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• Skewed: a rotating camera in a simple CPU-based voxel raycaster/raytracer

  - by voxelizr

  TL;DR -- in my first simple software voxel raycaster, I cannot get camera rotations to work, seemingly correct matrices notwithstanding. The result is skewed: like a flat rendering, correctly rotated, however distorted and without depth. (While axis-aligned ie. unrotated, depth and parallax are as expected.) I'm trying to write a simple voxel raycaster as a learning exercise. This is purely CPU based for now until I figure out how things work exactly -- fow now, OpenGL is just (ab)used to blit the generated bitmap to the screen as often as possible. Now I have gotten to the point where a perspective-projection camera can move through the world and I can render (mostly, minus some artifacts that need investigation) perspective-correct 3-dimensional views of the "world", which is basically empty but contains a voxel cube of the Stanford Bunny. So I have a camera that I can move up and down, strafe left and right and "walk forward/backward" -- all axis-aligned so far, no camera rotations. Herein lies my problem. Screenshot #1: correct depth when the camera is still strictly axis-aligned, ie. un-rotated. Now I have for a few days been trying to get rotation to work. The basic logic and theory behind matrices and 3D rotations, in theory, is very clear to me. Yet I have only ever achieved a "2.5 rendering" when the camera rotates... fish-eyey, bit like in Google Streetview: even though I have a volumetric world representation, it seems --no matter what I try-- like I would first create a rendering from the "front view", then rotate that flat rendering according to camera rotation. Needless to say, I'm by now aware that rotating rays is not particularly necessary and error-prone. Still, in my most recent setup, with the most simplified raycast ray-position-and-direction algorithm possible, my rotation still produces the same fish-eyey flat-render-rotated style looks: Screenshot #2: camera "rotated to the right by 39 degrees" -- note how the blue-shaded left-hand side of the cube from screen #2 is not visible in this rotation, yet by now "it really should"! Now of course I'm aware of this: in a simple axis-aligned-no-rotation-setup like I had in the beginning, the ray simply traverses in small steps the positive z-direction, diverging to the left or right and top or bottom only depending on pixel position and projection matrix. As I "rotate the camera to the right or left" -- ie I rotate it around the Y-axis -- those very steps should be simply transformed by the proper rotation matrix, right? So for forward-traversal the Z-step gets a bit smaller the more the cam rotates, offset by an "increase" in the X-step. Yet for the pixel-position-based horizontal+vertical-divergence, increasing fractions of the x-step need to be "added" to the z-step. Somehow, none of my many matrices that I experimented with, nor my experiments with matrix-less hardcoded verbose sin/cos calculations really get this part right. Here's my basic per-ray pre-traversal algorithm -- syntax in Go, but take it as pseudocode: fx and fy: pixel positions x and y rayPos: vec3 for the ray starting position in world-space (calculated as below) rayDir: vec3 for the xyz-steps to be added to rayPos in each step during ray traversal rayStep: a temporary vec3 camPos: vec3 for the camera position in world space camRad: vec3 for camera rotation in radians pmat: typical perspective projection matrix The algorithm / pseudocode: // 1: rayPos is for now "this pixel, as a vector on the view plane in 3d, at The Origin" rayPos.X, rayPos.Y, rayPos.Z = ((fx / width) - 0.5), ((fy / height) - 0.5), 0 // 2: rotate around Y axis depending on cam rotation. No prob since view plane still at Origin 0,0,0 rayPos.MultMat(num.NewDmat4RotationY(camRad.Y)) // 3: a temp vec3. planeDist is -0.15 or some such -- fov-based dist of view plane from eye and also the non-normalized, "in axis-aligned world" traversal step size "forward into the screen" rayStep.X, rayStep.Y, rayStep.Z = 0, 0, planeDist // 4: rotate this too -- 0,zstep should become some meaningful xzstep,xzstep rayStep.MultMat(num.NewDmat4RotationY(CamRad.Y)) // set up direction vector from still-origin-based-ray-position-off-rotated-view-plane plus rotated-zstep-vector rayDir.X, rayDir.Y, rayDir.Z = -rayPos.X - me.rayStep.X, -rayPos.Y, rayPos.Z + rayStep.Z // perspective projection rayDir.Normalize() rayDir.MultMat(pmat) // before traversal, the ray starting position has to be transformed from origin-relative to campos-relative rayPos.Add(camPos) I'm skipping the traversal and sampling parts -- as per screens #1 through #3, those are "basically mostly correct" (though not pretty) -- when axis-aligned / unrotated.

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• Guessing Excel Data Types

  - by AjarnMark

  Note to Self HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Jet\4.0\Engines\Excel: TypeGuessRows = 0 means scan everything. Note to Others About 10 years ago I stumbled across this bit of information just when I needed it and it saved my project.  Then for some reason, a few years later when it would have been nice, but not critical, for some reason I could not find it again anywhere.  Well, now I have stumbled across it again, and to preserve my future self from nightmares and sudden baldness due to pulling my hair out, I have decided to blog it in the hopes that I can find it again this way. Here’s the story…  When you query data from an Excel spreadsheet, such as with old-fashioned DTS packages in SQL 2000 (my first reference) or simply with an OLEDB Data Adapter from ASP.NET (recent task) and if you are using the Microsoft Jet 4.0 driver (newer ones may deal with this differently) then you can get funny results where the query reports back that a cell value is null even when you know it contains data. What happens is that Excel doesn’t really have data types.  While you can format information in cells to appear like certain data types (e.g. Date, Time, Decimal, Text, etc.) that is not really defining the cell as being of a certain type like we think of when working with databases.  But, presumably, to make things more convenient for the user (programmer) when you issue a query against Excel, the query processor tries to guess what type of data is contained in each column and returns it in an appropriate manner.  This is all well and good IF your data is consistent in every row and matches what the processor guessed.  And, for efficiency’s sake, when the query processor is trying to figure out each column’s data type, it does so by analyzing only the first 8 rows of data (default setting). Now here’s the problem, suppose that your spreadsheet contains information about clothing, and one of the columns is Size.  Now suppose that in the first 8 rows, all of your sizes look like 32, 34, 18, 10, and so on, using numbers, but then, somewhere after the 8th row, you have some rows with sizes like S, M, L, XL.  What happens is that by examining only the first 8 rows, the query processor inferred that the column contained numerical data, and then when it hits the non-numerical data in later rows, it comes back blank.  Major bummer, and a real pain to track down if you don’t know that Excel is doing this, because you study the spreadsheet and say, “the data is RIGHT THERE!  WHY doesn’t the query see it?!?!”  And the hair-pulling begins. So, what’s a developer to do?  One option is to go to the registry setting noted above and change the DWORD value of TypeGuessRows from the default of 8 to 0 (zero).  Setting this value to zero will force Jet to scan every row in the spreadsheet before making its determination as to what type of data the column contains.  And that means that in the example above, it would have treated the column as a string rather than as numeric, and presto! your query now returns all of the values that you know are in there. Of course, there is a caveat… if you are querying large spreadsheets, making Jet scan every row can be quite a performance hit.  You could enter a different number (more than 8) that you believe is a better sampling of rows to make the guess, but you still have the possibility that every row scanned looks alike, but that later rows are different, and that you might get blanks when there really is data there.  That’s the type of gamble, I really don’t like to take with my data. Anyone with a better approach, or with experience with more recent drivers that have a better way of handling data types, please chime in!

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• What C++ coding standard do you use?

  - by gablin

  For some time now, I've been unable to settle on a coding standard and use it concistently between projects. When starting a new project, I tend to change some things around (add a space there, remove a space there, add a line break there, an extra indent there, change naming conventions, etc.). So I figured that I might provide a piece of sample code, in C++, and ask you to rewrite it to fit your standard of coding. Inspiration is always good, I say. ^^ So here goes: #ifndef _DERIVED_CLASS_H__ #define _DERIVED_CLASS_H__ /** * This is an example file used for sampling code layout. * * @author Firstname Surname */ #include <stdio> #include <string> #include <list> #include "BaseClass.h" #include "Stuff.h" /** * The DerivedClass is completely useless. It represents uselessness in all its * entirety. */ class DerivedClass : public BaseClass { //////////////////////////////////////////////////////////// // CONSTRUCTORS / DESTRUCTORS //////////////////////////////////////////////////////////// public: /** * Constructs a useless object with default settings. * * @param value * Is never used. * @throws Exception * If something goes awry. */ DerivedClass (const int value) : uselessSize_ (0) {} /** * Constructs a copy of a given useless object. * * @param object * Object to copy. * @throws OutOfMemoryException * If necessary data cannot be allocated. */ ItemList (const DerivedClass& object) {} /** * Destroys this useless object. */ ~ItemList (); //////////////////////////////////////////////////////////// // PUBLIC METHODS //////////////////////////////////////////////////////////// public: /** * Clones a given useless object. * * @param object * Object to copy. * @return This useless object. */ DerivedClass& operator= (const DerivedClass& object) { stuff_ = object.stuff_; uselessSize_ = object.uselessSize_; } /** * Does absolutely nothing. * * @param useless * Pointer to useless data. */ void doNothing (const int* useless) { if (useless == NULL) { return; } else { int womba = *useless; switch (womba) { case 0: cout << "This is output 0"; break; case 1: cout << "This is output 1"; break; case 2: cout << "This is output 2"; break; default: cout << "This is default output"; break; } } } /** * Does even less. */ void doEvenLess () { int mySecret = getSecret (); int gather = 0; for (int i = 0; i < mySecret; i++) { gather += 2; } } //////////////////////////////////////////////////////////// // PRIVATE METHODS //////////////////////////////////////////////////////////// private: /** * Gets the secret value of this useless object. * * @return A secret value. */ int getSecret () const { if ((RANDOM == 42) && (stuff_.size() > 0) || (1000000000000000000 > 0) && true) { return 420; } else if (RANDOM == -1) { return ((5 * 2) + (4 - 1)) / 2; } int timer = 100; bool stopThisMadness = false; while (!stopThisMadness) { do { timer--; } while (timer > 0); stopThisMadness = true; } } //////////////////////////////////////////////////////////// // FIELDS //////////////////////////////////////////////////////////// private: /** * Don't know what this is used for. */ static const int RANDOM = 42; /** * List of lists of stuff. */ std::list <Stuff> stuff_; /** * Specifies the size of this object's uselessness. */ size_t uselessSize_; }; #endif

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• Script to UPDATE STATISTICS with time window

  - by Bill Graziano

  I recently spent some time troubleshooting odd query plans and came to the conclusion that we needed better statistics.  We’ve been running sp_updatestats but apparently it wasn’t sampling enough of the table to get us what we needed.  I have a pretty limited window at night where I can hammer the disks while this runs.  The script below just calls UPDATE STATITICS on all tables that “need” updating.  It defines need as any table whose statistics are older than the number of days you specify (30 by default).  It also has a throttle so it breaks out of the loop after a set amount of time (60 minutes).  That means it won’t start processing a new table after this time but it might take longer than this to finish what it’s doing.  It always processes the oldest statistics first so it will eventually get to all of them.  It defaults to sample 25% of the table.  I’m not sure that’s a good default but it works for now.  I’ve tested this in SQL Server 2005 and SQL Server 2008.  I liked the way Michelle parameterized her re-index script and I took the same approach. CREATE PROCEDURE dbo.UpdateStatistics ( @timeLimit smallint = 60 ,@debug bit = 0 ,@executeSQL bit = 1 ,@samplePercent tinyint = 25 ,@printSQL bit = 1 ,@minDays tinyint = 30 )AS/******************************************************************* Copyright Bill Graziano 2010*******************************************************************/SET NOCOUNT ON;PRINT '[ ' + CAST(GETDATE() AS VARCHAR(100)) + ' ] ' + 'Launching...'IF OBJECT_ID('tempdb..#status') IS NOT NULL DROP TABLE #status;CREATE TABLE #status( databaseID INT , databaseName NVARCHAR(128) , objectID INT , page_count INT , schemaName NVARCHAR(128) Null , objectName NVARCHAR(128) Null , lastUpdateDate DATETIME , scanDate DATETIME CONSTRAINT PK_status_tmp PRIMARY KEY CLUSTERED(databaseID, objectID));DECLARE @SQL NVARCHAR(MAX);DECLARE @dbName nvarchar(128);DECLARE @databaseID INT;DECLARE @objectID INT;DECLARE @schemaName NVARCHAR(128);DECLARE @objectName NVARCHAR(128);DECLARE @lastUpdateDate DATETIME;DECLARE @startTime DATETIME;SELECT @startTime = GETDATE();DECLARE cDB CURSORREAD_ONLYFOR select [name] from master.sys.databases where database_id > 4OPEN cDBFETCH NEXT FROM cDB INTO @dbNameWHILE (@@fetch_status <> -1)BEGIN IF (@@fetch_status <> -2) BEGIN SELECT @SQL = ' use ' + QUOTENAME(@dbName) + ' select DB_ID() as databaseID , DB_NAME() as databaseName ,t.object_id ,sum(used_page_count) as page_count ,s.[name] as schemaName ,t.[name] AS objectName , COALESCE(d.stats_date, ''1900-01-01'') , GETDATE() as scanDate from sys.dm_db_partition_stats ps join sys.tables t on t.object_id = ps.object_id join sys.schemas s on s.schema_id = t.schema_id join ( SELECT object_id, MIN(stats_date) as stats_date FROM ( select object_id, stats_date(object_id, stats_id) as stats_date from sys.stats) as d GROUP BY object_id ) as d ON d.object_id = t.object_id where ps.row_count > 0 group by s.[name], t.[name], t.object_id, COALESCE(d.stats_date, ''1900-01-01'') ' SET ANSI_WARNINGS OFF; Insert #status EXEC ( @SQL); SET ANSI_WARNINGS ON; END FETCH NEXT FROM cDB INTO @dbNameENDCLOSE cDBDEALLOCATE cDBDECLARE cStats CURSORREAD_ONLYFOR SELECT databaseID , databaseName , objectID , schemaName , objectName , lastUpdateDate FROM #status WHERE DATEDIFF(dd, lastUpdateDate, GETDATE()) >= @minDays ORDER BY lastUpdateDate ASC, page_count desc, [objectName] ASC OPEN cStatsFETCH NEXT FROM cStats INTO @databaseID, @dbName, @objectID, @schemaName, @objectName, @lastUpdateDateWHILE (@@fetch_status <> -1)BEGIN IF (@@fetch_status <> -2) BEGIN IF DATEDIFF(mi, @startTime, GETDATE()) > @timeLimit BEGIN PRINT '[ ' + CAST(GETDATE() AS VARCHAR(100)) + ' ] ' + '*** Time Limit Reached ***'; GOTO __DONE; END SELECT @SQL = 'UPDATE STATISTICS ' + QUOTENAME(@dBName) + '.' + QUOTENAME(@schemaName) + '.' + QUOTENAME(@ObjectName) + ' WITH SAMPLE ' + CAST(@samplePercent AS NVARCHAR(100)) + ' PERCENT;'; IF @printSQL = 1 PRINT '[ ' + CAST(GETDATE() AS VARCHAR(100)) + ' ] ' + @SQL + ' (Last Updated: ' + CAST(@lastUpdateDate AS VARCHAR(100)) + ')' IF @executeSQL = 1 BEGIN EXEC (@SQL); END END FETCH NEXT FROM cStats INTO @databaseID, @dbName, @objectID, @schemaName, @objectName, @lastUpdateDateEND__DONE:CLOSE cStatsDEALLOCATE cStatsPRINT '[ ' + CAST(GETDATE() AS VARCHAR(100)) + ' ] ' + 'Completed.'GO

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• Reducing Deadlocks - not a DBA issue ?

  - by steveh99999

   As a DBA, I'm involved on an almost daily basis troubleshooting 'SQL Server' performance issues. Often, this troubleshooting soon veers away from a 'its a SQL Server issue' to instead become a wider application/database design/coding issue.One common perception with SQL Server is that deadlocking is an application design issue - and is fixed by recoding...  I see this reinforced by MCP-type questions/scenarios where the answer to prevent deadlocking is simply to change the order in code in which tables are accessed....Whilst this is correct, I do think this has led to a situation where many 'operational' or 'production support' DBAs, when faced with a deadlock, are happy to throw the issue over to developers without analysing the issue further....A couple of 'war stories' on deadlocks which I think are interesting :- Case One , I had an issue recently on a third-party application that I support on SQL 2008.  This particular third-party application has an unusual support agreement where the customer is allowed to change the index design on the third-party provided database.  However, we are not allowed to alter application code or modify table structure..This third-party application is also known to encounter occasional deadlocks – indeed, I have documentation from the vendor that up to 50 deadlocks per day is not unusual !So, as a DBA I have to support an application which in my opinion has too many deadlocks - but, I cannot influence the design of the tables or stored procedures for the application. This should be the classic - blame the third-party developers scenario, and hope this issue gets addressed in a future application release - ie we could wait years for this to be resolved and implemented in our production environment...But, as DBAs  can change the index layout, is there anything I could do still to reduce the deadlocks in the application ?I initially used SQL traceflag 1222 to write deadlock detection output to the SQL Errorlog – using this I was able to identify one table heavily involved in the deadlocks.When I examined the table definition, I was surprised to see it was a heap – ie no clustered index existed on the table.Using SQL profiler to see locking behaviour and plan for the query involved in the deadlock, I was able to confirm a table scan was being performed.By creating an appropriate clustered index - it was possible to produce a more efficient plan and locking behaviour.So, less locks, held for less time = less possibility of deadlocks. I'm still unhappy about the overall number of deadlocks on this system - but that's something to be discussed further with the vendor.Case Two,  a system which hadn't changed for months suddenly started seeing deadlocks on a regular basis. I love the 'nothing's changed' scenario, as it gives me the opportunity to appear wise and say 'nothings changed on this system, except the data'.. This particular deadlock occurred on a table which had been growing rapidly. By using DBCC SHOW_STATISTICS - the DBA team were able to see that the deadlocks seemed to be occurring shortly after auto-update stats had regenerated the table statistics using it's default sampling behaviour.As a quick fix, we were able to schedule a nightly UPDATE STATISTICS WITH FULLSCAN on the table involved in the deadlock - thus, greatly reducing the potential for stats to be updated via auto_update_stats, consequently reducing the potential for a bad plan to be generated based on an unrepresentative sample of the data. This reduced the possibility of a deadlock occurring.  Not a perfect solution by any means, but quick, easy to implement, and needed no application code changes. This fix gave us some 'breathing space'  to properly fix the code during the next scheduled application release.   The moral of this post - don't dismiss deadlocks as issues that can only be fixed by developers...

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• Profiling Silverlight Applications after installing Visual Studio 2010 Service Pack 1

  - by mbcrump

  Introduction Now that the dust has settled and everyone has downloaded and installed Visual Studio 2010 Service Pack 1, its time to talk about a new feature included that will help Silverlight Developers profile their applications. Let’s take a look at what the official documentation says about it: Performance Wizard for Silverlight – taken from VS2010 SP1 KB. Visual Studio 2010 SP1 enables you to tune the Silverlight application performance by profiling the code. A traditional code profiler cannot tune the rendering performance for Silverlight applications. Many higher-level profilers are added to Visual Studio 2010 SP1 so that you can better determine which parts of the application consume time. So, how do you do it? After you finish installing VS2010 SP1, make sure it took by going to Help –> About. You should see SP1Rel under Visual Studio 2010 as shown below. Now, that we have verified you are on the most current release, let’s load up a Silverlight Application. I’m going to take my hobby Silverlight project that I created a month or so ago. The reason that I’m picking this project is that I didn’t focus so much on performance as it was just built for fun and to see what I could do with Silverlight. I believe this makes the perfect application to profile.  After the project is loaded, click on Analyze then Launch Performance Wizard. Go ahead and click on CPU Sampling (recommended). You will notice that it ask which application to target. By Default, it will select the .Web project in an Silverlight Application. Go ahead and leave the default Web Project checked. We are going to leave the client as Internet Explorer. Now, go ahead and click finish. Now your Silverlight Application will launch. While your application is running, you will see the following inside of Visual Studio 2010. Here is where you will need to attach your Silverlight Application to the web application that is current being profiled. Simply click on the  Attach/Detach button below and find your application to attach to the profiler. In my case, I am using IE8 and could find it by the title. After you close your browser, you will notice it generated a report: These files will end with a .VSP If you click on the .VSP you will it generated the following report: We could turn off “Just My Code” but it may pick up things that we didn’t want to profile as shown below: One other feature to note is that you may want to export the data to a CSV or XML. You can do that by looking at the toolbar and clicking the button highlighted below. Conclusion The profiler for Silverlight is a great addition to an already great product. So before you ship a Silverlight Application run it through the profile and see what comes up. Since its included and free I can’t see a reason not to do this. Thanks again for reading and I hope you subscribe to my blog or follow me on Twitter for more Silverlight/WP7 fun.  Subscribe to my feed

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• Profiling Startup Of VS2012 &ndash; dotTrace Profiler

  - by Alois Kraus

  Jetbrains which is famous for the Resharper tool has also a profiler in its portfolio. I downloaded dotTrace 5.2 Professional (569€+VAT) to check how far I can profile the startup of VS2012. The most interesting startup option is “.NET Process”. With that you can profile the next started .NET process which is very useful if you want to profile an application which is not started by you.     I did select Tracing as and Wall time to get similar options across all profilers. For some reason the attach option did not work with .NET 4.5 on my home machine. But I am sure that it did work with .NET 4.0 some time ago. Since we are profiling devenv.exe we can also select “Standalone Application” and start it from the profiler. The startup time of VS does increase about a factor 3 but that is ok. You get mainly three windows to work with. The first one shows the threads where you can drill down thread wise where most time is spent. I The next window is the call tree which does merge all threads together in a similar view. The last and most useful view in my opinion is the Plain List window which is nearly the same as the Method Grid in Ants Profiler. But this time we do get when I enable the Show system functions checkbox not a 150 but 19407 methods to choose from! I really tried with Ants Profiler to find something about out how VS does work but look how much we were missing! When I double click on a method I do get in the lower pane the called methods and their respective timings. This is something really useful and I can nicely drill down to the most important stuff. The measured time seems to be Wall Clock time which is a good thing to see where my time is really spent. You can also use Sampling as profiling method but this does give you much less information. Except for getting a first idea where to look first this profiling mode is not very useful to understand how you system does interact.   The options have a good list of presets to hide by default many method and gray them out to concentrate on your code. It does not filter anything out if you enable Show system functions. By default methods from these assemblies are hidden or if the checkbox is checked grayed out. All in all JetBrains has made a nice profiler which does show great detail and it has nice drill down capabilities. The only thing is that I do not trust its measured timings. I did fall several times into the trap with this one to optimize at places which were already fast but the profiler did show high times in these methods. After measuring with Tracing I was certain that the measured times were greatly exaggerated. Especially when IO is involved it seems to have a hard time to subtract its own overhead. What I did miss most was the possibility to profile not only the next started process but to be able to select a process by name and perhaps a count to profile the next n processes of this name. Next: YourKit

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• Webcast On-Demand: Building Java EE Apps That Scale

  - by jeckels

  With some awesome work by one of our architects, Randy Stafford, we recently completed a webcast on scaling Java EE apps efficiently. Did you miss it? No problem. We have a replay available on-demand for you. Just hit the '+' sign drop-down for access.Topics include: Domain object caching Service response caching Session state caching JSR-107 HotCache and more! Further, we had several interesting questions asked by our audience, and we thought we'd share a sampling of those here for you - just in case you had the same queries yourself. Enjoy! What is the largest Coherence deployment out there? We have seen deployments with over 500 JVMs in the Coherence cluster, and deployments with over 1000 JVMs using the Coherence jar file, in one system. On the management side there is an ecosystem of monitoring tools from Oracle and third parties with dashboards graphing values from Coherence's JMX instrumentation. For lifecycle management we have seen a lot of custom scripting over the years, but we've also integrated closely with WebLogic to leverage its management ecosystem for deploying Coherence-based applications and managing process life cycles. That integration introduces a new Java EE archive type, the Grid Archive or GAR, which embeds in an EAR and can be seen by a WAR in WebLogic. That integration also doesn't require any extra WebLogic licensing if Coherence is licensed. How is Coherence different from a NoSQL Database like MongoDB? Coherence can be considered a NoSQL technology. It pre-dates the NoSQL movement, having been first released in 2001 whereas the term "NoSQL" was coined in 2009. Coherence has a key-value data model primarily but can also be used for document data models. Coherence manages data in memory currently, though disk persistence is in a future release currently in beta testing. Where the data is managed yields a few differences from the most well-known NoSQL products: access latency is faster with Coherence, though well-known NoSQL databases can manage more data. Coherence also has features that well-known NoSQL database lack, such as grid computing, eventing, and data source integration. Finally Coherence has had 15 years of maturation and hardening from usage in mission-critical systems across a variety of industries, particularly financial services. Can I use Coherence for local caching? Yes, you get additional features beyond just a java.util.Map: you get expiration capabilities, size-limitation capabilities, eventing capabilites, etc. Are there APIs available for GoldenGate HotCache? It's mostly a black box. You configure it, and it just puts objects into your caches. However you can treat it as a glass box, and use Coherence event interceptors to enhance its behavior - and there are use cases for that. Are Coherence caches updated transactionally? Coherence provides several mechanisms for concurrency control. If a project insists on full-blown JTA / XA distributed transactions, Coherence caches can participate as resources. But nobody does that because it's a performance and scalability anti-pattern. At finer granularity, Coherence guarantees strict ordering of all operations (reads and writes) against a single cache key if the operations are done using Coherence's "EntryProcessor" feature. And Coherence has a unique feature called "partition-level transactions" which guarantees atomic writes of multiple cache entries (even in different caches) without requiring JTA / XA distributed transaction semantics.

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• Do SEO-friendly URLs really affect a page's ranking?

  - by Lee Harold

  SEO-friendly URLs are all the rage these days. But do they actually have a meaningful impact on a page's ranking in Google and other search engines? If so, why? If not, why not? (Note that I would absolutely agree that SEO-friendly URLs are nicer to use for human beings. My question is whether they actually make a difference to the ranking algorithms.) Update: As it turns out, the Google post that endorphine points to here has caused tremendous confusion in the SEO community. For a sampling of the discussion, see here, here, and here. Part of the problem is that the Google post is addressing the worst case where URL rewriting is done poorly and so you'd be better off sticking with a dynamic URL rather than a mangled static "SEO-friendly" URL. There's no question dynamic URLs can be crawled by Google and can achieve high rankings. Maybe it would be easier to reframe the question more concretely: given 2 otherwise equivalent pages, which will rank higher for the search "do seo friendly urls really affect page ranking"? A) http://stackoverflow.com/questions/505793/do-seo-friendly-urls-really-affect-a-pages-ranking or B) http://stackoverflow.com?question=505793 (a fake URL for comparison only)

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• YUV Textures and Shaders

  - by Luca

  I've always used RGB textures. Now comes up the need of use of YUV textures (a set of three texture, specifying 1 luminance and 2 chrominance channels). Of course the YUV texture could be converted on CPU, getting the RGB texture usable as usual... but I need to get RGB pixel directly on GPU, to avoid unnecessary processor load... The problem became strange, since I require to specifyin the shader source, because a single texture, the following items: Three samplers uniforms, one for each channel Two integer uniforms, for specifying the chrominance channels sampling a mat3 uniform, for specific YUV to RGB conversion matrix. This should be done for each YUV texture... Is it possible to "compress" required uniforms, and getting RGB values quite easily? Actually i think this could aid: Texture sizes, including mipmaps, could be queried. With this, its possible to save the two integer uniforms, since the uniform values are derived the ratio between texture extents The mat3 uniforms could be collected as globals, and with preprocessor could be selected. But what design should I use for specify three (related) textures? Is it possible to use textures levels for accessing multiple textures? Texture arrays could be usable? And what about using rectangle textures, which doesn't supports mipmaps? Maybe a shader abstraction (struct definition and related function) could aid? Thank you.

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• A catalogue of Cassandra log messages: What is the correct interpretation?

  - by knorv

  The following is a complete catalogue of all log messages generated by Cassandra 0.6 when stress-testing a Cassandra installation over an extended period of time: AntiEntropyService: Sending AEService tree for (,) to: [] CassandraDaemon: Binding thrift service to localhost/N.N.N.N:N CassandraDaemon: Cassandra starting up... ColumnFamilyStore: has reached its threshold; switching in a fresh Memtable at CommitLogContext(file='.../cassandra/commitlog/CommitLog-N.log', position=N) ColumnFamilyStore: Enqueuing flush of Memtable()@N CommitLog: Discarding obsolete commit log:CommitLogSegment(.../cassandra/commitlog/CommitLog-N.log) CommitLog: Log replay complete CommitLog: Replaying .../cassandra/commitlog/CommitLog-N.log, ... CommitLogSegment: Creating new commitlog segment .../cassandra/commitlog/CommitLog-N.log CompactionManager: Compacted to .../cassandra/data//-N-Data.db. N/N bytes for N keys. Time: Nms. CompactionManager: Compacting [org.apache.cassandra.io.SSTableReader(path='.../cassandra/data//-N-Data.db'), ...] DatabaseDescriptor: Auto DiskAccessMode determined to be mmap GCInspector: GC for ConcurrentMarkSweep: N ms, N reclaimed leaving N used; max is N GCInspector: GC for ParNew: N ms, N reclaimed leaving N used; max is N Memtable: Completed flushing .../cassandra/data//-N-Data.db Memtable: Writing Memtable()@N SSTable: Deleted .../cassandra/data//-N-Data.db SSTableDeletingReference: Deleted .../cassandra/data//-N-Data.db SSTableReader: Sampling index for .../cassandra/data//-N-Data.db StorageService: Starting up server gossip SystemTable: Saved ClusterName found: Test Cluster SystemTable: Saved ClusterName not found. Using Test Cluster SystemTable: Saved Token found: N SystemTable: Saved Token not found. Using N For each of the log messages listed - what is the correct interpretation of the log message?

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• Sparse parameter selection using Genetic Algorithm

  - by bgbg

  Hello, I'm facing a parameter selection problem, which I would like to solve using Genetic Algorithm (GA). I'm supposed to select not more than 4 parameters out of 3000 possible ones. Using the binary chromosome representation seems like a natural choice. The evaluation function punishes too many "selected" attributes and if the number of attributes is acceptable, it then evaluates the selection. The problem is that in these sparse conditions the GA can hardly improve the population. Neither the average fitness cost, nor the fitness of the "worst" individual improves over the generations. All I see is slight (even tiny) improvement in the score of the best individual, which, I suppose, is a result of random sampling. Encoding the problem using indices of the parameters doesn't work either. This is most probably, due to the fact that the chromosomes are directional, while the selection problem isn't (i.e. chromosomes [1, 2, 3, 4]; [4, 3, 2, 1]; [3, 2, 4, 1] etc. are identical) What problem representation would you suggest? P.S If this matters, I use PyEvolve.

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• How would the conversion of a custom CMS using a text-file-based database to Drupal be tackled?

  - by James Morris

  Just today I've started using Drupal for a site I'm designing/developing. For my own site http://jwm-art.net I wrote a user-unfriendly CMS in PHP. My brief experience with Drupal is making me want to convert from the CMS I wrote. A CMS whose sole method (other than comments) of automatically publishing content is by logging in via SSH and using NANO to create a plain text file in a format like so*: head<<END_HEAD title = Audio keywords= open,source,audio,sequencing,sampling,synthesis descr = Music, noise, and audio, created by James W. Morris. parent = home END_HEAD main<<END_MAIN text<<END_TEXT Digital music, noise, and audio made exclusively with @=xlink=http://www.linux-sound.org@:Linux Audio Software@_=@. END_TEXT image=gfb@--@;Accompanying image for penonpaper-c@right ilink=audio_2008 br= ilink=audio_2007 br= ilink=audio_2006 END_MAIN info=text<<END_TEXT I've been making PC based music since the early nineties - fortunately most of it only exists as tape recordings. END_TEXT ( http://jwm-art.net/dark.php?p=audio - There's just over 400 pages on there. ) *The jounal-entry form which takes some of the work out of it, has mysteriously broken. And it still required SSH access to copy the file to the main dat dir and to check I had actually remembered the format correctly and the code hadn't mis-formatted anything (which it always does). I don't want to drop all the old content (just some), but how much work would be involved in converting it, factoring into account I've been using Drupal for a day, have not written any PHP for a couple of years, and have zero knowledge of SQL? How might a team of developers tackle this? How do-able is it for one guy in his spare time?

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• How to speed up marching cubes?

  - by Dan Vinton

  I'm using this marching cube algorithm to draw 3D isosurfaces (ported into C#, outputting MeshGeomtry3Ds, but otherwise the same). The resulting surfaces look great, but are taking a long time to calculate. Are there any ways to speed up marching cubes? The most obvious one is to simply reduce the spatial sampling rate, but this reduces the quality of the resulting mesh. I'd like to avoid this. I'm considering a two-pass system, where the first pass samples space much more coarsely, eliminating volumes where the field strength is well below my isolevel. Is this wise? What are the pitfalls? Edit: the code has been profiled, and the bulk of CPU time is split between the marching cubes routine itself and the field strength calculation for each grid cell corner. The field calculations are beyond my control, so speeding up the cubes routine is my only option... I'm still drawn to the idea of trying to eliminate dead space, since this would reduce the number of calls to both systems considerably.

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• .NET: What's the difference between HttpMethod and RequestType of HttpRequest?

  - by Ian Boyd

  The HttpRequest class defines two properties: HttpMethod: Gets the HTTP data transfer method (such as GET, POST, or HEAD) used by the client. public string HttpMethod { get; } The HTTP data transfer method used by the client. and RequestType: Gets or sets the HTTP data transfer method (GET or POST) used by the client. public string RequestType { get; set; } A string representing the HTTP invocation type sent by the client. What is the difference between these two properties? When would i want to use one over the other? Which is the proper one to inspect to see what data transfer method was used by the client? The documentation indicates that HttpMethod will return whatever verb was used: such as GET, POST, or HEAD while the documentation on RequestType seems to indicate only one of two possible values: GET or POST i test with a random sampling of verbs, and both properties seem to support all verbs, and both return the same values: Testing: Client Used HttpMethod RequestType GET GET GET POST POST POST HEAD HEAD HEAD CONNECT CONNECT CONNECT MKCOL MKCOL MKCOL PUT PUT PUT FOOTEST FOOTEST FOOTEST What is the difference between: HttpRequest.HttpMethod HttpRequest.RequestType and when should i use one over the other? Keywords: iis asp.net http httprequest httphandler

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• Delphi: Fast(er) widestring concatenation

  - by Ian Boyd

  i have a function who's job is to convert an ADO Recordset into html: class function RecordsetToHtml(const rs: _Recordset): WideString; And the guts of the function involves a lot of wide string concatenation: while not rs.EOF do begin Result := Result+CRLF+ '<TR>'; for i := 0 to rs.Fields.Count-1 do Result := Result+'<TD>'+VarAsString(rs.Fields[i].Value)+'</TD>'; Result := Result+'</TR>'; rs.MoveNext; end; With a few thousand results, the function takes, what any user would feel, is too long to run. The Delphi Sampling Profiler shows that 99.3% of the time is spent in widestring concatenation (@WStrCatN and @WstrCat). Can anyone think of a way to improve widestring concatenation? i don't think Delphi 5 has any kind of string builder. And Format doesn't support Unicode. And to make sure nobody tries to weasel out: pretend you are implementing the interface: IRecordsetToHtml = interface(IUnknown) function RecordsetToHtml(const rs: _Recordset): WideString; end; Update One I thought of using an IXMLDOMDocument, to build up the HTML as xml. But then i realized that the final HTML would be xhtml and not html - a subtle, but important, difference. Update Two Microsoft knowledge base article: How To Improve String Concatenation Performance

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• Business Objects - Containers or functional?

  - by Walter

  Where I work, we've gone back and forth on this subject a number of times and are looking for a sanity check. Here's the question: Should Business Objects be data containers (more like DTOs) or should they also contain logic that can perform some functionality on that object. Example - Take a customer object, it probably contains some common properties (Name, Id, etc), should that customer object also include functions (Save, Calc, etc.)? One line of reasoning says separate the object from the functionality (single responsibility principal) and put the functionality in a Business Logic layer or object. The other line of reasoning says, no, if I have a customer object I just want to call Customer.Save and be done with it. Why do I need to know about how to save a customer if I'm consuming the object? Our last two projects have had the objects separated from the functionality, but the debate has been raised again on a new project. Which makes more sense? EDIT These results are very similar to our debates. One vote to one side or another completely changes the direction. Does anyone else want to add their 2 cents? EDIT Eventhough the answer sampling is small, it appears that the majority believe that functionality in a business object is acceptable as long as it is simple but persistence is best placed in a separate class/layer. We'll give this a try. Thanks for everyone's input...

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• What are some programming techniques for converting SD images to HD images

  - by Dr Dork

  I'm taking programming class and instructor loves to work with images so most of our assignments involve manipulating raw RGB image data. One of our assignments is to implement a standard image converter that converts SD images to HD images and vice versa. I always take advantage of these types of assignments to go a little beyond what we were asked to do, so I added a basic anti-aliasing process that uses the average pixel color of the 3x3 surrounding pixels to improve the converted image. While it helps a bit, the resulting image still doesn't look good, which is ok because it's not expected to for the assignment. I've learned that converting an SD to HD images has shown to be much harder than down sampling to SD from HD just because SD to HD effectively involves increasing resolution when it is not there. Obviously, it is hard to create pixels from nothing, but I'd like enhance my anti-aliasing to something that provides better results when upscaling an image. Most of the techniques I find and read on the internet are far beyond my level of image processing and programming. Can anybody suggest any better methods or processes to create good HD content from SD content that may be within my programming skill level? I know that's a difficult thing to gauge since you don't know me, but perhaps knowing that I can write c++ code to read in raw RGB data and upscale/downscale it with simple average-anti-aliasing will give you an idea. Thanks in advance for all your help!

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• acts_as_xapian jobs table

  - by Grnbeagle

  Hi, Can someone explain to me the inner workings of acts_as_xapian_jobs table? I ran into an issue with the acts_as_xapian plugin recently, where I kept getting the following error when it creates an object with xapian indexed fields: Mysql::Error: Duplicate entry 'String-2147483647' for key 2: INSERT INTO `acts_as_xapian_jobs` (`action`, `model`, `model_id`) VALUES ('update', 'String', 23730251831560) It turns out the model_id exceeded the max int value of 2147483647. The workaround was to update model_id to use bigint. Why would the model_id be so huge? By looking at content of acts_as_xapian_jobs, it seems it creates a row for every field that is being indexed.. Understanding how a job gets created in the table would help a great deal. Here's a sampling of the table: mysql> select * from acts_as_xapian_jobs limit 5\G *************************** 1. row *************************** id: 19 model: String model_id: 23804037900560 action: update *************************** 2. row *************************** id: 49 model: String model_id: 23804037191200 action: update *************************** 3. row *************************** id: 79 model: String model_id: 23804037932180 action: update *************************** 4. row *************************** id: 109 model: String model_id: 23804037101700 action: update *************************** 5. row *************************** id: 139 model: String model_id: 23804037722160 action: update Thanks in advance, Amie

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• Linux time sample based profiler.

  - by Caspin

  short version: Is there a good time based sampling profiler for Linux? long version: I generally use OProfile to optimize my applications. I recently found a shortcoming that has me wondering. The problem was a tight loop spawning c++filt to demangle a c++ name. I only stumbled upon the code by accident while chasing down another bottleneck. The OProfile didn't show anything unusual about the code so I almost ignored it but my code sense told me to optimize the call and see what happened. I changed the popen of c++filt to abi::__cxa_demangle. The runtime went from more than a minute to a little over a second. About a x60 speed up. Is there a way I could have configured OProfile to flag the popen call? As the profile data sits now OProfile thinks the bottle neck was the heap and std::string calls (which BTW once optimized dropped the runtime to less than a second, more than x2 speed up). Here is my OProfile configuration: $ sudo opcontrol --status Daemon not running Event 0: CPU_CLK_UNHALTED:90000:0:1:1 Separate options: library vmlinux file: none Image filter: /path/to/excutable Call-graph depth: 7 Buffer size: 65536 Is there another profiler for Linux that could have found the bottleneck? I suspect the issue is that OProfile only logs its samples to the currently running process. I'd like it to always log its samples to the process I'm profiling. So if the process is currently switched out (blocking on IO or a popen call) OProfile would just place its sample at the blocked call. If I can't fix this, OProfile will only be useful when the executable is pushing near 100% CPU. It can't help with executables that that have inefficient blocking calls.

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• Faster way to split a string and count characters using R?

  - by chrisamiller

  I'm looking for a faster way to calculate GC content for DNA strings read in from a FASTA file. This boils down to taking a string and counting the number of times that the letter 'G' or 'C' appears. I also want to specify the range of characters to consider. I have a working function that is fairly slow, and it's causing a bottleneck in my code. It looks like this: ## ## count the number of GCs in the characters between start and stop ## gcCount <- function(line, st, sp){ chars = strsplit(as.character(line),"")[[1]] numGC = 0 for(j in st:sp){ ##nested ifs faster than an OR (|) construction if(chars[[j]] == "g"){ numGC <- numGC + 1 }else if(chars[[j]] == "G"){ numGC <- numGC + 1 }else if(chars[[j]] == "c"){ numGC <- numGC + 1 }else if(chars[[j]] == "C"){ numGC <- numGC + 1 } } return(numGC) } Running Rprof gives me the following output: > a = "GCCCAAAATTTTCCGGatttaagcagacataaattcgagg" > Rprof(filename="Rprof.out") > for(i in 1:500000){gcCount(a,1,40)}; > Rprof(NULL) > summaryRprof(filename="Rprof.out") self.time self.pct total.time total.pct "gcCount" 77.36 76.8 100.74 100.0 "==" 18.30 18.2 18.30 18.2 "strsplit" 3.58 3.6 3.64 3.6 "+" 1.14 1.1 1.14 1.1 ":" 0.30 0.3 0.30 0.3 "as.logical" 0.04 0.0 0.04 0.0 "as.character" 0.02 0.0 0.02 0.0 $by.total total.time total.pct self.time self.pct "gcCount" 100.74 100.0 77.36 76.8 "==" 18.30 18.2 18.30 18.2 "strsplit" 3.64 3.6 3.58 3.6 "+" 1.14 1.1 1.14 1.1 ":" 0.30 0.3 0.30 0.3 "as.logical" 0.04 0.0 0.04 0.0 "as.character" 0.02 0.0 0.02 0.0 $sampling.time [1] 100.74 Any advice for making this code faster?

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• Re-order list in Python to ensure it starts with check values.

  - by S_Swede

  Dear all, I'm reading in serial data using Pyserial, to populate a list of 17 values (1byte each) at a sampling rate of 256Hz. The bytes I ultimately want to use are the 5th to 8th in the list. Providing no bytes are dropped, the first two values of the stream are always the same ('165','90'). I'm getting quite a few dropped values though, and my list values are shifting, so when I read the 5th-8th bytes, they aren't the correct values. I've partially combatted this by ensuring that before the wanted segement is captured, the first few values are checked against what they should be (i.e. if mylist[0]==165 &....). This is crude but ok since the chances of these two values appearing adjacent to each other in the list elsewhere is small. The problem is that this means as soon as the bytes shift, I'm losing a load of values, until it eventually realigns. My question is: what code can I use to either: a) Force the list to realign once it has been detected that it no longer starts with 165,90. (elif....). b) Detect where '165' & '90' are (next to each other) in the list and extract the values I want in relation to their position (next but one, onwards). Thanks in advance S_S Just noticed from the related Qs that I could use mylist.append(mylist.pop(0)) multiple times until they are in the right place. Is there a better way that anyone can suggest?

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• Unsupported smapling rate in flex/actionscript

  - by Rajeev

  In action script i need Loading configuration file /opt/flex/frameworks/flex-config.xml t3.mxml(10): Error: unsupported sampling rate (24000Hz) [Embed(source="music.mp3")] t3.mxml(10): Error: Unable to transcode music.mp3. [Embed(source="music.mp3")] The code is <?xml version="1.0"?> <!-- embed/EmbedSound.mxml --> <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"> <mx:Script> <![CDATA[ import flash.media.*; [Embed(source="sample.mp3")] [Bindable] public var sndCls:Class; public var snd:Sound = new sndCls() as Sound; public var sndChannel:SoundChannel; public function playSound():void { sndChannel=snd.play(); } public function stopSound():void { sndChannel.stop(); } ]]> </mx:Script> <mx:HBox> <mx:Button label="play" click="playSound();"/> <mx:Button label="stop" click="stopSound();"/> </mx:HBox> </mx:Application>

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• Where do I put the logic of my MFC program?

  - by Matthew

  I created an application core, in C++, that I've compiled into a static library in Visual Studio. I am now at the process of writing a GUI for it. I am using MFC to do this. I figured out how to map button presses to execute certain methods of my application core's main class (i.e. buttons to have it start and stop). The core class however, should always be sampling data from an external source every second or two. The GUI should then populate some fields after each sample is taken. I can't seem to find a spot in my MFC objects like CDialog that I can constantly check to see if my class has grabbed the data.. then if it has put that data into some of the text boxes. A friend suggested that I create a thread on the OnInit() routine that would take care of this, but that solution isn't really working for me. Is there no spot where I can put an if statement that keeps being called until the program quits? i.e. if( coreapp.dataSampleReady() ) { // put coreapp.dataItem1() in TextBox1 // set progress bar to coreapp.dataItem2() // etc. // reset dataSampleReady }

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• Generate random number from an arbitrary weighted list

  - by Fernando

  Here's what I need to do, I'll be doing this both in PHP and JavaScript. I have a list of numbers that will range from 1 to 300-500 (I haven't set the limit yet). I will be running a drawing were 10 numbers will be picked at random from the given range. Here's the tricky part: I want some numbers to be less likely to be drawn up. A small set of those 300-500 will be flagged as "lucky numbers". For example, out of 100 drawings, most numbers have equal chances of being drawn, except for a few, that will only be picked once every 30-50 drawings. Basically I need to artificially set the probability of certain numbers to be picked while maintaining an even distribution with the rest of the numbers. The only similar thing I've found so far is this question: Generate A Weighted Random Number, the problem being that my spec has considerably more numbers (up to 500) so the weights would get very small and supposedly this could be a problem with that solution (Rejection Sampling). I'm still trying it, though, but I wonder if there other solutions. Math is not my thing so I appreciate any input. Thanks.

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