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  • How I use schemas.

    - by Alexander Kuznetsov
    I use schemas to simplify granting permissions. For tables and views, I have three schemas: Data, the actual data my customers need. Can only be modified via sprocs. Staging, only visible to data loaders and devs. Full privileges on INSERT?UPDATE/DELETE for those who see it. Config, the configuration data used in loads, only visible to data loaders and devs. Can only be modified via sprocs. For sprocs/UDFs I have the following schemas: Readers Writers ETL ConfigReaders ConfigWriters Also I have dbo...(read more)

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  • Book Review: Pro SQL Server 2008 Relational Database Design and Implementation

    - by Alexander Kuznetsov
    Investing in proper database design is a very efficient way to cut maintenance costs. If we expect a system to last, we need to make sure it has a good solid foundation - high quality database design. Surely we can and sometimes do cut corners and save on database design to get things done faster. Unfortunately, such cutting corners frequently comes back and bites us: we may end up spending a lot of time solving issues caused by poor design. So, solid understanding of relational database design is...(read more)

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  • Survey: how do you unit test your T-SQL?

    - by Alexander Kuznetsov
    How do you unit test your T-SQL? Which libraries/tools do you use? What percentage of your code is covered by unit tests and how do you measure it? Do you think the time and effort which you invested in your unit testing harness has paid off or not? Share this post: email it! | bookmark it! | digg it! | reddit! | kick it! | live it!...(read more)

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  • Learning PostgreSql: polymorphism

    - by Alexander Kuznetsov
    Functions in PL/PgSql are polymorphic, which is very different from T-SQL. Demonstrating polymorphism For example, the second CREATE FUNCTION in the following script does not replace the first function - it creates a second one: CREATE OR REPLACE FUNCTION public .GetQuoteOfTheDay ( someNumber INTEGER ) RETURNS VARCHAR AS $body$ BEGIN RETURN 'Say my name.' ; END ; $body$ LANGUAGE plpgsql ; CREATE OR REPLACE FUNCTION public .GetQuoteOfTheDay ( someNumber REAL ) RETURNS VARCHAR AS $body$ BEGIN RETURN...(read more)

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  • Learning PostgreSql: Reading and Writing From .Net

    - by Alexander Kuznetsov
    In this post we shall do some setup tasks, save a few rows of data from a .Net client to PostgreSql, and read it back. Setting up We have set up a virtual machine running Red Hat Linux, installed PostgreSql 9.3 on it, and made sure there is enough disk space. 9.3 is a very recent version, released this September. Because PostgreSqlis not known for releasing before the full testing is complete, we did not have to wait for the next service pack or something like that. Smoke test On the client machine...(read more)

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  • Learning PostgreSql: First Steps

    - by Alexander Kuznetsov
    In this series of blog posts we shall migrate some functionality from SQL Server to PostgreSql 9.2. The emphasis of these blog posts will be on what PostgreSql does differently from Sql Server - I assume that the reader has considerable knowledge of Sql Server, but might know nothing of PostgreSql. Also we shall concentrate on development, not administration. In a true agile fashion, we shall learn only what we need to get this particular job done, and nothing else, but we shall strive to learn it...(read more)

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  • T-SQL Tuesday #13: Clarifying Requirements

    - by Alexander Kuznetsov
    When we transform initial ideas into clear requirements for databases, we typically have to make the following choices: Frequent maintenance vs doing it once. As we are clarifying the requirements, we need to determine whether we want to concinue spending considerable time maintaining the system, or if we want to finish it up and move on to other tasks. Race car maintenance vs installing electric wiring is my favorite analogy for this kind of choice. In some cases we need to sqeeze every last bit...(read more)

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  • Learning PostgreSql: bulk loading data

    - by Alexander Kuznetsov
    In this post we shall start loading data in bulk. For better performance of inserts, we shall load data into a table without constraints and indexes. This sounds familiar. There is a bulk copy utility, and it is very easy to invoke from C#. The following code feeds the output from a T-SQL stored procedure into a PostgreSql table: using ( var pgTableTarget = new PgTableTarget ( PgConnString , "Data.MyPgTable" , GetColumns ())) using ( var conn = new SqlConnection ( connectionString )) { conn.Open...(read more)

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  • Learning PostgreSql: old versions of rows are stored right in the table

    - by Alexander Kuznetsov
    PostgreSql features multi-version concurrency control aka MVCC. To implement MVCC, old versions of rows are stored right in the same table, and this is very different from what SQL Server does, and it leads to some very interesting consequences. Let us play with this thing a little bit, but first we need to set up some test data. Setting up. First of all, let us create a numbers table. Any production database must have it anyway: CREATE TABLE Numbers ( i INTEGER ); INSERT INTO Numbers ( i ) VALUES...(read more)

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  • In defense of SELECT * in production code, in some limited cases?

    - by Alexander Kuznetsov
    It is well known that SELECT * is not acceptable in production code, with the exception of this pattern: IF EXISTS( SELECT * We all know that whenever we see code code like this: Listing 1. "Bad" SQL SELECT Column1 , Column2 FROM ( SELECT c. * , ROW_NUMBER () OVER ( PARTITION BY Column1 ORDER BY Column2 ) AS rn FROM data.SomeTable AS c ) AS c WHERE rn < 5 we are supposed to automatically replace * with an explicit list of columns, as follows: Listing 2. "Good" SQL SELECT Column1 , Column2 FROM...(read more)

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  • How do I create a 2.5d parallax effect?

    - by Nikolay Dyankov
    I have a decent background in 3D graphics and programming, but I'm new to game development. I'm currently exploring different possibilities and I really want to make an RPG game. I was thinking about classic 2D isometric view, but I really love how Diablo 2 looks and feels to play. My question is - how can I achieve Diablo 2's parallax effect? Everything looks hand drawn with baked lights and shadows and looks awesome, but when you move around you notice some perspective. For example, let's say that I drew a big hall with columns in Photoshop with an orthographic perspective (classic pixel art style, just parallel lines). How would I give parallax effect to this scene when the character moves around? If I use camera-facing sprites for everything it would probably look OK in the distance, but it would be really fake when a character comes close to a column (cylinder) for example. Any suggestions? How did Blizzard make the parallax effect in Diablo 2? See this screenshot: http://guidesmedia.ign.com/guides/10629/images/act2tombs.jpg

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  • Learning PostgreSql: Functions and refcursors

    - by Alexander Kuznetsov
    In this post we shall create a function that returns data, and invoke it from our C# client. There are no stored procedures in PostgreSql, only functions. This is different from T-SQL, but consistent with many other languages, such as C#. Creating a function Functions can return many different types. Learning all the available options might take some time. However, for the project we are working on, we need to replicate several T-SQL stored procedures which take column list as a parameter, and use...(read more)

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  • Reproducing a Conversion Deadlock

    - by Alexander Kuznetsov
    Even if two processes compete on only one resource, they still can embrace in a deadlock. The following scripts reproduce such a scenario. In one tab, run this: CREATE TABLE dbo.Test ( i INT ) ; GO INSERT INTO dbo.Test ( i ) VALUES ( 1 ) ; GO SET TRANSACTION ISOLATION LEVEL SERIALIZABLE ; BEGIN TRAN SELECT i FROM dbo.Test ; --UPDATE dbo.Test SET i=2 ; After this script has completed, we have an outstanding transaction holding a shared lock. In another tab, let us have that another connection have...(read more)

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  • How to manage own bots at the server?

    - by Nikolay Kuznetsov
    There is a game server and people can play in game rooms of 2, 3 or 4. When a client connects to server he can send a request specifying a number of people or range he wants to play with. One of this value is valid: {2-4, 2-3, 3-4, 2, 3, 4} So the server maintains 3 separate queues for game room with 2, 3 and 4 people. So we can denote queues as #2, #3 and #4. It work the following way. If a client sends request, 3-4, then two separate request are added to queues #3 and #4. If queue #3 now have 3 requests from different people then game room with 3 players is created, and all other requests from those players are removed from all queues. Right now not many people are online simultaneously, so they apply for a game wait for some time and quit because game does not start in a reasonable time. That's a simple bot for beginning has been developed. So there is a need to patch server code to run a bot, if some one requests a game, but humans are not online. Input: request from human {2-4, 2-3, 3-4, 2, 3, 4} Output: number of bots to run and time to wait for each before connecting, depending on queues state. The problem is that I don't know how to manage bots properly at the server? Example: #3 has 1 request and #4 has 1 request Request from user is {3,4} then server can add one bot to play game with 3 people or two bots to play game of 4. Example: #3 has 1 request and #4 has 2 requests Request from user is {3,4} then in each case just one bot is needed so game with 4 players is more preferrable.

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  • Catching multiple exceptions on the client is robust and easy

    - by Alexander Kuznetsov
    Maria Zakourdaev has just demonstrated that if our T-SQL throws multiple exceptions, ERROR_MESSAGE() in TRY..CATCH block will only expose one. When we handle errors in C#, we have a very easy access to all errors. The following procedure throws two exceptions: CREATE PROCEDURE dbo.ThrowsTwoExceptions AS BEGIN ; RAISERROR ( 'Error 1' , 16 , 1 ) ; RAISERROR ( 'Error 2' , 16 , 1 ) ; END ; GO EXEC dbo.ThrowsTwoExceptions ; Both exceptions are shown by SSMS: Msg 50000 , LEVEL 16 , State 1 , PROCEDURE...(read more)

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  • I am not speaking at SQL Connections February 2011 meeting in Chicago suburbs

    - by Alexander Kuznetsov
    Usually it is an honor when we get to present to a user group, but not this time, so let me explain. I have no idea how my presentation got briefly mentioned in the invitation which went out today, without my consent. I have never asked or agreed to speak at SQL Connections February 2011 meeting in Chicago suburbs. Yet I apologize for any inconvenience it might have caused. I was going to speak at the meeting of December 2010, which was agreed by email with the person in charge. I had spent some...(read more)

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  • REST and PayPal

    - by Nikolay Fominyh
    Is it ok to query REST API and get redirect to third party from it, or it is only about resources? Let's look at following scenario: User gets to payment page User clicks on "Pay using paypal button" API query PayPal for redirect url API returns redirect url in response. Client side redirect goes here. User does PayPal routine and returns with token User query API with token API do token check and adds money Is this scenario complex for REST architecture?

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  • I am not speaking at SQL Connections February 2011 meeting in Chicago suburbs

    - by Alexander Kuznetsov
    Usually it is an honor when we get to present to a user group, but not this time, so let me explain. I have no idea how my presentation got briefly mentioned in the invitation which went out today, without my consent. I have never asked or agreed to speak at SQL Connections February 2011 meeting in Chicago suburbs. Yet I apologize for any inconvenience it might have caused. I was going to speak at the meeting of December 2010, which was agreed by email with the person in charge. I had spent some...(read more)

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  • Yet another use of OUTER APPLY in defensive programming

    - by Alexander Kuznetsov
    When a SELECT is used to populate variables from a subquery, it fails to change them if the subquery returns nothing - and that can lead to subtle bugs. We shall use OUTER APPLY to eliminate this problem. Prerequisites All we need is the following mock function that imitates a subquery: CREATE FUNCTION dbo.BoxById ( @BoxId INT ) RETURNS TABLE AS RETURN ( SELECT CAST ( 1 AS INT ) AS [Length] , CAST ( 2 AS INT ) AS [Width] , CAST ( 3 AS INT ) AS [Height] WHERE @BoxId = 1 ) ; Let us assume that this...(read more)

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  • Efficient existing rating system for multiplayer?

    - by Nikolay Kuznetsov
    I would like to add a rating for online version of a board game. In this game there are many game rooms each normally having 3-4 people. So I expect that player's rating adjustments (RA) should depends on Rating of opponents in the game room Number of players in game room and final place of a player Person gets rating increase if he plays more games and more frequently If a person leaves a game room (disconnect) before the game ends he should get punished with a high rating decrease I have found two related questions in here Developing an ELO like point system for a multiplayer gaming site Simplest most effective way to rank and measure player skill in a multi-player environment? Please, let me know what would be the most appropriate existing rating model to refer.

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  • Non-blocking ORM issues

    - by Nikolay Fominyh
    Once I had question on SO, and found that there are no non-blocking ORMs for my favorite framework. I mean ORM with callback support for asynchronous retrieval. The ORM would be supplied with a callback or some such to "activate" when data has been received. Otherwise ORM needs to be split of in a separate thread to guarantee UI responsiveness. I want to create one, but I have some questions that blocking me from starting development: What issues we can meet when developing ORM? Does word "non-blocking" before word "ORM" will dramatically increase complexity of ORM? Why there are not much non-blocking ORMs around? Update: It looks, that I have to improve my question. We have solutions that already allows us to receive data in non-blocking way. And I believe that not all companies that use such solutions - using raw SQL. We want to create more generic solution, that we can reuse in future projects. What difficulties we can meet?

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  • Learning PostgreSql: Embracing Change With Copying Types and VARCHAR(NO_SIZE_NEEDED)

    - by Alexander Kuznetsov
    PostgreSql 9.3 allows us to declare parameter types to match column types, aka Copying Types. Also it allows us to omit the length of VARCHAR fields, without any performance penalty. These two features make PostgreSql a great back end for agile development, because they make PL/PgSql more resilient to changes. Both features are not in SQL Server 2008 R2. I am not sure about later releases of SQL Server. Let us discuss them in more detail and see why they are so useful. Using Copying Types Suppose...(read more)

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  • Freebsd write access to group directory

    - by Nikolay Sergeev
    Hi. I'm confused. I have two users in system: u1 and u2, and group u1. both u1 and u2 belong to g1. I've created directory /opt/d with properties: drwxrwxr-x 2 u1 u1 512B May 26 17:55 d AFAIK, this configuration allows both users write to directory. But, from u2: touch /opt/d/x touch: /opt/d/x: Permission denied And same configuration on RHEL5 works fine. What i've missed? Thanks.

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