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• Stairway to T-SQL DML Level 4: The Mathematics of SQL: Part 1

  A relational database contains tables that relate to each other by key values. When querying data from these related tables you may choose to select data from a single table or many tables. If you select data from many tables, you normally join those tables together using specified join criteria. The concepts of selecting data from tables and joining tables together is all about managing and manipulating sets of data. In Level 4 of this Stairway we will explore the concepts of set theory and mathematical operators to join, merge, and return data from multiple SQL Server tables. Get Smart with SQL Backup Pro Powerful centralised management, encryption and more.SQL Backup Pro was the smartest kid at school Discover why.

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• Better way for calculating project euler's 2nd problem Fibonacci sequence)

  - by firephil

  object Problem_2 extends App { def fibLoop():Long = { var x = 1L var y = 2L var sum = 0L var swap = 0L while(x < 4000000) { if(x % 2 ==0) sum +=x swap = x x = y y = swap + x } sum } def fib:Int = { lazy val fs: Stream[Int] = 0 #:: 1 #:: fs.zip(fs.tail).map(p => p._1 + p._2) fs.view.takeWhile(_ <= 4000000).filter(_ % 2 == 0).sum } val t1 = System.nanoTime() val res = fibLoop val t2 = (System.nanoTime() - t1 )/1000 println(s"The result is: $res time taken $t2 ms ") } Is there a better functional way for calculating the fibonaci sequence and taking the sum of the the even values below 4million ? (projecteuler.net - problem 2) The imperative method is 1000x faster ?

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• If there's no problem treating a statement as an expression, why was there a distinction in the first place in some programming languages?

  - by cdmckay

  Why do we have the distinction between statements and expressions in most programming languages? For example, in Java, assuming f and g return ints, this still won't compile because it's a statement and statements don't return values. // won't compile int i = if (pred) { f(x); } else { g(x); } but in Scala, it's very happy with treating if as an expression. // compiles fine val i: Int = if (pred) f(x) else g(x) So if there's no problem treating an if statement as an expression, why was there a distinction in the first place?

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• Determining the angle to fire a shot when target and shooter moves, and bullet moves with shooter velocity added in

  - by Azaral

  I saw this question: Predicting enemy position in order to have an object lead its target and followed the link in the answer to stack overflow. In the stack overflow page I used the 2nd answer, the one that is a large mathematical derivation. My situation is a little different though. My first question though is will the answer provided in the stack overflow page even work to begin with, assuming the original circumstances of moving target and stationary shooter. My situation is a little different than that situation. My target moves, the shooter moves, and the bullets from the shooter start off with the velocities in x and y added to the bullets' x and y velocities. If you are sliding to the right, the bullets will remain in front of you as you move so as long as your velocity remains constant. What I'm trying to do is to get the enemy to be able to determine where they need to shoot in order to hit the player. Unless the player and enemy is stationary, the velocity from the ship adding to the velocity of the bullets will cause a miss. I'd rather like to prevent that. I used the formula in the stack overflow answer and did what I thought were the appropriate adjustments. I've been banging at this for the last four hours and I just can't make it click. It is probably something really simple and boneheaded that I am missing (that seems to be a lot of my problems lately). Here is the solution presented from the stack overflow answer: It boils down to solving a quadratic equation of the form: a * sqr(x) + b * x + c == 0 Note that by sqr I mean square, as opposed to square root. Use the following values: a := sqr(target.velocityX) + sqr(target.velocityY) - sqr(projectile_speed) b := 2 * (target.velocityX * (target.startX - cannon.X) + target.velocityY * (target.startY - cannon.Y)) c := sqr(target.startX - cannon.X) + sqr(target.startY - cannon.Y) Now we can look at the discriminant to determine if we have a possible solution. disc := sqr(b) - 4 * a * c If the discriminant is less than 0, forget about hitting your target -- your projectile can never get there in time. Otherwise, look at two candidate solutions: t1 := (-b + sqrt(disc)) / (2 * a) t2 := (-b - sqrt(disc)) / (2 * a) Note that if disc == 0 then t1 and t2 are equal. If there are no other considerations such as intervening obstacles, simply choose the smaller positive value. (Negative t values would require firing backward in time to use!) Substitute the chosen t value back into the target's position equations to get the coordinates of the leading point you should be aiming at: aim.X := t * target.velocityX + target.startX aim.Y := t * target.velocityY + target.startY Here is my code, after being corrected by Sam Hocevar (thank you again for your help!). It still doesn't work. For some reason it never enters the section of code inside the if(disc = 0) (obviously because it is always less than zero but...). However, if I plug the numbers from my game log on the enemy and player positions and velocities it outputs a valid firing solution. I have looked at the code side by side a couple of times now and I can't find any differences. There has got to be something simple I'm missing here. If someone else could look at this code and determine what is going on here I'd appreciate it. I know it's not going through that section because if it were, shouldShoot would become true and the enemy would be blasting away at the player. This section calls the function in question, CalculateShootHeading() if(shouldMove) { UseEngines(); } x += xVelocity; y += yVelocity; CalculateShootHeading(); if(shouldShoot) { ShootWeapons(); } UpdateWeapons(); This is CalculateShootHeading(). This is inside the enemy class so x and y are the enemy's x and y and the same with velocity. One output from my game log gives Player X = 2108, Player Y = -180.956, Player X velocity = 10.9949, Player Y Velocity = -6.26017, Enemy X = 1988.31, Enemy Y = -339.051, Enemy X velocity = 1.81666, Enemy Y velocity = -9.67762, 0 enemy projectiles. The output from the console tester is Bullet position = 2210.49, -239.313 and Player Position = 2210.49, -239.313. This doesn't make any sense. The only thing that could be different is the code or the input into my function in the game and I've checked that and I don't think that it is wrong as it's updated before this and never changed. float const bulletSpeed = 30.f; float const dx = playerX - x; float const dy = playerY - y; float const vx = playerXVelocity - xVelocity; float const vy = playerYVelocity - yVelocity; float const a = vx * vx + vy * vy - bulletSpeed * bulletSpeed; float const b = 2.f * (vx * dx + vy * dy); float const c = dx * dx + dy * dy; float const disc = b * b - 4.f * a * c; shouldShoot = false; if (disc >= 0.f) { float t0 = (-b - std::sqrt(disc)) / (2.f * a); float t1 = (-b + std::sqrt(disc)) / (2.f * a); if (t0 < 0.f || (t1 < t0 && t1 >= 0.f)) { t0 = t1; } if (t0 >= 0.f) { float shootx = vx + dx / t0; float shooty = vy + dy / t0; heading = std::atan2(shooty, shootx) * RAD2DEGREE; } shouldShoot = true; }

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• JavaOne 2012: JDBC Community Discussion

  - by sowmya

  At JavaOne2012, Mark Biamonte of DataDirect Technologies and Lance Andersen of Oracle organized a discussion about JDBC. To learn more about using JDBC to develop database applications, see the JDBC trail in the Java Tutorials. You will know how to use the basic JDBC API to * create tables * insert values into them * query the tables * retrieve the results of the queries * update the tables In this process, you will learn how to use simple statements and prepared statements, and see an example of a stored procedure. You will also learn how to perform transactions and how to catch exceptions and warnings. - Sowmya

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• Data Source Security Part 2

  - by Steve Felts

  In Part 1, I introduced the default security behavior and listed the various options available to change that behavior.  One of the key topics to understand is the difference between directly using database user and password values versus mapping from WLS user and password to the associated database values.   The direct use of database credentials is relatively new to WLS, based on customer feedback.  Some of the trade-offs are covered in this article. Credential Mapping vs. Database Credentials Each WLS data source has a credential map that is a mechanism used to map a key, in this case a WLS user, to security credentials (user and password).  By default, when a user and password are specified when getting a connection, they are treated as credentials for a WLS user, validated, and are converted to a database user and password using a credential map associated with the data source.  If a matching entry is not found in the credential map for the data source, then the user and password associated with the data source definition are used.  Because of this defaulting mechanism, you should be careful what permissions are granted to the default user.  Alternatively, you can define an invalid default user to ensure that no one can accidentally get through (in this case, you would need to set the initial capacity for the pool to zero so that the pool is populated only by valid users). To create an entry in the credential map: 1) First create a WLS user.  In the administration console, go to Security realms, select your realm (e.g., myrealm), select Users, and select New.  2) Second, create the mapping.  In the administration console, go to Services, select Data sources, select your data source name, select Security, select Credentials, and select New.  See http://docs.oracle.com/cd/E24329_01/apirefs.1211/e24401/taskhelp/jdbc/jdbc_datasources/ConfigureCredentialMappingForADataSource.html for more information. The advantages of using the credential mapping are that: 1) You don’t hard-code the database user/password into a program or need to prompt for it in addition to the WLS user/password and 2) It provides a layer of abstraction between WLS security and database settings such that many WLS identities can be mapped to a smaller set of DB identities, thereby only requiring middle-tier configuration updates when WLS users are added/removed. You can cut down the number of users that have access to a data source to reduce the user maintenance overhead.  For example, suppose that a servlet has the one pre-defined, special WLS user/password for data source access, hard-wired in its code in a getConnection(user, password) call.  Every WebLogic user can reap the specific DBMS access coded into the servlet, but none has to have general access to the data source.  For instance, there may be a ‘Sales’ DBMS which needs to be protected from unauthorized eyes, but it contains some day-to-day data that everyone needs. The Sales data source is configured with restricted access and a servlet is built that hard-wires the specific data source access credentials in its connection request.  It uses that connection to deliver only the generally needed day-to-day information to any caller. The servlet cannot reveal any other data, and no WebLogic user can get any other access to the data source.  This is the approach that many large applications take and is the reasoning behind the default mapping behavior in WLS. The disadvantages of using the credential map are that: 1) It is difficult to manage (create, update, delete) with a large number of users; it is possible to use WLST scripts or a custom JMX client utility to manage credential map entries. 2) You can’t share a credential map between data sources so they must be duplicated. Some applications prefer not to use the credential map.  Instead, the credentials passed to getConnection(user, password) should be treated as database credentials and used to authenticate with the database for the connection, avoiding going through the credential map.  This is enabled by setting the “use-database-credentials” to true.  See http://docs.oracle.com/cd/E24329_01/apirefs.1211/e24401/taskhelp/jdbc/jdbc_datasources/ConfigureOracleParameters.html "Configure Oracle parameters" in Oracle WebLogic Server Administration Console Help. Use Database Credentials is not currently supported for Multi Data Source configurations.  When enabled, it turns off credential mapping on Generic and Active GridLink data sources for the following attributes: 1. identity-based-connection-pooling-enabled (this interaction is available by patch in 10.3.6.0). 2. oracle-proxy-session (this interaction is first available in 10.3.6.0). 3. set client identifier (this interaction is available by patch in 10.3.6.0).  Note that in the data source schema, the set client identifier feature is poorly named “credential-mapping-enabled”.  The documentation and the console refer to it as Set Client Identifier. To review the behavior of credential mapping and using database credentials: - If using the credential map, there needs to be a mapping for each WLS user to database user for those users that will have access to the database; otherwise the default user for the data source will be used.  If you always specify a user/password when getting a connection, you only need credential map entries for those specific users. - If using database credentials without specifying a user/password, the default user and password in the data source descriptor are always used.  If you specify a user/password when getting a connection, that user will be used for the credentials.  WLS users are not involved at all in the data source connection process.

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• Getting Started with Component Architecture: DI?

  - by ashes999

  I just moved away from MVC towards something more component-architecture-like. I have no concept of messages yet (it's rough prototype code), objects just get internal properties and values of other classes for now. That issue aside, it seems like this is turning into an aspect-oriented-programming challenge. I've noticed that all entities with, for example, a position component will have similar properties (get/set X/Y/Z, rotation, velocity). Is it a common practice, and/or good idea, to push these behind an interface and use dependency injection to inject a generic class (eg. PositionComponent) which already has all the boiler-plate code? (I'm sure the answer will affect the model I use for message/passing)

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• Which is the appropriate content-type meta tag value ?

  - by Argoron

  I have a question about the meta tag content-type. When starting to build my site (HTML+PHP+JS), I copied a lot of the meta tags over from elsewhere, and I have, amongst others, the following: <meta http-equiv="content-type" content="application/xhtml+xml; charset=iso-8859-1" /> Now, I've seen that tag is being used a lot with the value "text/html". I've been searching the web but could not find a comprehensive explanation regarding what the difference between both is. The "text/html" intuitively sounds more straightforward to me. Should I change my tag to that, or might the "application/xhtml+xml" be an equivalent solution ? Alternatively, can anyone point me to a resource where the different values for these tags are listed and explained in a clear manner? Thanks in advance

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• Particles are not moving correctly [closed]

  - by cr33p

  I want to make a particle explosion, after something gets destroyed, but somehow only one line of mixed colors show up on the screen. Here's the header: http://pastebin.com/JW5bPLj2 Here's the source: http://pastebin.com/KHmFqytD I don't get what's wrong, as it's nearly the same as in "Programming Linux Games" Can somebody help me fix that? PS: "Uint32 delta" is needed to update the pixels based on time. PSS: Maybe I should add that it's programmed in C and includes SDL. EDIT: Found the problem. It was the "drawParticles" function. The problem was, that I passed a double to "offset" (as particles[i].x, etc are all doubles). So I ended up with values like ~MAX_INT because I didn't cast the doubles properly to ints.

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• Why is there a 20 and not 21 in some versions of Planning Poker?

  - by SuffixTreeMonkey

  In Planning Poker, cards usually contain numbers of the Fibonacci sequence, which is 0,1,1,2,3,5,8,13,21,34,55 etc. However, you can see on the Wikipedia page (and this has been confirmed to me by people that work at several positions where Planning Poker is applied) in some editions the cards stray away from Fibonacci sequence after 13. They lower 21 to 20 and then continue with 40 and 100. Is there some rationale on why these values have been changed, specifically 21 to 20? (Also note that some other cards are added, such as ? and 1/2, but these are easier for me to understand, compared to the 21 - 20 shift.)

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• Circular movement - eliminating speed ups near Y = 0

  - by Fibericon

  I have a basic algorithm to rotate an enemy around a 200 unit radius circle with center 0. This is how I'm achieving that: if (position.Y <= 0 && position.X > -200) { position.X -= 2; position.Y = 0 - (float)Math.Sqrt((200 * 200) - (position.X * position.X)); } else { position.X += 2; position.Y = (float)Math.Sqrt((200 * 200) - (position.X * position.X)); } It does work, and I've ensured that at no point does either X or Y equal NaN. However, when Y approaches 0, it seems to go significantly faster. This surprises me, because the Y values are locked to the X, which is being incremented by a steady amount. What can I do to smooth the speed?

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• Relative Positions Of Player And Enemy Are Different In XNA 3D Game

  - by CoOlDud3

  I am having a problem in my 3D Jet Fighter Game using XNA. I have a Player Jet and a few enemy drones built from a separate class. The problem is that when I set Player position and a drone's position to a height 10f in y direction. They aren't at the same height. But if i move Drone's Position up 500f in the y direction then it is pretty much close to the player. Relatively They are supposedly at the same height but with different position values. Can Any One Help Please?

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• Dynamic Fields/Columns

  - by DanMark

  What is the best way to allow for dynamic fields/database columns? For example, let's say we have a payroll system that allows a user to create unique salary structures for each employee. How could/should one handle this scenario? I thought of using a "salary" table that hold the salary component fields and joining these columns to a "salary_values" table that hold the actual values. Does this make sense? Example Salary Structures: Notice how the components of the salary can be shared or unique. -- Jon's Salary -- Basic 100 Annual Bonus 25 Tel. Allowances 15 -- Jane's Salary -- Basic 100 Travel Allowances 10 Bi-annual Bonus 30

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• MediaWiki plugin for dynamic content via forms

  - by Geek42

  Are there any plugins for MediaWiki that would allow me to create a page that has a form at the top that when filled in populates tags further down in the document? Say someone would put a form with "Source Server:" and "Destination Server:" fields at the top. Once those were typed in it would automatically populate those names into the content lower so that when following the instructions you could just read the docs and not have to mentally replace things, and possibly mess it all up. I'm not looking to make pages that are permanent, just ones that can have values entered before they are followed. Any suggestions?

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• arrays format (Javascript)

  - by João Melo

  i have a list of users, with minions, something like this: User52: minion10 minion12 User32: minion13 minion11 i've been keeping in an array where the "location" is the id, like this: Users: [52]User minions: [10]minion [12]minion [32]User minions: [13]minion [11]minion so i can access them easily like this: user[UserID].minions[MinionID] (ex: user[32].minions[11]) but when i print it or send it by json i get something like this: {,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,minion,,,,,,,,,,,,,,minion} but should i keep using like this or should i change to something like this: User = function(){ this.minions = ...; this.getMinion = function(value){ for(var m in this.minions){ if(this.minions[m].id == value){ return this.minions[m]; break; } } } } and get it like this: user.getMinion(MinionID); Question: i get better performance using a "short" array but using loops every time i need a minion, or using "long" arrays, but no need for loop and getting values directly from the id "name"?

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• Variable names for Contact Information bits

  - by RustyTheBoyRobot

  I am in the middle of refactoring code and would like to get some ideas on variable naming so that my new names clearly represent the data they hold. I have a class called ContactMethod which makes sense to me; each instance is a different way to contact someone. My problem comes when naming the properties of ContactMethod. For example, one instance might be a Fax number of 555-555-5555 while another could be an Email address of [email protected]; I've got a property called contactMethodType to hold the values "fax" or "email", but I don't know what to call the "555-555-5555" or "[email protected]" part. Has anyone here created a good generic name for this piece of contact information? (PS - the old convention was to call it a "Phone" with fields "phoneType" holding the "fax"/"email" value and "phoneId" holding the number/address. Yuck.)

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• Structuring an input file

  - by Ricardo

  I am in the process of structuring a small program to perform some hydraulic analysis of pipe flow. As I am envisioning this, the program will read an input file, store the input parameters in a suitable way, operate on them and finally output results. I am struggling with how to structure the input file in a sane way; that is, in a way that a human can write it easily and a machine can parse it easily. A sample input file made available to me for a similar program is just a stream of comma-separated numbers that don't make much sense on their own, so that's the scenario I am trying to avoid. Though I am giving the details of my particular problem, I am more interested in general input-file structuring strategies. Is a stream of comma-separated values my best bet? Would I be better off using some sort of key:value structure? I don't know much about this, so any help will probably put me in a better track than I am now.

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• Framework for interaction between web-page and server-side script

  - by Carrier

  I want to make a web-page that will have several controls elements, among which there are elements like check-boxes, radio-buttons, "range selectors" (one can specify the min and max value, like it is done when you select range for prices in the online markets). The new values shall be sent to the "server-side", once changed (without any Submit buttons etc), and the "server-side" can return something (one or more numbers, etc). Does anyone know a good ajax-like framework that allows (with minimal adaptation / changes) to make such solution in an easy way? It will be good if the server-side of existing solution will be in Perl (not a big deal, but I know it much better than PHP or something else). Set of controls might change and depend on other parameter, so adding one extra element should not cause rewriting the whole thing. P.S.: I haven't working in this area for quite a while, so not aware of existing solutions in this area, and don't want to invent the wheel and write everything from scratch for something that already exist (at least, I hope so). Thanks in advance!

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• How can I acheive a smooth 2D lighting effect?

  - by Cyral

  I'm making a tile based game in XNA. So currently my lightning looks like this: How can I get it to look like this? Instead of each block having its own tint, it has a smooth overlay. I'm assuming some sort of shader, and to tell it the lighting and blur it some how. But im not an expert with shaders. My current lighting calculates the light, and then passes it to a spritebatch and draws with a color parameter. EDIT: No longer uses spritebatch tint, I was testing and now pass parameters to set the light values. But still looking for a way to smooth it.

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• Concatenating Rows

  Often in database design we store different values in rows to take advantage of a normalized design. However many times we need to combine multiple rows of data into one row for a report of some sort. New author Carl P. Anderson brings us some interesting T-SQL code to accomplish this. Free trial of SQL Backup™“SQL Backup was able to cut down my backup time significantly AND achieved a 90% compression at the same time!” Joe Cheng. Download a free trial now.

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• The life saver HttpContext.Current.Items["ParameterName"]

  - by MoezMousavi

  I got stocked passing parameter to one master page for some reasons, seems the page lifecycle and dynamic loading of the master pages has got some issues with defining public properties in the masterpage within my project. It did not set my values and as a result, properties became useless. A collegue just mentioned using HttpContext. have a look what  MSDN saying "Encapsulates all HTTP-specific information about an individual HTTP request" http://msdn.microsoft.com/en-us/library/system.web.httpcontext.aspx HttpContext.Current.Items["ParameterName"] Also, Page.Items could do the same thing. Page.Items, "Gets a list of objects stored in the page context" http://msdn.microsoft.com/en-us/library/system.web.ui.page.items.aspx as your master page and content page are rendered as a single document anyway.

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• Search Result Organization

  - by Vecta

  I'm creating an AJAX live search on a website I'm working on. Users will select values from a few dropdowns and a list of products will be returned based on what they select. Some possible fields would be: color, model, make, etc. What type of organization of search results do users tend to find most useful? Is it better to lump them all together (alphabatized) or is it more useful to lump them together by make? In the past I've tended to group them by "make" but I'm not concerned that this will continually force some items with a make toward the end of the alphabet always to the bottom of the list. Any tips are greatly appreciated.

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• Unity, Unrealistic Sphere On Inclined Plane

  - by user1086516

  So I am trying to model a ball rolling down an inclined surface in Unity based on what I am observing in real life but it is still quite off. In Unity it takes the ball about 3 seconds to travel from a place to another specified place where in real life it only takes 1 second. The ball isn't as fast to react to the incline as in real life (even though I have tried giving the ball and surface low or zero friction values) The ball does not accelerate as nearly as fast as it does in real life What do I do to give the ball more realistic behavior ? I have tried messing around with mass, physics materials, drag, and angular drag on the ball and surface but it doesn't seem to be helping.

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• Content Weighting and Sociology

  - by Chris Massey

  I’ve had loads of fantastic feedback on the concept and early curation wireframes I posted on the labs, and it’s led to some further thoughts on the topic of voting. More specifically, thoughts about the kinds of behaviour and values a platform encourages in it’s users via the set of available actions. StackOverflow is a very good example of this kind of sociology in action, not only via the set of available actions, but through the reputation system it uses to both reward and control it’s users. In our case (specifically, in the case of the curation model I’ve been talking about thus far), the main considerations are how the quality of content is judged, and how to make sure each piece of curated content gets a fair hearing. Based on the feedback and conversations I’ve had with many of you over the last few days, a few considerations came to light about how we might need to weight and display our curations, and I’ve written about that more extensively over on the labs themselves – have a read and let me know what you think.

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• Should I try to write simple key-value storage by myself?

  - by shabunc

  I need a key-value storage in a simplest form we can think of. Keys should be some fixed-length strings, values should be some texts. This key-value storage should have an HTTP-backed API. That's basically it. As you can see, there is no big difference between such storage and some web application with some upload functionality. The thing is - it'll take few hours (including tests and coffee drinking) to write something like this. "Something like this" will be fully under my control and can be tuned on demand. Should I, in this specific case, not try to reinvent bicycles? Is it better to use some of existing NoSQL solutions. If yes, which one exactly? If, say, I'd needed something SQL-like, I won't ask and won't try to write something by myself. But with NoSQL I just don't know what is adequate and what is not.

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