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• Two radically different queries against 4 mil records execute in the same time - one uses brute force.

  - by IanC

  I'm using SQL Server 2008. I have a table with over 3 million records, which is related to another table with a million records. I have spent a few days experimenting with different ways of querying these tables. I have it down to two radically different queries, both of which take 6s to execute on my laptop. The first query uses a brute force method of evaluating possibly likely matches, and removes incorrect matches via aggregate summation calculations. The second gets all possibly likely matches, then removes incorrect matches via an EXCEPT query that uses two dedicated indexes to find the low and high mismatches. Logically, one would expect the brute force to be slow and the indexes one to be fast. Not so. And I have experimented heavily with indexes until I got the best speed. Further, the brute force query doesn't require as many indexes, which means that technically it would yield better overall system performance. Below are the two execution plans. If you can't see them, please let me know and I'll re-post then in landscape orientation / mail them to you. Brute-force query: Index-based exception query: My question is, based on the execution plans, which one look more efficient? I realize that thing may change as my data grows.

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• Doing coding in Linux through a virtual machine on Windows VS partitioning

  - by ihaveitnow

  I already have experience with setting up virtual machines, running them and other minor tasks. Im a gamer, so I wont get rid of windows (for now at least...) but I do want to be a great programmer and to be involved with the Open-Source community. Id like to know if its a good idea to do my programming in linux through a virtual machine, vs giving it a partitioned section of the HDD. Id like to know about performance pros and cons and functionality. All responses are appreciated, thanks in advance. The type of programming I intend to dive into : Android Dev, Web Dev, Desktop Dev...More Android and Web right now though. So im looking at C#,C,C++,Java,PHP,HTML,MySQL...Off the top of the dome. I do web designing as well, so dreamweaver is added as an "essential". But im sure I can do dreamweaver files and upload them to the server after programming in Linux...Right? And any info on IDE's in Linux for the above mentioned are appreciated, but i would prefer going the coding route and understanding the essence of whats happening "under the covers" Thanks to all for reading, I appreciate it. Hope this isnt confusing :S

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• Optimizing an embedded SELECT query in mySQL

  - by Crazy Serb

  Ok, here's a query that I am running right now on a table that has 45,000 records and is 65MB in size... and is just about to get bigger and bigger (so I gotta think of the future performance as well here): SELECT count(payment_id) as signup_count, sum(amount) as signup_amount FROM payments p WHERE tm_completed BETWEEN '2009-05-01' AND '2009-05-30' AND completed > 0 AND tm_completed IS NOT NULL AND member_id NOT IN (SELECT p2.member_id FROM payments p2 WHERE p2.completed=1 AND p2.tm_completed < '2009-05-01' AND p2.tm_completed IS NOT NULL GROUP BY p2.member_id) And as you might or might not imagine - it chokes the mysql server to a standstill... What it does is - it simply pulls the number of new users who signed up, have at least one "completed" payment, tm_completed is not empty (as it is only populated for completed payments), and (the embedded Select) that member has never had a "completed" payment before - meaning he's a new member (just because the system does rebills and whatnot, and this is the only way to sort of differentiate between an existing member who just got rebilled and a new member who got billed for the first time). Now, is there any possible way to optimize this query to use less resources or something, and to stop taking my mysql resources down on their knees...? Am I missing any info to clarify this any further? Let me know... EDIT: Here are the indexes already on that table: PRIMARY PRIMARY 46757 payment_id member_id INDEX 23378 member_id payer_id INDEX 11689 payer_id coupon_id INDEX 1 coupon_id tm_added INDEX 46757 tm_added, product_id tm_completed INDEX 46757 tm_completed, product_id

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• Non standard interaction among two tables to avoid very large merge

  - by riko

  Suppose I have two tables A and B. Table A has a multi-level index (a, b) and one column (ts). b determines univocally ts. A = pd.DataFrame( [('a', 'x', 4), ('a', 'y', 6), ('a', 'z', 5), ('b', 'x', 4), ('b', 'z', 5), ('c', 'y', 6)], columns=['a', 'b', 'ts']).set_index(['a', 'b']) AA = A.reset_index() Table B is another one-column (ts) table with non-unique index (a). The ts's are sorted "inside" each group, i.e., B.ix[x] is sorted for each x. Moreover, there is always a value in B.ix[x] that is greater than or equal to the values in A. B = pd.DataFrame( dict(a=list('aaaaabbcccccc'), ts=[1, 2, 4, 5, 7, 7, 8, 1, 2, 4, 5, 8, 9])).set_index('a') The semantics in this is that B contains observations of occurrences of an event of type indicated by the index. I would like to find from B the timestamp of the first occurrence of each event type after the timestamp specified in A for each value of b. In other words, I would like to get a table with the same shape of A, that instead of ts contains the "minimum value occurring after ts" as specified by table B. So, my goal would be: C: ('a', 'x') 4 ('a', 'y') 7 ('a', 'z') 5 ('b', 'x') 7 ('b', 'z') 7 ('c', 'y') 8 I have some working code, but is terribly slow. C = AA.apply(lambda row: ( row[0], row[1], B.ix[row[0]].irow(np.searchsorted(B.ts[row[0]], row[2]))), axis=1).set_index(['a', 'b']) Profiling shows the culprit is obviously B.ix[row[0]].irow(np.searchsorted(B.ts[row[0]], row[2]))). However, standard solutions using merge/join would take too much RAM in the long run. Consider that now I have 1000 a's, assume constant the average number of b's per a (probably 100-200), and consider that the number of observations per a is probably in the order of 300. In production I will have 1000 more a's. 1,000,000 x 200 x 300 = 60,000,000,000 rows may be a bit too much to keep in RAM, especially considering that the data I need is perfectly described by a C like the one I discussed above. How would I improve the performance?

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• How good is the memory mapped Circular Buffer on Wikipedia?

  - by abroun

  I'm trying to implement a circular buffer in C, and have come across this example on Wikipedia. It looks as if it would provide a really nice interface for anyone reading from the buffer, as reads which wrap around from the end to the beginning of the buffer are handled automatically. So all reads are contiguous. However, I'm a bit unsure about using it straight away as I don't really have much experience with memory mapping or virtual memory and I'm not sure that I fully understand what it's doing. What I think I understand is that it's mapping a shared memory file the size of the buffer into memory twice. Then, whenever data is written into the buffer it appears in memory in 2 places at once. This allows all reads to be contiguous. What would be really great is if someone with more experience of POSIX memory mapping could have a quick look at the code and tell me if the underlying mechanism used is really that efficient. Am I right in thinking for example that the file in /dev/shm used for the shared memory always stays in RAM or could it get written to the hard drive (performance hit) at some point? Are there any gotchas I should be aware of? As it stands, I'm probably going to use a simpler method for my current project, but it'd be good to understand this to have it in my toolbox for the future. Thanks in advance for your time.

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• OptimisticLockException in inner transaction ruins outer transaction

  - by Pace

  I have the following code (OLE = OptimisticLockException)... public void outer() { try { middle() } catch (OLE) { updateEntities(); outer(); } } @Transactional public void middle() { try { inner() } catch (OLE) { updateEntities(); middle(); } @Transactional public void inner() { //Do DB operation } inner() is called by other non-transactional methods which is why both middle() and inner() are transactional. As you can see, I deal with OLEs by updating the entities and retrying the operation. The problem I'm having is that when I designed things this way I was assuming that the only time one could get an OLE was when a transaction closed. This is apparently not the case as the call to inner() is throwing an OLE even when the stack is outer()->middle()->inner(). Now, middle() is properly handling the OLE and the retry succeeds but when it comes time to close the transaction it has been marked rollbackOnly by Spring. When the middle() method call finally returns the closing aspect throws an exception because it can't commit a transaction marked rollbackOnly. I'm uncertain what to do here. I can't clear the rollbackOnly state. I don't want to force create a transaction on every call to inner because that kills my performance. Am I missing something or can anyone see a way I can structure this differently? EDIT: To clarify what I'm asking, let me explain my main question. Is it possible to catch and handle OLE if you are inside of an @Transactional method? FYI: The transaction manager is a JpaTransactionManager and the JPA provider is Hibernate.

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• Testing approach for multi-threaded software

  - by Shane MacLaughlin

  I have a piece of mature geospatial software that has recently had areas rewritten to take better advantage of the multiple processors available in modern PCs. Specifically, display, GUI, spatial searching, and main processing have all been hived off to seperate threads. The software has a pretty sizeable GUI automation suite for functional regression, and another smaller one for performance regression. While all automated tests are passing, I'm not convinced that they provide nearly enough coverage in terms of finding bugs relating race conditions, deadlocks, and other nasties associated with multi-threading. What techniques would you use to see if such bugs exist? What techniques would you advocate for rooting them out, assuming there are some in there to root out? What I'm doing so far is running the GUI functional automation on the app running under a debugger, such that I can break out of deadlocks and catch crashes, and plan to make a bounds checker build and repeat the tests against that version. I've also carried out a static analysis of the source via PC-Lint with the hope of locating potential dead locks, but not had any worthwhile results. The application is C++, MFC, mulitple document/view, with a number of threads per doc. The locking mechanism I'm using is based on an object that includes a pointer to a CMutex, which is locked in the ctor and freed in the dtor. I use local variables of this object to lock various bits of code as required, and my mutex has a time out that fires my a warning if the timeout is reached. I avoid locking where possible, using resource copies where possible instead. What other tests would you carry out?

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• How to implement message queuing and handling in AWS with NServiceBus

  - by Pete Lunenfeld

  I am creating a new ASP MVC order application in the Amazon (AWS) cloud with the persistence layer at my local datacenter. I will be using the CQRS pattern. The goal of the project is high availability using Queue(s) to store and forward writes (commands/events) that can be picked up and handled asynchronously at my local datacenter. Then, ff the WAN or my local datacenter fails, my cloud MVC app can still take orders and just queue them up until processing can resume. My first thought was to use AWS SQS for the queuing and create my own queue consumer/dispatcher/handler in my own c# application to process the incoming messages/events. MVC (@ Amazon) -- Event/POCO -- SQS -- QueueReader (@ my datacenter) -- DB Then I found NServiceBus. NSB seems to handle lots of details very nicely: message handling, retries, error handling, etc. I hate to reinvent the wheel, and NServiceBus seems like a full featured and mature product that would be perfect for me. But on further research, it does NOT look like NServiceBus is really meant to be used over the WAN in physically separated environments (Cloud to my Datacenter). Google and SO don't really paint a good picture of using NServiceBus across the WAN like I need. How can I use NServiceBus across the WAN? Or is there a better solution to handle queuing and message handling between Amazon an my local datacenter?

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• Rails - any fancy ways to handle 404s?

  - by jyoseph

  I have a rails app I built for an old site I converted from another cms (in a non-rails language, hehe). Most of the old pages are mapped to the new pages using routes.rb. But there are still a few 404s. I am a rails newb so I'm asking if there are any advanced ways to handle 404s. For example, if I was programming in my old language I'd do this: Get the URL (script_name) that was being accessed and parse it. Do a lookup in the database for any keywords, ids, etc found in the new URL. If found, redirect to the page (or if multiple records are found, show them all on a results page and let user choose). With rails I'd probably want to do :status = :moved_permanently I'm guessing? If not found, show a 404. Are there any gems/plugins or tutorials you know of that would handle such a thing, if it's even possible. Or can you explain on a high level how that can be done? I don't need a full code sample, just a push in the right direction. PS. It's a simple rails 3 app that uses a single Content model.

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• Mamimum page fetch with maximum bandwith

  - by Ehsan

  Hi I want to create an application like a spider I've implement fetching page as the following code in multi-thread application but there is two problem 1) I want to use my maximum bandwidth to send/receive request, how should I config my request to do so (Like Download Accelerator application and the like) cause I heard the normal application will use 66% of the available bandwidth. 2) I don't know what exactly HttpWebRequest.KeepAlive do, but as its name implies I think i can create a connection to a website and without closing the connection sending another request to that web site using existing connection. does it boost performance or Im wrong public PageFetchResult Fetch() { PageFetchResult fetchResult = new PageFetchResult(); try { HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(URLAddress); HttpWebResponse resp = (HttpWebResponse)req.GetResponse(); Uri requestedURI = new Uri(URLAddress); Uri responseURI = resp.ResponseUri; if (Uri.Equals(requestedURI, responseURI)) { string resultHTML = ""; byte[] reqHTML = ResponseAsBytes(resp); if (!string.IsNullOrEmpty(FetchingEncoding)) resultHTML = Encoding.GetEncoding(FetchingEncoding).GetString(reqHTML); else if (!string.IsNullOrEmpty(resp.CharacterSet)) resultHTML = Encoding.GetEncoding(resp.CharacterSet).GetString(reqHTML); req.Abort(); resp.Close(); fetchResult.IsOK = true; fetchResult.ResultHTML = resultHTML; } else { URLAddress = responseURI.AbsoluteUri; relayPageCount++; if (relayPageCount > 5) { fetchResult.IsOK = false; fetchResult.ErrorMessage = "Maximum page redirection occured."; relayPageCount = 0; return fetchResult; } req.Abort(); resp.Close(); return Fetch(); } } catch (Exception ex) { fetchResult.IsOK = false; fetchResult.ErrorMessage = ex.Message; } return fetchResult; }

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• Python optimization problem?

  - by user342079

  Alright, i had this homework recently (don't worry, i've already done it, but in c++) but I got curious how i could do it in python. The problem is about 2 light sources that emit light. I won't get into details tho. Here's the code (that I've managed to optimize a bit in the latter part): import math, array import numpy as np from PIL import Image size = (800,800) width, height = size s1x = width * 1./8 s1y = height * 1./8 s2x = width * 7./8 s2y = height * 7./8 r,g,b = (255,255,255) arr = np.zeros((width,height,3)) hy = math.hypot print 'computing distances (%s by %s)'%size, for i in xrange(width): if i%(width/10)==0: print i, if i%20==0: print '.', for j in xrange(height): d1 = hy(i-s1x,j-s1y) d2 = hy(i-s2x,j-s2y) arr[i][j] = abs(d1-d2) print '' arr2 = np.zeros((width,height,3),dtype="uint8") for ld in [200,116,100,84,68,52,36,20,8,4,2]: print 'now computing image for ld = '+str(ld) arr2 *= 0 arr2 += abs(arr%ld-ld/2)*(r,g,b)/(ld/2) print 'saving image...' ar2img = Image.fromarray(arr2) ar2img.save('ld'+str(ld).rjust(4,'0')+'.png') print 'saved as ld'+str(ld).rjust(4,'0')+'.png' I have managed to optimize most of it, but there's still a huge performance gap in the part with the 2 for-s, and I can't seem to think of a way to bypass that using common array operations... I'm open to suggestions :D

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• Dangers when deploying Flash/Flex UI test automation hooks to production?

  - by Merlyn Morgan-Graham

  I am interested in doing automated testing against a Flex based UI. I have found out that my best options for UI automation (due to being C# controllable, good licensing conditions, etc) all seem to require that I compile test hooks into my application. Because of this, I am thinking of recommending that these hooks be compiled into our build. I have found a few places on the net that recommend not deploying bits with this instrumentation enabled, and I'd like to know why. Is it a performance drain, or a security risk? If it is a security risk, can you explain how the attack surface is increased? I am not a Flash or Flex developer, though I have some experience with threat modeling. For reference, here's the tools I'm specifically considering: QTP Selenium-Flex API I am having problems finding all the warnings/suggestions I found last night, but here's an example that I can find: http://www.riatest.com/products/getting-started.html Warning! Automation enabled applications expose all properties of all GUI components. This makes them vulnerable to malicious use. Never make automation enabled application publicly available. Always restrict access to such applications and to RIATest Loader to trusted users only. Related question (how to do conditional compilation to insert/remove those hooks): Conditionally including Flex libraries (SWCs) in mxmlc/compc ant tasks

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• Entity Framework autoincrement key

  - by Tommy Ong

  I'm facing an issue of duplicated incremental field on a concurrency scenario. I'm using EF as the ORM tool, attempting to insert an entity with a field that acts as a incremental INT field. Basically this field is called "SequenceNumber", where each new record before insert, will read the database using MAX to get the last SequenceNumber, append +1 to it, and saves the changes. Between the getting of last SequenceNumber and Saving, that's where the concurrency is happening. I'm not using ID for SequenceNumber as it is not a unique constraint, and may reset on certain conditions such as monthly, yearly, etc. InvoiceNumber | SequenceNumber | DateCreated INV00001_08_14 | 1 | 25/08/2014 INV00001_08_14 | 1 | 25/08/2014 <= (concurrency is creating two SeqNo 1) INV00002_08_14 | 2 | 25/08/2014 INV00003_08_14 | 3 | 26/08/2014 INV00004_08_14 | 4 | 27/08/2014 INV00005_08_14 | 5 | 29/08/2014 INV00001_09_14 | 1 | 01/09/2014 <= (sequence number reset) Invoice number is formatted based on the SequenceNumber. After some research I've ended up with these possible solutions, but wanna know the best practice 1) Optimistic Concurrency, locking the table from any reads until the current transaction is completed (not fancy of this idea as I guess performance will be of a great impact?) 2) Create a Stored Procedure solely for this purpose, does select and insert on a single statement as such concurrency is at minimum (would prefer a EF based approach if possible)

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• WPF data-bound ComboBox only shows first item of ItemsSource list

  - by Mark

  Hi all, I'm sure I'm doing something stupid but for the life of me I can't think of right now. I have a ComboBox that is data-bound to a list of Layout objects. The list is initially empty but things are added over time. When the list is updated by the model the first time, this update reflects properly in the ComboBox. However, subsequent updates never show up in the ComboBox even though I can see that the list itself contains these items. Since the first update works, I know the data-binding is OK - so what am I doing wrong here? Here's the XAML (abridged): <Grid HorizontalAlignment="Stretch"> <ComboBox ItemsSource="{Binding Path=SavedLayouts, diagnostics:PresentationTraceSources.TraceLevel=High}" DisplayMemberPath="Name" SelectedValuePath="Name" SelectedItem="{Binding LoadLayout}" Height="25" Grid.Row="1" Grid.Column="0"></ComboBox> </Grid> And the related part of the model: public IList<Layout> SavedLayouts { get { return _layouts; } } public Layout SaveLayout( String data_ ) { Layout theLayout = new Layout( SaveLayoutName ); _layouts.Add( theLayout ); try { return theLayout; } finally { PropertyChangedEventHandler handler = PropertyChanged; if( handler != null ) { handler( this, new PropertyChangedEventArgs( "SavedLayouts" ) ); } } } And finally, the layout class (abridged): public class Layout { public String Name { get; private set; } } In the output window, I can see the update occurring: System.Windows.Data Warning: 91 : BindingExpression (hash=64564967): Got PropertyChanged event from TickerzModel (hash=43624632) System.Windows.Data Warning: 97 : BindingExpression (hash=64564967): GetValue at level 0 from TickerzModel (hash=43624632) using RuntimePropertyInfo(SavedLayouts): List`1 (hash=16951421 Count=11) System.Windows.Data Warning: 76 : BindingExpression (hash=64564967): TransferValue - got raw value List`1 (hash=16951421 Count=11) System.Windows.Data Warning: 85 : BindingExpression (hash=64564967): TransferValue - using final value List`1 (hash=16951421 Count=11) But I get do not get this 11th item in the ComboBox. Any ideas?

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• OpenGLES - Rendering a background image only once and not wiping it

  - by chaosbeaker

  Hello, first time asking a question here but been watching others answers for a while. My own question is one for improving the performance of my program. Currently I'm wiping the viewFrameBuffer on each pass through my program and then rendering the background image first followed by the rest of my scene. I was wondering how I go about rendering the background image once, and only wiping the rest of the scene for updating/re-rendering. I tried using a seperate buffer but I'm not sure how to present this new buffer to the render buffer. // Set the current EAGLContext and bind to the framebuffer. This will direct all OGL commands to the // framebuffer and the associated renderbuffer attachment which is where our scene will be rendered [EAGLContext setCurrentContext:context]; glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer); // Define the viewport. Changing the settings for the viewport can allow you to scale the viewport // as well as the dimensions etc and so I'm setting it for each frame in case we want to change i glViewport(0, 0, screenBounds.size.width , screenBounds.size.height); // Clear the screen. If we are going to draw a background image then this clear is not necessary // as drawing the background image will destroy the previous image glClearColor(0.0f, 1.0f, 0.0f, 1.0f); glClear(GL_COLOR_BUFFER_BIT); // Setup how the images are to be blended when rendered. This could be changed at different points during your // render process if you wanted to apply different effects glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); switch (currentViewInt) { case 1: { [background render:CGPointMake(240, 0) fromTopLeftBottomRightCenter:@"Bottom"]; // Other Rendering Code }} // Bind to the renderbuffer and then present this image to the current context glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer); [context presentRenderbuffer:GL_RENDERBUFFER_OES]; Hopefully by solving this I'll also be able to implement another buffer just for rendering particles as I can set them to always use a black background as their alpha source. Any help is greatly appreciated

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• AppFabric caching's local cache isnt working for us... What are we doing wrong?

  - by Olly

  We are using appfabric as the 2ndlevel cache for an NHibernate asp.net application comprising a customer facing website and an admin website. They are both connected to the same cache so when admin updates something, the customer facing site is updated. It seems to be working OK - we have a CacheCLuster on a seperate server and all is well but we want to enable localcache to get better performance, however, it dosnt seem to be working. We have enabled it like this... bool UseLocalCache = int LocalCacheObjectCount = int.MaxValue; TimeSpan LocalCacheDefaultTimeout = TimeSpan.FromMinutes(3); DataCacheLocalCacheInvalidationPolicy LocalCacheInvalidationPolicy = DataCacheLocalCacheInvalidationPolicy.TimeoutBased; if (UseLocalCache) { configuration.LocalCacheProperties = new DataCacheLocalCacheProperties( LocalCacheObjectCount, LocalCacheDefaultTimeout, LocalCacheInvalidationPolicy ); // configuration.NotificationProperties = new DataCacheNotificationProperties(500, TimeSpan.FromSeconds(300)); } Initially we tried using a timeout invalidation policy (3mins) and our app felt like it was running faster. HOWEVER, we noticed that if we changed something in the admin site, it was immediatley updated in the live site. As we are using timeouts not notifications, this demonstrates that the local cache isnt being queried (or is, but is always missing). The cache.GetType().Name returns "LocalCache" - so the factory has made a local cache. Running "Get-Cache-Statistics MyCache" in PS on my dev environment (asp.net app running local from vs2008, cache cluster running on a seperate w2k8 machine) show a handful of Request Counts. However, on the Production environment, the Request Count increases dramaticaly. We tried following the method here to se the cache cliebt-server traffic... http://blogs.msdn.com/b/appfabriccat/archive/2010/09/20/appfabric-cache-peeking-into-client-amp-server-wcf-communication.aspx but the log file had nothing but the initial header in it - i.e no loggin either. I cant find anything in SO or Google. Have we done something wrong? Have we got a screwy install of AppFabric - we installed it via WebPlatform Installer - I think? (note: the IIS box running ASp.net isnt in yhe cluster - it is just the client). Any insights greatfully received!

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• How to justify using a scripting language as part of a project

  - by sylvanaar

  I have a specific project in which I want to use either a scripting language + C, or as an alternative a 100% Java solution. The program adapts a legacy system for use with other moderns systems. Basically, I have few choices as to what language I can use. I have C/C++, Java 1.4, and I have also compiled the Lua for this environment. The program does 'screen scraping' and has to deal with alot of strings. That part of the code is highly variable. Most of the developers at my company use C, so - my original design was to write some portions in C, and use Lua for the part that dealt with strings and changed freqently. I was told 'You have to justify your use of the scripting language.' So i reworked my design using 100% Java, and was told - Java wont have enough performance. You should do the whole thing in C. I'm not controlling lasers or doing image processing - just some screen scraping. I still have to provide justification for using anything but C - so what justification can I provide?

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• PreparedStatement question in Java against Oracle.

  - by fardon57

  Hi everyone, I'm working on the modification of some code to use preparedStatement instead of normal Statement, for security and performance reason. Our application is currently storing information into an embedded derby database, but we are going to move soon to Oracle. I've found two things that I need your help guys about Oracle and Prepared Statement : 1- I've found this document saying that Oracle doesn't handle bind parameters into IN clauses, so we cannot supply a query like : Select pokemon from pokemonTable where capacity in (?,?,?,?) Is that true ? Is there any workaround ? ... Why ? 2- We have some fields which are of type TIMESTAMP. So with our actual Statement, the query looks like this : Select raichu from pokemonTable where evolution = TO_TIMESTAMP('2500-12-31 00:00:00.000', 'YYYY-MM-DD HH24:MI:SS.FF') What should be done for a prepared Statement ? Should I put into the array of parameters : 2500-12-31 or TO_TIMESTAMP('2500-12-31 00:00:00.000', 'YYYY-MM-DD HH24:MI:SS.FF') ? Thanks for your help, I hope my questions are clear ! Regards,

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• The CLR has been unable to transition from COM context [...] for 60 seconds

  - by BlueRaja The Green Unicorn

  I am getting this error on code that used to work. I have not changed the code. Here is the full error: The CLR has been unable to transition from COM context 0x3322d98 to COM context 0x3322f08 for 60 seconds. The thread that owns the destination context/apartment is most likely either doing a non pumping wait or processing a very long running operation without pumping Windows messages. This situation generally has a negative performance impact and may even lead to the application becoming non responsive or memory usage accumulating continually over time. To avoid this problem, all single threaded apartment (STA) threads should use pumping wait primitives (such as CoWaitForMultipleHandles) and routinely pump messages during long running operations. And here is the code that caused it: var openFileDialog1 = new System.Windows.Forms.OpenFileDialog(); openFileDialog1.DefaultExt = "mdb"; openFileDialog1.Filter = "Management Database (manage.mdb)|manage.mdb"; //Stalls indefinitely on the following line, then gives the CLR error //one minute later. The dialog never opens. if(openFileDialog1.ShowDialog() == DialogResult.OK) { .... } Yes, I am sure the dialog is not open in the background, and no, I don't have any explicit COM code or unmanaged marshalling or multithreading. I have no idea why the OpenFileDialog won't open - any ideas?

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• Async task ASP.net HttpContext.Current.Items is empty - How do handle this?

  - by GuruC

  We are running a very large web application in asp.net MVC .NET 4.0. Recently we had an audit done and the performance team says that there were a lot of null reference exceptions. So I started investigating it from the dumps and event viewer. My understanding was as follows: We are using Asyn Tasks in our controllers. We rely on HttpContext.Current.Items hashtable to store a lot of Application level values. Task<Articles>.Factory.StartNew(() => { System.Web.HttpContext.Current = ControllerContext.HttpContext.ApplicationInstance.Context; var service = new ArticlesService(page); return service.GetArticles(); }).ContinueWith(t => SetResult(t, "articles")); So we are copying the context object onto the new thread that is spawned from Task factory. This context.Items is used again in the thread wherever necessary. Say for ex: public class SomeClass { internal static int StreamID { get { if (HttpContext.Current != null) { return (int)HttpContext.Current.Items["StreamID"]; } else { return DEFAULT_STREAM_ID; } } } This runs fine as long as number of parallel requests are optimal. My questions are as follows: 1. When the load is more and there are too many parallel requests, I notice that HttpContext.Current.Items is empty. I am not able to figure out a reason for this and this causes all the null reference exceptions. 2. How do we make sure it is not null ? Any workaround if present ? NOTE: I read through in StackOverflow and people have questions like HttpContext.Current is null - but in my case it is not null and its empty. I was reading one more article where the author says that sometimes request object is terminated and it may cause problems since dispose is already called on objects. I am doing a copy of Context object - its just a shallow copy and not a deep copy.

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• I'm having an issue to use GLshort for representing Vertex, and Normal.

  - by Xylopia

  As my project gets close to optimization stage, I notice that reducing Vertex Metadata could vastly improve the performance of 3D rendering. Eventually, I've dearly searched around and have found following advices from stackoverflow. Using GL_SHORT instead of GL_FLOAT in an OpenGL ES vertex array How do you represent a normal or texture coordinate using GLshorts? Advice on speeding up OpenGL ES 1.1 on the iPhone Simple experiments show that switching from "FLOAT" to "SHORT" for vertex and normal isn't tough, but what troubles me is when you're to scale back verticies to their original size (with glScalef), normals are multiplied by the reciprocal of the scale. Natural remedy for this is to multiply the normals w/ scale before you submit to GPU. Then, my short normals almost become 0, because the scale factor is usually smaller than 0. Duh! How do you use "short" for both vertex and normal at the same time? I've been trying this and that for about a full day, but I could only go for "float vertex w/ byte normal" or "short vertex w/ float normal" so far. Your help would be truly appreciated.

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• Midiplayer stops playing sounds after 16 notes.

  - by user349673

  Hi. I am currently programming a Piano Keyboard editor, much like the one you can find in Cubase, Logic, Reason etc.. I have this big grid, double array new int [13][9], which makes it 13 rows, 9 columns. The first column [0-12][0] is the Keyboard, at the top there's "high C" (midi note 72) and at the bottom there's "low C" (midi note 60). That column is an array of JButtons and when you press for example "low C", note 60 is being played by the Synthesizer. I've gotten this to work pretty OK as for now, but one problem I have is that I can only play 16 notes in a row, then it's like the Synthesizer shuts down or something. Do you guys have ANY idea of what the problem is? A bit of the code: import java.awt.*; import javax.swing.*; import java.awt.event.*; import java.util.*; import javax.sound.midi.*; actionPerformed(ActionEvent ae){ for(int i = 0; i<13; i++){ if(o== instr[i]){//instr is the button array SpelaTangent(i); } } } public void SpelaTangent(int tangent){ int [] klaviatur = new int[13]; for(int i = 0; i<13; i++){ klaviatur[i] = (72-i); } try { Synthesizer synth = MidiSystem.getSynthesizer(); synth.open(); final MidiChannel[] mc = synth.getChannels(); Instrument[] instrument = synth.getDefaultSoundbank().getInstruments(); synth.loadInstrument(instrument[1]); mc[0].noteOn(klaviatur[tangent],350); mc[0].noteOff(klaviatur[tangent],350); } catch (MidiUnavailableException e) {} } Help is very much appreciated!

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• HTML5 audio object doesn't play on iPad (when called from a setTimeout)

  - by Dan Halliday

  I have a page with a hidden <audio> object which is being started and stopped using a custom button via javascript. (The reason being I want to customise the button, and that drawing an audio player seems to destroy rendering performance on iPad anyway). A simplified example (in coffeescript): // Works fine on all browsers constructor: (@_button, @_audio) -> @_button.on 'click', @_play // Bind button's click event with jQuery _play: (e) => @_audio[0].play() // Call play() on audio element The audio plays fine when triggered from a function bound to a click event, but I actually want an animation to complete before the file plays so I put .play() inside a setTimeout. However I just can't get this to work: // Will not play on iPad constructor: (@_button, @_audio) -> @_button.on 'click', @_play // Bind button's click event with jQuery _play: (e) => setTimeout (=> // Declare a 300ms timeout @_audio[0].play() // Call play() on audio element ), 300 I've checked that @_audio (this._audio) is in scope and that its play() method exists. Why doesn't this work on iPad?

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• Java Executor: Small tasks or big ones?

  - by Arash Shahkar

  Consider one big task which could be broken into hundreds of small, independently-runnable tasks. To be more specific, each small task is to send a light network request and decide upon the answer received from the server. These small tasks are not expected to take longer than a second, and involve a few servers in total. I have in mind two approaches to implement this using the Executor framework, and I want to know which one's better and why. Create a few, say 5 to 10 tasks each involving doing a bunch of send and receives. Create a single task (Callable or Runnable) for each send & receive and schedule all of them (hundreds) to be run by the executor. I'm sorry if my question shows that I'm lazy to test these and see for myself what's better (at least performance-wise). My question, while looking after an answer to this specific case, has a more general aspect. In situations like these when you want to use an executor to do all the scheduling and other stuff, is it better to create lots of small tasks or to group those into a less number of bigger tasks?

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• ReaderWriterLockSlim and Pulse/Wait

  - by Jono

  Is there an equivalent of Monitor.Pulse and Monitor.Wait that I can use in conjunction with a ReaderWriterLockSlim? I have a class where I've encapsulated multi-threaded access to an underlying queue. To enqueue something, I acquire a lock that protects the underlying queue (and a couple of other objects) then add the item and Monitor.Pulse the locked object to signal that something was added to the queue. public void Enqueue(ITask task) { lock (mutex) { underlying.Enqueue(task); Monitor.Pulse(mutex); } } On the other end of the queue, I have a single background thread that continuously processes messages as they arrive on the queue. It uses Monitor.Wait when there are no items in the queue, to avoid unnecessary polling. (I consider this to be good design, but any flames (within reason) are welcome if they help me learn otherwise.) private void DequeueForProcessing(object state) { while (true) { ITask task; lock (mutex) { while (underlying.Count == 0) { Monitor.Wait(mutex); } task = underlying.Dequeue(); } Process(task); } } As more operations are added to this class (requiring read-only access to the lock protected underlying), someone suggested using ReaderWriterLockSlim. I've never used the class before, and assuming it can offer some performance benefit, I'm not against it, but only if I can keep the Pulse/Wait design.

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