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• HSM - cryptoki - opening sessions overhead

  - by Raj

  I am having a query regarding sessions with HSM. I am aware that there is an overhead if you initialise and finalise the cryptoki api for every file you want to encrypt/decrypt. My queries are, Is there an overhead in opening and closing individual sessions for every file, you want to encrypt/decrypt.(C_Initialize/C_Finalize) How many maximum number of sessions can i have for a HSM simultaneously, with out affecting the performance? Is opening and closing the session for processing individual files the best approach or opening a session and processing multiple files and then closing the session the best approach? Thanks

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• Avoiding Nested Queries

  - by Midhat

  How Important is it to avoid nested queries. I have always learnt to avoid them like a plague. But they are the most natural thing to me. When I am designing a query, the first thing I write is a nested query. Then I convert it to joins, which sometimes takes a lot of time to get right. And rarely gives a big performance improvement (sometimes it does) So are they really so bad. Is there a way to use nested queries without temp tables and filesort

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• What is the best possible technology for pulling huge data from 4 remote servers

  - by Habib Ullah Bahar

  Hello, For one of our project, we need to pull huge real time stock data from 4 remote servers across two countries. The trivial process here, check the sources for a regular interval and save the update to database. But as these are real time stock data of more than 1000 companies, I have to pull every second, which isn't good in case of memory, bandwidth I think. Please give me suggestion on which technology/platform [We are flexible here. PHP, Python, Java, PERL - anyone of them will be OK for us] we should choose, it can be achieved easily and with better performance.

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• General zoom algorithm for drawing program

  - by Steven Sproat

  My GUI toolkit, wxPython provides some methods for implementing a user zoom factor, however the quality isn't too good. I'm looking for ideas on how to create a zooming feature, which I know is complicated. I have a bitmap representing my canvas which is drawn to. This is displayed inside a scrolled window. Problems I forsee: - performance when zoomed in and panning around the canvas - difficulties with "real" coordinates and zoomed in coordinates - image quality not degrading with the zoom Using wxPython's SetUserScale() on its device contexts presents image quality like this - this is with a 1px line, at 30% zoomed in. I'm just wondering the general steps I'll need to take and the challenges I'll encounter. Thanks for any suggestions

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• Manipulating the address of a variable to store a smaller type?

  - by Sidnicious

  This is what I get for pampering myself with high-level programming languages. I have a function which writes a 32-bit value to a buffer, and a uint64_t on the stack. Is the following code a sane way to store it? uint64_t size = 0; // ... getBytes((uint32_t*)&size+0x1); I'm assuming that this would be the canonical, safe style: uint64_t size = 0; // ... uint32_t smallSize; getBytes(&smallSize); size = smallSize;

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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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• checking if records exists in DB, in single step or 2 steps?

  - by Sinan

  Suppose you want to get a record from database which returns a large data and requires multiple joins. So my question would be is it better to use a single query to check if data exists and get the result if it exists. Or do a more simple query to check if data exists then id record exists, query once again to get the result knowing that it exists. Example: 3 tables a, b and ab(junction table) select * from from a, b, ab where condition and condition and condition and condition etc... or select id from a, b ab where condition then if exists do the query above. So I don't know if there is any reason to do the second. Any ideas how this affects DB performance or does it matter at all?

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• Java multiline string

  - by skiphoppy

  Coming from Perl, I sure am missing the "here-document" means of creating a multi-line string in source code: $string = <<"EOF" # create a three line string text text text EOF In Java I have to have cumbersome quotes and plus signs on every line as I concatenate my multiline string from scratch. What are some better alternatives? Define my string in a properties file? Edit: Two answers say StringBuilder.append() is preferable to the plus notation. Could anyone elaborate as to why they think so? It doesn't look more preferable to me at all. I'm looking for away around the fact that multiline strings are not a first-class language construct, which means I definitely don't want to replace a first-class language construct (string concatenation with plus) with method calls. Edit: To clarify my question further, I'm not concerned about performance at all. I'm concerned about maintainability and design issues.

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• Why should I reuse XmlHttpRequest objects?

  - by Xavi

  From what I understand, it's a best practice to reuse XmlHttpRequest objects whenever possible. Unfortunately, I'm having a hard time understanding why. It seems like trying to reuse XHR objects can increase code complexity, introduce possible browser incompatibilities, and lead to other subtle bugs. After researching this question for a while, I did come up with a list of possible explanations: Fewer objects created means less garbage collecting Reusing XHR objects reduces the chance of memory leaks The overhead of creating a new XHR object is high The browser is able to perform some sort of network optimization under hood But I'm not sure if any of these reasons are actually valid. Any light you can shed on this question would be much appreciated.

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• [C#] Async threaded tcp server

  - by mark_dj

  I want to create a high performance server in C# which could take about ~10k clients. Now i started writing a TcpServer with C# and for each client-connection i open a new thread. I also use one thread to accept the connections. So far so good, works fine. The server has to deserialize AMF incoming objects do some logic ( like saving the position of a player ) and send some object back ( serializing objects ). I am not worried about the serializing/deserializing part atm. My main concern is that I will have a lot of threads with 10k clients and i've read somewhere that an OS can only hold like a few hunderd threads. Are there any sources/articles available on writing a decent async threaded server ? Are there other possibilties or will 10k threads work fine ? I've looked on google, but i couldn't find much info about design patterns or ways which explain it clearly

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• Loading a XML, but for asp.net 2.0

  - by Blankman

  I need to load an XML document into my Dictionary<string,string> object. XML looks like: <nodes> <node id="123"> <text>text goes here</text> </node> </nodes> How can I do this using XmlDocument? I want readability over performance, and I find XmlReader to be hard to read b/c you have to keep checking the node type.

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• how to implement unitofwork pattern when using subsonic 2.1(Repository pattern) ?

  - by ROHITH

  I am using subsonic repository pattern(2.1) for asp.net mvc application.In my application,there are many repositories like categoryRepository,Blogrepository etc.Inside each of this repository i am calling subsonic's DB.Select().From()...ExecuteReader() and then loading domain objects from those reader. In the controller action i make multiple calls from these repositories for e.g. List<IBlog> blogs=_blogRepository.GetHottestBlogs(); List<ICategory> categories=_categoryRepository.GetAll(); do i have to implement any unitofwork pattern for this ?.My doubt is that how subsonic performs each operation DB.Update/Insert/Select .Is a TransactionScope is enough for batch update or do i have to use SharedDbConnectionScope to get better performance?

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• RoR - Paperclip - How to set minimal width of an attachement

  - by sNiCKY

  Hi, my layout's requirement is to keep all thumbnails at 80px height, not higher, not smaller. In my model I set the style to :thumb= "500x80", so basically almost every picture which is not too wide gets its perfect miniature with 80px height. Sometimes, however, my pictures are narrow and high, so the thumb can have unclickable dimensions of like 5x80. So I dont want to crop pictures as long as thumbnails are not getting crazy narrow, but I think I can make a little sacrifice and crop them if thumb's width is getting smaller than 25px. So my questions is - is it possible in paperclip to set minimal proportions of a picture by which the style will be "500x80" and beyond that it will turn to sth like "25x80#"?

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• Audio processing in C# or C++

  - by melculetz

  Hi, I would like to create an application that uses AI techniques and allows the user to record a part of a song and then tries to find that song in a database of wav files. I would have liked to use some already existing libraries for the audio processing part. So, could you recommend any libraries in C# which can read a wav file, get input from microphone, have some audio filters (low pass, high pass, FFT etc) and maybe have the ability to plot the audio signal as well. I would prefer to develop in C#, but if there aren't good libraries for audio processing, I guess I could work in C++ as well. As far as I know, Mathlab already has the above mentioned functionalities, but I can't use it in my application.

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• What are the main benefits of implementing a virtual machine as part of an application?

  - by Marplesoft

  Several databases I've been looking at recently implement a virtual machine internally to perform the respective data reads and writes. For an example, check out this article on SQLite's virtual machine they call the 'VDBE'. I'm curious as to what the benefits of such an architecture are. I would assume performance is one but why would a virtual machine like this run faster? In fact, it seems to be that this extra layer could cause it to run slower. So perhaps it's for security? Or portability? Anyway, just curious about this.

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• How do you control the playback levels (decibles?) using the iPhone AVAudioPlayer? Or do I need to u

  - by Joshua

  My audio clips sound perfect when I upload them to the iPhone via iTunes. And I am pretty sure it is because the iPod has a maximum playback level, so the audio doesn't sound overdriven. In my app, I include the same audio files, and when I play them [myAudio play]; the levels are so high that the audio becomes indiscernible. I found in the library http://developer.apple.com/iphone/library/documentation/AVFoundation/Reference/AVAudioPlayerClassReference/Reference/Reference.html#//apple_ref/doc/uid/TP40008067-CH1-SW2 that it says that you can "Control relative playback level for each sound you are playing" but I've been searching this issue out for hours and I haven't gotten anywhere. Any help would be wonderful!

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• Measuring daemon CPU utilization over a portion of it's wall clock run time

  - by WhirlWind

  I am dealing with a network-related daemon: it takes data in, processes it, and spits it out. I would like to increase the performance of this daemon by profiling it and reducing it's CPU utilization. I can do this easily on Linux with gprof. However, I would also like to use something like "time" to measure it's total CPU utilization over a period of time. If possible, I would like to time it over a period that is less than its total run time: thus, I would like to start the daemon, wait awhile, generate CPU statistics, stop generating them, then stop the daemon at some later time. The "time" command would work well for me, but it seems to require that I start and stop the daemon as a child of time. Is there a way to measure CPU utilization for only a portion of the daemon's wall clock time?

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• PyPy -- How can it possibly beat CPython?

  - by Vulcan Eager

  From the Google Open Source Blog: PyPy is a reimplementation of Python in Python, using advanced techniques to try to attain better performance than CPython. Many years of hard work have finally paid off. Our speed results often beat CPython, ranging from being slightly slower, to speedups of up to 2x on real application code, to speedups of up to 10x on small benchmarks. How is this possible? Which Python implementation was used to implement PyPy? CPython? And what are the chances of a PyPyPy or PyPyPyPy beating their score? (On a related note... why would anyone try something like this?)

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• MySQL triggers cannot update rows in same table the trigger is assigned to. Suggested workaround?

  - by Cory House

  MySQL doesn't currently support updating rows in the same table the trigger is assigned to since the call could become recursive. Does anyone have suggestions on a good workaround/alternative? Right now my plan is to call a stored procedure that performs the logic I really wanted in a trigger, but I'd love to hear how others have gotten around this limitation. Edit: A little more background as requested. I have a table that stores product attribute assignments. When a new parent product record is inserted, I'd like the trigger to perform a corresponding insert in the same table for each child record. This denormalization is necessary for performance. MySQL doesn't support this and throws: Can't update table 'mytable' in stored function/trigger because it is already used by statement which invoked this stored function/trigger. A long discussion on the issue on the MySQL forums basically lead to: Use a stored proc, which is what I went with for now. Thanks in advance!

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• Single SignOn - Best practice

  - by halfdan

  Hi Guys, I need to build a scalable single sign-on mechanism for multiple sites. Scenario: Central web application to register/manage account (Server in Europe) Several web applications that need to authenticate against my user database (Servers in US/Europe/Pacific region) I am using MySQL as database backend. The options I came up with are either replicating the user database across all servers (data security?) or allowing the servers to directly connect to my MySQL instance by explicitly allowing connections from their IPs in my.cnf (high load? single point of failure?). What would be the best way to provide a scalable and low-latency single sign-on for all web applications? In terms of data security would it be a good idea to replicate the user database across all web applications? Note: All web applications provide an API which users can use to embed widgets into their own websites. These widgets work through a token auth mechanism which will again need to authenticate against my user database.

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• Why does my UIScrollView change it's original content offset when I scroll?

  - by Tony

  Before I scroll, my UIScrollView is laid out perfectly. See here However if I scroll up, the view bounces as I go out of bounds and then resets too high. See here I am going to guess this has to do with a hack that I did earlier to get the view to originally show like in the first screen shot. For some reason, to get my view to look like the second screen shot, I do: [scrollView setContentOffset:CGPointMake(0,-50) animated:YES]; in viewDidLoad But if I set the content offset to 0,0 in viewDidLoad, I get something that looks like the second screen shot when the view loads. This doesn't make much sense to me because if the content offset is 0,0 I would think the content should begin in the upper right corner of the screen. Does anyone know what could be going on here? Thanks!

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• vector<vector<largeObject>> vs. vector<vector<largeObject>*> in c++

  - by Leif Andersen

  Obviously it will vary depending on the compiler you use, but I'm curious as to the performance issues when doing vector<vector<largeObject>> vs. vector<vector<largeObject>*>, especially in c++. In specific: let's say that you have the outer vector full, and you want to start inserting elements into first inner vector. How will that be stored in memory if the outer vector is just storing pointers, as apposed to storing the whole inner vector. Will the whole outer vector have to be moved to gain more space, or will the inner vector be moved (assuming that space wasn't pre-allocated), causing problems with the outer vector? Thank you

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• Taking Responsibilites too early - danger or boon?

  - by narresh

  Just I am only six months experienced guy in software industry.Due to recession season,a large volume of employees from our company are asked to leave.This impact affects the new inexperienced guys. The problem is We have to interact with the client directly to gather the requirement We have to design all HLD and LLD ,use cases and DB Diagrams ,that should staisfy the customers who keeping the high software insdutry standards In this do or die situation (Client gives us narrow dead line),we spend most of time with interacting client (only less time is available for development and testing,even sit out for 24 X 7 won't help us to finish our task) If task will not be finished with in the expected time frame ,that will trigger poor performance ration to our profile There are two important questions flashing in our mind : (1) Quit the job and do other business (2) Face the challenge : (if the option is to face the challenge ,What are all the tools should we follow to automate requirement gathering,testing,DB diagram,Code review and the rest.(We are working on ASP.NET 3.5 with SQL Server 2005).

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• SDL versus GLFW?

  - by user697111

  What are the pros and cons to each? It seems they serve the same purpose. I have a few demos with each and they seem about the same. Performance or cross platform wise, is one better than the other? The only thing I notice is that SDL seems to have more "helper" libraries (fonts, images, mixer, built in sound support, etc). On its site, GLFW claims to be more "OpenGL" focused, but still have to use a GLEW to get any newer OpenGL features (same with SDL). I guess I'm leaning towards using SDL now (more mature, more features, more community). Are there any reasons I've missed why GLFW stands out and I should use it instead of SDL?

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• Reading files from an embedded ZIP archive

  - by aix

  I have a ZIP archive that's embedded inside a larger file. I know the archive's starting offset within the larger file and its length. Are there any Java libraries that would enable me to directly read the files contained within the archive? I am thinking along the lines of ZipFile.getInputStream(). Unfortunately, ZipFile doesn't work for this use case since its constructors require a standalone ZIP file. For performance reasons, I cannot copy the ZIP achive into a separate file before opening it. edit: Just to be clear, I do have random access to the file.

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