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• Articles about replication schemes/algorithms?

  - by jkff

  I'm designing an hierarchical distributed system (every node has zero or more "master" nodes to which it propagates its current data). The data gets continuously updated and I'd like to guarantee that at least N nodes have almost-current data at any given time. I do not need complete consistency, only eventual consistency (t.i. for any time instant, the current snapshot of data should eventually appear on at least N nodes. It is tricky to define the term "current" here, but still). Nodes may fail and go back up at any moment, and there is no single "central" node. O overflowers! Point me to some good papers describing replication schemes. I've so far found one: Consistency Management in Optimistic Replication Algorithms

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• Is ActiveMQ unreliable?

  - by user122991

  Hello, We have been using ActiveMQ 5.2 in our distributed enterprise application for about 3 months. During that time, we have experienced debilitating failures at least twice weekly. In particular, we see: 1) Topic publisher has its connection arbitrarily closed and experiences EOF on attempt to publish. Note well that this issue is not a function of some timeout. It does not correlate reliably with any inactivity. 2) Queue listeners never receive message. Message simply sits on Queue. 2) is much rarer (hardly ever) than 1). In both cases, the failures are highly intermittent-- they cannot be reliably reproduced through any testing usage pattern. Also, there are no errors or warning in the AMQ logs. Have others experienced similar problems? Is there an opinion that some other JMS provider is more reliable? thanks, Joe

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• What should I learn to improve my Java skills ?

  - by hory.incpp

  Hello, I currently know Java SE and I want to learn something more 'enterprise'. I would like something more distributed (app server, server programming, web, content management system ...) but any suggestion is ok. There are many frameworks which I've heard: spring, hibernate, persistence, ejb, jsp, servlet, jsf, jboss, glassfish, ant etc etc etc etc. I'm very confused where to start. So the question is: Can somebody explain to me what actually there frameworks are; and which one should I start with ? Thank you.

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• Building a minimal plugin architecture in Python.

  - by dF

  I have an application, written in Python, which is used by a fairly technical audience (scientists). I'm looking for a good way to make the application extensible by the users, i.e. a scripting/plugin architecture. I am looking for something extremely lightweight. Most scripts, or plugins, are not going to be developed and distributed by a third-party and installed, but are going to be something whipped up by a user in a few minutes to automate a repeating task, add support for a file format, etc. So plugins should have the absolute minimum boilerplate code, and require no 'installation' other than copying to a folder (so something like setuptools entry points, or the Zope plugin architecture seems like too much.) Are there any systems like this already out there, or any projects that implement a similar scheme that I should look at for ideas / inspiration?

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• NoSQL or Ehcache caching ?

  - by paddydub

  I'm building a Route Planner Webapp using Spring/Hibernate/Tomcat and a mysql database, I have a database containing read only data, such as Bus Stop Coordinates, Bus times which is never updated. I'm trying to make the app run faster, each time the application is run it will preform approx 1000 reads to the database to calculate a route. I have setup a Ehcache which greatly improves the read from database times. I'm now setting terracotta + Ehcache distributed caching to share the cache with multiple Tomcat JVMs. This seems a bit complicated. I've tried memcached but it was not performing as fast as ehcache. I'm wondering if a MongoDb or Redis would be better suited. I have no experience with nosql but I would appreciate if anyone has any ideas. What i need is quick access to the read only database.

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• c# multi threaded file processing

  - by user177883

  There is a folder that contains 1000 of small text files. I aim to parse and process all of them while more files are being populated in to the folder. My intention is to multithread this operation as the single threaded prototype took 6 minutes to process 1000 files. I like to have reader and writer thread(s) as following : while the reader thread(s) are reading the files, I d like to have writer thread(s) to process them. Once the reader is started reading a file, I d like to mark it as being processed, such as by renaming it, once it s read, rename it to completed. How to approach such multithreaded application ? Is it better to use a distributed hash table or a queue? Which data structure to use that would avoid locks? Would you have a better approach to this scheme that you like to share?

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• C / JSON Library in popular Linux distros?

  - by Tim Post

  I have a program written in C that has to input and output JSON over a local domain socket. I've found several C / JSON libraries that 'almost work' through searches. Prior to taking one of the libraries that I found .. I want to be sure that I'm not over-looking a library that is commonly found on modern Linux distros. I'd also really appreciate links to libraries that you use. Most likely, I'll just drop it in tree, unless I realize that I've over looked something widely distributed. I am tagging this as subjective because the answer that I select is the one linking to a library that works for me, that does not mean its the 'best' library. I want to take an existing array and easily convert it to a buffer that can be sent, or take a buffer and easily convert it into an allocated array. Thanks in advance!

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• assistance with classifying tests

  - by amateur

  I have a .net c# library that I have created that I am currently creating some unit tests for. I am at present writing unit tests for a cache provider class that I have created. Being new to writing unit tests I have 2 questions These being: My cache provider class is the abstraction layer to my distributed cache - AppFabric. So to test aspects of my cache provider class such as adding to appfabric cache, removing from cache etc involves communicating with appfabric. Therefore the tests to test for such, are they still categorised as unit tests or integration tests? The above methods I am testing due to interacting with appfabric, I would like to time such methods. If they take longer than a specified benchmark, the tests have failed. Again I ask the question, can this performance benchmark test be classifed as a unit test? The way I have my tests set up I want to include all unit tests together, integration tests together etc, therefore I ask these questions that I would appreciate input on.

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• Question about mysql indexes on low to medium cardinality columns

  - by Kevin J

  I have a general question about the way that database indexing works, particularly in mysql. Let's say I have a table with a million rows with a column "ClientID" that is distributed relatively equally among 30 values. Thus, this column is very low cardinality (30) relative to the primary key (1 million). Now, I understand that you shouldn't create indexes on low cardinality fields. However, in this case, queries are only ever done with one of the 30 clientIDs. Thus, wouldn't creating an index on ClientID be helpful, as the search space is automatically reduced to 1/30th what it normally would be? Or is my understanding of how the index works flawed? Thanks

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• continuous integration web service

  - by Josh Moore

  I am in a position where I could become a team leader of a team distributed over two countries. This team would be the tech. team for a start up company that we plan to bootstrap on limited funds. So I am trying to find out ways to minimize upfront expenses. Right now we are planning to use Java and will have a lot of junit tests. I am planing on using github for VCS and lighthouse for a bug tracker. In addition I want to add a continuous integration server but I do not know of any continuous integration servers that are offered as a web service. Does anybody know if there are continuous integration servers available in a software as a service model? P.S. if anybody knows were I can get these three services at one location that would be great to know to.

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• Reverse massive text file in Java

  - by DanJanson

  What would be the best approach to reverse a large text file that is uploaded asynchronously to a servlet that reverses this file in a scalable and efficient way? text file can be massive (gigabytes long) can assume mulitple server/clustered environment to do this in a distributed manner. open source libraries are encouraged to consider I was thinking of using Java NIO to treat file as an array on disk (so that I don't have to treat the file as a string buffer in memory). Also, I am thinking of using MapReduce to break up the file and process it in separate machines. Any input is appreciated. Thanks. Daniel

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• Backing up locally modified and new source files

  - by eran

  I'm wondering how other programmers are backing up changes that are not under source control yet, be it new files or modified ones. I'm mostly referring to medium size jobs - hardly worth the effort of making a private branch, but taking more than a day to complete. This is not a vendor-specific question - I'd like to see if various products have different solutions to the problem. I'd appreciate answers referring to SVN and distributed SCCs, though. I'm mostly wondering about that latters (Mercurial, GIT etc.) - it's great that you have your own local repo, but do you back it up on a regular basis along with your source files? Note - I'm not asking about a general backup strategy. For that, we have IT. I'm seeking the best way to keep locally modified stuff backed-up before they are checked back into the main repo.

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• Algorithm to distribute objects in a box (like InDesign, Illustrator, Draw!)

  - by Rafael Almeida

  I have a set of rectangles with their corresponding positions and a big rectangle which serves as the 'bounding box' for these rectangles. I would like to know of an algorithm that would 'distribute the free space' evenly among the rectangles. Some of you may be familiar with the Distribute Spacing option in Adobe InDesign and similar layout-oriented apps. That would be what I'm looking for. I did try looking it up, but I'm not familiar with 'graphical' algorithms terminology and trying only terms relating to 'distribute' mainly yields results about Distributed Computing. So, even the names of the algorithms or better terms to look up would be a big help. Finally, the algorithm doesn't need to be rigorously the same as InDesign's one: pretty much any algorithm that 'distributes' objects inside a region will work fine. In fact, since I'm striving for visual appeal mainly, the more suggestions the better. =D

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• Is there a language designed for code golf?

  - by J S

  I am not really a fan of code golf, but I have to wonder, is there an esoteric language designed for it? I mean a language with following properties: Common programs may be expressed in very short amount of characters It uses ASCII character set effectively (for example, common operators are not identifiers, so they don't have to be separated by whitespace, character usage is distributed more or less evenly because we cannot use Huffman coding and so on) Except the terse syntax, it should have very expressible and clean semantics (like, let's say, Python or Scheme); it shouldn't be difficult to program in It doesn't need features for large scale programs, such as OOP, but it definitely should allow custom functions and data structures It should have a large standard library, identifiers in this library should be as short as possible Maybe it should be called CG? Languages that can be a source of inspiration are Forth, APL and Joy.

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• SOLR and Natural Language Parsing - Can I use it?

  - by andy

  hey guys, my requirements are pretty similar to this: Requirements http://stackoverflow.com/questions/90580/word-frequency-algorithm-for-natural-language-processing Using Solr While the answer for that question is excellent, I was wondering if I could make use of all the time I spent getting to know SOLR for my NLP. I thought of SOLR because: It's got a bunch of tokenizers and performs a lot of NLP. It's pretty use to use out of the box. It's restful distributed app, so it's easy to hook up I've spent some time with it, so using could save me time. Can I use Solr? Although the above reasons are good, I don't know SOLR THAT well, so I need to know if it would be appropriate for my requirements. Ideal Usage Ideally, I'd like to configure SOLR, and then be able to send SOLR some text, and retrieve the indexed tonkenized content. Context So you guys know, I'm working on a small component of a bigger recommendation engine.

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• Verifying serialisation streams when used for messaging

  - by Nick

  I want to add distributed messaging to some applications. One target would be embedded and the other applications would be running on Windows. I'm thinking of having a connection manager, to which all of the applications would connect and communicate. I only need some simple kind of RPC mechanism. I've looked at Google Protocol Buffers, but I don't really like the idea of code generation. I'd rather use serialisation and somehow verify the format of the serialised stream. I.e. Perhaps send metadata about what the stream would contain so that each endpoint can verify it is reading the correct version. Does anyone know of any examples of this? Perhaps the message format could be read from a file which all the applications read to verify the stream format?

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• Plastic SCM vs. Mercurial? Need Source Control for Visual Studio 2005 on Windows 7

  - by Pete Alvin

  1) Has anyone used Plastic SCM? Is it reliable? 2) How does it compare with Mercurial? (It seems like this is a good candidate for DVCS on Windows. I tried Git and really didn't like it.) 3) I really like TortoiseSVN. I like a central model because of the piece of mind that if it's in the respository it's "safe" and tracked. Here is the question: Is the excitement over distributed version control (DVCS) worth the hype? My environment: Windows 7 Windows development (Dev. Studio 2005, SQL Server 2003); integration would be nice Two developers sharing same code push code to production servers almost daily

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• Is it possible to do have Capistrano do a checkout over a reverse SSH tunnel?

  - by James A. Rosen

  I am developing an application that resides on a public host but whose source I must keep in a Git repository behind a corporate firewall. I'm getting very tired of the slowness of deploying via scp (copying the whole repository and shipping it over SSH on each deploy) and would like to have the remote host simply do a git pull to update. The problem is that the firewall prohibits incoming SSH connections. Would it be possible for me to set up an SSH tunnel from my computer to the deployment computer and use my repository as the source for the git pull? After all, git is distributed, so my copy is just as valid a repository as the central one. If this is possible, what would the tunnel command and the Capistrano configuration be? I think the tunnel will look something like ssh -R something:deployserver.com:something [email protected]

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• Task vs. process, is there really any difference?

  - by DASKAjA

  Hi there, I'm studying for my final exams in my CS major on the subject distributed systems and operating systems. I'm in the need for a good definition for the terms task, process and threads. So far I'm confident that a process is the representation of running (or suspended, but initiated) program with its own memory, program counter, registers, stack, etc (process control block). Processes can run threads which share memory, so that communication via shared memory is possible in contrast to processes which have to communicate via IPC. But what's the difference between tasks and process. I often read that they're interchangable and that the term task isn't used anymore. Is that really true?

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• Best data store for billions of rows

  - by Jody Powlette

  I need to be able to store small bits of data (approximately 50-75 bytes) for billions of records (~3 billion/month for a year). The only requirement is fast inserts and fast lookups for all records with the same GUID and the ability to access the data store from .net. I'm a SQL server guy and I think SQL Server can do this, but with all the talk about BigTable, CouchDB, and other nosql solutions, it's sounding more and more like an alternative to a traditional RDBS may be best due to optimizations for distributed queries and scaling. I tried cassandra and the .net libraries don't currently compile or are all subject to change (along with cassandra itself). I've looked into many nosql data stores available, but can't find one that meets my needs as a robust production-ready platform. If you had to store 36 billion small, flat records so that they're accessible from .net, what would choose and why?

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• Are there any tools to optimize the number of consumer and producer threads on a JMS queue?

  - by lindelof

  I'm working on an application that is distributed over two JBoss instances and that produces/consumes JMS messages on several JMS queues. When we configured the application we had to determine which threading model we would use, in particular the number of producing and consuming threads per queue. We have done this in a rather ad-hoc fashion but after reading the most recent columns by Herb Sutter in Dr Dobbs (in particular this one) I would like to size our threads in a more rigorous manner. Are there any methods/tools to measure the throughput of JMS queues (in particular JBoss Messaging queues) as a function of the number of producing/consuming threads?

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• Compiling Qt for Windows 98

  - by wrp

  I need to support Windows 98. The Qt documentation claims this is possible, but there are no instructions. The distributed binaries don't run on Win98 and the majority of Qt applications I have sampled also don't. For several apps that do run on 98, I have asked authors how they did it, but the common answer is that it was accidental and they don't know what factors caused it. In searching the forums for help, I found only guesses that turned out to be wrong. For example, one belief is that to compile for Win9x, you must build the tools and the apps on that platform. Yet, things I found to run were built on newer versions of Windows. What is required to build the Qt dev tools and then applications for Win98? How about cross-compiling from WinXP or Linux? Are there specific components that can't be made to run on Win98? Are there particular difficulties with dynamic or static linking for Win98 support?

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• Good IM/Chat solution for pasting code

  - by Matt Miller

  We've got several distributed developers working together on a couple of projects. We've been using Skype to host chats with all the developers, and it works okay except for one thing: It REALLY mangles any code we copy and paste into the chats -- especially the whitespace in Python. This question has tons of opinions about chat clients & servers, but no one has much to say about pasting in code. (http://stackoverflow.com/questions/36415/best-chat-im-tool-for-developers) Is anybody out there using a chat or im client that handles source code really well?

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• How can I plot a time series graph with Perl?

  - by Jazz

  I have some data from a database (SQLite), mapping a value (an integer) to a date. A date is a string with this format: YYYY-MM-DD hh:mm. The dates are not uniformly distributed. I want do draw a line graph with the dates on X and the values on Y. What is the easiest way to do this with Perl? I tried DBIx::Chart but I could not make it recognize my dates. I also tried GD::Graph, but as the documentation says: GD::Graph does not support numerical x axis the way it should. Data for X axes should be equally spaced

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• .NET ClickOnce not installing prerequisite files?

  - by proudgeekdad

  I have a .NET project that uses Crystal Reports. The application is distributed using ClickOnce. Things work great if the user has Crystal installed on their computer. However, not all of the end users have Crystal Reports installed on their computers. These users are receiving the following error... "Unable to install or run the application. The application requires that assembly CrystalDecisions.ReportAppServer.XmlSerialize Version 10.5.3700.0 be installed in the Global Assembly Cache (GAC) first." Is there a way to force ClickOnce installs to ensure that a prerequisite is installed?

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