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  • How to reliably measure available memory in Linux?

    - by Alex B
    Linux /proc/meminfo shows a number of memory usage statistics. MemTotal: 4040732 kB MemFree: 23160 kB Buffers: 163340 kB Cached: 3707080 kB SwapCached: 0 kB Active: 1129324 kB Inactive: 2762912 kB There is quite a bit of overlap between them. For example, as far as I understand, there can be active page cache (belongs to "cached" and "active") and inactive page cache ("inactive" + "cached"). What I want to do is to measure "free" memory, but in a way that it includes used pages that are likely to be dropped without a significant impact on overall system's performance. At first, I was inclined to use "free" + "inactive", but Linux's "free" utility uses "free" + "cached" in its "buffer-adjusted" display, so I am curious what a better approach is. When the kernel runs out of memory, what is the priority of pages to drop and what is the more appropriate metric to measure available memory?

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  • Database structure for storing Bank-like accounts and transactions

    - by user1241320
    We're in the process of adding a bank-like sub-system to our own shop. We already have customers, so each will be given a sort of account and transactions of some kind will be possible (adding to the account or subtracting from it). So we at least need the account entity, the transaction one and operations will then have to recalculate overall balances. How would you structure your database to handle this? Is there any standard bank system have to use that I could mock? By the way, we're on mysql but will also look at some nosql solution for performance boost.

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  • Best practice with respect to NPE and multiple expressions on single line

    - by JRL
    I'm wondering if it is an accepted practice or not to avoid multiple calls on the same line with respect to possible NPEs, and if so in what circumstances. For example: getThis().doThat(); vs Object o = getThis(); o.doThat(); The latter is more verbose, but if there is an NPE, you immediately know what is null. However, it also requires creating a name for the variable and more import statements. So my questions around this are: Is this problem something worth designing around? Is it better to go for the first or second possibility? Is the creation of a variable name something that would have an effect performance-wise? Is there a proposal to change the exception message to be able to determine what object is null in future versions of Java ?

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  • Linux, how to capture screen, and simulate mouse movements.

    - by 2di
    Hi All I need to capture screen (as print screen) in the way so I can access pixel color data, to do some image recognition, after that I will need to generate mouse events on the screen such as left click, drag and drop (moving mouse while button is pressed, and then release it). Once its done, image will be deleted. Note: I need to capture whole screen everything that user can see, and I need to simulate clicks outside window of my program (if it makes any difference) Spec: Linux ubuntu Language: C++ Performance is not very important,"print screen" function will be executed once every ~10 sec. Duration of the process can be up to 24 hours so method needs to be stable and memory leaks free (as usuall :) I was able to do in windows with win GDI and some windows events, but I'ev no idea how to do it in Linux. Thanks a lot

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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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  • Silverlight/Web Service Serializing Interface for use Client Side

    - by Steve Brouillard
    I have a Silverlight solution that references a third-party web service. This web service generates XML, which is then processed into objects for use in Silverlight binding. At one point we the processing of XML to objects was done client-side, but we ran into performance issues and decided to move this processing to the proxies in the hosting web project to improve performance (which it did). This is obviously a gross over-simplification, but should work. My basic project structure looks like this. Solution Solution.Web - Holds the web page that hosts Silverlight as well as proxies that access web services and processes as required and obviously the references to those web services). Solution.Infrastructure - Holds references to the proxy web services in the .Web project, all genned code from serialized objects from those proxies and code around those objects that need to be client-side. Solution.Book - The particular project that uses the objects in question after processed down into Infrastructure. I've defined the following Interface and Class in the Web project. They represent the type of objects that the XML from the original third-party gets transformed into and since this is the only project in the Silverlight app that is actually server-side, that was the place to define and use them. //Doesn't get much simpler than this. public interface INavigable { string Description { get; set; } } //Very simple class too public class IndexEntry : INavigable { public List<IndexCM> CMItems { get; set; } public string CPTCode { get; set; } public string DefinitionOfAbbreviations { get; set; } public string Description { get; set; } public string EtiologyCode { get; set; } public bool HighScore { get; set; } public IndexToTabularCommandArguments IndexToTabularCommandArgument { get; set; } public bool IsExpanded { get; set; } public string ManifestationCode { get; set; } public string MorphologyCode { get; set; } public List<TextItem> NonEssentialModifiersAndQualifyingText { get; set; } public string OtherItalics { get; set; } public IndexEntry Parent { get; set; } public int Score { get; set; } public string SeeAlsoReference { get; set; } public string SeeReference { get; set; } public List<IndexEntry> SubEntries { get; set; } public int Words { get; set; } } Again; both of these items are defined in the Web project. Notice that IndexEntry implments INavigable. When the code for IndexEntry is auto-genned in the Infrastructure project, the definition of the class does not include the implmentation of INavigable. After discovering this, I thought "no problem, I'll create another partial class file reiterating the implmentation". Unfortunately (I'm guessing because it isn't being serialized), that interface isn't recognized in the Infrastructure project, so I can't simply do that. Here's where it gets really weird. The BOOK project CAN see the INavigable interface. In fact I use it in Book, though Book has no reference to the Web Service in the Web project where the thing is define, though Infrastructure does. Just as a test, I linked to the INavigable source file from indside the Infrastructure project. That allowed me to reference it in that project and compile, but causes havoc in the Book project, because now there's a conflick between the one define in Infrastructure and the one defined in the Web project's web service. This is behavior I would expect. So, to try and sum up a bit. Web project has a web service that process data from a third-party service and has a class and interface defined in it. The class implements the interface. The Infrastructure project references the web service in the Web Project and the Book project references the Infrastructure project. The implmentation of the interface in the class does NOT serialize down, so the auto-genned code in INfrastructure does not show this relationship, breaking code further down-stream. The Book project, whihc is further down-stream CAN see the interface as defined in the Web Project, even though its only reference is through the Infrastructure project; whihc CAN'T see it. Am I simple missing something easy here? Can I apply an attribute to either the Interface definition or to the its implmentation in the class to ensure its visibility downstream? Anything else I can do here? I know this is a bit convoluted and anyone still with me here, thanks for your patience and any advice you might have. Cheers, Steve

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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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  • Maximizing the number of threads to fully utilize all available resources without hindering overall

    - by Matt
    Let's say I have to generate a bunch of result files, and I want to make it as fast as possible. Each result file is generated independently of any other result file; in fact, one could say that each result file is agnostic to every other result file. The resources used to generate each result file is also unique to each. How can I dynamically decide the optimal number of threads to run simultaneously in order to minimize the overall run time? Is my only option to write my own thread manager that watches performance counters and adjust accordingly or does there exists some solid classes that already accomplish this?

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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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  • 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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  • 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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  • 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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  • [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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  • 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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  • Site images don't refresh after setting expired headers on .htaccess

    - by Miguel Hernandez
    I have a site that uses a CSS sprite for all the images. I set the .htaccess file to set the expired headers to a future time as they recommend to improve site performance. However, when I updated the sprite image none of my browsers on two different computers seem to fetch the new image. I deleted the .htaccess serveral times but no luck. I am sure this must be easy as pie to fix but right now I am out of options. Here is the code inside my .htaccess file: # CONFIGURE media caching # Header unset ETag FileETag None <FilesMatch "(?i)^.*\.(ico|flv|jpg|jpeg|png|gif|js|css)$"> Header unset Last-Modified Header set Expires "Fri, 21 Dec 2012 00:00:00 GMT" Header set Cache-Control "public, no-transform" </FilesMatch> <IfModule mod_deflate.c> <FilesMatch "\.(js|css)$"> SetOutputFilter DEFLATE </FilesMatch> </IfModule> 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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  • What is the difference between "LINQ to Entities", "LINQ to SQL" and "LINQ to Dataset".

    - by Marcel
    I've been working for quite a while now with LINQ. However, it remains a bit of a mystery what the real differences are between the mentioned flavours of LINQ. The successful answer will contain a short differentiation between them. What is the main goal of each flavor, what is the benefit, and is there a performance impact... P.S. I know that there are a lot of information sources out there, but I'm looking for a kind of a "cheat sheet" which instructs a newbie where to head for a specific goal.

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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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  • Append in Dom taking more time in IE than Firefox or any other browser.

    - by user307635
    Hi , I m working on .net framework 3.0 visual studio 08 and Testing it in IE8 and other browsers. Whenever I m inserting new elements in DOM (ex. 300 divs at one time) than I m getting the performance very slow in IE . Why?. If its a javascript debugging which is taking time or what else. Is it really true that IE Dom Append takes much time than any other browser. Please help me , I m stuck badly.

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  • Is is better to store serialized data or raw html in mysql?

    - by Yegor
    I de-normalized my database, since the application was crawling otherwise, and Im storing a list of categories for each item in the DB as a raw html version, and simply echoing it out in my design. Each category is actually a link, which is include a tag. Naturally, this is abit of a pain, especially if I want to change the look of how the category links are displayed, since I gotta update all the old cached entries. What if I were to store this data as a serialized array instead, and simply unserialize it, and then apply formatting to it in php. Would there be a significant performance decrease over simply echoing out the raw html?

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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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  • 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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  • Using Rails and Rspec, how do you test that the database is not touched by a method

    - by Will Tomlins
    So I'm writing a test for a method which for performance reasons should achieve what it needs to achieve without using SQL queries. I'm thinking all I need to know is what to stub: describe SomeModel do describe 'a_getter_method' do it 'should not touch the database' do thing = SomeModel.create something_inside_rails.should_not_receive(:a_method_querying_the_database) thing.a_getter_method end end end EDIT: to provide a more specific example: class Publication << ActiveRecord::Base end class Book << Publication end class Magazine << Publication end class Student << ActiveRecord::Base has_many :publications def publications_of_type(type) #this is the method I am trying to test. #The test should show that when I do the following, the database is queried. self.publications.find_all_by_type(type) end end describe Student do describe "publications_of_type" do it 'should not touch the database' do Student.create() student = Student.first(:include => :publications) #the publications relationship is already loaded, so no need to touch the DB lambda { student.publications_of_type(:magazine) }.should_not touch_the_database end end end So the test should fail in this example, because the rails 'find_all_by' method relies on SQL.

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  • What messaging technologies in windows-ce for guaranteed msg delivery?

    - by Aidanapword
    We are building a windows-ce (6.0R3) based device that requires guaranteed and audit-ready message delivery (including store & forward) up to and down from the cloud. I have been looking for choices beyond: MSMQ a proprietary solution (what our prototype device is using) AMQP (I have not found any RabbitMQ clients for CE, by example) ... are there any others? We will be transporting sensitive data (who isn't?!?!) over a public network, and large scale options are required. Anything running on an embedded device will be performance sensitive too.

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  • Getting latest Subsonic builds

    - by Alex Yakunin
    I need the latest Subsonic build or build it by my own. Subsonic project web site shows the latest available version is Subsonic v3.0.0.3 released at July 15, 2009. Questions: Are there any later builds - e.g. maintained by community members? If so, how can I get the latest one? In worst case I'm ready to get the latest source code and try to build it by my own. Are there any instructions for this? Please note, that I'm not interested in almost 1 year old builds - I need a build based on the latest code for tests (LINQ, performance), ideally - compiled for .NET 4.0.

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