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  • Persistent (purely functional) Red-Black trees on disk performance

    - by Waneck
    I'm studying the best data structures to implement a simple open-source object temporal database, and currently I'm very fond of using Persistent Red-Black trees to do it. My main reasons for using persistent data structures is first of all to minimize the use of locks, so the database can be as parallel as possible. Also it will be easier to implement ACID transactions and even being able to abstract the database to work in parallel on a cluster of some kind. The great thing of this approach is that it makes possible implementing temporal databases almost for free. And this is something quite nice to have, specially for web and for data analysis (e.g. trends). All of this is very cool, but I'm a little suspicious about the overall performance of using a persistent data structure on disk. Even though there are some very fast disks available today, and all writes can be done asynchronously, so a response is always immediate, I don't want to build all application under a false premise, only to realize it isn't really a good way to do it. Here's my line of thought: - Since all writes are done asynchronously, and using a persistent data structure will enable not to invalidate the previous - and currently valid - structure, the write time isn't really a bottleneck. - There are some literature on structures like this that are exactly for disk usage. But it seems to me that these techniques will add more read overhead to achieve faster writes. But I think that exactly the opposite is preferable. Also many of these techniques really do end up with a multi-versioned trees, but they aren't strictly immutable, which is something very crucial to justify the persistent overhead. - I know there still will have to be some kind of locking when appending values to the database, and I also know there should be a good garbage collecting logic if not all versions are to be maintained (otherwise the file size will surely rise dramatically). Also a delta compression system could be thought about. - Of all search trees structures, I really think Red-Blacks are the most close to what I need, since they offer the least number of rotations. But there are some possible pitfalls along the way: - Asynchronous writes -could- affect applications that need the data in real time. But I don't think that is the case with web applications, most of the time. Also when real-time data is needed, another solutions could be devised, like a check-in/check-out system of specific data that will need to be worked on a more real-time manner. - Also they could lead to some commit conflicts, though I fail to think of a good example of when it could happen. Also commit conflicts can occur in normal RDBMS, if two threads are working with the same data, right? - The overhead of having an immutable interface like this will grow exponentially and everything is doomed to fail soon, so this all is a bad idea. Any thoughts? Thanks! edit: There seems to be a misunderstanding of what a persistent data structure is: http://en.wikipedia.org/wiki/Persistent_data_structure

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  • Simple/Basic steganography algorithms and methods

    - by tomp
    What are the basic and simpliest steganography algorithms and methods? I mean the steganography applied to images. How does simple program that hides data to images work? How does the program recognize the encrypted message in image without the source image? What are the main techniques used?

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  • what are sparse voxel octrees?

    - by pdeva
    I have reading a lot about the potential use of sparse voxel octrees in future graphics engines. However I have been unable to find technical information on them. I understand what a voxel is, however I dont know what sparse voxel octrees are or how are they any more efficient than the polygonal techniques in use now. Could somebody explain or point me to an explanation for this?

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  • What do you use two monitors for when you develop?

    - by Yishai
    Although I have two monitors on my desk, I just find that I don't use the second one very often. I see that often people are extolling the virtues of two (or three) monitors, but I haven't gotten into the groove. It gets me thinking that I may be missing some productivity techniques. So how do you organize your two monitors?

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  • How to use Rx to asynchronously query Twitter search ?

    - by Jalfp
    Hi, I'm thinking about using Rx (Reactive Framework) in order to asynchronously query Twitter search API on a given keyword. The sample app I'd like to build should be able to display new tweets in the console. Do you think it is possible to do that ? Would it be simpler than using standard programming techniques ? How would you do that ? Thank ! Jeremy

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  • Add string to another string

    - by daemonfire300
    Hi there, I currently encountered a problem: I want to handle adding strings to other strings very efficiently, so I looked up many methods and techniques, and I figured the "fastest" method. But I quite can not understand how it actually works: def method6(): return ''.join([`num` for num in xrange(loop_count)]) From source (Method 6) Especially the ([numfor num in xrange(loop_count)]) confused me totally.

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  • Is there a method to include CSS background images in print?

    - by jitendra
    Is there a method to include CSS background images in print? If i use image replace techniques for (which is considered as a best practice) Logo then logo doesn't come in print. and many places in site CSS background is saving bandwidth and my time both. but client is asking to include many things in print also. What should i do?

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  • The simplest concurrency pattern

    - by Ilya Kogan
    Please, would you help me in reminding me of one of the simplest parallel programming techniques. How do I do the following in C#: Initial state: semaphore counter = 0 Thread 1: // Block until semaphore is signalled semaphore.Wait(); // wait until semaphore counter is 1 Thread 2: // Allow thread 1 to run: semaphore.Signal(); // increments from 0 to 1 It's not a mutex because there is no critical section, or rather you can say there is an infinite critical section. So what is it?

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  • Accelerometer data analysis

    - by jrrt
    Hello, I would like to know if there are some libraries/algorithms/techniques (python, if at all possible) that help to extract features from accelerometer data (extracted from and android phone, btw), like periodicity of movements, energy of acceleration and the like. Has anyone done this kind of task before? Thank you very much in advance :)

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  • pandas read rotated csv files

    - by EricCoding
    Is there any function in pandas that can directly read a rotated csv file? To be specific, the header information in the first col instead of the first row. For example: A 1 2 B 3 5 C 6 7 and I would like the final DataFrame this way A B C 1 3 5 2 5 7 Of corse we can get around this problem using some data wangling techniques like transpose and slicing. I am wondering there should be a quick way in API but I could not find it.

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  • Initial Modelling/Design Activities on Agile Projects

    - by dalton
    When developing an application using agile techniques, what if any initial modelling/architecture activities do you do, and how do you capture that knowledge?? The closest thing I've seen so far is Scott Ambler's Initial Architecture Modelling, but was wondering what alternatives are used out there?

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  • Database maintenance, big binary table optimization

    - by jgemedina
    Hi i have a huge database, around 1 TB in size, most of the space is consumed by a table which stores images, the tables has right now almost 800k rows. server response time has increased, i would like to know which techniques should i use or you recomend, partitioning? o how to reorganize the table every row is accessed by the image id column, and it has its clustered index by that column, and every two days i reorganize the index and every 7 days i rebuild it, but it seems not to be working any suggestions?

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  • Suggest a good book for Quantitative Methods & R Programming

    - by Rahul
    Hi folks, Please suggest a good book for beginner in Quantitative Methods/Techniques. Adding to this, a good book for beginners in R programming language, used in Quantitative Methods. And I've a few questions about this: ? Should I have to learn the other subjects like Probability, Statics, etc. before learning Quantitative Methods ? Is there any relation between Quantitative Methods & Data Mining

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  • Sub-millisecond precision timing in C or C++

    - by andand
    What techniques / methods exist for getting sub-millisecond precision timing data in C or C++, and what precision and accuracy do they provide? I'm looking for methods that don't require additional hardware. The application involves waiting for approximately 50 microseconds +/- 1 microsecond while some external hardware collects data. EDIT: OS is Wndows, probably with VS2010. If I can get drivers and SDK's for the hardware on Linux, I can go there. Thanks.

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  • What is the best way to create a shortcut hook mechanism for Office

    - by rak3sh
    I am looking to create shortcut handler for MS Office. I am creating an addin with VS2010 for Office 2010. The handler needs to listen to all keyboard events when Word/PowerPoint is active. Although there is a lot of material for creating application level shortcut handlers, I couldn't find one that was specific to Office. It would be great if somebody could suggest techniques with sample c# code. Thanks

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  • HTML5 vs Flash ... Resources

    - by Barbara
    I'm a novice ...in that i've taken a few courses n poured through bunches of cool flash widgets, components and techniques. now it's time for my own website ... I do graphic design n really want to use some of the ready mades for convenience and economy...r there similar non flash products?

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