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• Non use of persisted data – Part deux

  - by Dave Ballantyne

  In my last blog I showed how persisted data may not be used if you have used the base data on an include on an index. That wasn't the only problem ive had that showed the same symptom.  Using the same code as before,  I was executing similar to the below : select BillToAddressID,SOD.SalesOrderDetailID,SOH.CleanedGuid from sales.salesorderheader SOH join Sales.SalesOrderDetail SOD on SOH.SalesOrderID = SOD.SalesOrderID But,  due to a distribution error in statistics i found it necessary to use a table hint.  In this case, I wanted to force a loop join select BillToAddressID,SOD.SalesOrderDetailID,SOH.CleanedGuid from sales.salesorderheader SOH inner loop join Sales.SalesOrderDetail SOD on SOH.SalesOrderID = SOD.SalesOrderID   But, being the diligent  TSQL developer that I am ,looking at the execution plan I noticed that the ‘compute scalar’ operator was again calling the function.  Again,  profiler is a more graphic way to view this…..   All very odd,  just because ive forced a join , that has NOTHING, to do with my persisted data then something is causing the data to be re-evaluated. Not sure if there is any easy fix you can do to the TSQL here, but again its a lesson learned (or rather reinforced) examine the execution plan of every query you write to ensure that it is operating as you thought it would.

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• update-apt-xapian-index uses 100% CPU, even when Update Manager is set to not check for updates

  - by Dave M G

  I have a slightly older laptop running Ubuntu 11.10. It runs fine, but frequently, when I start it up, the CPU monitor in my Gnome Panel shows 100% usage for for what can be up to five minutes or so. It seems that the offending process is update-apt-xapian-index, which, if I understand correctly, is the update manager checking for updates. I have gone into the update manager settings, and selected to never check for updates. I'll do that manually when I feel like I have the time to leave the laptop running for that. However, despite my selection, this still happens. Roughly 50% of the time or more, when I start my laptop, it runs update-apt-xapian-index. How can I get the update manager to respect my settings, or at least to get this process to stop eating my CPU cycles?

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• Is using ELSE bad programming?

  - by dave.b

  I've often come across bugs that have been caused by using the ELSE construct. A prime example is something along the lines of: If (passwordCheck() == false){ displayMessage(); }else{ letThemIn(); } To me this screams security problem. I know that passwordCheck is likely to be a boolean, but I wouldn't place my applications security on it. What would happen if its a string, int etc? I usually try to avoid using ELSE, and instead opt for two completely separate IF statements to test for what I expect. Anything else then either gets ignored OR is specifically handled. Surely this is a better way to prevent bugs / security issues entering your app. How do you guys do it?

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• C-states and P-states : confounding factors for benchmarking

  - by Dave

  I was recently looking into a performance issue in the java.util.concurrent (JUC) fork-join pool framework related to particularly long latencies when trying to wake (unpark) threads in the pool. Eventually I tracked the issue down to the power & scaling governor and idle-state policies on x86. Briefly, P-states refer to the set of clock rates (speeds) at which a processor can run. C-states reflect the possible idle states. The deeper the C-state (higher numerical values) the less power the processor will draw, but the longer it takes the processor to respond and exit that sleep state on the next idle to non-idle transition. In some cases the latency can be worse than 100 microseconds. C0 is normal execution state, and P0 is "full speed" with higher Pn values reflecting reduced clock rates. C-states are P-states are orthogonal, although P-states only have meaning at C0. You could also think of the states as occupying a spectrum as follows : P0, P1, P2, Pn, C1, C2, ... Cn, where all the P-states are at C0. Our fork-join framework was calling unpark() to wake a thread from the pool, and that thread was being dispatched onto a processor at deep C-state, so we were observing rather impressive latencies between the time of the unpark and the time the thread actually resumed and was able to accept work. (I originally thought we were seeing situations where the wakee was preempting the waker, but that wasn't the case. I'll save that topic for a future blog entry). It's also worth pointing out that higher P-state values draw less power and there's usually some latency in ramping up the clock (P-states) in response to offered load. The issue of C-states and P-states isn't new and has been described at length elsewhere, but it may be new to Java programmers, adding a new confounding factor to benchmarking methodologies and procedures. To get stable results I'd recommend running at C0 and P0, particularly for server-side applications. As appropriate, disabling "turbo" mode may also be prudent. But it also makes sense to run with the system defaults to understand if your application exhibits any performance sensitivity to power management policies. The operating system power management sub-system typically control the P-state and C-states based on current and recent load. The scaling governor manages P-states. Operating systems often use adaptive policies that try to avoid deep C-states for some period if recent deep idle episodes proved to be very short and futile. This helps make the system more responsive under bursty or otherwise irregular load. But it also means the system is stateful and exhibits a memory effect, which can further complicate benchmarking. Forcing C0 + P0 should avoid this issue.

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• When row estimation goes wrong

  - by Dave Ballantyne

  Whilst working at a client site, I hit upon one of those issues that you are not sure if that this is something entirely new or a bug or a gap in your knowledge. The client had a large query that needed optimizing.  The query itself looked pretty good, no udfs, UNION ALL were used rather than UNION, most of the predicates were sargable other than one or two minor ones.  There were a few extra joins that could be eradicated and having fixed up the query I then started to dive into the plan. I could see all manor of spills in the hash joins and the sort operations,  these are caused when SQL Server has not reserved enough memory and has to write to tempdb.  A VERY expensive operation that is generally avoidable.  These, however, are a symptom of a bad row estimation somewhere else, and when that bad estimation is combined with other estimation errors, chaos can ensue. Working my way back down the plan, I found the cause, and the more I thought about it the more i came convinced that the optimizer could be making a much more intelligent choice. First step is to reproduce and I was able to simplify the query down a single join between two tables, Product and ProductStatus,  from a business point of view, quite fundamental, find the status of particular products to show if ‘active’ ,’inactive’ or whatever. The query itself couldn’t be any simpler The estimated plan looked like this: Ignore the “!” warning which is a missing index, but notice that Products has 27,984 rows and the join outputs 14,000. The actual plan shows how bad that estimation of 14,000 is : So every row in Products has a corresponding row in ProductStatus.  This is unsurprising, in fact it is guaranteed,  there is a trusted FK relationship between the two columns.  There is no way that the actual output of the join can be different from the input. The optimizer is already partly aware of the foreign key meta data, and that can be seen in the simplifiction stage. If we drop the Description column from the query: the join to ProductStatus is optimized out. It serves no purpose to the query, there is no data required from the table and the optimizer knows that the FK will guarantee that a matching row will exist so it has been removed. Surely the same should be applied to the row estimations in the initial example, right ?  If you think so, please upvote this connect item. So what are our options in fixing this error ? Simply changing the join to a left join will cause the optimizer to think that we could allow the rows not to exist. or a subselect would also work However, this is a client site, Im not able to change each and every query where this join takes place but there is a more global switch that will fix this error,  TraceFlag 2301. This is described as, perhaps loosely, “Enable advanced decision support optimizations”. We can test this on the original query in isolation by using the “QueryTraceOn” option and lo and behold our estimated plan now has the ‘correct’ estimation. Many thanks goes to Paul White (b|t) for his help and keeping me sane through this

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• SilverlightShow for November 07 - 13, 2011

  - by Dave Campbell

  Check out the Top Five most popular news at SilverlightShow for SilverlightShow Top 5 News for November 07 - 13, 2011. Here are the top 5 news on SilverlightShow for last week: Will there be a Silverlight 6 (and does it matter)? Silverlight 5 - the end of the line Microsoft confirms move to align Windows & Windows Phone JavaScript, MVVM and Silverlight - Papa's Perspective How TO: Virtualizing WrapPanel .NET Visit and bookmark SilverlightShow. Stay in the 'Light 

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• SQL Auto Close Options

  - by Dave Noderer

  Found an interesting thing that others have run across but it is the first time I’ve seen it. A customer emailed to say that the SQL 2008 db that I had helped him with seemed to be going into recovery mode on a regular basis while watching the SQL Management Studio screen. Needless to say he was a bit nervous and about to take some drastic steps. Eventually he found that the Auto Close option was set to true. When this is set to true, the database automatically closes all connections and unlocks the mdf file after 300 milliseconds. When a new connection is made it spins backup… Great for xcopy deployment on a client machine but not a multi-user server based application. So the warning… if you have started a database with SQL express and then move it to a production SQL server, make sure you check that the Auto Close option is set to false. See options screen below:

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• Proper policy for user setup

  - by Dave Long

  I am still fairly new to linux hosting and am currently working on some policies for our production ubuntu servers. The servers are public facing webservers with ssh access from the public network and database servers with ssh access from the internal private network. We are a small hosting company so in the past with windows servers we used one user account and one password that each of us used internally. Anyone outside of the company who needed to access the server for FTP or anything else had their own user account. Is that okay to do in the linux world, or would most people recommend using individual accounts for each person who needs to access the server?

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• Window manager not loading when gnome-classic starts

  - by Dave M G

  When I boot up or log into gnome-classic (no effects), windows don't have the frame around them that has the minimize and close buttons and all that. After that, there all sorts of issues - for example, when I open a new window, it's in the very top left corner, obscuring the menu on the gnome panel... just a whole bunch of minor annoyances. I can get things working by by loading the compiz fusion icon and then selecting to reload the window manager. Of course this is less than ideal. How do I get the window manager to load automatically? Update: It seems that I get no window manager whenever I load Compiz, even after logging in. So it looks like the problem is more generally with Compiz's window manager.

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• "Walking" along a rotating surface in LimeJS

  - by Dave Lancea

  I'm trying to have a character walk along a plank (a long, thin rectangle) that works like a seesaw, being rotated around a central point by box2d physics (falling objects). I want the left and right arrow keys to move the player up and down the plank, regardless of it's slope, and I don't want to use real physics for the player movement. My idea for achieving this was to compute the coordinate based on the rotation of the plank and the current location "up" or "down" the board. My math is derived from here: http://math.stackexchange.com/questions/143932/calculate-point-given-x-y-angle-and-distance Here's the code I have so far: movement = 0; if(keys[37]){ // Left movement = -3; } if(keys[39]){ // Right movement = 3; } // this.plank is a LimeJS sprite. // getRotation() Should return an angle in degrees var rotation = this.plank.getRotation(); // this.current_plank_location is initialized as 0 this.current_plank_location += movement; var x_difference = this.current_plank_location * Math.cos(rotation); var y_difference = this.current_plank_location * Math.sin(rotation); this.setPosition(seesaw.PLANK_CENTER_X + x_difference, seesaw.PLANK_CENTER_Y + y_difference); This code causes the player to swing around in a circle when they are out of the center of the plank given a slight change in rotation of the plank. Any ideas on how I can get the player position to follow the board position?

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• Performance triage

  - by Dave

  Folks often ask me how to approach a suspected performance issue. My personal strategy is informed by the fact that I work on concurrency issues. (When you have a hammer everything looks like a nail, but I'll try to keep this general). A good starting point is to ask yourself if the observed performance matches your expectations. Expectations might be derived from known system performance limits, prototypes, and other software or environments that are comparable to your particular system-under-test. Some simple comparisons and microbenchmarks can be useful at this stage. It's also useful to write some very simple programs to validate some of the reported or expected system limits. Can that disk controller really tolerate and sustain 500 reads per second? To reduce the number of confounding factors it's better to try to answer that question with a very simple targeted program. And finally, nothing beats having familiarity with the technologies that underlying your particular layer. On the topic of confounding factors, as our technology stacks become deeper and less transparent, we often find our own technology working against us in some unexpected way to choke performance rather than simply running into some fundamental system limit. A good example is the warm-up time needed by just-in-time compilers in Java Virtual Machines. I won't delve too far into that particular hole except to say that it's rare to find good benchmarks and methodology for java code. Another example is power management on x86. Power management is great, but it can take a while for the CPUs to throttle up from low(er) frequencies to full throttle. And while I love "turbo" mode, it makes benchmarking applications with multiple threads a chore as you have to remember to turn it off and then back on otherwise short single-threaded runs may look abnormally fast compared to runs with higher thread counts. In general for performance characterization I disable turbo mode and fix the power governor at "performance" state. Another source of complexity is the scheduler, which I've discussed in prior blog entries. Lets say I have a running application and I want to better understand its behavior and performance. We'll presume it's warmed up, is under load, and is an execution mode representative of what we think the norm would be. It should be in steady-state, if a steady-state mode even exists. On Solaris the very first thing I'll do is take a set of "pstack" samples. Pstack briefly stops the process and walks each of the stacks, reporting symbolic information (if available) for each frame. For Java, pstack has been augmented to understand java frames, and even report inlining. A few pstack samples can provide powerful insight into what's actually going on inside the program. You'll be able to see calling patterns, which threads are blocked on what system calls or synchronization constructs, memory allocation, etc. If your code is CPU-bound then you'll get a good sense where the cycles are being spent. (I should caution that normal C/C++ inlining can diffuse an otherwise "hot" method into other methods. This is a rare instance where pstack sampling might not immediately point to the key problem). At this point you'll need to reconcile what you're seeing with pstack and your mental model of what you think the program should be doing. They're often rather different. And generally if there's a key performance issue, you'll spot it with a moderate number of samples. I'll also use OS-level observability tools to lock for the existence of bottlenecks where threads contend for locks; other situations where threads are blocked; and the distribution of threads over the system. On Solaris some good tools are mpstat and too a lesser degree, vmstat. Try running "mpstat -a 5" in one window while the application program runs concurrently. One key measure is the voluntary context switch rate "vctx" or "csw" which reflects threads descheduling themselves. It's also good to look at the user; system; and idle CPU percentages. This can give a broad but useful understanding if your threads are mostly parked or mostly running. For instance if your program makes heavy use of malloc/free, then it might be the case you're contending on the central malloc lock in the default allocator. In that case you'd see malloc calling lock in the stack traces, observe a high csw/vctx rate as threads block for the malloc lock, and your "usr" time would be less than expected. Solaris dtrace is a wonderful and invaluable performance tool as well, but in a sense you have to frame and articulate a meaningful and specific question to get a useful answer, so I tend not to use it for first-order screening of problems. It's also most effective for OS and software-level performance issues as opposed to HW-level issues. For that reason I recommend mpstat & pstack as my the 1st step in performance triage. If some other OS-level issue is evident then it's good to switch to dtrace to drill more deeply into the problem. Only after I've ruled out OS-level issues do I switch to using hardware performance counters to look for architectural impediments.

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• Why can't i ping server? VMware set to 'Bridged' loses IP address on 10.04.

  - by Dave

  I have installed a fresh 10.04 server onto a laptop on a home network as a VMware machine and set network connection to 'Bridged: connect directly to the physical network' from within VMware and rebooted the server. It then loses its IP address. 'dhclient eth0' says "No working leases in persistent database - sleeping" DHCP is working fine on the wi-fi router. The laptop is wired to a wireless router and from there wirelessly to a desktop. Desktop and Laptop can ping each other from Windows. I can ping the VM from Windows on the same laptop, but not from the desktop. Strangely ping has started to resolve hostnames to IPv6 addresses and not IPv4. Don't know whether that's connected? A kick in the right direction would be greatly appreciated. I've been an Ubuntu desktkop user for a few years, but new to ubuntu servers.

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• Using elapsed time for SlowMo in XNA

  - by Dave Voyles

  I'm trying to create a slow-mo effect in my pong game so that when a player is a button the paddles and ball will suddenly move at a far slower speed. I believe my understanding of the concepts of adjusting the timing in XNA are done, but I'm not sure of how to incorporate it into my design exactly. The updates for my bats (paddles) are done in my Bat.cs class: /// Controls the bat moving up the screen /// </summary> public void MoveUp() { SetPosition(Position + new Vector2(0, -moveSpeed)); } /// <summary> /// Controls the bat moving down the screen /// </summary> public void MoveDown() { SetPosition(Position + new Vector2(0, moveSpeed)); } /// <summary> /// Updates the position of the AI bat, in order to track the ball /// </summary> /// <param name="ball"></param> public virtual void UpdatePosition(Ball ball) { size.X = (int)Position.X; size.Y = (int)Position.Y; } While the rest of my game updates are done in my GameplayScreen.cs class (I'm using the XNA game state management sample) Class GameplayScreen { ........... bool slow; .......... public override void Update(GameTime gameTime, bool otherScreenHasFocus, bool coveredByOtherScreen) base.Update(gameTime, otherScreenHasFocus, false); if (IsActive) { // SlowMo Stuff Elapsed = (float)gameTime.ElapsedGameTime.TotalSeconds; if (Slowmo) Elapsed *= .8f; MoveTimer += Elapsed; double elapsedTime = gameTime.ElapsedGameTime.TotalMilliseconds; if (Keyboard.GetState().IsKeyDown(Keys.Up)) slow = true; else if (Keyboard.GetState().IsKeyDown(Keys.Down)) slow = false; if (slow == true) elapsedTime *= .1f; // Updating bat position leftBat.UpdatePosition(ball); rightBat.UpdatePosition(ball); // Updating the ball position ball.UpdatePosition(); and finally my fixed time step is declared in the constructor of my Game1.cs Class: /// <summary> /// The main game constructor. /// </summary> public Game1() { IsFixedTimeStep = slow = false; } So my question is: Where do I place the MoveTimer or elapsedTime, so that my bat will slow down accordingly?

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• Best scripting language for project [on hold]

  - by Dave

  This is a subjective question, but I don't know where else to ask it. I'd appreciate it if someone could direct me to an appropriate scripting language for my project. I'm a little new at this so I'd appreciate any help. The project is a website that will display a list of photo subject groups (such as "nature" "people" "sports" etc) on the home page. The photos will all be in subdirectories of the main photo directory (photos) and each subject group will represent a subdirectory in photos. For example in directory photos there might be 3 subdirectories, "nature" "people" "sports" and in each of those subdirectories there will be the actual photos. The idea is that when the website owner wants to update/add/delete a subject group all he has to do is add, delete or update a subdirectory of the photos directory. This means, I think, that I need a scripting language that can read the directories and files in the website and then send a web page with the information in it. What is the simplest and easiest scripting language to do this in? Any ideas? Thanks

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• How can I force a preferred sound output device to be used?

  - by Dave M G

  In my sound settings interface, there are two devices for sound output: Both refer to the same physical device, which is a network sound device. Both work, but only with the second one, Simultaneous output to Kenwook Audio Device Digital Stereo (IEC958) on mythbuntu@mythbuntu, does the output volume respond to being changed. The first one always plays at the same level, and ignores volume settings. Every time I boot, the first one is selected. How can I make it so the second one is the default and the first one is disabled or at least never selected?

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• Viewport / Camera Calculation in 2D Game

  - by Dave

  we have a 2D game with some sprites and tiles and some kind of camera/viewport, that "moves" around the scene. so far so good, if we wouldn't had some special behaviour for your camera/viewport translation. normally you could stick the camera to your player figure and center it, resulting in a very cheap, undergraduate, translation equation, like : vec_translation -/+= speed (depending in what keys are pressed. WASD as default.) buuuuuuuuuut, we want our player figure be able to actually reach the bounds, when the viewport/camera has reached a maximum translation. we came up with the following solution (only keys a and d are the shown here, the rest is just adaption of calculation or maybe YOUR super-cool and elegant solution :) ): if(keys[A]) { playerX -= speed; if(playerScreenX <= width / 2 && tx < 0) { playerScreenX = width / 2; tx += speed; } else if(playerScreenX <= width / 2 && (tx) >= 0) { playerScreenX -= speed; tx = 0; if(playerScreenX < 0) playerScreenX = 0; } else if(playerScreenX >= width / 2 && (tx) < 0) { playerScreenX -= speed; } } if(keys[D]) { playerX += speed; if(playerScreenX >= width / 2 && (-tx + width) < sceneWidth) { playerScreenX = width / 2; tx -= speed; } if(playerScreenX >= width / 2 && (-tx + width) >= sceneWidth) { playerScreenX += speed; tx = -(sceneWidth - width); if(playerScreenX >= width - player.width) playerScreenX = width - player.width; } if(playerScreenX <= width / 2 && (-tx + width) < sceneWidth) { playerScreenX += speed; } } i think the code is rather self explaining: keys is a flag container for currently active keys, playerX/-Y is the position of the player according to world origin, tx/ty are the translation components vital to background / npc / item offset calculation, playerOnScreenX/-Y is the actual position of the player figure (sprite) on screen and width/height are the dimensions of the camera/viewport. this all looks quite nice and works well, but there is a very small and nasty calculation error, which in turn sums up to some visible effect. let's consider following piece of code: if(playerScreenX <= width / 2 && tx < 0) { playerScreenX = width / 2; tx += speed; } it can be translated into plain english as : if the x position of your player figure on screen is less or equal the half of your display / camera / viewport size AND there is enough space left LEFT of your viewport/camera then set players x position on screen to width half, increase translation (because we subtract the translation from something we want to move). easy, right?! doing this will create a small delta between playerX and playerScreenX. after so much talking, my question appears now here at the bottom of this document: how do I stick the calculation of my player-on-screen to the actual position of the player AND having a viewport that is not always centered aroung the players figure? here is a small test-case in processing: http://pastebin.com/bFaTauaa thank you for reading until now and thank you in advance for probably answering my question.

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• Drawing a texture at the end of a trace (crosshair?) UDK

  - by Dave Voyles

  I'm trying to draw a crosshair at the end of my trace. If my crosshair does not hit a pawn or static mesh (ex, just a skybox) then the crosshair stays locked on a certain point at that actor - I want to say its origin. Ex: Run across a pawn, then it turns yellow and stays on that pawn. If it runs across the skybox, then it stays at one point on the box. Weird? How can I get my crosshair to stay consistent? I've included two images for reference, to help illustrate. Note: The wrench is actually my crosshair. The "X" is just a debug crosshair. Ignore that. /// Image 1 /// /// Image 2 /// /*************************************************************************** * Draws the crosshair ***************************************************************************/ function bool CheckCrosshairOnFriendly() { local float CrosshairSize; local vector HitLocation, HitNormal, StartTrace, EndTrace, ScreenPos; local actor HitActor; local MyWeapon W; local Pawn MyPawnOwner; /** Sets the PawnOwner */ MyPawnOwner = Pawn(PlayerOwner.ViewTarget); /** Sets the Weapon */ W = MyWeapon(MyPawnOwner.Weapon); /** If we don't have an owner, then get out of the function */ if ( MyPawnOwner == None ) { return false; } /** If we have a weapon... */ if ( W != None) { /** Values for the trace */ StartTrace = W.InstantFireStartTrace(); EndTrace = StartTrace + W.MaxRange() * vector(PlayerOwner.Rotation); HitActor = MyPawnOwner.Trace(HitLocation, HitNormal, EndTrace, StartTrace, true, vect(0,0,0),, TRACEFLAG_Bullet); DrawDebugLine(StartTrace, EndTrace, 100,100,100,); /** Projection for the crosshair to convert 3d coords into 2d */ ScreenPos = Canvas.Project(HitLocation); /** If we haven't hit any actors... */ if ( Pawn(HitActor) == None ) { HitActor = (HitActor == None) ? None : Pawn(HitActor.Base); } } /** If our trace hits a pawn... */ if ((Pawn(HitActor) == None)) { /** Draws the crosshair for no one - Grey*/ CrosshairSize = 28 * (Canvas.ClipY / 768) * (Canvas.ClipX /1024); Canvas.SetDrawColor(100,100,128,255); Canvas.SetPos(ScreenPos.X - (CrosshairSize * 0.5f), ScreenPos.Y -(CrosshairSize * 0.5f)); Canvas.DrawTile(class'UTHUD'.default.AltHudTexture, CrosshairSize, CrosshairSize, 600, 262, 28, 27); return false; } /** Draws the crosshair for friendlies - Yellow */ CrosshairSize = 28 * (Canvas.ClipY / 768) * (Canvas.ClipX /1024); Canvas.SetDrawColor(255,255,128,255); Canvas.SetPos(ScreenPos.X - (CrosshairSize * 0.5f), ScreenPos.Y -(CrosshairSize * 0.5f)); Canvas.DrawTile(class'UTHUD'.default.AltHudTexture, CrosshairSize, CrosshairSize, 600, 262, 28, 27); return true; }

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• How do I create my own programming language and a compiler for it

  - by Dave

  I am thorough with programming and have come across languages including BASIC, FORTRAN, COBOL, LISP, LOGO, Java, C++, C, MATLAB, Mathematica, Python, Ruby, Perl, Javascript, Assembly and so on. I can't understand how people create programming languages and devise compilers for it. I also couldn't understand how people create OS like Windows, Mac, UNIX, DOS and so on. The other thing that is mysterious to me is how people create libraries like OpenGL, OpenCL, OpenCV, Cocoa, MFC and so on. The last thing I am unable to figure out is how scientists devise an assembly language and an assembler for a microprocessor. I would really like to learn all of these stuff and I am 15 years old. I always wanted to be a computer scientist some one like Babbage, Turing, Shannon, or Dennis Ritchie. I have already read Aho's Compiler Design and Tanenbaum's OS concepts book and they all only discuss concepts and code in a high level. They don't go into the details and nuances and how to devise a compiler or operating system. I want a concrete understanding so that I can create one myself and not just an understanding of what a thread, semaphore, process, or parsing is. I asked my brother about all this. He is a SB student in EECS at MIT and hasn't got a clue of how to actually create all these stuff in the real world. All he knows is just an understanding of Compiler Design and OS concepts like the ones that you guys have mentioned (ie like Thread, Synchronisation, Concurrency, memory management, Lexical Analysis, Intermediate code generation and so on)

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• Why can't I ping server? VMware set to 'Bridged' loses IP address

  - by Dave

  I have installed a fresh 10.04 server onto a laptop on a home network as a VMware machine and set network connection to 'Bridged: connect directly to the physical network' from within VMware and rebooted the server. It then loses its IP address. dhclient eth0 says "No working leases in persistent database - sleeping" DHCP is working fine on the wi-fi router. The laptop is wired to a wireless router and from there wirelessly to a desktop. Desktop and Laptop can ping each other from Windows. I can ping the VM from Windows on the same laptop, but not from the desktop. Strangely ping has started to resolve hostnames to IPv6 addresses and not IPv4. Don't know whether that's connected? A kick in the right direction would be greatly appreciated. I've been an Ubuntu desktkop user for a few years, but new to ubuntu servers.

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• Execution plan warnings–All that glitters is not gold

  - by Dave Ballantyne

  In a previous post, I showed you the new execution plan warnings related to implicit and explicit warnings.  Pretty much as soon as i hit ’post’,  I noticed something rather odd happening. This statement : select top(10) SalesOrderHeader.SalesOrderID, SalesOrderNumberfrom Sales.SalesOrderHeaderjoin Sales.SalesOrderDetail on SalesOrderHeader.SalesOrderID = SalesOrderDetail.SalesOrderID   Throws the “Type conversion may affect cardinality estimation” warning.     Ive done no such conversion in my statement why would that be ?  Well, SalesOrderNumber is a computed column , “(isnull(N'SO'+CONVERT([nvarchar](23),[SalesOrderID],0),N'*** ERROR ***'))”,  so thats where the conversion is.   Wait!!! Am i saying that every type conversion will throw the warning ?  Thankfully, no.  It only appears for columns that are used in predicates ,even if the predicate / join condition is fine ,  and the column is indexed ( and/or , presumably has statistics).    Hopefully , this wont lead to to many wild goose chases, but is definitely something to bear in mind.  If you want to see this fixed then upvote my connect item here.

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• 301 redirects mirrored domain

  - by Dave

  I'm redesigning a site for a friend on my localhost. His old site is an .asp based site and we're replacing it with a WordPress site on LAMP hosting. The old site sits on domain A and also has another domain, domain B parked on top of it mirroring it. Google has picked up domain B for most of his search engine results and yahoo and bing etc have picked up domain A. The plan is to 301 redirect the the old pages of his site on domain A to the new WordPress versions and park domain B on top of it like before. My question is, will this work, if not what would be a better way to approach it? We'd prefer not to lose any of the search engine listings in the redesign, and the search engines don't appear to have penalized him for duplicate content. Thanks very much in advance!

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• I created a program based on an LGPL project, and I'm not allowed to publish the source code

  - by Dave

  I thought LGPL was a permissive license, just like MIT, BSD or Apache. But today I read, that only linking to LGPL (libraries etc) is allowed from closed-source code - other than that, it's copyleft - so I have to publish code that is based on an LGPL program. I created a program for my employer that is based on an LGPL program, but has considerable modifications to it. Of course, I am not allowed to put that modified source code out there. At the same time, I have to, if I distribute it (right?). So I wonder whether there is a workaround to this, so I can keep this closed-source (I wish I could publish the source) - any suggestions? My idea: can I put most functions of the original LGPL app into an external library, write the core executable from scratch, but refer back to the library for all functions that I haven't modified? Currently, everything is in a .jar file (it's Java/Swing). if you think my idea is legally/technically feasible - how much effort would it be to seperate what I wrote and what the original is? I'm not the most java savvy.

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• Two Copies of "Silverlight 5 In Action" to Give Away and a FREE chapter!

  - by Dave Campbell

  I know most of you have seen my post from Tuesday where I talked about giving away 2 copies of Pete's book on Monday morning July 18th. Well... I'm repeating it, because it's a smoking deal... for the cost of an email you too can take a shot at getting Pete's latest released "Silverlight 5 In Action" free. 2 Important Pieces of Information 1) The deadline: midnight Sunday night, July 17, 2012, Arizona time... if you know me, you know I've lived here too long and am timezone stupid... so don't make me calculate it out :) 2) The how: I have a special email address for submittals: mailto:[email protected]?Subject=Giveaway. 3) oh yeah... I lied about only 2 pieces of info... number 3 ... there may be other surprises on Monday morning... 'nuff said 4) and just to pump up the volume on the book... how about a Free chapter you can read right here on Working with RSS and Atom! 5) send me an email and Stay in the 'Light!

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• Blogging from 37,000ft

  - by Dave Ballantyne

  Im currently on my way to Sql Rally nordic and looking forward to a few days of full on SQL geekery and “Unleashing my inner Viking”.  I shall be speaking on Wednesday afternoon on one of my favourite subjects “Cursors are Evil”.  Ok,  so lets put it into perspective, “Evil” is a bit dramatic , but “Often use inappropriately and can cause serious performance bottlenecks” didn't have quite the same ring If you are not going to be at SQL Rally,  im going to be repeating it at the Leeds and Manchester user groups on the 23rd and 24th of November respectively.  Presenting with me on these nights will be James Boother, so make it along to those if you can.  I look forward to seeing you at one of these events.

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• Not mounting/finding 1TB NTFS drive

  - by Dave

  I am having trouble with Ubuntu recognizing/finding/mounting one of my hard drives. I dual boot Ubuntu and Windows 7. I had Ubuntu 10.04 and all drives showed up under "Places" I could click on any of my Windows/NTFS drives and they would mount as they should. I have since updated to Ubuntu 10.10. One of my drives no longer shows up in "Places" or in Nautilus. I can open gparted and it is listed there, but if I try to click the mount button, I get an error. I am currently at work and can not post any screenshots or errors, but will happily do so later. I was just hoping that someone might be able to give me something to try when I get home. 250gig SATA hard drive (Windows7/NTFS) - recognized/mountable 200gig PATA hard drive (Ubuntu 10.10) - recognized (obviously) 1TB SATA hard drive (NTFS) - not recognized/won't mount Thanks!

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