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• Can Microsoft store three-valued fields in a single bit?

  - by fenomas

  I'm completely ignorant of SQL/databases, but I was chatting with a friend who does a lot of database work about how some databases use a "boolean" field that can take a value of NULL in addition to true and false. Regarding this, he made a comment along these lines: "To Microsoft's credit, they have never referred to that kind of field as a boolean, they just call it a bit. And it's a true bit - if you have eight or fewer bit fields in a record, it only requires one byte to store them all." Naturally that seems impossible to me - if the field can hold three values you're not going to fit eight of them into a byte. My friend agreed that it seemed odd, but begged ignorance of the low-level internals and said that so far as he knew, such fields can hold three values when viewed from the SQL side, and it does work out to require a byte of storage. I imagine one of us has a wire crossed. Can anyone explain what's really going on here?

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• Need an encrypted online source code backup service.

  - by camelCase

  Please note this is not a question about online/hosted SVN services. I am working on a home based, solo developer, project that now has commercial significance and it is time to think about remote source code backup. There is no need for file level check in/out, all I need is once a day or once a week directory level snapshot to remote storage. Automatic encryption would be a bonus to protect my IP. What I have in mind is some sort of GUI interface app that will squirt a source code snapshot off to an Amazon S3 bucket on an automatic schedule. (My development PC runs on MS Windows.)

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• Remove first 'n' elements from list without itterating

  - by Eldhose M Babu

  I need an efficient way of removing items from list. If some condition happens, I need to remove first 'n' elements from a list. Can some one suggest the best way to do this? Please keep in mind: performance is a factor for me, so I need a faster way than itterating. Thanks. I'm thinking of a way through which the 'n'th item can be made as the starting of the list so that the 0-n items will get garbage collected. Is it possible?

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• getting window screenshot windows API

  - by Oliver

  Hi, I am trying to make a program to work on top of an existing GUI to annotate it and provide extra calculations and statistical information. I want to do this using image recognition, as I have learned a fair amount about this in University using Matlab and similar things. I can get a handle to the window I want to perform image recognition on, but I don't know how to turn that handle into an image of that window, and all its visible child windows. I suppose I am looking for something like the screenshot function, but restricted to a single window. How would I go about doing this? I suppose I'd need something like a .bmp to mess about with. Also, it would have to be efficient enough that I could call it several times a second without my PC grinding to a halt. Hopefully this isn't an obvious question, I typed some things into google but didn't get anything related.

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• Why Banks or Financial Companies prefer Oracle than other RDBMS for their "Core" systems?

  - by edwin.nathaniel

  I'd like to know why most Banks or Financial companies prefer Oracle than other RDBMS for their core systems (the absolutely minimum features that a Bank must support). I found a few answers that didn't satisfy me. For example: Oracle has more features. But features for what? Can't you implement that in application level if you were not using Oracle? Could someone please describe a bit more technical but still on high-level overview of what the bank needs and how Oracle would solve it and the others can't or don't have the features yet? I came from the web-app (web 2.0) crowd who normally hear news about MySQL, PostgreSQL or even key-value/column-oriented storage solution. I have almost zero knowledge on how Banks or Financial companies operates from technical perspective. Thank you, Ed

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• How would I best address this object type heirachy? Some kind of enum heirarchy?

  - by FerretallicA

  I'm curious as to any solutions out there for addressing object heirarchies in an ORM approach (in this instance, using Entity Framework 4). I'm working through some docs on EF4 and trying to apply it to a simple inventory tracking program. The possible types for inventory to fall into are as follows: INVENTORY ITEM TYPES: Hardware PC Desktop Server Laptop Accessory Input (keyboards, scanners etc) Output (monitors, printers etc) Storage (USB sticks, tape drives etc) Communication (network cards, routers etc) Software What recommendations are there for handling enums in a situation like this? Are enums even the solution? I don't really want to have a ridiculously normalised database for such a relatively simple experiment (eg tables for InventoryType, InventorySubtype, InventoryTypeToSubtype etc). I don't really want to over-complicate my data model with each subtype being inherited even though no additional properties or methods are included (except PC types which would ideally have associated accessories and software but that's probably out of scope here). It feels like there should be a really simple, elegant solution to this but I can't put my finger on it. Any assistance or input appreciated!

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• Php using unserialize() and serialize() changing values in a saved file

  - by Doodle

  I have a serialized array of values saved to a file and need to change the value of one of the variables. In the example I change the value of $two and then save the whole array back into the file with the new value. Is there a more efficient way of altering just the single value with out having to read and write the entire file/array. $data = file_get_contents('./userInfo'); $data = unserialize($data); extract($data); $two="this is a altered value"; $userData = array( 'one' => $one, 'two' => $two, 'three' => $three ); $file=fopen("../userInfo",'w'); fwrite($file, $userData); fclose($file);

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• Effective Android Programming Techniques

  - by kunjaan

  Please Help me compile a list of Effective Android Programming techniques Don't forget to free resources after use. Lot of resources like Cursors are overlooked. Free them too. Don't Use magic Numbers. values[0] is meaningless. The framework provides very useful accessors like values[SensorManager.DATA_X] "Make use of onPause()/onResume to save or close what does not need to be opened the whole time." protected void onResume() { mSensorManager.registerListener(...); } protected void onStop() { mSensorManager.unregisterListener(...); super.onStop(); } Make your Android UI Fast and Efficient from the Google I/O has a lot of useful UI Performance tips.

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• I do not write tests. Am I stupid?

  - by Josh Stodola

  I've done a little bit of reading on unit testing and TDD, and I've never seriously considered writing tests to such a precise extent. Granted, I am not working on any projects that are ridiculously huge. If all I build are small apps, am I stupid for not writing tests? Edit: To clarify, when I say "small apps", I mean apps that are not going to control a persons life and/or their belongings. I generally build things that are supposed to make peoples lives easier and to make them more efficient.

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• The fastest way to do a collection subtraction

  - by Tony

  I have two Sets. Set<B> b is the subset of Set<A> a. they're both very huge Sets. I want to subtract b from a , what's the best practice to do this common operation ? I've written to many codes like this , and I don't think it's efficient. what's your idea ? for(int i = 0 ; i < a.size(); i++) { for (int j=0 ; j < b.size() ;j++) { // do comparison , if found equals ,remove from a break; } } And I want to find an algorithm , not only applies to Sets, also works for Array.

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• Chart Control Inside SSRS ReportViewer is Viewable From Localhost But Not Internet

  - by Daniel Coffman

  A project I own was just moved from an older server to a new one, and in the process of moving the web folder, re-deploying the SSRS reports, restoring the database, configuring IIS, etc... I have lost the ability to view the Microsoft Chart Controls that are embedded in the SSRS reports, that are then displayed by a Microsoft.ReportViewer. I could view them both locally and remotely (via the internet) on the old server. I can view them if I preview the SSRS report in Visual Studio. The report displays fine, only missing all the embedded charts. I can still view them locally through the web browser, just not from the internet. What am I missing? I tried giving permissions to the ChartImageHandler temp storage folder, but it didn't work. I'm getting the Javascript error: Error: ClientReport380ec8ca0c294a809e9986c1bef9db1c is undefined

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• Foreign keys in MySQL?

  - by icco

  I have been slowly learning SQL the last few weeks. I've picked up all of the relational algebra and the basics of how relational databases work. What I'm trying to do now is learn how it's implemented. A stumbling block I've come across in this, is foreign keys in MySQL. I can't seem to find much about the other than that they exist in the InnoDB storage schema that MySQL has. What is a simple example of foreign keys implemented in MySQL? Here's part of a schema I wrote that doesn't seem to be working if you would rather point out my flaw than show me a working example. CREATE TABLE `posts` ( `pID` bigint(20) NOT NULL auto_increment, `content` text NOT NULL, `time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP, `uID` bigint(20) NOT NULL, `wikiptr` bigint(20) default NULL, `cID` bigint(20) NOT NULL, PRIMARY KEY (`pID`), Foreign Key(`cID`) references categories, Foreign Key(`uID`) references users ) ENGINE=InnoDB;

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• Memory Issues When DOM Parsing A Large XML File on Android Devices

  - by tonyc

  Hey awesome SO users, I have an Android application that parses an XML file for users and displays results in a much more mobile friendly format. The app works great for most users, but some users have lots and lots of data and the app crashes on them because it runs out of memory. Is there any way I have a DOM style XML parser quit parsing data after a certain amount of parsing? I only need the first 30 or so elements so it would make the application much more efficient. I'd like to use a SAX or pull parser instead, but the XML I'm parsing is not valid and I have no control over it. Unless anyone has some good SAX solutions that let me parse messy, invalid XML, I think DOM is the only way to go. Thanks for reading!

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• Concurrent web requests with Ruby (Sinatra?)?

  - by cbmeeks

  I have a Sinatra app that basically takes some input values and then finds data matching those values from external services like Flickr, Twitter, etc. For example: input:"Chattanooga Choo Choo" Would go out and find images at Flickr on the Chattanooga Choo Choo and tweets from Twitter, etc. Right now I have something like: @images = Flickr::...find...images.. @tweets = Twitter::...find...tweets... @results << @images @results << @tweets So my question is, is there an efficient way in Ruby to run those requests concurrently? Instead of waiting for the images to finish before the tweets finish. Thanks.

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• Are there any programs to aid in the mass-editing of Visual SourceSafe checkin comments?

  - by Schnapple

  I know that in Visual SourceSafe you can go in and drill down to the history of an individual file and then drill down to an individual check-in and apply a comment to the check-in that way but that's tedious and time consuming - if you have a lot of files that were checked in at the same time and you want the same comment to apply to all of them this will take forever. I use the tool VSSReporter to generate reports of checkins and other stuff from VSS, but it cannot edit anything, only report on them. Are there any tools which will let you go back and retroactively apply comments to check-ins in an efficient and easy manner?

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• Locking NFS files in PHP

  - by Oli

  Part of my latest webapp needs to write to file a fair amount as part of its logging. One problem I've noticed is that if there are a few concurrent users, the writes can overwrite each other (instead of appending to file). I assume this is because of the destination file can be open in a number of places at the same time. flock(...) is usually superb but it doesn't appear to work on NFS... Which is a huge problem for me as the production server uses a NFS array. The closest thing I've seen to an actual solution involves trying to create a lock dir and waiting until it can be created. To say this lacks elegance is understatement of the year, possibly decade. Any better ideas? Edit: I should add that I don't have root on the server and doing the storage in another way isn't really feasible any time soon, not least within my deadline.

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• Efficiency of checking for null varbinary(max) column ?

  - by Moe Sisko

  Using SQL Server 2008. Example table : CREATE table dbo.blobtest (id int primary key not null, name nvarchar(200) not null, data varbinary(max) null) Example query : select id, name, cast((case when data is null then 0 else 1 end) as bit) as DataExists from dbo.blobtest Now, the query needs to return a "DataExists" column, that returns 0 if the blob is null, else 1. This all works fine, but I'm wondering how efficient it is. i.e. does SQL server need to read in the whole blob to its memory, or is there some optimization so that it just does enough reads to figure out if the blob is null or not ? (FWIW, the sp_tableoption "large value types out of row" option is set to OFF for this example).

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• bi-directional o2m/m2o beats uni-directional o2m in SQL efficiency?

  - by Henry

  Use these 2 persistent CFCs for example: // Cat.cfc component persistent="true" { property name="id" fieldtype="id" generator="native"; property name="name"; } // Owner.cfc component persistent="true" { property name="id" fieldtype="id" generator="native"; property name="cats" type="array" fieldtype="one-to-many" cfc="cat" cascade="all"; } When one-to-many (unidirectional) Note: inverse=true on unidirectional will yield undesired result: insert into cat (name) values (?) insert into Owner default values update cat set Owner_id=? where id=? When one-to-many/many-to-one (bi-directional, inverse=true on Owner.cats): insert into Owner default values insert into cat (name, ownerId) values (?, ?) Does that mean setting up bi-directional o2m/m2o relationship is preferred 'cause the SQL for inserting the entities is more efficient?

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• How to use Haar wavelet to detect LINES on an image?

  - by Ole Jak

  So I have Image like this I want to get something like this (I hevent drawn all lines I want but I hope you can get my idea) I want to use SURF ( (Speeded Up Robust Features) is a robust image descriptor, first presented by Herbert Bay et al. in 2006 ) or something that is based on sums of 2D Haar wavelet responses and makes an efficient use of integral images for finding all straight lines on image. I want to get relative to picture pixel coords start and end points of lines. So on this picture to find all lines between tiles and thouse 2 black lines on top. Is there any such Code Example (with lines search capability) to start from? I love C and C++ but any other readable code will probably work for me=)

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• Check if BigDecimal is integer value

  - by Adamski

  Can anyone recommend an efficient way of determining whether a BigDecimal is an integer value in the mathematical sense? At present I have the following code: private boolean isIntegerValue(BigDecimal bd) { boolean ret; try { bd.toBigIntegerExact(); ret = true; } catch (ArithmeticException ex) { ret = false; } return ret; } ... but would like to avoid the object creation overhead if necessary. Previously I was using bd.longValueExact() which would avoid creating an object if the BigDecimal was using its compact representation internally, but obviously would fail if the value was too big to fit into a long. Any help appreciated.

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• Optimization of running total calculation in SQL for multiple values per join condition

  - by Kiril

  I have the following table (test_table): date value --------------- d1 10.0 d1 20.0 d2 60.0 d2 10.0 d2 -20.0 d3 40.0 I calculate the running total as follows. I use the same query twice, because first I need to calculate the values for a specifi date, and afterwards I can calculate the running total. Otherwise, joining the two tables where date is not unique, I would get too many results from the join: SELECT t1.date, SUM(t2.value) AS total FROM (SELECT date, SUM(value) AS value FROM test_table GROUP BY date) AS t1 JOIN (SELECT date, SUM(value) AS value FROM test_table GROUP BY date) AS t2 ON t1.date >= t2.date GROUP BY t1.date ORDER BY t1.date This gives me (which is fine): date total ------------- d1 30.0 d2 80.0 d3 120.0 BUT, this query isn't very efficient, because I need to change conditions in two places, if necessary. In production, the test_table is a lot bigger ( 4 Mio. rows), and the query takes too much time to complete. Question: How can I avoid using the same query twice?

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• Distributed datastore

  - by Julien Genestoux

  We're trying to add some kind of persistence in our app. The app generates about 250 entries per second. Each of these entries belong to one of 2M files. For each file, we want to keep the last 10 entries, so we can look them up later. The way our client application works : it gets a stream of all the data it fetches the right file (GET) it adds the new content it saves the file back (PUT) We're looking for an efficient way to store this data that can scale horizontally as the amount of data we're getting is doubling every few weeks. We initially looked at S3. It works fine, but becomes very expensive very fast ($1000 monthly just in PUT operations!) We then gave a shot at Riak. But it seems we can't get more than 60 write/sec on each node, which is very very slow. Any other solution out there?

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• How to achieve a palette effect on iPhone using OpenGL

  - by Joe

  I'm porting a 2d retro game to iPhone that has the following properties: targets OpenGL ES 1.1 entire screen is filled with tiles (textured triangle strip tile textured using a single 256x256 RGBA texture image the texture is passed to OpenGL once at the start of the game only 4 displayed colours are used one of the displayed colours is black The original game flashed the screen when time starts to run out by toggling the black pixels to white using an indexed palette. What is the best (i.e. most efficient) way to achieve this in OpenGL ES 1.1? My thoughts so far: Generate an alternative texture with white instead of black pixels, and pass to OpenGL when the screen is flashing Render a white poly underneath the background and render the texture with alpha on to display it Try and render a poly on top with some blending that achieves the effect (not sure this is possible) I'm fairly new to OpenGL so I'm not sure what the performance drawbacks of each of these are, or if there's a better way of doing this.

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• how does NTFS actually work with B-tree ?

  - by bakra

  To improve performance, NTFS directories use a special data management structure called a B-tree. "B-tree" concept here refers to a "tree of storage units" that hold the contents of an individual directory. What I don't understand is where on the disk is this tree stored? Its surely not created every-time we reboot...that would take lots of time. and since its a tree(dynamic Data structure) unlike arrays it will grow. so space needs to be allocated every-time it grows. so how is this "dynamic meta-data" stored ?

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• Remove Duplicates from List of HashMap Entries

  - by HonorGod

  I have a List<HashMap<String,Object>> which represents a database where each list record is a database row. I have 10 columns in my database. There are several rows where the values of 2 particular columns are equals. I need to remove the duplicates from the list after the list is updated with all the rows from database. What is the efficient way? FYI - I am not able to do distinct while querying the database, because the GroupName is added at a later stage to the Map after the database is loaded. And since Id column is not primary key, once you add GroupName to the Map. You will have duplicates based on Id + GroupName combination! Hope my question makes sense. Let me know if we need more clarification.

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