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  • Understanding T-SQL Expression Short-Circuiting

    Understanding the basics of how T-SQL logic works in branching is important to ensure you code works as expected. This article will help you learn how this impacts control of flow language. Join SQL Backup’s 35,000+ customers to compress and strengthen your backups "SQL Backup will be a REAL boost to any DBA lucky enough to use it." Jonathan Allen. Download a free trial now.

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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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  • Sharing SCTP connection with multiple threads

    - by poly
    I have an application that needs to run in SCTP environment, I have a question in sharing the connection among multiple threads for packet receiving only, I've tried with the sctp_sendmsg and it worked without even locking the threads (is that been taking care of by the OS, in other words, is it thread safe to do that). I've tested many cases with the send and I can't see them out of sync. Anyway, back to the receiving, is it possible to create multiple threads and send each thread the sctp descriptor to start receiving messages? Do I need a lock here or is it ok without lock? I'm using C in linux.

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  • Make Money by Building Findable Websites

    Do you want to put up an online business? Then, you need a website to promote your business. A professional quality website will enable you to reach out to more potential customers, no matter how small or big your business is. If you own a business, building findable websites for it will boost up your online presence. Moreover, you also get the chance to generate more profit.

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  • The EXCEPT and INTERSECT Operators in SQL Server

    The UNION, EXCEPT and INTERSECT operators of SQL enable you to combine more than one SELECT statement to form a single result set. Rob Sheldon explains all, with plenty of examples. Join SQL Backup’s 35,000+ customers to compress and strengthen your backups "SQL Backup will be a REAL boost to any DBA lucky enough to use it." Jonathan Allen. Download a free trial now.

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  • Is there now any way to convert mp3 files to m4a or aac 192kbit?

    - by piedro
    Since about two years now I am trying to find a way to convert high quality mp3 files to m4a or aac files with a fixed bitrate 192k. Please don't suggest using another format - i thought this through as far as it goes. The problem here is: ffmpeg obvioulsy can't convert to a higher bitrate than 152k. Even when it says it does so the resulting files still have 152k instead of 192k. ffmpeg also has/had a bug not writing the bitrate into the audio file tags which means when testing you have to calculate the bitrate manually by dividing the filesize by the length of the audio in seconds (resulting in 152k - see above) choosing faac as converter gets me the same results other programs don't work reliably (see this thread Howto convert audio files to *.m4a? I know that this is not an original new problem but I am wondering if there is still no way to convert with ubuntu/kubuntu 12.04 after a lot time passed and I can't find some of the bug issues mentioned in the other thread anymore. So: Is there a solution after all?

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  • How do I get the Netgear N150 USB wifi adapter working on 12.04?

    - by Jon
    Just installed latest version of ubuntu. I'm using a Netgear N150 Wireless USB Micro Adapter WNA1000M which keeps asking for network password over and over. I read elsewhere that I needed to install the latest driver for my chipset (RTL8188CUS) which I have and still no joy. If I run the steps listed in this thread while connected through ethernet, the wireless will connect just fine. If I disconnect the ethernet, the wifi will even continue to work, but after a restart or two I will lose connection. If I repeat the steps listed in the aforementioned thread, it will not re-connect wifi unless I run those steps while connected to ethernet.......so strange...

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  • TSQL Challenge 47 - Read the modification history and identify the fir

    A table contains the list of modifications made to each card. Your job is to write a query that shows the first number, current number (most recent) and the number of changes made. Join SQL Backup’s 35,000+ customers to compress and strengthen your backups "SQL Backup will be a REAL boost to any DBA lucky enough to use it." Jonathan Allen. Download a free trial now.

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  • Criteria for selecting timeout value?

    - by stijn
    Situation: a piece of software reads frames of data from a file in a seperate thread and puts it on a queue, emptied by another thread. That second thread periodically checks on the queue and fails rather gracefully, by showing an error message stating the read timed out, if no data is available within a certain amount of time. Initially this timeout was set to 200mSec. There was no real reasoning behind that constant though, but it worked fine. We measured on a couple of machines and for large data frames, larger than what would be used by customers, a read took like 20mSec whith no other load on the machine. However one customer now gets timeout errors now and then (on the second try all is fine, probably the file is in cache or the virus scanner leaves it alone). The programmers are like 'well, yeah, but that customer's machine is full of cruft, virus scanners, tons of unneeded background processes etc'. Of course the customer is like 'hey this should just work, shouldn't it'? While the programers have a point, since the software is heavy enough to validate the need for a dedicated machine, that does not make the customer happy. Increasing the timeout to 2 seconds, for example, solves the problem. But I'd like to make a proper decision now instead of just randomly pick some magic constant that is probably ok in 99% of cases. What criteria should be used for that? We could just pick a large number, but that feels wrong. (and then we end up with a program that has the horrible bahaviour of hanging when trying to read from a disconnected drive for instance, whereas we'd rather make it show an error right away). Or we could make the timeout value a user setting, but then we need to ducument it clearly and even then not all customers are tech savy enough to really understand what it does. Or we could try and wait until another customer reports timeouts and increase the value again. And again. Until we find something ok for 99.99% of the cases.. Any good practice for this type of situation?

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  • LightView: JavaFX 2 real-time visualizer for GlassFish

    - by arungupta
    Adam Bien launched LightFish, a light-weight monitoring and visualization application for GlassFish. It comes with a introduction and a screencast to get you started. The tool provides monitoring information about threads and memory (such as heap size, thread count, peak thread count), transactions (commits and rollbacks), HTTP sessions, JDBC sessions, and even "paranormal activity". In a recently released first part of a tri-part article series at OTN, Adam explains how REST services can be exposed as bindable set of properties for JavaFX. The article titled "Enterprise side of JavaFX" shows how a practical combination of REST and JavaFX together. It explains how read-only and dynamic properties can be created. The fine-grained binding model allows clear separation of the view, presentation, and business logic. Read the first part here.

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  • Simple rendering produces minor stutter

    - by Ben
    For some reason, this game loop renders the movement of a simple rectangle with no stuttering. double currTime; double prevTime = System.nanoTime() / NANO_TO_SEC; double FPSTIMER = System.nanoTime(); double maxTimeDiff = 100.0 / 1000.0; double delta = 1.0 / 60.0; int processes = 0, frames = 0; while(true){ currTime = System.nanoTime() / NANO_TO_SEC; if(currTime - prevTime > maxTimeDiff) prevTime = currTime; if(currTime >= prevTime){ process(); processes++; prevTime += delta; if(currTime < prevTime){ render(); frames++; } } else{ try{ Thread.sleep((long) (1000 * (prevTime - currTime))); } catch(Exception e){} } if(System.nanoTime() - FPSTIMER > 1000000000.0){ System.out.println("Process: " + (1000 / processes) + "ms FPS: " + (1000 / frames) + "ms"); processes = frames = 0; FPSTIMER += 1000000000.0; } } But for this game loop, I get really minor stuttering where the movement does not look smooth. long prevTime = System.currentTimeMillis(); long prevRenderTime = 0; long currRenderTime = 0; long delta = 0; long msPerTick = 1000 / 60; int frames = 0; int ticks = 0; double FPSTIMER = System.currentTimeMillis(); while (true){ long currTime = System.currentTimeMillis(); delta += (currTime - prevTime) / msPerTick; prevTime = currTime; while (delta >= 1){ ticks++; process(); delta -= 1; } prevRenderTime = System.currentTimeMillis(); render(); frames++; currRenderTime = System.currentTimeMillis(); try{ Thread.sleep((long) ((1000 / FPS) - (currRenderTime - prevRenderTime))); } catch(Exception e){} if(System.currentTimeMillis() - FPSTIMER > 1000.0){ System.out.println("Process: " + (1000.0 / ticks) + "ms FPS: " + (1000.0 / frames) + "ms"); ticks = frames = 0; FPSTIMER += 1000.0; } Is there any critical difference that I'm missing here? The one thing I noticed is that if I uncap the fps for the second game loop, the stuttering goes away. It doesn't make sense to me. Also, the second game loop came from Notch's Minicraft code with just my thread sleeping code added in.

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  • Profiling Database Activity in the Entity Framework

    It’s important to profile your database queries to see what happens in response to Entity Framework queries and other data access activities, says Julie Lerman, who gives you the details on several profiling options to improve you coding. Join SQL Backup’s 35,000+ customers to compress and strengthen your backups "SQL Backup will be a REAL boost to any DBA lucky enough to use it." Jonathan Allen. Download a free trial now.

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  • Is premature optimization really the root of all evil?

    - by Craig Day
    A colleague of mine today committed a class called ThreadLocalFormat, which basically moved instances of Java Format classes into a thread local, since they are not thread safe and "relatively expensive" to create. I wrote a quick test and calculated that I could create 200,000 instances a second, asked him was he creating that many, to which he answered "nowhere near that many". He's a great programmer and everyone on the team is highly skilled so we have no problem understanding the resulting code, but it was clearly a case of optimizing where there is no real need. He backed the code out at my request. What do you think? Is this a case of "premature optimization" and how bad is it really?

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  • 4 Best Website Building Tips to Learn

    If you want to boost up your exposure in the business industry, you will need an effective marketing tool. And one great tool to use for this purpose is a website. There are many businesses today which have benefited much on having a website. So you think it is hard to build a website? Well actually you need more patience to learn the best website building technique.

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  • Data Everywhere - Step 3 in the Stairway to Reporting Services

    In this article, MVP Jessica Moss talks about data sources and how to connect them to your report. Learn how to add the reusable data sets and data sources for your reporting projects. Join SQL Backup’s 35,000+ customers to compress and strengthen your backups "SQL Backup will be a REAL boost to any DBA lucky enough to use it." Jonathan Allen. Download a free trial now.

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  • Some tips for working with big data models

    The main goal of this article is to present some tips to help professionals that need to work with complex, big, and hard to understand database models that anyone may came across some day. Join SQL Backup’s 35,000+ customers to compress and strengthen your backups "SQL Backup will be a REAL boost to any DBA lucky enough to use it." Jonathan Allen. Download a free trial now.

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  • Delay command execution over sockets

    - by David
    I've been trying to fix the game loop in a real time (tick delay) MUD. I realized using Thread.Sleep would seem clunky when the user spammed commands through their choice of client (Zmud, etc) e.g. east;south;southwest would wait three move ticks and then output everything from the past couple rooms. The game loop basically calls a Flush and Fill method for each socket during each tick (50ms) private void DoLoop() { Stopwatch stopWatch = new Stopwatch(); stopWatch.Start(); while (running) { // for each socket, flush and fill ConnectionMonitor.Update(); stopWatch.Stop(); WaitIfNeeded(stopWatch.ElapsedMilliseconds); stopWatch.Reset(); } } The Fill method fires the command events, but as mentioned before, they currently block using Thread.Sleep. I tried adding a "ready" flag to the state object that attempts to execute the command along with a queue of spammed commands, but it ends up executing one command and queuing up the rest i.e. each subsequent command executes something that got queued up that should've been executed before. I must be missing something about the timer. private readonly Queue<SpammedCommand> queuedCommands = new Queue<SpammedCommand>(); private bool ready = true; private void TryExecuteCommand(string input) { var commandContext = CommandContext.Create(input); var player = Server.Current.Database.Get<Player>(Session.Player.Key); var commandInfo = Server.Current.CommandLookup .FindCommand(commandContext.CommandName, player.IsAdmin); if (commandInfo != null) { if (!ready) { // queue command queuedCommands.Enqueue(new SpammedCommand() { Context = commandContext, Info = commandInfo }); return; } if (queuedCommands.Count > 0) { // queue the incoming command queuedCommands.Enqueue(new SpammedCommand() { Context = commandContext, Info = commandInfo, }); // dequeue and execute var command = queuedCommands.Dequeue(); command.Info.Command.Execute(Session, command.Context); setTimeout(command.Info.TickLength); return; } commandInfo.Command.Execute(Session, commandContext); setTimeout(commandInfo.TickLength); } else { Session.WriteLine("Command not recognized"); } } Finally, setTimeout was supposed to set the execution delay (TickLength) for that command, and makeReady just sets the ready flag on the state object to true. private void setTimeout(TickDelay tickDelay) { ready = false; var t = new System.Timers.Timer() { Interval = (long) tickDelay, AutoReset = false, }; t.Elapsed += makeReady; t.Start(); // fire this in tickDelay ms } // MAKE READYYYYY!!!! private void makeReady(object sender, System.Timers.ElapsedEventArgs e) { ready = true; } Am I missing something about the System.Timers.Timer created in setTimeout? How can I execute (and output) spammed commands per TickLength without using Thread.Sleep?

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