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• Tuning OS X Virtual Memory

  - by dcolish

  I've noticed some really odd results form vm_stat on OSX 10.6. According to this, its barely hitting the cache. Searches of pretty much everywhere I could think of turn up little to explain why the rate is so low. I asked a few friends and they're seeing the same thing. What gives and how can I make it better? Mach Virtual Memory Statistics: (page size of 4096 bytes) Pages free: 78609. Pages active: 553411. Pages inactive: 191116. Pages speculative: 6198. Pages wired down: 153998. "Translation faults": 116031508. Pages copy-on-write: 2274338. Pages zero filled: 33360804. Pages reactivated: 264378. Pageins: 1197683. Pageouts: 43756. Object cache: 20 hits of 1550639 lookups (0% hit rate)

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• HBase schema help

  - by Jody Powlette

  Coming from a SQL Server background, I'm a newbie with regard to HBase, but the technology looks to be a good fit for what we're doing and the cost is definitely right! I need to maintain a list of log entries which normally I would create in an RDBS as: create table Log ( UserID int, SiteID int, Page varchar(50), Date smalldatetime ) where one user may have 0 or 1000 rows in this simple table. Typical queries would be to find all the rows for one user or all the rows for one user on one site. How does this translate into a "map" in HBase where there is no "row key" AND the same (SiteID,Page) may appear many times. My first thought is that UserID is a row key, but I still don't understand "column families" and the other terminology well enough to understand how to setup the table to hold this data where the one UserID can have many (SiteID,Page,Date) "rows". Any direction is appreciated!

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• Troubles configuring SSL for an Apache host

  - by Ryan

  I configured it on Friday night and all worked well. Today for some reason it stopped working and I can't figure out why. When you goto the secure page it's acting like I have a self-signed certificate and I don't. I have the host configured like so ServerAdmin [email protected] DocumentRoot "/path/to/site" Servername www.mydomain.com ServerAlias mydomain.com DirectoryIndex index.cfm index.htm SSLEngine on SSLCipherSuite ALL:!ADH:!EXPORT56:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP:+eNULL SSLCertificateFile /etc/httpd/path/to/mydomain.com.crt SSLCertificateKeyFile /etc/httpd/path/to/www.mydomain.com.key SSLCertificateChainFile /etc/httpd/path/to/gd_bundle.crt Apache starts with no errors and I can't seem to find anything meaningful in any of the logs. It's got to be something minor but I can't seem to see it. It's an updated Centos/Apache VM. I have worn Google out.

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• Isn't INT more efficient than UNIQUEIDENTIFIER?

  - by ck

  I have a parent table and child table where the columns that join them together are the UNIQUEIDENTIFIER type. The child table has a clustered index on the column that joins it to the parent table (its PK, which is also clustered). I have created a copy of both of these tables but changed the relationship columns to be INTs instead, have rebuilt the indexes so that they are essentially the same structure and can be queried in the same way. When I query for a known 20 records from the parent table, pulling in all the related records from the child tables, I get identical query costs across both, i.e. 50/50 cost for the batches. If this is true, then my giant project to change all of the tables like this appears to be pointless, other than speeding up inserts. Can anyone provide any light on the situation?

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• How do You Get a Specific Value From a System.Data.DataTable Object?

  - by Giffyguy

  I'm a low-level algorithm programmer, and databases are not really my thing - so this'll be a n00b question if ever there was one. I'm running a simple SELECT query through our development team's DAO. The DAO returns a System.Data.DataTable object containing the results of the query. This is all working fine so far. The problem I have run into now: I need to pull a value out of one of the fields of the first row in the resulting DataTable - and I have no idea where to even start. Microsoft is so confusing about this! Arrrg! Any advice would be appreciated. I'm not providing any code samples, because I believe that context is unnecessary here. I'm assuming that all DataTable objects work the same way, no matter how you run your queries - and therefore any additional information would just make this more confusing for everyone.

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• Can you help me think of problems for my programming language?

  - by I can't tell you my name.

  I've created an experimental toy programming language with a (now) working interpreter. It is turing-complete and has a pretty low-level instruction set. Even if everything takes four to six times more code and time than in PHP, Python or Ruby I still love programming all kinds of things in it. So I got the "basic" things that are written in many languages working: Hello World Input - Output Countdowns (not as easy as you think as there are no loops) Factorials Array emulation 99 Bottles of Beer (simple, wrong inflection) 99 Bottles of Beer (canonical) Conjatz conjecture Quine (that was a fun one!) Brainf*ck interpreter (To proof turing-completeness, made me happy) So I implemented all of the above examples because: They all used many different aspects of the language They are pretty interesting They don't take hours to write Now my problem is: I've run out of ideas! I don't find any more examples of what problems I could solve using my language. Do you have any programming problems which fit into some of the criteria above for me to work out?

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• DotnetNuke redirect

  - by X-Dev

  our client needs to shortcuts to particular pages We need to redirect non existent urls like http://site.com/promotion1 to the actual URL similar to http://site.com/promotions/promotion1/tabid/799/language/en-AU/Default.aspx ... I've sent a list of appropriate DNN modules to our client but it may take them forever to get back to me. In the mean time they still submitting requests to us to create redirects for them. if there's no cost involved then i wont have to wait for them to get back to me. so I'm looking for a Quick and free way to enable the clients to set these up on this own. I've looked at: http://www.snowcovered.com/snowcovered2/Default.aspx?tabid=242&PackageID=3302 http://www.ventrian.com/Resources/Projects/FriendlyUrls.aspx http://www.codeproject.com/kb/aspnet/dnn2url_rewrite.aspx But haven't had much luck in the small amount of time i have available. Has anyone got some suggestions on how to achieve our goal with either the above resources or maybe some additional resource i haven't found yet? (DNN v4.9)

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• How do you implement Software Transactional Memory?

  - by Joseph Garvin

  In terms of actual low level atomic instructions and memory fences (I assume they're used), how do you implement STM? The part that's mysterious to me is that given some arbitrary chunk of code, you need a way to go back afterward and determine if the values used in each step were valid. How do you do that, and how do you do it efficiently? This would also seem to suggest that just like any other 'locking' solution you want to keep your critical sections as small as possible (to decrease the probability of a conflict), am I right? Also, can STM simply detect "another thread entered this area while the computation was executing, therefore the computation is invalid" or can it actually detect whether clobbered values were used (and thus by luck sometimes two threads may execute the same critical section simultaneously without need for rollback)?

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• How to prevent DOS attacks using image resizing in an ASP.NET application?

  - by Waleed Eissa

  I'm currently developing a site where users can upload images to use as avatars, I know this makes me sound a little paranoid but I was wondering what if a malicious user uploads an image with incredibly large dimensions that will eat the server memory (as a DOS attack), I already have a limit on the file size that can be uploaded (250 k) but even that size can allow for an image with incredibly large dimensions if the image for example is a JPEG that contains one color and created with a very low quality setting. Taking into consideration that the image is uploaded as a bitmap in memory when being resized (ie. not compressed), I wonder if such DOS attacks occur, even to check the image dimensions it has to be uploaded in memory first, did you hear about any attacks that exploited this? Am I too worried?

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• DB2 Transaction log is full. How to flush / clear it?

  - by Mestika

  Hi, I’m working on a experiment regarding to a course I’m taking about tuning DB2. I’m using the EC2 from Amazon (aws) to conduct the experiment. My problem is, however, that I have to test a non-compression against row-compression in DB2 and to do that I’ve created a bsh file that run those experiments. But when I reach to my compression part I get the error ”Transaction log is full”; and no matter how low I set the inserts for it is complaining about my transaction log. I’ve scouted Google for a day now trying to find some way to flush / clear the log or just get rit of it, i don’t need it. I’ve tried to increase the size but nothing has helped. Please, I hope someone has an answer to solve this frustrating problem Thanks - Mestika

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• How do I make "simple" throughput servlet-filter?

  - by Tommy

  I'm looking to create a filter that can give me two things: number of request pr minute, and average responsetime pr minute. I already got the individual readings, I'm just not sure how to add them up. My filter captures every request, and it records the time each request takes: public void doFilter(ServletRequest request, ...() { long start = System.currentTimeMillis(); chain.doFilter(request, response); long stop = System.currentTimeMillis(); String time = Util.getTimeDifferenceInSec(start, stop); } This information will be used to create some pretty Google Chart charts. I don't want to store the data in any database. Just a way to get current numbers out when requested As this is a high volume application; low overhead is essential. I'm assuming my applicationserver doesn't provide this information.

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• Image 8-connectivity without excessive branching?

  - by shoosh

  I'm writing a low level image processing algorithm which needs to do alot of 8-connectivity checks for pixels. For every pixel I often need to check the pixels above it, below it and on its sides and diagonals. On the edges of the image there are special cases where there are only 5 or 3 neighbors instead of 8 neighbors for a pixels. The naive way to do it is for every access to check if the coordinates are in the right range and if not, return some default value. I'm looking for a way to avoid all these checks since they introduce a large overhead to the algorithm. Are there any tricks to avoid it altogether?

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• Tools to create maximum velocity in a .NET dev team

  - by Søren Spelling Lund

  If you were to self-fund a software project which tools, frameworks, components would you employ to ensure maximum productivity for the dev team and that the "real" problem is being worked on. What I'm looking for are low friction tools which get the job done with a minimum of fuss. Tools I'd characterize as such are SVN/TortioseSVN, ReSharper, VS itself. I'm looking for frameworks which solve the problems inherient in all software projects like ORM, logging, UI frameworks/components. An example on the UI side would be ASP.NET MVC vs WebForms vs MonoRail.

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• How-to limit feature functionality

  - by ph0enix

  Are there any standard or "best practice" ways of limiting feature functionality for a particular application? Example: We have a product with a variety of features, and our customers can pick and choose which features they would like to use, and the cost of the product varies based on which features they are actually using. In the past, we have distributed along with our software installer an encrypted license file that contains information about the customer, as well as the collection of features that they have enabled. In code, we read from the license file and enable the functionality according to the license file. This seems to work fine, except there a few disadvantages: Upgrading users with new functionality can be sort of a pain If a particular feature shows up in multiple places throughout the application, a developer might not realize that this feature should be licensed, and forget to check the license file before granting functionality to the user If the license file becomes corrupted, deleted, moved, renamed, etc. the application will not run We're getting ready to roll out a new set of features, and I was just curious what others in the community have done to tackle this problem?

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• Mobile development decision - Future wise (Iphone,android,symbian)

  - by Idan

  Hi, I would like to learn mobile development, but I'm not sure which category would be the most cost effective one. I know it's kind of a prophecy question, but anyhow, suggestions would be welcomed. So, as i'm pretty familiar with C++ development , I though about learning QT. I understand that using QT, I can develop once and then deploy to symbian,Mee-go, and of course to windows, linux and more. (does that mean I won't have to lean each OS internal calls, and just learn the QT library ? ) Learning development for android , mean I will have to learn Java, which is not my preferred way of action right now. Another option is to learn Objective-C, but as it only apply to Iphone development, I think it's a pretty narrow zone for me. I want to learn a library, which would be a wise decision career wise. Any recommendations ?

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• Can you recommend an effective and cheap CDN for video streaming?

  - by Shaul Dar

  I am looking for a streaming CDN recommendation. Cost and performance are my chief concerns. Video viewers may be all over the globe, with the, US, Europe, Russia and South America topping the list (yes, I know that leaves out a little :-). I saw the following list of streaming CDNs in LinkedIn: Akamai, BitGravity, EdgeCast, Highwinds, Internap, Level3, Limelight, Mirror Image, Move Networks, Qbrick, SimpleCDN, StreamZilla, Swarmcast (streaming via HTTP), WINK Streaming... (+Amazon's S3 and CloudFront) Can anyone recommend any of these or others? Or a different type of technology (e.g. P2P).

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• Using core plot for iPhone, drawing date on x axis

  - by xmax

  I have available an array of dictionary that contains NSDate and NSNumber values. I wanted to plot date on X axis. for plotting I need to supply xRanges to plot with some decimal values.I don't understand how can i supply NSdate values to xRange (low and length). And what should be there in this method: -(NSNumber *)numberForPlot:(CPPlot *)plot field:(NSUInteger)fieldEnum recordIndex:(NSUInteger)index I mean how my date value will be returned as NSNumber..? I think i should use some interval over there.but what should be the exact conversion..? can any one explain me what are the exact requirement to plot the date on xAxis..? I am plotting my plot in half of the view.

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• What is better, a STL list or a STL Map for 20 entries, considering order of insertion is as importa

  - by Abhijeet

  I have the following scenario.The implementation is required for a real time application. 1)I need to store at max 20 entries in a container(STL Map, STL List etc). 2)If a new entry comes and 20 entries are already present i have to overwrite the oldest entry with the new entry. Considering point 2, i feel if the container is full (Max 20 entries) 'list' is the best bet as i can always remove the first entry in the list and add the new one at last (push_back). However, search won't be as efficient. For only 20 entries, does it really make a big difference in terms of searching efficiency if i use a list in place of a map? Also considering the cost of insertion in map i feel i should go for a list? Could you please tell what is a better bet for me ?

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• Most optimized way to calculate modulus in C

  - by hasanatkazmi

  I have minimize cost of calculating modulus in C. say I have a number x and n is the number which will divide x when n == 65536 (which happens to be 2^16): mod = x % n (11 assembly instructions as produced by GCC) or mod = x & 0xffff which is equal to mod = x & 65535 (4 assembly instructions) so, GCC doesn't optimize it to this extent. In my case n is not x^(int) but is largest prime less than 2^16 which is 65521 as I showed for n == 2^16, bit-wise operations can optimize the computation. What bit-wise operations can I preform when n == 65521 to calculate modulus.

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• Why does my UITableView change from UITableViewStyleGrouped to UITableViewStylePlain

  - by casper

  My application has a view controller that extends UITableViewController. The initialization method looks like this: - (id)initWithCoder:(NSCoder*)coder { if (self = [super initWithCoder:coder]) { self.tableView = [[UITableView alloc] initWithFrame:self.tableView.frame style:UITableViewStyleGrouped]; } return self; } When the view is initially loaded, it's displayed as UITableViewStyleGrouped. However, if my app ever receives a low memory warning, the above view changes to UITableViewStylePlain. There is no associated xib file with the View/Controller. The viewDidUnload and didReceiveMemoryWarning methods are straightforward: - (void)didReceiveMemoryWarning { // Releases the view if it doesn't have a superview. [super didReceiveMemoryWarning]; // Release any cached data, images, etc that aren't in use. } - (void)viewDidUnload { // Release any retained subviews of the main view. // e.g. self.myOutlet = nil; } My question is, why does the table style change when I receive a memory warning?

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• iCloud + Storage of media in iPhone Documents folder

  - by Michael Morrison

  I, like many developers, got an email from Apple recently that stated we should move our data from the documents directory into another folder to permit more streamlined backup to iCloud. In recent testing it appears that [your app] stores a fair amount of data in its Documents folder. Since iCloud backups are performed daily over Wi-Fi for each user's iOS device, it's important to ensure the best possible user experience by minimizing the amount of data being stored by your app. Marco Arment, of instapaper fame, has a good take on the issue, which is that the recommended location for storing downloadable files is in /Library/Caches. However, the problem is that both /tmp and /Caches can be 'cleaned' anytime the OS decides that the device is running low on storage. If your app is cleaned then the data downloaded by your app and stored by your user is gone. Naturally, the user will blame you and not Apple. What to do?

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• AS3: How to access pixel data efficiently?

  - by JonoRR

  I'm working a game. The game requires entities to analyse an image and head towards pixels with specific properties (high red channel, etc.) I've looked into Pixel Bender, but this only seems useful for writing new colors to the image. At the moment, even at a low resolution (200x200) just one entity scanning the image slows to 1-2 Frames/second. I'm embedding the image and instance it as a Bitmap as a child of the stage. The 1-2 FPS situation is using BitmapData.getPixel() (on each pixel) with a distance calculation beforehand. I'm wondering if there's any way I can do this more efficiently... My first thought was some sort of spatial partioning coupled with splitting the image up into many smaller pieces. I also feel like Pixel Bender should be able to help somehow, however I've had little experience with it. Cheers for any help. Jonathan

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• Why darcs instead of git?

  - by Ctrl Alt D-1337

  Using pure functional languages can have a lot of benefits over using impure imperatives but low level systems languages will generally allow you to achieve much greater performance especially when they are imperative because it allows you to specify the exact steps in how the cpu should compute the result. If there is ever list of tools where high performance is an absolute must then I would put source version controls systems right at the top of that list and git achieves this very well but performance is not it's only advantage over many other other types of version control systems anyway. The git team are handling the unsafe c code very well and I never worry about my type system or any other features of the language it is written in so why is it that there is a lot of haskell developers that must use darcs when they will only be using the finished product?

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• Slow SelectSingleNode

  - by Simon

  I have a simple structured XML file like this: <ttest ID="ttest00001", NickName="map00001"/> <ttest ID="ttest00002", NickName="map00002"/> <ttest ID="ttest00003", NickName="map00003"/> <ttest ID="ttest00004", NickName="map00004"/> ..... This xml file can be around 2.5MB. In my source code I will have a loop to get nicknames In each loop, I have something like this: nickNameLoopNum = MyXmlDoc.SelectSingleNode("//ttest[@ID=' + testloopNum + "']").Attributes["NickName"].Value This single line will cost me 30 to 40 millisecond. I searched some old articles (dated back to 2002) saying, use some sort of compiled "xpath" can help the situation, but that was 5 years ago. I wonder is there a mordern practice to make it faster? (I'm using .NET 3.5)

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• How do I find out what the windows constants like WM_MOUSEMOVE and WM_MOUSEDOWN are if I'm using C#?

  - by Siracuse

  I'm writing some code that uses some unmanaged calls into user32 functions such as SetWindowsHookEx, etc. This requires me to use lots of constants that I'm not sure what their value is. For example, if I want to set the hook as a low-level mouse hook I need to know that WM_MOUSE_LL = 14. Where can I look these up? I need to know what WM_MOUSEMOVE, WM_MOUSEDOWN, and more are. When I'm dealing with interop code, what is the easiest way for me to find these? Is it possible for me to import them into C# so they will be defined?

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