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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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• What is the "task" in twitter Storm parallelism

  - by John Wang

  I'm trying to learn twitter storm by following the great article "Understanding the parallelism of a Storm topology" However I'm a bit confused by the concept of "task". Is a task an running instance of the component(spout or bolt) ? A executor having multiple tasks actually is saying the same component is executed for multiple times by the executor, am I correct ? Moreover in a general parallelism sense, Storm will spawn a dedicated thread(executor) for a spout or bolt, but what is contributed to the parallelism by an executor(thread) having multiple tasks ? I think having multiple tasks in a thread, since a thread executes sequentially, only make the thread a kind of "cached" resource, which avoids spawning new thread for next task run. Am I correct? I may clear those confusion by myself after taking more time to investigate, but you know, we both love stackoverflow ;-) Thanks in advance.

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• In which order are CSS styles applied?

  - by citronas

  I have the following HTML. <ul> <li> <a>asdas</a> </li> </ul> In my CSS stylesheet I have general settings for the a tag, and several hundered lines later settings for ul li a. Like this: a:link { color: red; } ... ul li a { color:blue; } Firebug tells me, that first the color:blue is loaded, and afterwards overriden by color:red So far I've always thought, that the order of loading css files and the order of style inside a single css file tell the browser how html elements should be formatted. Unfortunately I'm now experiencing it vice versa. So tell me, how must I correct my style to achieve the a tag inside the li to be rendered blue and not red?

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• Why does Java not have any destructor like C++?

  - by Abhishek Jain

  Java has its own garbage collection implementation so it does not require any destructor like C++ . This makes Java developer lazy in implementing memory management. And Garbage Collection is very expensive. Still we can have destructor along with garbage collector where developer can free resources and which can save garbage collector's work. This might improves the performance of application. Why does Java not provide any destructor kind of mechanism? Developer does not have control over GC but he/she can control or create object. Then why not give them ability to destruct the objects?

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• ASP.NET MVC 2: Deserialize SPROC Response

  - by dcolumbus

  I need to ask a general question. I don't have the code in front of me because I'm writing this on my iPhone. I have a Class that represents a certain XML schema. I have a SPROC that returns this XML. What I need to do is deserialize the XML to this Class. XML: <xml> <person> <firstName>Bob</firstName> <lastName>Robby</lastName> </person> </xml> I need to deserialize this XML into the custom Person Class so I can loop through this Model and spit it out in the View. I'm sure there's some kind of casting involved, I just don't know how to do it.

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• Best way to deal with multiple layouts in symfony

  - by Pierre

  Hey folks. I'm looking for the best way to do something simple in symfony. Basically, I have a module in which all the pages will contain the same header and footer. That module also shares the same general layout as the other modules. I'm just wondering, should I create one file and have my content pages called up as partials or should all files have their own content and somehow call the two other templates. I made a quick example of my setup: http://grab.by/3Riy Hopefully, it'll help understand what I'm trying to do. Thanks!

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• Database: relational/not relational/object oriented... What to choose?

  - by Damian

  I'm porting a website that I made for app engine to run on a dedicated server. It is coded in java and I'm looking for a database to replace google datastore. My first thougt was MySql because everybody uses it, but i dont like SQL and I think I would feel more comfortable using OODB or anything else. With google datastore I could modify my models and don't worry about the database definition at all. I know using MySql that isn't possible. And I don't want to miss that. And if I use a OODB, which should I use? What about performance compared to MySql? Well, any idea or tip will really help me since I know nothing about databases.

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• Java NullPointerException when traversing a non-null recordset

  - by Tim

  Hello again - I am running a query on Sybase ASE that produces a ResultSet that I then traverse and write the contents out to a file. Sometimes, this will throw a NullPointerException, stating that the ResultSet is null. However, it will do this after printing out one or two records. Other times, with the same exact input, I will receive no errors. I have been unable to consistently produce this error. The error message is pointing to a line: output.print(rs.getString(1)); It appears to happen when the query takes a little longer to run, for some reason. The recordset returns thus far have been very small (4 to 7 records). Sometimes I'll have to run the app 3 or 4 times, then the errors will just stop, as though the query was getting "warmed up". I've run the query manually and there doesn't appear to be any performance problems. Thanks again!

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• What is the best way to convert a hexidecimal string to a byte array (.NET)?

  - by Robert Wagner

  I have a hexidecimal string that I need to convert to a byte array. The best way (ie efficient and least code) is: string hexstr = "683A2134"; byte[] bytes = new byte[hexstr.Length/2]; for(int x = 0; x < bytes.Length; x++) { bytes[x] = Convert.ToByte(hexstr.Substring(x * 2, 2), 16); } In the case where I have a 32bit value I can do the following: string hexstr = "683A2134"; byte[] bytes = BitConverter.GetBytes(Convert.ToInt32(hexstr, 16)); However what about in the general case? Is there a better built in function, or a clearer (doesn't have to be faster, but still performant) way of doing this? I would prefer a built in function as there seems to be one for everything (well common things) except this particular conversion.

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• Lock HTML select element, allow value to be sent on submit

  - by ILMV

  I have a select box (for a customer field) on a complex order form, when the user starts to add lines to the order they should not be allowed to change the customer select box (unless all lines are deleted). My immediate thought was that I could use the disabled attribute, but when the box is disabled the selected value is no longer passed to the target. When the problem arose a while ago one of the other developers worked around this by looping through all the options and disabling all but the selected option, and sure enough the value was passed to the target and we've been using since. But now I'm looking for a proper solution, I don't want to loop through all the options because are data is expanding and it's starting to introduce performance issues. I'd prefer not to enable this / all the elements when the submit button is hit. How can I lock the input, whilst maintaining the selected option and passing that value to the target script? I would prefer a non-JavaScript solution if possible, but if needed we are running jQuery 1.4.2 so that could be used.

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• Fastest way of converting a quad to a triangle strip?

  - by Tina Brooks

  What is the fastest way of converting a quadrilateral (made up of foyr x,y points) to a triangle strip? I'm well aware of the general triangulation algorithms that exist, but I need a short, well optimized algorithm that deals with quadrilaterals only. My current algorithm does this, which works for most quads but still gets the points mixed up for some: #define fp(f) bounds.p##f /* Sort four points in ascending order by their Y values */ point_sort4_y(&fp(1), &fp(2), &fp(3), &fp(4)); /* Bottom two */ if (fminf(-fp(1).x, -fp(2).x) == -fp(2).x) { out_quad.p1 = fp(2); out_quad.p2 = fp(1); } else { out_quad.p1 = fp(1); out_quad.p2 = fp(2); } /* Top two */ if (fminf(-fp(3).x, -fp(4).x) == -fp(3).x) { out_quad.p3 = fp(3); out_quad.p4 = fp(4); } else { out_quad.p3 = fp(4); out_quad.p4 = fp(3); }

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• Javscript filter vs map problem

  - by graham.reeds

  As a continuation of my min/max across an array of objects I was wondering about the performance comparisons of filter vs map. So I put together a test on the values in my code as was going to look at the results in FireBug. This is the code: var _vec = this.vec; min_x = Math.min.apply(Math, _vec.filter(function(el){ return el["x"]; })); min_y = Math.min.apply(Math, _vec.map(function(el){ return el["x"]; })); The mapped version returns the correct result. However the filtered version returns NaN. Breaking it out, stepping through and finally inspecting the results, it would appear that the inner function returns the x property of _vec but the actual array returned from filter is the unfiltered _vec. I believe my usage of filter is correct - can anyone else see my problem?

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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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• Java 2D clip area to shape

  - by user2923880

  I'm quite new to graphics in java and I'm trying to create a shape that clips to the bottom of another shape. Here is an example of what I'm trying to achieve: Where the white line at the base of the shape is the sort of clipped within the round edges. The current way I am doing this is like so: g2.setColor(gray); Shape shape = getShape(); //round rectangle g2.fill(shape); Rectangle rect = new Rectangle(shape.getBounds().x, shape.getBounds().y, width, height - 3); Area area = new Area(shape); area.subtract(new Area(rect)); g2.setColor(white); g2.fill(area); I'm still experimenting with the clip methods but I can't seem to get it right. Is this current method ok (performance wise, since the component repaints quite often) or is there a more efficient way? Thanks in advance.

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• How do I temporarily monkey with a global module constant?

  - by Daniel

  Greetings, I want to tinker with the global memcache object, and I found the following problems. Cache is a constant Cache is a module I only want to modify the behavior of Cache globally for a small section of code for a possible major performance gain. Since Cache is a module, I can't re-assign it, or encapsulate it. I Would Like To Do This: Deep in a controller method... code code code... old_cache = Cache Cache = MyCache.new code code code... Cache = old_cache code code code... However, since Cache is a constant I'm forbidden to change it. Threading is not an issue at the moment. :) Would it be "good manners" for me to just alias_method the special code I need just for a small section of code and then later unalias it again? That doesn't pass the smell test IMHO. Does anyone have any ideas? TIA, -daniel

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• make: invoke command for multiple targets of multiple files?

  - by marvin2k

  Hi, I looking to optimize an existing Makefile. It's used to create multiple plots (using Octave) for every logfile in a given directory using an scriptfile for every plot which takes a logfilename as an argument. In the Moment, I use one single rule for every kind of plot available, with a handwritten call to Octave, giving the specific scriptfile/logfile as an argument. It would be nice, if every plot has "his" octave-script as a dependency (plus the logfile, of course), so only one plot is regenerated if his script is changed. Since I don't want to type that much, I wonder how I can simplifiy this by using only one general rule to build "a" plot? To make it clearer: Logfile: "$(LOGNAME).log" Scriptfile: "plot$(PLOTNAME).m" creates "$(LOGNAME)_$(PLOTNAME).png" The first thing I had in mind: %1_%2.png: %1.log $(OCTAVE) --eval "plot$<2('$<1')" But this seems not to be allowed. Could someone give me a hint?

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• Ajax foreign key filter in Django admin interface

  - by Googol

  http://blog.philippmetzler.com/?p=52 Just tried django-ajax-filtered-fields and like it very much. I’m looking for a solution for this problem: My model looks like this: class Song(models.Model): Album = models.ForeignKey(Album) class Artist(models.Model): album = models.ForeignKey(Album) song = models.ForeignKey(Song, blank=True, null=True) So the user has to define a topic. He can also define a subtopic but doesn’t have to. The subtopic belongs to a topic. In the admin interface I’d like to limit the choices for subtopic based upon what he selects in topics. That should change dynamically with AJAX. I will have a closer look to django-ajax-filtered-fields but didn’t find a solution to that specific problem. Perhaps it’s another usecase for django-ajax-filtered-fields in general? Or do you know another solution to my specific requirements?

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• Are there any layout comparison / vssetting sharing places?

  - by Wil

  Well, I reinstalled Visual Studio 2008 and did not have a backup of my vssetting file. I did not think it was that important as I had barely customised it, however it just doesn't feel right! The general windows feel correct but When I switch between views (source code, Windows forms, web editor), all the toolbars get muddled up. In the past few years, I have seen so many "post your desktop" type items and I could swear there there would be some "post your IDE", but after looking on Google and several other programming sites, I just can't find one! I don't want this turning in to a post your IDE unless others want to, but can anyone point me to a site where they have done this, or even better - are there any vssetting sharing places where you can download ones made by others?

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• How Do I See The Final Text Of A Query Resulting From A Call To mysqli->prepare?

  - by Joshua

  After code like this: $stmt = $mysqli->prepare("SELECT District FROM City WHERE Name=?")) { $stmt->bind_param("s", $city); $stmt->execute(); $stmt->bind_result($district); $stmt->fetch(); printf("%s is in district %s\n", $city, $district); How Do I See The Actual SQL Statement That Was Executed? (It Should Look Something Like "SELECT District FROM City WHERE Name='Simi Valley';") I already realize that in this simplistic case it would be very easy to simply reconstruct the query... but how can I access it in a general way that will work for very complicated prepared statements, and cases where I don't necessarily already understand the intended structure of the query, etc. Isn't there some function or method that can be called on the statement object that will return the actual text of the SQL query, after binding?

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• Templating Engine Pros and Cons with Zend Framework

  - by manyxcxi

  I am getting familiar with Zend Framework (and MVC with PHP in general) for a personal project. I have previous experience with Smarty and have no major gripes with it, but I would like to use this project as a good in-depth learning exercise. Those of you familiar with different templating engines and ZF: Do you believe there are better templating engines than Smarty in conjunction with ZF and why? I would like to apply what I learn to the real world and production environments. The personal project will be fairly robust. User management, sessions, security, database interaction, form input, jQuery, etc.

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• Can a single solution hold projects from multiple repositories?

  - by cyclotis04

  I've begun setting up SVN repositories to store my code, and am wondering if a single Visual Studio solution can have projects from multiple repositories. I have a shared library with different helper functions, generic custom controls, etc, that are used by multiple projects, and hosted in its own repository. Then I have my project repository, which contains all of the program-specific code such as forms, etc. I know I could copy the shared library into the program's repository, then copy them back when I make changes, but I'd much rather keep them in different repositories so I can hit "Commit" and the general library commits to it's repository, and the program code commits to it. I'm currently using AnkhSVN, but if it's possible with other tools, I'll look into it. Preemptive clarification for all the "just use one repository" answers: The shared library is hosted in an online repository, viewable by anyone, but the program code is proprietary and resides on our office servers, so they need different repositories.

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• Avoid hourglass mouse cursor when calling a web-service?

  - by BigMoose

  I don't know if this is a general web-services issue or just my specific scenario, which is a WPF application with a DispatcherTimer calling a web-service method. Whenever the timer is called, the mouse cursor automatically changes to an hourglass cursor. The processing of the call is very short and happens every 3 seconds, so the user experience is that every 3 seconds the mouse filckers as an hourglass for a split-second and then goes back to the normal cursor representation. How can I avoid this inconvenience? Thanks.

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• Interpreters: How much simplification?

  - by Ray

  In my interpreter, code like the following x=(y+4)*z echo x parses and "optimizes" down to four single operations performed by the interpreter, pretty much assembly-like: add 4 to y multiply <last operation result> with z set x to <last operation result> echo x In modern interpreters (for example: CPython, Ruby, PHP), how simplified are the "opcodes" for which are in end-effect run by the interpreter? Could I achieve better performance when trying to keep the structures and commands for the interpreter more complex and high-level? That would be surely a lot harder, or?

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• xml and external swf documents

  - by VideoDnd

  My XML scripts work fine in the local swf. If I load an external swf, can I still retreive XML data from the same way, or do I have to declare the root somewhere? It's a general question. I know that when animating external swf files, you have to set it up differently, if so I would like an example, and a pitcher of beer. It's St. Patrick's weekend. SAMPLE CODE ONLY XML <?xml version="1.0" encoding="utf-8"?> <SESSION> <COUNT TITLE="starting position">-77777</COUNT> </SESSION> loader swf 'nodes' //grab the data as a string myString = myXML.COUNT.text(); //grab the data as an int count = int(myXML.COUNT.text()); external swf 'variables' var myString:String = ""; var count:int = int(myString); trace(count);

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• Assigning a view controller to be the delegate of a subview which is not directly descendent?

  - by ambertch

  I am writing an iphone app where in numerous cases a subview needs to talk to its superview. For example: View A has a table view that contains photos A has a subview B which allows users to add photos, upon which I want to auto append them to A's table view So far I have been creating a @protocol in B, and registering A as the delegate. The problem in my case is that B has a subview C that allows users to add content, and I want actions in C to invoke changes in its grandparent, A. Currently I am working around this by passing around a self pointer to my base view controller (C.delegate = B.delegate), but it doesn't seem very proper to me. Any thoughts? (and/or general advice on code organization when all sort of subviews needs to talk to superviews would be greatly appreciated) Thanks!

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