faster - Page 153 - Developer IT

SQL Server 2008 spatial index and CPU utilization with MapGuide Open Source 2.1

- by Antonio de la Peña

I have a SQL Server table with hundreds of thousands of geometry type parcels. I have made indexes on them trying different combinations of density and objects per cell settings. So far I'm settiling for LOW, LOW, MEDIUM, MEDIUM and 16 objects per cell and I made a SP that sets the bounding box according to the extents of the entities in the table. There is an incredible performance boost from queries taking almost minutes without index to less than seconds, it gets faster when the zoom is closer thus less objects are displayed. Yet the CPU utilization gets to 100% when querying for features, even when the queries themselves are fast. I'm worrying this will not fly in a production environment. I am using MapGuide Open Source 2.1 for this project, but I am positive the CPU load is caused by SQL Server. I wonder if my indexes are set properly. I haven't found any clear documentation on how to properly set them up. Every article I've read basically says "it depends..." but nothing specific. Do you have any recommendations for me, including books, articles? Thank you.

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I need to speed up a function. Should I use cython, ctypes, or something else?

- by Peter Stewart

I'm having a lot of fun learning Python by writing a genetic programming type of application. I've had some great advice from Torsten Marek, Paul Hankin and Alex Martelli on this site. The program has 4 main functions: generate (randomly) an expression tree. evaluate the fitness of the tree crossbreed mutate As all of generate, crossbreed and mutate call 'evaluate the fitness'. it is the busiest function and is the primary bottleneck speedwise. As is the nature of genetic algorithms, it has to search an immense solution space so the faster the better. I want to speed up each of these functions. I'll start with the fitness evaluator. My question is what is the best way to do this. I've been looking into cython, ctypes and 'linking and embedding'. They are all new to me and quite beyond me at the moment but I look forward to learning one and eventually all of them. The 'fitness function' needs to compare the value of the expression tree to the value of the target expression. So it will consist of a postfix evaluator which will read the tree in a postfix order. I have all the code in python. I need advice on which I should learn and use now: cython, ctypes or linking and embedding. Thank you.

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How do I rewrite a for loop with a shared dependency using actors

- by Thomas Rynne

We have some code which needs to run faster. Its already profiled so we would like to make use of multiple threads. Usually I would setup an in memory queue, and have a number of threads taking jobs of the queue and calculating the results. For the shared data I would use a ConcurrentHashMap or similar. I don't really want to go down that route again. From what I have read using actors will result in cleaner code and if I use akka migrating to more than 1 jvm should be easier. Is that true? However, I don't know how to think in actors so I am not sure where to start. To give a better idea of the problem here is some sample code: case class Trade(price:Double, volume:Int, stock:String) { def value(priceCalculator:PriceCalculator) = (priceCalculator.priceFor(stock)-> price)*volume } class PriceCalculator { def priceFor(stock:String) = { Thread.sleep(20)//a slow operation which can be cached 50.0 } } object ValueTrades { def valueAll(trades:List[Trade], priceCalculator:PriceCalculator):List[(Trade,Double)] = { trades.map { trade => (trade,trade.value(priceCalculator)) } } def main(args:Array[String]) { val trades = List( Trade(30.5, 10, "Foo"), Trade(30.5, 20, "Foo") //usually much longer ) val priceCalculator = new PriceCalculator val values = valueAll(trades, priceCalculator) } } I'd appreciate it if someone with experience using actors could suggest how this would map on to actors.

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Some optimization about the code (computing ranks of a vector)?

- by user1748356

The following code is a function (performance-critical) to compute tied ranks of a vector: mergeSort(x,inds,ci); //a sort function to sort vector x of length ci, also returns keys (inds) of x. int tj=0; double xi=x[0]; for (int j = 1; j < ci; ++j) { if (x[j] > xi) { double rankvalue = 0.5 * (j - 1 + tj); for (int k = tj; k < j; ++k) { ranks[inds[k]]=rankvalue; }; tj = j; xi = x[j]; }; }; double rankvalue = 0.5 * (ci - 1 + tj); for (int k = tj; k < ci; ++k) { ranks[inds[k]]=rankvalue; }; The problem is, the supposed performance bottleneck mergeSort(), which is O(NlogN) is several times faster than the other part of codes (which is O(N)), which suggests there is room for huge improvment with the other part of the codes, any advices?

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Is it possible to definitively identify whether a DML command was issued from a stored procedure?

- by Ed Harper

I have inherited a SQL Server 2008 database to which calling applications have access through stored procedures. Each table in the database has a shadow audit table into which Insert/Update/Delete operations for are logged. Performance testing on populating the audit tables showed that inserting the audit records using OUTPUT clauses was 20% or so faster than using triggers, so this has been implemented in the stored procedures. However, because this design cannot track changes made directly to the tables through DML statements issued directly against the tables, triggers have also been implemented which use the value of @@NESTLEVEL to determine whether or not to run the trigger (the assumption being that all DML run through stored procedures will have @@NESTLEVEL 1). i.e. the body of the trigger code looks something like: IF @@NESTLEVEL = 1 -- implies call is direct sql so generate history from here BEGIN ... insert into audit table This design is flawed because it won't track updates where DML statements are executed in dynamic SQL, or any other context where @@NESTLEVEL is raised above 1. Can anyone suggest a completely reliable method we can use in the triggers to execute them only if not triggered by a stored procedure? Or is this (as I suspect) not possible?

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How to efficiently compare the sign of two floating-point values while handling negative zeros

- by François Beaune

Given two floating-point numbers, I'm looking for an efficient way to check if they have the same sign, given that if any of the two values is zero (+0.0 or -0.0), they should be considered to have the same sign. For instance, SameSign(1.0, 2.0) should return true SameSign(-1.0, -2.0) should return true SameSign(-1.0, 2.0) should return false SameSign(0.0, 1.0) should return true SameSign(0.0, -1.0) should return true SameSign(-0.0, 1.0) should return true SameSign(-0.0, -1.0) should return true A naive but correct implementation of SameSign in C++ would be: bool SameSign(float a, float b) { if (fabs(a) == 0.0f || fabs(b) == 0.0f) return true; return (a >= 0.0f) == (b >= 0.0f); } Assuming the IEEE floating-point model, here's a variant of SameSign that compiles to branchless code (at least with with Visual C++ 2008): bool SameSign(float a, float b) { int ia = binary_cast<int>(a); int ib = binary_cast<int>(b); int az = (ia & 0x7FFFFFFF) == 0; int bz = (ib & 0x7FFFFFFF) == 0; int ab = (ia ^ ib) >= 0; return (az | bz | ab) != 0; } with binary_cast defined as follow: template <typename Target, typename Source> inline Target binary_cast(Source s) { union { Source m_source; Target m_target; } u; u.m_source = s; return u.m_target; } I'm looking for two things: A faster, more efficient implementation of SameSign, using bit tricks, FPU tricks or even SSE intrinsics. An efficient extension of SameSign to three values.

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ASP .NET page runs slow in production

- by Brandi

I have created an ASP .NET page that works flawlessly and quickly from Visual Studio. It does a very large database read from a database on our network to load a gridview inside of an update panel. It displays progress in an Ajax modalpopupextender. Of course I don't expect it to be instant what with the large db reads, but it takes on the order of seconds, not on the order of minutes. This is all working great until I put it up on the server - it is very, VERY slow when I access it via the internet - takes several minutes to load the database information into the gridview. I'm baffled why it would not perform the exact same as it had from Visual Studio. (It is in release mode and I have taken off the debug flag) I have since been trying things like eliminating unneeded update panels and throwing out the ajax tool. Nothing has made it any faster on production. It is not the database as far as I know, since it has been consistently fast from my computer (from visual studio) and consistently slow from the server. I am wondering, where do I look next? Has anyone else had this problem before? Could this be caused by update panels or Ajax modalpopupextenders in different parts of the application? Why would the live behaviour differ so much from the localhost behaviour? Both the server with the ASP .NET page and the server with the database are servers on our network. I'm using Visual Studio 2008. Thank you in advance for any insight or advice.

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Beginner Question: For extract a large subset of a table from MySQL, how does Indexing, order of tab

- by chongman

Sorry if this is too simple, but thanks in advance for helping. This is for MySQL but might be relevant for other RDMBSs tblA has 4 columns: colA, colB, colC, mydata, A_id It has about 10^9 records, with 10^3 distinct values for colA, colB, colC. tblB has 3 columns: colA, colB, B_id It has about 10^4 records. I want all the records from tblA (except the A_id) that have a match in tblB. In other words, I want to use tblB to describe the subset that I want to extract and then extract those records from tblA. Namely: SELECT a.colA, a.colB, a.colC, a.mydata FROM tblA as a INNER JOIN tblB as b ON a.colA=b.colA a.colB=b.colB ; It's taking a really long time (more than an hour) on a newish computer (4GB, Core2Quad, ubuntu), and I just want to check my understanding of the following optimization steps. ** Suppose this is the only query I will ever run on these tables. So ignore the need to run other queries. Now my questions: 1) What indexes should I create to optimize this query? I think I just need a multiple index on (colA, colB) for both tables. I don't think I need separate indexes for colA and colB. Another stack overflow article (that I can't find) mentioned that when adding new indexes, it is slower when there are existing indexes, so that might be a reason to use the multiple index. 2) Is INNER JOIN correct? I just want results where a match is found. 3) Is it faster if I join (tblA to tblB) or the other way around, (tblB to tblA)? This previous answer says that the optimizer should take care of that. 4) Does the order of the part after ON matter? This previous answer say that the optimizer also takes care of the execution order.

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Will Learning C++ Help for Building Fast/No-Additional-Requirements Desktop Applications?

- by vito

Will learning C++ help me build native applications with good speed? Will it help me as a programmer, and what are the other benefits? The reason why I want to learn C++ is because I'm disappointed with the UI performances of applications built on top of JVM and .NET. They feel slow, and start slow too. Of course, a really bad programmer can create a slower and sluggish application using C++ too, but I'm not considering that case. One of my favorite Windows utility application is Launchy. And in the Readme.pdf file, the author of the program wrote this: 0.6 This is the first C++ release. As I became frustrated with C#’s large .NET framework requirements and users lack of desire to install it, I decided to switch back to the faster language. I totally agree with the author of Launchy about the .NET framework requirement or even a JRE requirement for desktop applications. Let alone the specific version of them. And some of the best and my favorite desktop applications don't need .NET or Java to run. They just run after installing. Are they mostly built using C++? Is C++ the only option for good and fast GUI based applications? And, I'm also very interested in hearing the other benefits of learning C++.

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BasicDBObject or QueryBuilder and some newbie questions of Java and mongo

- by Kevin Xu

hi I'm a fresh newbie to mongodb Q1 using query=new BasicDBObject(); query.put("i", new BasicDBObject("$gt",13)); and query=new QueryBuilder().put("i").Greaterthan(13).get() is there any difference inside of the system? Q2 I've created a class class findkv extends BasicDBObject{ //is gt gte lt lte public findkv(String fieldname,String op,Object tvalue) { if (op=="") this.put(fieldname,tvalue); else this.put(fieldname, new BasicDBObject(op,tvalue)); } } shall I use it or shall I just use original function? Q3 I've used mongo shell for a few weeks, and was customed to it, and find writing in mongo shell faster and shorter, which side has more advantage, writing in mongo or in java? I shall dump them from mongo to mysql Q4 I've an if (statement==true) return else dowhat; seems can't be compiled I know I can write if (statement!=true) dowhat else return, but can I still write in first style? q5 my eclipse is Eclipse Java EE IDE for Web Developers. Version: Juno Release Build id: 20120614-1722 I'd like to install Perl which I haven't learned yet I choose Install Update http://e-p-i-c.sf.net/updates/testing but it doesn't work, any method to install perl to eclipse manually?

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'Fixed' for loop - what is more efficient?

- by pimvdb

I'm creating a tic-tac-toe game, and one of the functions has to iterate through each of the 9 fields (tic-tac-toe is played on a 3x3 grid). I was wondering what is more efficient (which one is perhaps faster, or what is the preferred way of scripting in such situation) - using two for nested loops like this: for(var i=0; i<3; i++) { for(var j=0; j<3; j++) { checkField(i, j); } } or hard-coding it like this: checkField(0, 0); checkField(0, 1); checkField(0, 2); checkField(1, 0); checkField(1, 1); checkField(1, 2); checkField(2, 0); checkField(2, 1); checkField(2, 2); As there are only 9 combinations, it would be perhaps overkill to use two nested for loops, but then again this is clearer to read. The for loop, however, will increment variables and check whether i and j are smaller than 3 every time as well. In this example, the time saving at least might be negligible, but what is the preferred way of coding in this case? Thanks.

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Optimize a MySQL count each duplicate Query

- by Onema

I have the following query That gets the city name, city id, the region name, and a count of duplicate names for that record: SELECT Country_CA.City AS currentCity, Country_CA.CityID, globe_region.region_name, ( SELECT count(Country_CA.City) FROM Country_CA WHERE City LIKE currentCity ) as counter FROM Country_CA LEFT JOIN globe_region ON globe_region.region_id = Country_CA.RegionID AND globe_region.country_code = Country_CA.CountryCode ORDER BY City This example is for Canada, and the cities will be displayed on a dropdown list. There are a few towns in Canada, and in other countries, that have the same names. Therefore I want to know if there is more than one town with the same name region name will be appended to the town name. Region names are found in the globe_region table. Country_CA and globe_region look similar to this (I have changed a few things for visualization purposes) CREATE TABLE IF NOT EXISTS `Country_CA` ( `City` varchar(75) NOT NULL DEFAULT '', `RegionID` varchar(10) NOT NULL DEFAULT '', `CountryCode` varchar(10) NOT NULL DEFAULT '', `CityID` int(11) NOT NULL DEFAULT '0', PRIMARY KEY (`City`,`RegionID`), KEY `CityID` (`CityID`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8; AND CREATE TABLE IF NOT EXISTS `globe_region` ( `country_code` char(2) COLLATE utf8_unicode_ci NOT NULL, `region_code` char(2) COLLATE utf8_unicode_ci NOT NULL, `region_name` varchar(50) COLLATE utf8_unicode_ci NOT NULL, PRIMARY KEY (`country_code`,`region_code`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci; The query on the top does exactly what I want it to do, but It takes way too long to generate a list for 5000 records. I would like to know if there is a way to optimize the sub-query in order to obtain the same results faster. the results should look like this City CityID region_name counter sheraton 2349269 British Columbia 1 sherbrooke 2349270 Quebec 2 sherbrooke 2349271 Nova Scotia 2 shere 2349273 British Columbia 1 sherridon 2349274 Manitoba 1

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table design for storing large number of rows

- by hyperboreean

I am trying to store in a postgresql database some unique identifiers along with the site they have been seen on. I can't really decide which of the following 3 option to choose in order to be faster and easy maintainable. The table would have to provide the following information: the unique identifier which unfortunately it's text the sites on which that unique identifier has been seen The amount of data that would have to hold is rather large: there are around 22 millions unique identifiers that I know of. So I thought about the following designs of the table: id - integer identifier - text seen_on_site - an integer, foreign key to a sites table This approach would require around 22 mil multiplied by the number of sites. id - integer identifier - text seen_on_site_1 - boolean seen_on_site_2 - boolean ............ seen_on_site_n - boolean Hopefully the number of sites won't go past 10. This would require only the number of unique identifiers that I know of, that is around 20 millions, but it would make it hard to work with it from an ORM perspective. one table that would store only unique identifiers, like in: id - integer unique_identifier - text, one table that would store only sites, like in: id - integer site - text and one many to many relation, like: id - integer, unique_id - integer (fk to the table storing identifiers) site_id - integer (fk to sites table) another approach would be to have a table that stores unique identifiers for each site So, which one seems like a better approach to take on the long run?

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Why is debugging better in an IDE?

- by Bill Karwin

I've been a software developer for over twenty years, programming in C, Perl, SQL, Java, PHP, JavaScript, and recently Python. I've never had a problem I could not debug using some careful thought, and well-placed debugging print statements. I respect that many people say that my techniques are primitive, and using a real debugger in an IDE is much better. Yet from my observation, IDE users don't appear to debug faster or more successfully than I can, using my stone knives and bear skins. I'm sincerely open to learning the right tools, I've just never been shown a compelling advantage to using visual debuggers. Moreover, I have never read a tutorial or book that showed how to debug effectively using an IDE, beyond the basics of how to set breakpoints and display the contents of variables. What am I missing? What makes IDE debugging tools so much more effective than thoughtful use of diagnostic print statements? Can you suggest resources (tutorials, books, screencasts) that show the finer techniques of IDE debugging? Sweet answers! Thanks much to everyone for taking the time. Very illuminating. I voted up many, and voted none down. Some notable points: Debuggers can help me do ad hoc inspection or alteration of variables, code, or any other aspect of the runtime environment, whereas manual debugging requires me to stop, edit, and re-execute the application (possibly requiring recompilation). Debuggers can attach to a running process or use a crash dump, whereas with manual debugging, "steps to reproduce" a defect are necessary. Debuggers can display complex data structures, multi-threaded environments, or full runtime stacks easily and in a more readable manner. Debuggers offer many ways to reduce the time and repetitive work to do almost any debugging tasks. Visual debuggers and console debuggers are both useful, and have many features in common. A visual debugger integrated into an IDE also gives you convenient access to smart editing and all the other features of the IDE, in a single integrated development environment (hence the name).

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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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JVM GC demote object to eden space?

- by Kevin

I'm guessing this isn't possible...but here goes. My understanding is that eden space is cheaper to collect than old gen space, especially when you start getting into very large heaps. Large heaps tend to come up with long running applications (server apps) and server apps a lot of the time want to use some kind of caches. Caches with some kind of eviction (LRU) tend to defeat some assumptions that GC makes (temporary objects die quickly). So cache evictions end up filling up old gen faster than you'd like and you end up with a more costly old gen collection. Now, it seems like this sort of thing could be avoided if java provided a way to mark a reference as about to die (delete keyword)? The difference between this and c++ is that the use is optional. And calling delete does not actually delete the object, but rather is a hint to the GC that it should demote the object back to Eden space (where it will be more easily collected). I'm guessing this feature doesn't exist, but, why not (is there a reason it's a bad idea)?

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Submit form with POST data in Android app

- by datguywhowanders

I've been searching the web for a way to do this for about a week now, and I just can't seem to figure it out. I'm trying to implement an app that my college can use to allow users to log in to various services on the campus with ease. The way it works currently is they go to an online portal, select which service they want, fill in their user name and pwd, and click login. The form data is sent via post (it includes several hidden values as well as just the user name and pwd) to the corresponding login script which then signs them in and loads the service. I've been trying to come at the problem in two ways. I first tried a WebView, but it doesn't seem to want to support all of the html that normally makes this form work. I get all of the elements I need, fields for user and pwd as well as a login button, but clicking the button doesn't do anything. I wondered if I needed to add an onclick handler for it, but I can't see how as the button is implemented in the html of the webview not using a separate android element. The other possibility was using the xml widgets to create the form in a nice relative layout, which seems to load faster and looks better on the android screen. I used EditText fields for the input, a spinner widget for the service select, and the button widget for the login. I know how to make the onclick and item select handlers for the button and spinner, respectively, but I can't figure out how to send that data via POST in an intent that would then launch a browser. I can do an intent with the action url, but can't get the POST data to feed into it. Anyone have any suggestions?

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High Runtime for Dictionary.Add for a large amount of items

- by aaginor

Hi folks, I have a C#-Application that stores data from a TextFile in a Dictionary-Object. The amount of data to be stored can be rather large, so it takes a lot of time inserting the entries. With many items in the Dictionary it gets even worse, because of the resizing of internal array, that stores the data for the Dictionary. So I initialized the Dictionary with the amount of items that will be added, but this has no impact on speed. Here is my function: private Dictionary<IdPair, Edge> AddEdgesToExistingNodes(HashSet<NodeConnection> connections) { Dictionary<IdPair, Edge> resultSet = new Dictionary<IdPair, Edge>(connections.Count); foreach (NodeConnection con in connections) { ... resultSet.Add(nodeIdPair, newEdge); } return resultSet; } In my tests, I insert ~300k items. I checked the running time with ANTS Performance Profiler and found, that the Average time for resultSet.Add(...) doesn't change when I initialize the Dictionary with the needed size. It is the same as when I initialize the Dictionary with new Dictionary(); (about 0.256 ms on average for each Add). This is definitely caused by the amount of data in the Dictionary (ALTHOUGH I initialized it with the desired size). For the first 20k items, the average time for Add is 0.03 ms for each item. Any idea, how to make the add-operation faster? Thanks in advance, Frank

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MySQL query optimization - distinct, order by and limit

- by Manuel Darveau

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Python: Most efficient way to concatenate and rearrange files

- by user300890

Hi, I am reading from several files, each file is divided into 2 pieces, first a header section of a few thousand lines followed by a body of a few thousand. My problem is I need to concatenate these files into one file where all the headers are on the top followed by the body. Currently I am using two loops; one to pull out all the headers and write them, and the second to write the body of each file (I also include a tmp_count variable to limit the number of lines to be loading into memory before dumping to file). This is pretty slow - about 6min for 13gb file. Can anyone tell me how to optimize this or if there is a faster way to do this in python ? Thanks! Here is my code: def cat_files_sam(final_file_name,work_directory_master,file_count): final_file = open(final_file_name,"w") if len(file_count) > 1: file_count=sort_output_files(file_count) # only for @ headers for bowtie_file in file_count: #print bowtie_file tmp_list = [] tmp_count = 0 for line in open(os.path.join(work_directory_master,bowtie_file)): if line.startswith("@"): if tmp_count == 1000000: final_file.writelines(tmp_list) tmp_list = [] tmp_count = 0 tmp_list.append(line) tmp_count += 1 else: final_file.writelines(tmp_list) break for bowtie_file in file_count: #print bowtie_file tmp_list = [] tmp_count = 0 for line in open(os.path.join(work_directory_master,bowtie_file)): if line.startswith("@"): continue if tmp_count == 1000000: final_file.writelines(tmp_list) tmp_list = [] tmp_count = 0 tmp_list.append(line) tmp_count += 1 final_file.writelines(tmp_list) final_file.close()

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Web Audio API and mobile browsers

- by Michael

I've run into a problem while implementing sound and music into an HTML game that I'm building. I'm using the Web Audio API, loading all the sound files with XMLHttpRequests and decoding them into an AudioBufferSourceNode with AudioContext.prototype.decodeAudioData(). It looks something like this: var request = new XMLHttpRequest(); request.open("GET", "soundfile.ogg", true); request.responseType = "arraybuffer"; request.onload = function() { context.decodeAudioData(request.response) } request.send(); Everything plays fine, but on mobile the decodeAudioData takes an absurdly long time for the background music. I then tried using AudioContext.prototype.createMediaElementSource() to load the music from an HTML Audio object, since they support streaming and don't have to load the whole file into memory at once. It looked something like this: var audio = new Audio('soundfile.ogg'); var source = context.createMediaElementSource(audio); var mainVolume = context.createGain(); source.connect(mainVolume); mainVolume.connect(context.destination); This loads much faster, but the audio volume isn't affected by the gain node. Works fine on desktop, so I'm assuming this is a bug/limitation of mobile Chrome (testing on Android). Is there actually no good, well-performing way to handle sound on mobile browsers or am just I doing something stupid?

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real time stock quotes, StreamReader performance optimization

- by sean717

I am working on a program that extracts real time quote for 900+ stocks from a website. I use HttpWebRequest to send HTTP request to the site and store the response to a stream and open a stream using the following code: HttpWebResponse response = (HttpWebResponse)request.GetResponse(); Stream stream = response.GetResponseStream (); StreamReader reader = new StreamReader( stream ) the size of the received HTML is large (5000+ lines), so it takes a long time to parse it and extract the price. For 900 files, It takes about 6 mins for parsing and extracting. Which my boss isn't happy with, he told me he'd want the whole process to be done in TWO mins. I've identified the part of the program that takes most of time to finish is parsing and extracting. I've tried to optimize the code to make it faster, the following is what I have now after some optimization: // skip lines at the top for(int i=0;i<1500;++i) reader.ReadLine(); // read the line that contains the price string theLine = reader.ReadLine(); // ... extract the price from the line now it takes about 4 mins to process all the files, there is still a significant gap to what my boss's expecting. So I am wondering, is there other way that I can further speed up the parsing and extracting and have everything done within 2 mins?

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Sending files using Winsock - optimal send() data length?

- by Meta

I am using Winsock with non-blocking sockets to send a file to a client. The way I'm doing it right now is that I read a chunk of 8192 bytes from the file, and then loop until all of it successfully goes through send() (obviously handling WSAEWOULDBLOCK as it occurs). I then move on and read the next 8192 bytes, and so on... Although I can use any other number than 8192 when I test the transfer on my local machine, once I try it over a network, it seems like 8191 is the largest number I can use. When I try to use any number higher than 8191 (starting with 8192), the file transfer becomes extremely slow (about 5 times slower). Is there any reason why 8191 is so special? I've done some more testing and it turns out that using 8000 is slightly faster (by 0.5%). If you understand why 8191 is so special, can you tell me if there is a number better than the others (better than 8000)? I have a feeling that it has something to do with the fact that the default send buffer allocated to the socket by Winsock is 8KB, but I don't understand why. It might also have something to do with the Nagle algorithm, but again, I'm not sure how. Note that I have not modified the SO_SNDBUF option nor the TCP_NODELAY option. Or am I doing this all wrong? What's the best way of sending a file over a non-blocking socket?

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Is A Web App Feasible For A Heavy Use Data Entry System?

- by Rob

Looking for opinions on this, we're working on a project that is essentially a data entry system for a production line. Heavy data input by users who normally work in Excel or other thick client data systems. We've been told (as a consequence) that we have to develop this as a thick client using .NET. Our argument was to develop as a web app, as it resolves a lot of issues and would be easier to write and maintain. Their argument against the web is that (supposedly) the web is not ready yet for a heavy duty data entry system, and that the web in a browser does not offer the speed, responsiveness, and fluid experience for the end-user that a thick client can (citing things such as drag and drop, rapid auto-entry and data navigation, etc.) Personally, I think that with good form design and JQuery/AJAX, a web app could do everything a thick client does just as well, and they just don't know what they're talking about. The irony is that a thick client has to go to a lot more effort to manage the deployment and connectivity back to the central data server than a web app would need to do, so in terms of speed I would expect a web app to be faster. What are the thoughts of those out there? Are there any technologies currently in production use that modern data entry systems are being developed as web apps in? Appreciate any feedback. Regards, Rob.

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SqlCE DB occasionally freezes on one handheld, not another

- by Michael

I have two types of custom handhelds which are similar, but slightly different, each running the same WinForm application and a WinCE database: Type 1: WinCE 4.2, 400 mhz, 93244 kb Type 2: WinCE 5.0, 520 mhz, 84208 kb Type 1 will happily proceed through a large batch db operation (initiated) by the app, by Type 2 will consistently begin c-r-a-w-l-i-n-g (for several to many cycles) at around the 200 cycle mark. As several points it will begin running normally and then crawl again. The app does several db op's (inserts, updates and selects, no deletes). To simplify my situation, I've built a small test app which essentially does this: command_s.CommandText = "select dvr from vr where vid = 2211250"; command_u.CommandText = "update pvr set LocationID=81 where Status='OK' and vri = 27861"; while(going) { command_s.ExecuteScalar(); command_u.ExecuteNonQuery(); } and set it off running on the two units side by side. Sure enough, the slower (400 mhz) unit is outpacing the faster (520 mhz) unit (it's about 5000 cycles ahead right now) and I can see noticable pauses on the 520 mhz unit. What is causing this?

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