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  • Data access strategy for a site like SO - sorted SQL queries and simultaneous updates that affect th

    - by Kaleb Brasee
    I'm working on a Grails web app that would be similar in access patterns to StackOverflow or MyLifeIsAverage - users can vote on entries, and their votes are used to sort a list of entries based on the number of votes. Votes can be placed while the sorted select queries are being performed. Since the selects would lock a large portion of the table, it seems that normal transaction locking would cause updates to take forever (given enough traffic). Has anyone worked on an app with a data access pattern such as this, and if so, did you find a way to allow these updates and selects to happen more or less concurrently? Does anyone know how sites like SO approach this? My thought was to make the sorted selects dirty reads, since it is acceptable if they're not completely up to date all of the time. This is my only idea for possibly improving performance of these selects and updates, but I thought someone might know a better way.

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  • How to generate a number in arbitrary range using random()={0..1} preserving uniformness and density?

    - by psihodelia
    Generate a random number in range [x..y] where x and y are any arbitrary floating point numbers. Use function random(), which returns a random floating point number in range [0..1] from P uniformly distributed numbers (call it "density"). Uniform distribution must be preserved and P must be scaled as well. I think, there is no easy solution for such problem. To simplify it a bit, I ask you how to generate a number in interval [-0.5 .. 0.5], then in [0 .. 2], then in [-2 .. 0], preserving uniformness and density? Thus, for [0 .. 2] it must generate a random number from P*2 uniformly distributed numbers. The obvious simple solution random() * (x - y) + y will generate not all possible numbers because of the lower density for all abs(x-y)>1.0 cases. Many possible values will be missed. Remember, that random() returns only a number from P possible numbers. Then, if you multiply such number by Q, it will give you only one of P possible values, scaled by Q, but you have to scale density P by Q as well.

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  • is there a tool to see the difference between two database tables in SQL Server?

    - by reinier
    What is a good tool to see the differences between 2 tables (or even better, the datasets returned by 2 queries). EDIT: I'm not interested in the schema changes. Just assume that the schemas are the same. background as to why: I'm porting some legacy code which can fill a database with some pre-calced data. The easiest way to see if I got everything right, is to check the output of the old program, with the new one. I was thinking that if there is some kind of 'diff' tool for databases, this might be great.

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  • How can I make this SQL query more efficient? PHP.

    - by Alan Grant
    Hi all, I have a system whereby a user can view categories that they've subscribed to individually, and also those that are available in the region they belong in by default. So, the tables are as follows: Categories UsersCategories RegionsCategories I'm querying the db for all the categories within their region, and also all the individual categories that they've subscribed to. My query is as follows: Select * FROM (categories c) LEFT JOIN users_categories uc on uc.category_id = c.id LEFT JOIN regions_categories rc on rc.category_id = c.id WHERE (rc.region_id = ? OR uc.user_id = ?) At least I believe that's the query, I'm creating it using Cake's ORM layer, so the exact one is: $conditions = array( array( "OR" => array ( 'RegionsCategories.region_id' => $region_id, 'UsersCategories.user_id' => $user_id ) )); $this->find('all', $conditions); This turns out to be incredibly slow (sometimes around 20 seconds or so. Each table has around 5,000 rows). Is my design at fault here? How can I retrieve both the users' individual categories and those within their region all in one query without it taking ages? Thanks!

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  • LINQ to SQL -- Can't modify return type of stored procedure.

    - by Kyle Ryan
    When I drag a particular stored procedure into the VS 2008 dbml designer, it shows up with Return Type set to "none", and it's read only so I can't change it. The designer code shows it as returning an int, and if I change that manually, it just gets undone on the next build. But with another (nearly identical) stored procedure, I can change the return type just fine (from "Auto Generated Type" to what I want.) I've run into this problem on two separate machines. Any idea what's going on? Here's the stored procedure that works: USE [studio] GO /****** Object: StoredProcedure [dbo].[GetCourseAnnouncements] Script Date: 05/29/2009 09:44:51 ******/ SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER OFF GO CREATE PROCEDURE [dbo].[GetCourseAnnouncements] @course int AS SELECT * FROM Announcements WHERE Announcements.course = @course RETURN And this one doesn't: USE [studio] GO /****** Object: StoredProcedure [dbo].[GetCourseAssignments] Script Date: 05/29/2009 09:45:32 ******/ SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER OFF GO CREATE PROCEDURE [dbo].[GetCourseAssignments] @course int AS SELECT * FROM Assignments WHERE Assignments.course = @course ORDER BY date_due ASC RETURN

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  • How do I create a SQL Server 2008 Reporting Services Template to a Default Font?

    - by David Stein
    I'm creating a new template to create reports from at a later date. I know how to create one, and I know where to save it. However, the problem is this. Everything that is created on the report uses the default font of Arial with a size of 10pt. I need to set mine to default to Tahoma 11pt. I can create a mock title, mock tables, etc and save those to Tahoma 11pt, but any new controls that are used on any version of this report will default back to Arial 10pt. How do I fix this?

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  • Download databasename.bak file

    - by Jordon
    I have downloaded databasename.bak file from my hosting company, when i tried to restore that DB file in SQL server 2008 it is keep on giving me following error. The media family on device 'C:\go4sharepoint_1384_8481.bak' is incorrectly formed. SQL Server cannot process this media family. RESTORE HEADERONLY is terminating abnormally. (Microsoft SQL Server, Error: 3241) According to this error and from following link http://www.sqlcoffee.com/Troubleshooting047.htm It is clear that either file i am downloading is corrupt or it is getting corrupted on the way? Any idea, why I am keep on receiving this error? I tried almost all ways but unable to fix this problem, please help me.

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  • How to grant permissions to single SELECT/UPDATE statment (sql server) ?

    - by Albert
    I have a problem when trying to execute this update statement (below) using C# SqlCommand when I execute it locally it works fine, but when deployed to another machine I got a permission error The SELECT permission was denied on the object Order ... The UPDATE permission was denied on the object Order ... Update Statement "UPDATE Order SET Request = @request WHERE Id = @ID"; Is there any way to add GRANT SELECT and GRANT UPDATE to a single statement like the update above without using a stored procedure? or the SP is the way to go on this? Thanks in advance

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  • How can I export images from SQL Server to a file on disk?

    - by rball
    I have a User table that has all of their avatars saved in an image field. I'd like to just take that out of the database and store it as a regular file on disk. I looked around and saw some code for textcopy, but that doesn't seem to be on my machine for some reason. Here is the code I wrote up anyway. Anyone know a way to get this done? DECLARE @exec_str varchar (255) SELECT @exec_str = 'textcopy /S (local)\SQLEXPRESS' + --' /U ' + @login + --' /P ' + @password + ' /D thedatabase' + ' /T User'+ ' /C AvatarImage' + ' /F "d:\Avatars\' + User.Name + '.jpg"' + ' /O' FROM [User] WHERE UserID = 2 EXEC master..xp_cmdshell @exec_str

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  • How to pull a RANDOM and UNIQUE record from SQL via LINQ.

    - by Jeremy H
    Okay, I found lots of posts on SO about how to pull a RANDOM item from the database when using LINQ. There seems to be a couple of differnet ways to handle this. What I need to do though is pull a RANDOM item from the database that the user has not seen before. The data I am pulling from the database is very small. Is there any way I can just hit the database once for 1000 records and then randomly scroll through those? Should I put a cookie on the users system recording the IDs of which items they have seen, pull a random record, check to see if it is seen and if so, pull from the database again? That seems like performance issues just waiting to happen. I don't expect anyone to code it for me, I am just looking for concepts and pointing in the right direction of how I should go about this. Need more details? Just let me know!

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  • How to find largest common sub-tree in the given two binary search trees?

    - by Bhushan
    Two BSTs (Binary Search Trees) are given. How to find largest common sub-tree in the given two binary trees? EDIT 1: Here is what I have thought: Let, r1 = current node of 1st tree r2 = current node of 2nd tree There are some of the cases I think we need to consider: Case 1 : r1.data < r2.data 2 subproblems to solve: first, check r1 and r2.left second, check r1.right and r2 Case 2 : r1.data > r2.data 2 subproblems to solve: - first, check r1.left and r2 - second, check r1 and r2.right Case 3 : r1.data == r2.data Again, 2 cases to consider here: (a) current node is part of largest common BST compute common subtree size rooted at r1 and r2 (b)current node is NOT part of largest common BST 2 subproblems to solve: first, solve r1.left and r2.left second, solve r1.right and r2.right I can think of the cases we need to check, but I am not able to code it, as of now. And it is NOT a homework problem. Does it look like?

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  • Attach an entity that is not new, perhaps having been loaded from another DataContext. LINQ to SQL -

    - by soldieraman
    Alright How I got this error I got one application sitting on a server 2 users accessing this application - doing some bulk data processing . eg. entering values and then the application is working with another system to extract values for them and then saving. I can't recreate the error The error logs show: The error happend at the same time in both the application Both happend on a Attach/Submit (but two different functions) There is no way they are using the same DataContext object as I save the DataContext in the HttpContext.Items My hunch / guess is: One datacontext was not refreshed i.e. the an object was created for the same item twice as it was new in both the forms. eg. Customer Number - a customer was created (as one couldn't be found) by one datacontext - the other one couldn't find it either (i am using compiled queries to find it in the datacontext) so it created another object and on attaching failed. The HttpContext.Items lost its value somehow (i am using a virtual pc as server - maybe something went wrong there) I am going more of the second as I can't recreate the error - but it just might be a timing (for attach/save) thing - also the error makes me think of the 2nd too.

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  • How to add second JOIN clause in Linq To Sql?

    - by Refracted Paladin
    I am having a lot of trouble coming up with the Linq equivalent of this legacy stored procedure. The biggest hurdle is it doesn't seem to want to let me add a second 'clause' on the join with tblAddress. I am getting a Cannot resolve method... error. Can anyone point out what I am doing wrong? Below is, first, the SPROC I need to convert and, second, my LINQ attempt so far; which is FULL OF FAIL! Thanks SELECT dbo.tblPersonInsuranceCoverage.PersonInsuranceCoverageID, dbo.tblPersonInsuranceCoverage.EffectiveDate, dbo.tblPersonInsuranceCoverage.ExpirationDate, dbo.tblPersonInsuranceCoverage.Priority, dbo.tblAdminInsuranceCompanyType.TypeName AS CoverageCategory, dbo.tblBusiness.BusinessName, dbo.tblAdminInsuranceType.TypeName AS TypeName, CASE WHEN dbo.tblAddress.AddressLine1 IS NULL THEN '' ELSE dbo.tblAddress.AddressLine1 END + ' ' + CASE WHEN dbo.tblAddress.CityName IS NULL THEN '' ELSE '<BR>' + dbo.tblAddress.CityName END + ' ' + CASE WHEN dbo.tblAddress.StateID IS NULL THEN '' WHEN dbo.tblAddress.StateID = 'ns' THEN '' ELSE dbo.tblAddress.StateID END AS Address FROM dbo.tblPersonInsuranceCoverage LEFT OUTER JOIN dbo.tblInsuranceCompany ON dbo.tblPersonInsuranceCoverage.InsuranceCompanyID = dbo.tblInsuranceCompany.InsuranceCompanyID LEFT OUTER JOIN dbo.tblBusiness ON dbo.tblBusiness.BusinessID = dbo.tblInsuranceCompany.BusinessID LEFT OUTER JOIN dbo.tblAddress ON dbo.tblAddress.BusinessID = dbo.tblBusiness.BusinessID and tblAddress.AddressTypeID = 'b' LEFT OUTER JOIN dbo.tblAdminInsuranceCompanyType ON dbo.tblPersonInsuranceCoverage.InsuranceCompanyTypeID = dbo.tblAdminInsuranceCompanyType.InsuranceCompanyTypeID LEFT OUTER JOIN dbo.tblAdminInsuranceType ON dbo.tblPersonInsuranceCoverage.InsuranceTypeID = dbo.tblAdminInsuranceType.InsuranceTypeID WHERE tblPersonInsuranceCoverage.PersonID = @PersonID var coverage = from insuranceCoverage in context.tblPersonInsuranceCoverages where insuranceCoverage.PersonID == personID join insuranceCompany in context.tblInsuranceCompanies on insuranceCoverage.InsuranceCompanyID equals insuranceCompany.InsuranceCompanyID join address in context.tblAddresses on insuranceCompany.tblBusiness.BusinessID equals address.BusinessID where address.AddressTypeID = 'b' select new { insuranceCoverage.PersonInsuranceCoverageID, insuranceCoverage.EffectiveDate, insuranceCoverage.ExpirationDate, insuranceCoverage.Priority, CoverageCategory = insuranceCompany.tblAdminInsuranceCompanyType.TypeName, insuranceCompany.tblBusiness.BusinessName, TypeName = insuranceCoverage.InsuranceTypeID, Address = };

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  • What is the differnce between "LINQ to Entities", "LINQ to SQL" and "LINQ to Dataset".

    - by Marcel
    Hi all, I'm working for quite a while now with LINQ. However, it remained still a bit of a mystery what are the real differences between the mentioned flavours of LINQ. The successful answer will contain a short differentiation between them. What is the main goal if it, what is the benefit, and is there a performance impact... P.S. I know that there are a lot of information sources out there, but I look for a kind of a "cheat sheet" which instructs a newbie where to head to for a specific goal.

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  • How do I handle a low job offer for an entry level position?

    - by user229269
    Hi guys! I recently graduated with MS in CS and I am excited because I just received a job offer from a company I really like for an entry-level sw engineer position. The thing is that, although the salary is not my priority and I care way more about gaining experience, their offer unfortunately is way below of what I expected. Actually after I did some research I realized that, comparing to the average salary range for the entry-level sw engineering positions in my area (one of the most expensive areas in the US) supposedly [X - Y]$ (where X is the lowest average and Y the highest), their offer is 20% below X! I wouldnt have a problem accepting an offer around X but this one is even lower than the lowest. Can I counter offer the X which is 20% more than what they offered me but at the same time is the minimum average? -- And mind you that I didnt even take under consideration the fact that I hold a MS degree which in many cases yields to a 5-10% more pay.

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  • ASP MVC LINQ to SQL IQueryable Array out of bounds?

    - by Jacob Huggart
    Hey guys, I have an Iqueryable that is populated from the database and then converted to an Array. That works fine. The issue is when I only have 1 element in the Array. I try to use the 0th element and it says "ArrayOutOfBoundsException". When I have 2+ elements in the array and pull elements 0 and 1 it works fine. What gives?

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  • What database strategy to choose for a large web application

    - by Snoopy
    I have to rewrite a large database application, running on 32 servers. The hardware is up to date, each machine has two quad core Xeon and 32 GByte RAM. The database is multi-tenant, each customer has his own file, around 5 to 10 GByte each. I run around 50 databases on this hardware. The app is open to the web, so I have no control on the load. There are no really complex queries, so SQL is not required if there is a better solution. The databases get updated via FTP every day at midnight. The database is read-only. C# is my favourite language and I want to use ASP.NET MVC. I thought about the following options: Use two big SQL servers running SQL Server 2012 to serve the 32 servers with data. On the 32 servers running IIS hosting providing REST services. Denormalize the database and use Redis on each webserver. Use booksleeve as a Redis client. Use a combination of SQL Server and Redis Use SQL Server 2012 together with Hadoop Use Hadoop without SQL Server What is the best way for a read-only database, to get the best performance without loosing maintainability? Does Map-Reduce make sense at all in such a scenario? The reason for the rewrite is, the old app written in C++ with ISAM technology is too slow, the interfaces are old fashioned and not nice to use from an website, especially when using ajax. The app uses a relational datamodel with many tables, but it is possible to write one accerlerator table where all queries can be performed on, and all other information from the other tables are possible by a simple key lookup.

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  • Upload large database SQL file

    - by Devy
    I've a database of more than 20Gb of size on my hard disk. What is the best way to upload it with the least (money) load possible on the server? - I'm on Windows 7. - I have FTP and SSH access on the server. I avoid using FTP because my connection cuts off a lot, I can't imagine I re-upload again the file after failing on 99%. I found some tools that split the large .sql file to small .sql files, but they didn't mention how to gather these files again into one file. Another way is to archive the big .sql file to .rar with -v option, upload them through FTP then unpack them. But unpacking will also cost, right? I know it will cost in any cases, but any best practice will be strongly appreciated.

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