem workshop (CLSF), and the China Linux Kernel conference (CLK), which were held in Shanghai. Here are the highlights for both events. CLSF - 17th October XFS update (led by Jeff Liu) XFS keeps rapid progress with a lot of changes, especially focused on the infrastructure/performance improvements as well as  new feature development.  This can be reflected with a sample statistics among XFS/Ext4+JBD2/Btrfs via: # git diff --stat --minimal -C -M v3.7..v3.12-rc4 -- fs/xfs|fs/ext4+fs/jbd2|fs/btrfs XFS: 141 files changed, 27598 insertions(+), 19113 deletions(-) Ext4+JBD2: 39 files changed, 10487 insertions(+), 5454 deletions(-) Btrfs: 70 files changed, 19875 insertions(+), 8130 deletions(-) What made up those changes in XFS? Self-describing metadata(CRC32c). This is a new feature and it contributed about 70% code changes, it can be enabled via `mkfs.xfs -m crc=1 /dev/xxx` for v5 superblock. Transaction log space reservation improvements. With this change, we can calculate the log space reservation at mount time rather than runtime to reduce the the CPU overhead. User namespace support. So both XFS and USERNS can be enabled on kernel configuration begin from Linux 3.10. Thanks Dwight Engen's efforts for this thing. Split project/group quota inodes. Originally, project quota can not be enabled with group quota at the same time because they were share the same quota file inode, now it works but only for v5 super block. i.e, CRC enabled. CONFIG_XFS_WARN, an new lightweight runtime debugger which can be deployed in production environment. Readahead log object recovery, this change can speed up the log replay progress significantly. Speculative preallocation inode tracking, clearing and throttling. The main purpose is to deal with inodes with post-EOF space due to speculative preallocation, support improved quota management to free up a significant amount of unwritten space when at or near EDQUOT. It support backgroup scanning which occurs on a longish interval(5 mins by default, tunable), and on-demand scanning/trimming via ioctl(2). Bitter arguments ensued from this session, especially for the comparison between Ext4 and Btrfs in different areas, I have to spent a whole morning of the 1st day answering those questions. We basically agreed on XFS is the best choice in Linux nowadays because: Stable, XFS has a good record in stability in the past 10 years. Fengguang Wu who lead the 0-day kernel test project also said that he has observed less error than other filesystems in the past 1+ years, I own it to the XFS upstream code reviewer, they always performing serious code review as well as testing. Good performance for large/small files, XFS does not works very well for small files has already been an old story for years. Best choice (maybe) for distributed PB filesystems. e.g, Ceph recommends delopy OSD daemon on XFS because Ext4 has limited xattr size. Best choice for large storage (>16TB). Ext4 does not support a single file more than around 15.95TB. Scalability, any objection to XFS is best in this point? :) XFS is better to deal with transaction concurrency than Ext4, why? The maximum size of the log in XFS is 2038MB compare to 128MB in Ext4. Misc. Ext4 is widely used and it has been proved fast/stable in various loads and scenarios, XFS just need more customers, and Btrfs is still on the road to be a manhood. Ceph Introduction (Led by Li Wang) This a hot topic.  Li gave us a nice introduction about the design as well as their current works. Actually, Ceph client has been included in Linux kernel since 2.6.34 and supported by Openstack since Folsom but it seems that it has not yet been widely deployment in production environment. Their major work is focus on the inline data support to separate the metadata and data storage, reduce the file access time, i.e, a file access need communication twice, fetch the metadata from MDS and then get data from OSD, and also, the small file access is limited by the network latency. The solution is, for the small files they would like to store the data at metadata so that when accessing a small file, the metadata server can push both metadata and data to the client at the same time. In this way, they can reduce the overhead of calculating the data offset and save the communication to OSD. For this feature, they have only run some small scale testing but really saw noticeable improvements. Test environment: Intel 2 CPU 12 Core, 64GB RAM, Ubuntu 12.04, Ceph 0.56.6 with 200GB SATA disk, 15 OSD, 1 MDS, 1 MON. The sequence read performance for 1K size files improved about 50%. I have asked Li and Zheng Yan (the core developer of Ceph, who also worked on Btrfs) whether Ceph is really stable and can be deployed at production environment for large scale PB level storage, but they can not give a positive answer, looks Ceph even does not spread over Dreamhost (subject to confirmation). From Li, they only deployed Ceph for a small scale storage(32 nodes) although they'd like to try 6000 nodes in the future. Improve Linux swap for Flash storage (led by Shaohua Li) Because of high density, low power and low price, flash storage (SSD) is a good candidate to partially replace DRAM. A quick answer for this is using SSD as swap. But Linux swap is designed for slow hard disk storage, so there are a lot of challenges to efficiently use SSD for swap. SWAPOUT swap_map scan swap_map is the in-memory data structure to track swap disk usage, but it is a slow linear scan. It will become a bottleneck while finding many adjacent pages in the use of SSD. Shaohua Li have changed it to a cluster(128K) list, resulting in O(1) algorithm. However, this apporoach needs restrictive cluster alignment and only enabled for SSD. IO pattern In most cases, the swap io is in interleaved pattern because of mutiple reclaimers or a free cluster is shared by all reclaimers. Even though block layer can merge interleaved IO to some extent, but we cannot count on it completely. Hence the per-cpu cluster is added base on the previous change, it can help reclaimer do sequential IO and the block layer will be easier to merge IO. TLB flush: If we're reclaiming one active page, we should first move the page from active lru list to inactive lru list, and then reclaim the page from inactive lru to swap it out. During the process, we need to clear PTE twice: first is 'A'(ACCESS) bit, second is 'P'(PRESENT) bit. Processors need to send lots of ipi which make the TLB flush really expensive. Some works have been done to improve this, including rework smp_call_functiom_many() or remove the first TLB flush in x86, but there still have some arguments here and only parts of works have been pushed to mainline. SWAPIN: Page fault does iodepth=1 sync io, but it's a little waste if only issue a page size's IO. The obvious solution is doing swap readahead. But the current in-kernel swap readahead is arbitary(always 8 pages), and it always doesn't perform well for both random and sequential access workload. Shaohua introduced a new flag for madvise(MADV_WILLNEED) to do swap prefetch, so the changes happen in userspace API and leave the in-kernel readahead unchanged(but I think some improvement can also be done here). SWAP discard As we know, discard is important for SSD write throughout, but the current swap discard implementation is synchronous. He changed it to async discard which allow discard and write run in the same time. Meanwhile, the unit of discard is also optimized to cluster. Misc: lock contention For many concurrent swapout and swapin , the lock contention such as anon_vma or swap_lock is high, so he changed the swap_lock to a per-swap lock. But there still have some lock contention in very high speed SSD because of swapcache address_space lock. Zproject (led by Bob Liu) Bob gave us a very nice introduction about the current memory compression status. Now there are 3 projects(zswap/zram/zcache) which all aim at smooth swap IO storm and promote performance, but they all have their own pros and cons. ZSWAP It is implemented based on frontswap API and it uses a dynamic allocater named Zbud to allocate free pages. Zbud means pairs of zpages are "buddied" and it can only store at most two compressed pages in one page frame, so the max compress ratio is 50%. Each page frame is lru-linked and can do shink in memory pressure. If the compressed memory pool reach its limitation, shink or reclaim happens. It decompress the page frame into two new allocated pages and then write them to real swap device, but it can fail when allocating the two pages. ZRAM Acts as a compressed ramdisk and used as swap device, and it use zsmalloc as its allocator which has high density but may have fragmentation issues. Besides, page reclaim is hard since it will need more pages to uncompress and free just one page. ZRAM is preferred by embedded system which may not have any real swap device. Now both ZRAM and ZSWAP are in driver/staging tree, and in the mm community there are some disscussions of merging ZRAM into ZSWAP or viceversa, but no agreement yet. ZCACHE Handles file page compression but it is removed out of staging recently. From industry (led by Tang Jie, LSI) An LSI engineer introduced several new produces to us. The first is raid5/6 cards that it use full stripe writes to improve performance. The 2nd one he introduced is SandForce flash controller, who can understand data file types (data entropy) to reduce write amplification (WA) for nearly all writes. It's called DuraWrite and typical WA is 0.5. What's more, if enable its Dynamic Logical Capacity function module, the controller can do data compression which is transparent to upper layer. LSI testing shows that with this virtual capacity enables 1x TB drive can support up to 2x TB capacity, but the application must monitor free flash space to maintain optimal performance and to guard against free flash space exhaustion. He said the most useful application is for datebase. Another thing I think it's worth to mention is that a NV-DRAM memory in NMR/Raptor which is directly exposed to host system. Applications can directly access the NV-DRAM via a memory address - using standard system call mmap(). He said that it is very useful for database logging now. This kind of NVM produces are beginning to appear in recent years, and it is said that Samsung is building a research center in China for related produces. IMHO, NVM will bring an effect to current os layer especially on file system, e.g. its journaling may need to redesign to fully utilize these nonvolatile memory. OCFS2 (led by Canquan Shen) Without a doubt, HuaWei is the biggest contributor to OCFS2 in the past two years. They have posted 46 upstream patches and 39 patches have been merged. Their current project is based on 32/64 nodes cluster, but they also tried 128 nodes at the experimental stage. The major work they are working is to support ATS (atomic test and set), it can be works with DLM at the same time. Looks this idea is inspired by the vmware VMFS locking, i.e, http://blogs.vmware.com/vsphere/2012/05/vmfs-locking-uncovered.html CLK - 18th October 2013 Improving Linux Development with Better Tools (Andi Kleen) This talk focused on how to find/solve bugs along with the Linux complexity growing. Generally, we can do this with the following kind of tools: Static code checkers tools. e.g, sparse, smatch, coccinelle, clang checker, checkpatch, gcc -W/LTO, stanse. This can help check a lot of things, simple mistakes, complex problems, but the challenges are: some are very slow, false positives, may need a concentrated effort to get false positives down. Especially, no static checker I found can follow indirect calls (“OO in C”, common in kernel): struct foo_ops { int (*do_foo)(struct foo *obj); } foo->do_foo(foo); Dynamic runtime checkers, e.g, thread checkers, kmemcheck, lockdep. Ideally all kernel code would come with a test suite, then someone could run all the dynamic checkers. Fuzzers/test suites. e.g, Trinity is a great tool, it finds many bugs, but needs manual model for each syscall. Modern fuzzers around using automatic feedback, but notfor kernel yet: http://taviso.decsystem.org/making_software_dumber.pdf Debuggers/Tracers to understand code, e.g, ftrace, can dump on events/oops/custom triggers, but still too much overhead in many cases to run always during debug. Tools to read/understand source, e.g, grep/cscope work great for many cases, but do not understand indirect pointers (OO in C model used in kernel), give us all “do_foo” instances: struct foo_ops { int (*do_foo)(struct foo *obj); } = { .do_foo = my_foo }; foo>do_foo(foo); That would be great to have a cscope like tool that understands this based on types/initializers XFS: The High Performance Enterprise File System (Jeff Liu) [slides] I gave a talk for introducing the disk layout, unique features, as well as the recent changes.   The slides include some charts to reflect the performances between XFS/Btrfs/Ext4 for small files. About a dozen users raised their hands when I asking who has experienced with XFS. I remembered that when I asked the same question in LinuxCon/Japan, only 3 people raised their hands, but they are Chris Mason, Ric Wheeler, and another attendee. The attendee questions were mainly focused on stability, and comparison with other file systems. Linux Containers (Feng Gao) The speaker introduced us that the purpose for those kind of namespaces, include mount/UTS/IPC/Network/Pid/User, as well as the system API/ABI. For the userspace tools, He mainly focus on the Libvirt LXC rather than us(LXC). Libvirt LXC is another userspace container management tool, implemented as one type of libvirt driver, it can manage containers, create namespace, create private filesystem layout for container, Create devices for container and setup resources controller via cgroup. In this talk, Feng also mentioned another two possible new namespaces in the future, the 1st is the audit, but not sure if it should be assigned to user namespace or not. Another is about syslog, but the question is do we really need it? In-memory Compression (Bob Liu) Same as CLSF, a nice introduction that I have already mentioned above. Misc There were some other talks related to ACPI based memory hotplug, smart wake-affinity in scheduler etc., but my head is not big enough to record all those things. -- Jeff Liu

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• Automated Error Reporting = More Robust Software

  - by Laila

  I would like to tell you how to revolutionize your software development process </marketing hyperbole> On a more serious note, we (Red Gate's .NET Development team) recently rolled a new tool into our development process which has made our lives dramatically easier AND improved the quality of our software, and I (& one of our developers, Alex Davies) just wanted to take a quick moment to share the love. I work with a development team that takes pride in what they ship, so we take software testing rather seriously. For every development project we run, we allocate at least one software tester for every two developers, and we never ship software without first shipping early access releases and betas to get user feedback. And therein lies the challenge -encouraging users to provide consistent, useful feedback is a headache, but without that feedback, improving the software is. tricky. Until fairly recently, we used the standard (if long-winded) approach of receiving bug reports of variable quality via email or through our support forums. If that didn't give us enough information to reproduce the problem - which was most of the time - we had to enter into a time-consuming to-and-fro conversation with the end-user, to get scrape together the data we needed to work out where the problem lay. As I'm sure you're aware, this is painfully slow. To the delight of the team, we recently got to work with SmartAssembly, which lets us embed automated exception and error reporting into our software with very little pain, and we decided to do a little dogfooding. As a result, we've have made a really handy (if perhaps slightly obvious) discovery: As soon as we release a beta, or indeed any release of software, we now get tonnes of customer feedback through automated error reports. Making this process easier for our users has dramatically increased the amount (and quality) of feedback we get. From their point of view, they get an experience similar to Microsoft's error reporting, and process is essentially idiot-proof. From our side of things, we can now react much faster to the information we get, fixing the bugs and shipping a new-and-improved release, which our users rather appreciate. Smiles and hugs all round. Even more so because, as we're use SmartAssembly's Automated Error Reporting, we get to avoid having to spend weeks building an exception reporting mechanism. It takes just a few minutes to add reporting to a project, and we get a bunch of useful information back, like a stack trace and the values of all the local variables, which we can use to fix bugs. Happily, "Automated Error Reporting = More Robust Software" can actually be read two ways: we've found that we not only ship higher quality software, but we also release within a shorter time. We can ship stable software that our users are happy to upgrade to, and we then bask in the glory of lots of positive customer feedback. Once we'd starting working with SmartAssembly, we were curious to know how widespread error reporting was as a practice. Our product manager ran a survey in autumn last year, and found that 40% of software developers never really considered deploying error reporting. Considering how we've now got plenty of experience on the subject, one of our dev guys, Alex Davies, thought we should share what we've learnt, and he's kindly offered to host a webinar on delivering robust software with Automated Error Reporting. Drawing on our own in-house development experiences, he'll cover how to add error reporting to your program, how to actually use the error reports to fix bugs (don't snigger, not everyone's as bright as you), how to customize the error report dialog that your users see, and how to automatically get log files from your users' machine. The webinar will take place on Jan 25th (that's next week). It's free to attend, but you'll still need to register to hear Alex's dulcet tones.

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• josso newbie setup problems - can't use tomcat's manager page

  - by opensas

  I'm trying to setup josso on an apache tomcat server running on windows. I've installed Apache Tomcat/6.0.26 fro zip file to c:\tomcat then installed josso following the documentation at http://www.josso.org/confluence/display/JOSSO1/Quick+Start started tomcat with c:\tomcat\bin\startup.bat, and noticed the following warnings ADVERTENCIA: [SetPropertiesRule]{Server/Service/Engine/Realm} Setting property ' debug' to '1' did not find a matching property. 21/03/2010 15:55:03 org.apache.tomcat.util.digester.SetPropertiesRule begin ADVERTENCIA: [SetPropertiesRule]{Server/Service/Engine/Host/Valve} Setting prope rty 'appName' to 'josso' did not find a matching property. ... ADVERTENCIA: Unable to find required classes (javax.activation.DataHandler and j avax.mail.internet.MimeMultipart). Attachment support is disabled. ... ADVERTENCIA: Bean with key 'josso:type=SSOAuditManager' has been registered as a n MBean but has no exposed attributes or operations ... but then everything seems to work fine, the problem is I can no longer access http://localhost:8080/manager/html using user tomcat /tomcat, as configured in \conf\tomcat-users.xml (before installing josso it worked) I tried with tomcat/tomcatpwd as defined in \lib\josso-credentials.xml and even added tomcat and the manager role to \lib\josso-users.xml, with no luck... Is anybody having the same problem? how can I access tomcat's manager page? Thanks a lot saludos sas This is my config: C:\tomcat\bincatalina version Using CATALINA_BASE: "C:\tomcat" Using CATALINA_HOME: "C:\tomcat" Using CATALINA_TMPDIR: "C:\tomcat\temp" Using JRE_HOME: "c:\java" Using CLASSPATH: "C:\tomcat\bin\bootstrap.jar" Server version: Apache Tomcat/6.0.26 Server built: March 9 2010 1805 Server number: 6.0.26.0 OS Name: Windows XP OS Version: 5.1 Architecture: x86 JVM Version: 1.5.0_22-b03 JVM Vendor: Sun Microsystems Inc ps: moreover, when shutting down, I get a couple of error like this GRAVE: A web application appears to have started a thread named [JOSSOAssertionM onitor] but has failed to stop it. This is very likely to create a memory leak. 21/03/2010 15:57:06 org.apache.catalina.loader.WebappClassLoader clearReferences Threads and then tomcat's shutdown freezes at 21/03/2010 15:57:07 org.apache.coyote.ajp.AjpAprProtocol destroy INFO: Parando Coyote AJP/1.3 en ajp-8009 ps: sorry for this lengthy question...

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• How can I call from my PC through my cisco ip phone?

  - by Enjoy coding

  Hi gurus, I am trying to call a telephone number fro my PC through my ip phone once my application completes its work. So I am searching for a way to access my ip phone from my PC. Please correct me if I am wrong or missing the obvious. On my PC in office selecting a phone in Microsoft office communicator and making calls from PC through my Cisco IP Phone is disabled. Is there any way i can programmatically call a external phone or mobile number from my PC as my ip phone is connected to my PC. I tried out etQuickDial and Make/Drop calls. But I am not able to find the appropriate way or setup to make calls. I also googled for any libraries and i saw some TAPI but was not able to get correct way. Please help me out with this. My cisco ip phone is 7940. My environment is Windows XP. Please let me know if you need more details. No problems with me even if you propose a solution involving coding or a non coding way of downloading and installing any applications. Thanks in advance. If you dont want me to post it here and If I need to put it in super user or server fault or some where else please direct me appropriately. I did not use any of these two before so I posted this question here.

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• How to mark array value types in PHP (Java)Doc?

  - by Christian Sciberras

  It might be a bit difficult to explain, so I'll give some example code. Note that I'm using NetBeans IDE (latest). class Dummy { public function say(){ } } /** * Builds dummy class and returns it. * @return Dummy The dummy class. */ function say_something(){ return new Dummy(); } $s=say_something(); While developing in netbeans I can invoke auto-complete by hitting ctrl+space after typing "$s-". In the the hint window that follows, there is the item "say()". This is because the javadoc says say_something returns a Dummy and NetBeans parsed Dummy class to know that it has a method called "say()". So far so good. My problem is with arrays. Example code follows: /** * Builds array of 2 dummy classes and returns it. * @return Array The dummy class. (*) */ function say_something2(){ return array(new Dummy(),new Dummy()); } $s=say_something2(); If I try the auto-complete thing again but with "$s[0]-" instead, I don't get the methods fro Dummy class. This is because in the JavaDoc I only said that it is an array, but not the values' type. So the question would be, is there any JavaDoc syntax, cheat, whatever which allows me to tell JavaDoc what type of variables to expect in an array?

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• Does anyone have documentation on SHGetSysColor?

  - by Paulo Santos

  I'm trying to find any reference for this function, but I haven't found anything. All I have is an obscure KB from Microsoft referencing that a programmer made boo-boo when coding a part of the Windows Mobile 6 where he should call SHGetSysColor but instead he called GetSysColor that gives a complete different color, for the same spec. From what I could gather the GetSysColor read a color value in the registry from HKEY_LOCAL_MACHINE\Software\Microsoft\Color\SHColor or HKEY_LOCAL_MACHINE\Software\Microsoft\Color\DefSHColor and returns the color according to the index. In that registry I have the following value for a standard Win Mobile 6.5 "DefSHColor"=hex:\ ff,00,00,00,00,00,00,00,dd,dd,dd,00,ff,ff,cc,00,ff,ff,ff,00,15,af,bc,00,15,\ af,bc,00,c9,e7,e9,00,14,9c,a7,00,ff,ff,ff,00,14,9c,a7,00,14,9c,a7,00,14,9c,\ a7,00,15,af,bc,00,14,9c,a7,00,ff,ff,ff,00,c9,e7,e9,00,37,c7,d3,00,37,c7,d3,\ 00,ff,ff,ff,00,00,b7,c9,00,14,9c,a7,00,ff,ff,ff,00,15,af,bc,00,84,84,c3,00,\ 15,af,bc,00,14,9c,a7,00,ff,ff,ff,00,ff,ff,ff,00,00,00,00,00,ff,ff,ff,00,00,\ 00,00,00,ff,ff,ff,00,2e,44,4f,00,00,14,3c,00,00,f0,ff,00,ff,ff,ff,00,c9,e7,\ e9,00,14,9c,a7,00,ff,ff,ff,00,14,9c,a7,00 And I realized that each four bytes represents a different color (RR,GG,BB,AA -- The AA I'm assuming here, as every color there has the AA byte as 00 which would mean that it's a solid color). What I can't get a fix on is what each index mean, as I have 41 different colors in there. Googling for SHGetSysColor in gives me only 7 matches, two of them are the KB from Microsoft (one in English, the other in French) one is from a Russian site (which I don't read), yet another two are from the freepascal.org and one from Koders.com that is describing the commctl.def file. I went to the commctl.h trying to see if I could find reference tom this function, and found absolutely nothing. No search on MSDN, either fro Google, Bing, or the default MSDN search gave me any result. So, does anyone know what indexes are we talking about here?

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