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• very large string in memory

  - by bushman

  Hi, I am writing a program for formatting 100s of MB String data (nearing a gig) into xml == And I am required to return it as a response to an HTTP (GET) request . I am using a StringWriter/XmlWriter to build an XML of the records in a loop and returning the stringWriter.ToString() during testing I saw a few --out of memory exceptions-- and quite clueless on how to find a solution? do you guys have any suggestions for a memory optimized delivery of the response? is there a memory efficient way of encoding the data? or maybe chunking the data -- I just can not think of how to return it without building the whole thing into one HUGE string object thanks

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• PHP Special Characters Test

  - by pws5068

  What's an efficient way of checking if a username contains a number of special characters that I define. Examples: % # ^ . ! @ & ( ) + / " ? ` ~ < { } [ ] | = - ; I need to detect them and return a boolean, not just strip them out. Probably a super easy question but I need a better way of doing this than a huge list of conditionals or a sloppy loop.

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• Optimization of running total calculation in SQL for multiple values per join condition

  - by Kiril

  I have the following table (test_table): date value --------------- d1 10.0 d1 20.0 d2 60.0 d2 10.0 d2 -20.0 d3 40.0 I calculate the running total as follows. I use the same query twice, because first I need to calculate the values for a specifi date, and afterwards I can calculate the running total. Otherwise, joining the two tables where date is not unique, I would get too many results from the join: SELECT t1.date, SUM(t2.value) AS total FROM (SELECT date, SUM(value) AS value FROM test_table GROUP BY date) AS t1 JOIN (SELECT date, SUM(value) AS value FROM test_table GROUP BY date) AS t2 ON t1.date >= t2.date GROUP BY t1.date ORDER BY t1.date This gives me (which is fine): date total ------------- d1 30.0 d2 80.0 d3 120.0 BUT, this query isn't very efficient, because I need to change conditions in two places, if necessary. In production, the test_table is a lot bigger ( 4 Mio. rows), and the query takes too much time to complete. Question: How can I avoid using the same query twice?

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• Setting Sql server security rights for multiple situations

  - by DanDan

  We have an application which uses an instance of Sql Server locally for its backend storage. The administrator windows login has had its sysadmin right revoked, and instead two sql logins have been created; one for the application with a secret password and one read only login we let users view the raw data with. This was working fine until we moved on FileStreams, which requires intergrated windows authentication. So now the sql server logins must be replaced. As a result, I am now reviewing all of our logins but I am not sure how it is possible. It seems that the application needs full read/write access, yet I still need to lock down writing to the tables so the user cannot login into the database and delete data randomly. Does anyone have any tips for setting multiple levels of security using intergrated windows logins, or can you direct me to any further reading? Some answers can also be found on serverfault: http://serverfault.com/questions/138763/setting-sql-server-security-rights-for-multiple-situations

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• image archive VS image strip

  - by DevA

  Hi, i've noticed that plenty of games / applications (very common on mobile builds) pack numerous images into an image strip. I figured that the advantages in this are making the program more tidy (file system - wise) and reducing (un)installation time. During the runtime of the application, the entire image strip is allocated and copied from FS to RAM. On the contrary, images can be stored in an image archive and unpacked during runtime to a number of image structures in RAM. The way I see it, the image strip approach is less efficient because of worse caching performance and because that even if the optimal rectangle packing algorithm is used, there will be empty spaces between the stored images in the strip, causing a waste of RAM. What are the advantages in using an image strip over using an image archive file?

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• How to rotate an SSE/AVX vector

  - by user1584773

  I need to perform a rotate operation with as little clock cycle as possible. In the first case let's assume __m128i as source and dest type source: || A0 || A1 || A2 || A3 || dest : || A1 || A2 || A3 || A0 || dest = (__m128i)_mm_shuffle_epi32((__m128i)source, _MM_SHUFFLE(0,3,2,1)); Now I want to do the same whit AVX intrinsics So let's assume this time __m256i as source and dest type source: || A0 || A1 || A2 || A3 || A4 || A5 || A6 || A7 || dest : || A1 || A2 || A3 || A4 || A5 || A6 || A7 || A0 || The Avx intrinsics is missing most of the corresponding SSE integer operations. Maybe there is some way go get the desider output working with the floating point version. I've tryed with: dest = (__m256i)_mm256_shuffle_ps((__m256)source, (__m256)source, _MM_SHUFFLE(0,3,2,1)); but what I get is: || A0 || A2 || A3 || A4 || A5 || A6 || A7 || A1 || Any Idea on how to solve this in an efficient way? (without mixing SSE and AVX operation and without "manually" inverting A0 and A1 Thanks in advance!

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• Trying to speed up a SQLITE UNION QUERY

  - by user142683

  I have the below SQLITE code SELECT x.t, CASE WHEN S.Status='A' AND M.Nomorebets=0 THEN S.PriceText ELSE '-' END AS Show_Price FROM sb_Market M LEFT OUTER JOIN (select 2010 t union select 2020 t union select 2030 t union select 2040 t union select 2050 t union select 2060 t union select 2070 t ) as x LEFT OUTER JOIN sb_Selection S ON S.MeetingId=M.MeetingId AND S.EventId=M.EventId AND S.MarketId=M.MarketId AND x.t=S.team WHERE M.meetingid=8051 AND M.eventid=3 AND M.Name='Correct Score' With the current interface restrictions, I have to use the above code to ensure that if one selection is missing, that a '-' appears. Some feed would be something like the following SelectionId Name Team Status PriceText =================================== 1 Barney 2010 A 10 2 Jim 2020 A 5 3 Matt 2030 A 6 4 John 2040 A 8 5 Paul 2050 A 15/2 6 Frank 2060 S 10/11 7 Tom 2070 A 15 Is using the above SQL code the quickest & efficient?? Please advise of anything that could help. Messages with updates would be preferable.

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• Instantiating a context in LINQ to Entities

  - by Jagd

  I've seen two different manners that programmers approach when creating an entity context in their code. The first is like such, and you can find it all over the MSDN code examples: public void DoSomething() { using TaxableEducationEntities context = new TaxableEducationEntities()) { // business logic and whatever else } } The second is to create the context as a private attribute in some class that encapsulates your business logic. So you would have something like: public class Education_LINQ { private TaxableEducationEntities context = new TaxableEducationEntities(); public void DoSomething() { var result = from a in context.luAction select a; // business logic and whatever else } } Which way is more efficient? Assume that you have two methods, one called DoSomething1() and another called DoSomething2(), and both methods incorporate the using statement to open the context and do whatever with it. Were you to call one method after the other, would there be any superfluous overhead going on, since essentially both methods create the context and then clean it up when they're done? As opposed to having just one private attribute that is created when a class object is instantiated, and then in turn cleaned up when the object goes out of scope?

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• OpenLayers, Layers: Tiled vs. single tile

  - by Chau

  Each time we add a new layer to our OpenLayers based website (data provided primarily by a GeoServer server), we discuss whether to use a single-tile or a tiled approach. Some of the parameters we evaluate are the following: Using the tiled approach we get: Slow but continuous buildup of the viewport Lots of small images Client side caching possibilities Blocking of the loading pipeline (6 requests at a time) Jerky feeling when navigating during load Using the single-tile approach we get: Smoother feeling when navigating during load Time delay before layer is loaded One large image for each layer No caching of the single tile We have a lot of data editing in the layers, thus a tile-cache might not be that efficient. Are there any best-practices when it comes to tiling? Progressing towards infinitely fast hardware and unlimited data connections, the discussion becomes irrelevant, but what configuration do you percieve as the most user-pleasing?

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• Ruby on Rails: Model.all.each vs find_by_sql("SELECT * FROM model").each ?

  - by B_

  I'm fairly new to RoR. In my controller, I'm iterating over every tuple in the database. For every table, for every column I used to call SomeOtherModel.find_by_sql("SELECT column FROM model").each {|x| #etc } which worked fine enough. When I later changed this to Model.all(:select => "column").each {|x| #etc } the loop starts out at roughly the same speed but quickly slows down to something like 100 times slower than the the find_by_sql command. These calls should be identical so I really don't know what's happening. I know these calls are not the most efficient but this is just an intermediate step and I will optimize it more once this works correctly. Thanks!

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• Tilecache standalone server with nginx in production environment

  - by farhan khan

  Hi, I am really new to tilecache. I would like to know how good is the tilecache http server that comes with the tilecache installation. Is it practical to deploy it behind nginx in production environment? (i.e. nohup tilecache_http_server.py -p 8000 & and then editting the nginx.conf). The VPS we are using has nginx installed already so I thought that would be the easiest for me. However, how practical/efficient is it?

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• Web Services: more frequent "small" calls, or less frequent "big" calls

  - by Klay

  In general, is it better to have a web application make lots of calls to a web service getting smaller chunks of data back, or to have the web app make fewer calls and get larger chunks of data? In particular, I'm building a Silverlight app that needs to get large amounts of data back from the server in response to a query created by a user. Each query could return anywhere from a few hundred records to a few thousand. Each record has around thirty fields of mostly decimal-type data. I've run into the situation before where the payload size of the response exceeded the maximum allowed by the service. I'm wondering whether it's better (more efficient for the server/client/web service) to cut this payload vertically--getting all values for a single field with each call--or horizontally--getting batches of complete records with each call. Or does it matter?

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• Jquery Accordion and Fading

  - by Slick Willis

  I am trying to create a jquery accordion that fades the header of the accordion out when the page is loaded then fades it in when the mouse hovers. The accordion also opens when the mouse hovers. I am able to get all of this working, the problem I am having is when the accordion opens the header moves away and the mouse is no longer on it to keep it lit. I would like the links to keep the header lit as well as if the mouse is on the header itself. Below is the code that I wrote for it. <html> <head <script type='text/javascript' src='http://accidentalwords.squarespace.com/storage/jquery/jquery-1.4.2.min.js'></script> <script type='text/javascript' src='http://accidentalwords.squarespace.com/storage/jquery/jquery-custom-181/jquery-ui-1.8.1.custom.min.js'></script> </head> <body bgcolor="black"> <style = "css/text"> .links { font-family: "Georgia", "Verdana", serif; line-height: 30px; margin-left: 20px; margin-top: 5px; } .Title { font-family: "Geneva", "Verdana", serif; font-weight: bold; font-size: 2em; text-align: left; font-variant: small-caps; border-bottom: solid 2px #25FF00; padding-bottom:5px; margin-bottom: 10px; } </style> <script type="text/javascript"> $(document).ready(function(){ $(".Title").fadeTo(1,0.25); $(".Title").hover(function () { $(this).stop().fadeTo(250,1) .closest(".Title").find(".links").fadeTo(250,0.75); }, function() { $(this).stop().fadeTo(250,0.25); }); }); $(function() { $("#accordion").accordion({ event: "mouseover" }); }); </script> <p>&nbsp</p> <div id="accordion"> <div class="Title"><a href="#"STYLE="TEXT-DECORATION: NONE; color: #25FF00;">Reference</a></div> <div class="links"> <a href="http://docs.jquery.com/Main_Page" STYLE="TEXT-DECORATION: NONE; color: #25FF00;">Jquery Documentation/Help</a><br> <a href="http://stackoverflow.com/" STYLE="TEXT-DECORATION: NONE; color: #25FF00;">Stack Overflow</a><br> <a href="http://www.w3schools.com/" STYLE="TEXT-DECORATION: NONE; color: #25FF00;">w3schools.com</a><br> </div> <div class="Title"><a href="#"STYLE="TEXT-DECORATION: NONE; color: #FF7200;">Gaming</a></div> <div class="links"> <a href="http://docs.jquery.com/Main_Page" STYLE="TEXT-DECORATION: NONE; color: #FF7200;">Jquery Documentation/Help</a><br> <a href="http://stackoverflow.com/" STYLE="TEXT-DECORATION: NONE; color: #FF7200;">Stack Overflow</a><br> <a href="http://www.w3schools.com/" STYLE="TEXT-DECORATION: NONE; color: #FF7200;">w3schools.com</a><br></div> <div class="Title"><a href="#"STYLE="TEXT-DECORATION: NONE; color: #00DEFF;">Grub</a></div> <div class="links"> <a href="http://docs.jquery.com/Main_Page" STYLE="TEXT-DECORATION: NONE; color: #00DEFF;">Jquery Documentation/Help</a><br> <a href="http://stackoverflow.com/" STYLE="TEXT-DECORATION: NONE; color: #00DEFF;">Stack Overflow</a><br> <a href="http://www.w3schools.com/" STYLE="TEXT-DECORATION: NONE; color: #00DEFF;">w3schools.com</a><br> </div> <div class="Title"><a href="#"STYLE="TEXT-DECORATION: NONE; color: #F8FF00;">Drinks</a></div> <div class="links"> <a href="http://docs.jquery.com/Main_Page" STYLE="TEXT-DECORATION: NONE; color: #F9FF00;">Jquery Documentation/Help</a><br> <a href="http://stackoverflow.com/" STYLE="TEXT-DECORATION: NONE; color: #F8FF00;">Stack Overflow</a><br> <a href="http://www.w3schools.com/" STYLE="TEXT-DECORATION: NONE; color: #F8FF00;">w3schools.com</a><br> </div> </div> </body> </html>

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• Raspberry Pi cluster, neuron networks and brain simulation

  - by jokoon

  Since the RBPI (Raspberry Pi) has very low power consumption and very low production price, it means one could build a very big cluster with those. I'm not sure, but a cluster of 100000 RBPI would take little power and little room. Now I think it might not be as powerful as existing supercomputers in terms of FLOPS or others sorts of computing measurements, but could it allow better neuronal network simulation ? I'm not sure if saying "1 CPU = 1 neuron" is a reasonable statement, but it seems valid enough. So does it mean such a cluster would more efficient for neuronal network simulation, since it's far more parallel than other classical clusters ?

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• effective retrieve for a voting system in PHP and MySQL

  - by Adnan

  Hello, I have a system where registered users can vote up/vote down comment for a picture. Something very similar to SO's voting system. I store the votes in a table with values as such; vote_id | vote_comment_id | vote_user_id | vote_date | vote_type Now I have few a question concerned the speed and efficiency for the following; PROB: Once a user opens the picture page with comments I need, if that user has already voted UP/DOWN a comment to show it like; "you voted up" or "you voted down" next to the comment (in SO it the vote image is highlighted) MY POSSIBLE SOL: Right now when I open a picture page for each comment I loop thru, I loop thru my table of votes as well and check if a user has voted and show the status (I compare the vote_user_id with the user's session). How efficient is this? Anyone have a better approach to tackle this kind of problem?

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• On-the-fly lossless image compression

  - by geschema

  I have an embedded application where an image scanner sends out a stream of 16-bit pixels that are later assembled to a grayscale image. As I need to both save this data locally and forward it to a network interface, I'd like to compress the data stream to reduce the required storage space and network bandwidth. Is there a simple algorithm that I can use to losslessly compress the pixel data? I first thought of computing the difference between two consecutive pixels and then encoding this difference with a Huffman code. Unfortunately, the pixels are unsigned 16-bit quantities so the difference can be anywhere in the range -65535 .. +65535 which leads to potentially huge codeword lengths. If a few really long codewords occur in a row, I'll run into buffer overflow problems.

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• AJAX, PHP, XML, and cascading drop-down lists

  - by Dave Jarvis

  What PHP libraries would you recommend to implement the following: Three dependent drop-down lists Three XML data sources AJAX-based Essentially, I'd like to create an XML database and wire up a form that allows the user to select three different dependent parameters: User clicks Region User clicks District (filtered by Region) User clicks Station (filtered by District) Even though I would like to use PHP and XML, the general problem is: One XHTML form Three dependent, cascading drop-down lists Three flat files (no relational database) for the list data The solution must be efficient, simple, reliable, and cross-browser. What technologies would you recommend to solve the problem? Thank you!

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• Huge dataset point in polygon in .net (collision detection)

  - by Rickard Liljeberg

  I have a pretty big mesh with polygons, usually triangles but sometimes rectangles. Each point in my mesh has a value (value has nothing to do with coordinates). Now I am creating a second mesh in the same coordinate-space as the old mesh. I now want to interpolate out values for all points (vertices) in the new mesh using the values from the old mesh. Now I could loop each polygon in the new mesh and detect which old vertices are in each polygon by making 2d collision detection (altho even this I don't get to function properly so if anyone has simple and fast code for 2d collision detection (triangle is enough) I would gladly see it). However to my main point again. looping each old vertice for each new polygon seems less than efficient. is there a better way?

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• Multilangual Unicode rendering in opengl

  - by sum1stolemyname

  Hi Folks, I have to extend an OpenGL-Rendering System to support international characters (especially Hebrew, Arabic and cyrillic). Development Platform is Windows(XP|Vista|7), Alas using Embercardero Delphi 2010. I currently use wglOutLineFont(...) to build my font's display list and glCallLists(length(m_Text), UNSIGNED_SHORT, PWchar(m_Text) ) to render my strings. While this is feasable for Latin-1 Characters, building the full unicode character set in advanced is pretty time-consuming (about 8.5 minutes on my machine), so i am looking for a more efficient solution. I thought about limiting the range from u+0020 - u+077f (latin, greek, cyrillic, arbaic and hebrew) to include just the glyphs i need, but that would just be a solution for my current needs, and will become insufficent once other encoding is needed. On the upside, i do not have to worry about left-to right or right-to left direction as our application can handle this already. I would expect this to be a well-known problem, so i would like to ask if there is any reference material on this on the web, or if you could share some insight on this?

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• Best practice? iphone: sync data

  - by Andy Jacobs

  So i'm working on a project where there is data visualization. My ultimate goal is that i have a set of data shipped with the download of the iphone app. But i want it connected to a backend, that if the iphone has a connection with the internet. it can sync the changes from the backend. The syncing is no problem or the connection between the backend & the iphone. But what should i use as data storage on my iphone? what is the best way. my data is purely text and doesn't have to be secure. But it's main feature should be updating certain parts of data ( adding and deleting are not so important ) so what is the easiest (read: least time consuming development ) or the best way? sqlite? plist? ..?

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• McAfee Virus Scan and Oracle RAC

  - by Lee Gathercole

  Hi, We're experiencing a strange problem with Oracle RAC and McAfee anti-virus. As part of the installation of the Oracle RAC we disable anti virus as directed. We have had our RAC running fine, but when we came to re-enable the AV and reboot we got the BSOD. Abnormal Program Termination (BugCheck, STOP: 0x00000035 (0x8E984678, 0x00000000, 0x00000000, 0x00000000 NO_MORE_IRP_STACK_LOCATIONS Following the standard process of raising this problem with Microsoft they identify the problem and also a fix. Microsoft talk about too many file filter drivers being present and pushing the DFS upper limit beyond the default size. Upping this value, as per msdn, has no impact. We're able to recover from this BSOD by disabling AV. We don't have the problem if we run the AV service manually whilst the system is up. However, if we make the service automatic we fail to boot. Tech Details 2 Node Oracle 10g Cluster 2 * Windows 2003 SP2, 16GB RAM, Quad Core 3ghz Processor SAN attached storage McAfee VirusScan Enterprise 8.5.0i, Scan Engine (5300.2777), DAT Version (5536.0000) Thanks Lee

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• Must have JavaScript pro developer tools, libs, utilities and workshop configuration.

  - by WooYek

  This is a followup question to the Pro JavaScript programmer interview questions (with answers). What is considered professional and industrial standard for a professional browser side Java Script developer when it comes to his workshop configuration, and maybe from-concept-to-shipment process? What are the most popular IDE's, utilities and probably libraries, not limited to the free ones. These that can help cut development time (eg. IDE), help with achieve better quality (eg. unit testing tools), reliability and maintainability. I'm looking for a baseline to which I could compare potential candidates based on their ability to keep their tools sharp and workshop efficient (pro's should invest time&money in good tools, right?).

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• Django, making a page activate for a fixed time

  - by Hellnar

  Greetings I am hacking Django and trying to test something such as: Like woot.com , I want to sell "an item per day", so only one item will be available for that day (say the default www.mysite.com will be redirected to that item), Assume my urls for calling these items will be such: www.mysite.com/item/<number> my model for item: class Item(models.Model): item_name = models.CharField(max_length=30) price = models.FloatField() content = models.TextField() #keeps all the html content start_time = models.DateTimeField() end_time = models.DateTimeField() And my view for rendering this: def results(request, item_id): item = get_object_or_404(Item, pk=item_id) now = datetime.now() if item.start_time > now: #render and return some "not started yet" error templete elif item.end_time < now: #render and return some "item selling ended" error templete else: # render the real templete for selling this item What would be the efficient and clever model & templete for achieving this ?

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• Discrete and Continuous Classifier on Sparse Data

  - by Chris S

  I'm trying to classify an example, which contains discrete and continuous features. Also, the example represents sparse data, so even though the system may have been trained on 100 features, the example may only have 12. What would be the best classifier algorithm to use to accomplish this? I've been looking at Bayes, Maxent, Decision Tree, and KNN, but I'm not sure any fit the bill exactly. The biggest sticking point I've found is that most implementations don't support sparse data sets and both discrete and continuous features. Can anyone recommend an algorithm and implementation (preferably in Python) that fits these criteria? Libraries I've looked at so far include: Orange (Mostly academic. Implementations not terribly efficient or practical.) NLTK (Also academic, although has a good Maxent implementation, but doesn't handle continuous features.) Weka (Still researching this. Seems to support a broad range of algorithms, but has poor documentation, so it's unclear what each implementation supports.)

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• Technology stack for very frequent gps data collection

  - by gvaswani

  I am working on a project that involves gps data collection from many users (say 1000) every second (while they move). I am planning on using a dedicated database instance on EC2 with the mysql persistent block storage and run a ruby on rails application with nginx frontend. I haven't worked on such data collection application before. Am I missing something here? I will have a another instance which will act as application server and use the data from the same EBS. If anybody has dealt with such a system before, Any advise would be much appreciated?

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