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• Avoiding dog-piling or thundering herd in a memcached expiration scenario

  - by Quintin Par

  I have the result of a query that is very expensive. It is the join of several tables and a map reduce job. This is cached in memcached for 15 minutes. Once the cache expires the queries are obviously run and the cache warmed again. But at the point of expiration the thundering herd problem issue can happen. One way to fix this problem, that I do right now is to run a scheduled task that kicks in the 14th minute. But somehow this looks very sub optimal to me. Another approach I like is nginx’s proxy_cache_use_stale updating; mechanism. The webserver/machine continues to deliver stale cache while a thread kicks in the moment expiration happens and updates the cache. Has someone applied this to memcached scenario though I understand this is a client side strategy? If it benefits, I use Django.

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• Getting Started with Fluent NHibernate

  - by Andy

  I'm trying to get into using Fluent NHibernate, and I have a couple questions. I'm finding the documentation to be lacking. I understand that Fluent NHibernate / NHibernate allows you to auto-generate a database schema. Do people usually only do this for Test/Dev databases? Or is that OK to do for a production database? If it's ok for production, how do you make sure that you're not blowing away production data every time you run your app? Once the database schema is already created, and you have production data, when new tables/columns/etc. need to be added to the Test and/or Production database, do people allow NHibernate to do this, or should this be done manually? Is there any REALLY GOOD documentation on Fluent NHibernate? (Please don't point me to the wiki because in following along with the "Your first project" code building it myself, I was getting run-time errors because they forget to tell you to add a reference. Not cool.) Thanks, Andy

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• Optimising (My)SQL Query

  - by Simon

  I usually use ORM instead of SQL and I am slightly out of touch on the different JOINs... SELECT `order_invoice`.*, `client`.*, `order_product`.*, SUM(product.cost) as net FROM `order_invoice` LEFT JOIN `client` ON order_invoice.client_id = client.client_id LEFT JOIN `order_product` ON order_invoice.invoice_id = order_product.invoice_id LEFT JOIN `product` ON order_product.product_id = product.product_id WHERE (order_invoice.date_created >= '2009-01-01') AND (order_invoice.date_created <= '2009-02-01') GROUP BY `order_invoice`.`invoice_id` The tables/ columns are logically names... it's an shop type application... the query works... it's just very very slow... I use the Zend Framework and would usually use Zend_Db_Table_Row::find(Parent|Dependent)Row(set)('TableClass') but I have to make lots of joins and I thought it'll improve performance by doing it all in one query instead of hundreds... Can I improve the above query by using more appropriate JOINs or a different implementation? Many thanks.

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• Access 2007 - Forms created on the fly

  - by glinch

  Hi There, Hopefully I can find some words of advice from somebody. Is it possible to create forms 'on-the fly' so to speak in MS-Access 2007 I have a structure of tables: tblCustomer tblQuestAns A customer may answer the questionnaire answers many times as they relate to all products. I propose to hopefully have an initial input form that will ask how many products of which there could be more than 1 eg: TV, Video (say the user selects 2) On entering that data the next form should hopefully update itself to include the list of questions eg TV Q1, Q2 Q3 - Video (1) Q1, Q2 Q3 - Video (2) Q1, Q2 Q3 Is that possible? Any point in the right direction would be appreciated. Thanks Noel

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• Int PK inner join Vs Guid PK inner Join on SQL Server. Execution plan.

  - by bigb

  I just did some testing for Int PK join Vs Guid PK. Tables structure and number of records looking like that: Performance of CRUD operations using EF4 are pretty similar in both cases. As we know Int PK has better performance rather than strings. So SQL server execution plan with INNER JOINS are pretty different Here is an execution plan. As i understand according with execution plan from attached image Int join has better performance because it is taking less resources for Clustered index scan and it is go in two ways, am i right? May be some one may explain this execution plan in more details?

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• Hibernate bug using Oracle?

  - by Lothar

  Hello, I've got the problem, that I use a property in the persistence.xml which forces Hibernate to look only for tables in the given schema. <property name="hibernate.default_schema" value="FOO"/> Because we are using now 4 different schemas the actual solution is to generate 4 war files with a modified persistence.xml. That not very elegant. Does anybody know, how I can configure the schema with a property or by manipulation the JDBC connection string? I'm using Oracle 10g, 10_2_3 Patch. Thanks a lot.

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• ASP.net MVC3 entities, don't know how to count

  - by Spedax

  I have 2 tables, 1 with countries, 1 with states. The states table has a column with Population. I'm using entities and I have created a List of states for the countries public class TblCountries { //Entities for my table country ... public List<tblStates> States { get; set; } } So now I can for example List all the states that belong to a country. Now what I want to do is count the population, so I can show the population that of an entire country. I tried using in my view @foreach (var item in Model.Countries) { @Html.DisplayFor(modelItem => item.States.Count<population>) } But this doesn't work, anyone know how to do this? Thanks in advanced!

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• Interview question - c#

  - by ltech

  I was tasked to conduct my first interview and would like to pose my question to this world for both their feedback on my question and also on their solutions. Question: I have a legacy system with users and files, the info of all files pertaining to a user are stored on a flat file. I want to upgrade this system by storing all info on a db, design tables, and create a C# system that will populate the new db as well as ftp the files to a new path. Define the desgin consideration and develop a prototype. Note: We are looking more for what design one would use and why rather than code that compiles. If it does then kudos to you and we will give it more weight. @Tim C, I did show the interviewee the file: User1234.txt UserID=1234 ParentPath=\\somewhere\nowehere\everywhere\1234 FileCount=20 File0=something0.ext .. File19=something19.ext @Tim C, I have never conducted an interview and I followed a script given to me by my senior developer who was absent.

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• When calling CRUD check if "parent" exists with read or join?

  - by Trick

  All my entities can not be deleted - only deactivated, so they don't appear in any read methods (SELECT ... WHERE active=TRUE). Now I have some 1:M tables on this entities on which all CRUD operations can be executed. What is more efficient or has better performance? My first solution: To add to all CRUD operations: UPDATE ... JOIN entity e ... WHERE e.active=TRUE My second solution: Before all CRUD operations check if entity is active: if (getEntity(someId) != null) { //do some CRUD } In getEntity there's just SELECT * FROM entity WHERE id=? AND active=TRUE. Or any other solution, recommendation,...?

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• dataset using where condition from another query

  - by refer

  here's my code. I have a dataset that has its values and then i run an independent query which uses the same tables as dataset. now when i run the dataset, i want it to get a where condition on the query result. here's the code - sql = "SELECT ID, name FROM books WITH(NOLOCK) WHERE id =" & Session("ID") ds = FillDataset(sql) Sql1 = "SELECT n.id as id,a.name as title FROM books n WITH(NOLOCK)" & _ "LEFT JOIN new_books a WITH(NOLOCK) ON a.id = n.book_id " rd = ExecuteReader(SqlCnn, SqlStr) Now after this i make an htmltable and all the cells are loaded with the data from datareader(rd). but 1 dropdown is loaded from the dataset. i want that dropdown to have the selectedvalue which is the value from the datareader(rd). how can i do that?

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• Import de-normalized relational data from Excel into SQL Server

  - by roryf

  I need to import data from an Excel spreadsheet into SQL Server, but the data isn't in a relational/normalized format so the import wizard isn't going to cut it (as far as I know). The data is in this format: Category SubCategory Name Description Category#1 SubCategory#1 Product#1 Description#1 Category#1 SubCategory#1 Product#2 Description#2 Category#1 SubCategory#2 Product#3 Description#3 Category#1 SubCategory#2 Product#4 Description#4 Category#2 SubCategory#3 Product#5 Description#5 (apologies I'm lacking the inventiveness to come up with 'real' data at this time in the morning...) Each row contains a unique product, but the cateogry structure is duplicated. I want to import this data into three tables: Category SubCategory Product (I know SubCategory should really be contained within Category, DB was not my design) I need a way to import unique rows based on the Category and then SubCategory columns, and then when importing the other columns into Product, obtain a reference to the SubCategory based on name. Short of scripting this, is there any way to do it using the import wizard or some other tool?

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• Composite Primary and Cardinality

  - by srini.venigalla

  I have some questions on Composite Primary Keys and the cardinality of the columns. I searched the web, but did not find any definitive answer, so I am trying again. The questions are: Context: Large (50M - 500M rows) OLAP Prep tables, not NOSQL, not Columnar. MySQL and DB2 1) Does the order of keys in a PK matter? 2) If the cardinality of the columns varies heavily, which should be used first. For example, if I have CLIENT/CAMPAIGN/PROGRAM where CLIENT is highly cardinal, CAMPAIGN is moderate, PROGRAM is almost like a bitmap index, what order is the best? 3) What order is the best for Join, if there is a Where clause and when there is no Where Clause (for views) Thanks in advance.

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• PHP/MySQL won't update decimal field

  - by Serhiy

  I have this query: UPDATE table_name SET field_1 = field_1 +100, field_2 = field_2 +100, field_3 = field_3 +100 WHERE id = 1 LIMIT 1; Where Field_1 is regular integer, Field_2 is decimal(15,6) and Field_3 is double(15,6). When I run this query from php script they update just field_1 and nothing happen with field_2 and field_3 they just stay as before. But when I run in phpMyAdmin it's work without any problems. I'm tried to lock tables, make round() before run update, nothing help. Please help... why I can't update decimal and float fields from php? PHP version: 5.2 Mysql version 5

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• MySQL Many to Many with Unique keys and Update/Select if Exists otherwise Insert

  - by Jayrox

  In my goal to have a Many-to-Many relationship in my MySQL database I have arrived at another bridge to build. Current Tables: Users (id, name) Tags (id, name) User_Tags (user_id, tag_id) Here is the goal: I would like to have the ability to take a tag i.e: #fb and insert it into my Tags database which has a unique constraint on name and if the tag exists I would like to return it's id I would like to insert the tag.id and the current user's user.id into User_Tags. I do not have any unique constraints on the User_Tags table because I would like to be able to track the user's most commonly used tags and present them in a list ordered by frequency of use. I am currently developing this project in PHP using prepared statements. Additionally, performance is not currently an issue as my user count is still fairly small, but it is steadily growing and may be an issue in the future.

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• tabcontainer button postback problem

  - by yousof

  I have a dropdownlist in my web page and two command buttons and a tabcontainer. The tabcontainer does not appear after the load of page according to my code. Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load If Not IsPostBack Then TabContainer1.Visible = False If CtvAct.GetRecords("Fill_RequestTypeTb") = True Then ReqTypeCmbo.DataSource = CtvAct.MainDataset.Tables("tbOLRequestType").DefaultView ReqTypeCmbo.DataTextField = "RequestTypeName" ReqTypeCmbo.DataValueField = "RequestTypeId" ReqTypeCmbo.DataBind() Dim itm As New ListItem itm.Text = "-- ??? ??? ????? --" itm.Value = "-1" itm.Selected = True ReqTypeCmbo.Items.Insert(0, itm) ReqTypeCmbo.SelectedIndex = 0 End If End If End Sub Protected Sub PrntCmd_Click(ByVal sender As Object, ByVal e As EventArgs) Handles PrntCmd.Click TextBox6.Text = "gggg" End Sub If I press any button after page load the button work very selecting any item from dropdownlist make the tabcontainer appear but after the tabcontainer appear, the buttons does not work (postback) how can I solve these problems

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• MySQL query : all records of one table plus count of another table

  - by Ricardo

  Hello Guys! I have 2 tables: User and Picture. The Picture table has the key of the user. So basically each user can have multiple pictures, and each picture belongs to one user. Now, I am trying to make the following query: I want to select all the user info plus the total number of pictures that he has (even if it's 0). How can I do that? Probably it sounds quite simple, but I am trying and trying and can't seem to find the right query. The only thing I could select is this info, but only for users that have at least 1 picture, meaning that the Pictures table has at least one record for that key... But I also wanna consider the users that don't have any. Any idea? Thanks!

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• Use where condition with unjoined table

  - by Dragos D

  I have the following problem: I am trying to retreive a sum value based on one condition. Problem is that I can't join the conditional value since my tables aren't joined. Here is my syntax: SELECT SUM(value) FROM value v join day d on v.day_id = d.day_id join budget b on d.budget_id = b.budget_id join unit u on v.unit_id = u.unit_id where #output.class = (SELECT distinct s.class FROM sale s where s.id = #output.sale_id) AND u.unit_name in ('electronics') With this sybtax I get no error but neither values. Can you please tell me where I do wrong?

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• Dependency Injection -Colloquial explanation

  - by nettguy

  Recently I was asked to express the DI in colloquial explanation. I answered : 1) I am going to a hotel.I ordered food.The hotel management asks me to clean the plates and clean the tables.So here i am a client,I am responsible for managing the service (Instantiating,executing,disposing).But DI decouples such tasks so the service consumer no need not worry about controlling the life cycle of the service. 2) He also asked is there any microsoft API follows DI ?.I answered (This was my guess) In WCF you can create a Proxy using ChannelFactory that controls the life time of your factory. for item (1) he said only 10% is correct for item(2) he said that is factory pattern not dependency injection. Actually what went wrong in my explanation (apart from my bad English) ? What is the real answers for those? I am waiting for your valuable suggestions.

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• How to Import Excel Data into Silverlight App for Visualization?

  - by Ulf

  Hi there, Im building an Silverlight Application (Silverlight 4, Visual Studio 2010), in which the user can generate Charts (line-Charts, Bar Chart) dynamically, by entering a specific time period. At the Moment i have no idea how to import the data to Silverlight, to generate the Charts. My data is stored in 4 Excel Tables and i have no clue what would be the best way to get that data into Silverlight? I read a lot of examples using SQL Server as Database, but unfortunatly SQL Server is no choice for me. Any help would be great!

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• Export Multiple Sheets to Excel Through Browser

  - by ProfK

  I need to export multiple data tables to Excel on the clients machine, each to their own sheet. If it was just one sheet, I'd use the Excel/csv content type, but I've heard something about an XML format that can represent an entire workbook. I don't want to go down the Packaging and .xlsx route, so I need standard .xls. Our bug tracker, Gemini, used to have an export function that produced an XML file that Excel automatically opened as a multi-sheet workbook, but I can't find it. Is there still such a mechanism, and where can I find that schema?

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• SQL - Joining multiple records to one record

  - by ho

  I've got a SQL Server database with the the following tables: Client (ClientID, ClientName) SalesAgent (AgentID, AgentName) Item (ItemID, Description) Purchase (PurchaseID, ClientID, Price) PurchaseSalesAgent (PurchaseID, AgentID) Each purchase is only ever one item to one client but there can have been multiple agents involved. I want to return the following list of columns: ClientName, Description, Price, Agents Where Agents is the names of all the agents involved in the purchase. Either as a comma separated list or as multiple columns with one agent in each. I'm looking for a way that's compatible with SQL Server 2000 but I'd also be interested in if there's a better way of doing it in SQL Server 2008.

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• zfdatagrid : how to set the relative order of columns?

  - by user522350

  To those of you who are familiar with zfdatagrid for the Zend framework: I got a recordset by a JOIN query, say from tables s and t, now I want to set the order in which the columns appear in the deployed table. For example, 5th column of table t to appear at the leftmost side, then 3rd column of table s, then 2nd column of table t, then 4th column of table s. How do I do this? Whatever I tried, it always shows first the columns of the left table of the JOIN, then the columns of the right table of the JOIN. I only know how to tell it which columns to show, but not their order. Thanks!

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• How do I add multiple joins (Fetches) to a joined table using nhibernate and LINQ ?

  - by ooo

  i have these tables /entities VacationRequestDate table which has a VacationRequestId field that links with VacationRequest table VacationRequest has PersonId and RequestStatusId fields that links with Person and RequestStatus respectively. i have this query so far: IEnumerable<VacationRequestDate> dates = Session.Query<VacationRequestDate>().Fetch(r => r.VacationRequest).ThenFetch(p=>p.RequestStatus).ToList(); this works fine and joins with VacationRequest and then VacationRequest joins with RequestStatus but i can't figure out how to add an additional EAGER join to the VacationRequest table. If i add a Fetch at the end, it refers to the VacationRequestDate table If i add a ThenFetch at the end, it refers to the RequestStatus table I can't find any api that will refer to the VacationRequest table as the reference point. how would you add multiple joins to a joined table using nhibernate LINQ ?

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• How I can make Recycle Bin for Database ?Application?

  - by Wael Dalloul

  Hi, I have database application, I want to allow the user to restore the deleted records from the database, like in windows we have Recycle bin for files I want to do the same thing but for database records, Assume that I have a lot of related tables that have a lot of fields. Edit: let's say that I have the following structures: Reports table RepName primary key ReportData Users table ID primary key Name UserReports table RepName primary key UserID primary key IsDeleted now if I put isdeleted field in UserReports table, the user can't add same record again if it marked as deleted, because the record is already and this will make duplication.

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• MySQL SELECT results from 1 table, but exclude results depending on another table?

  - by Brandon

  Hey, What SQL query would I have to use if I want to get the results from a table 'messages' but exclude rows that have the value in 'messages_view' where field messages.message=messages_view.id AND messages.deleted=1 AND messages_view.user=$somephpvariable In more laymen terms, I have a messages table with each message denoted by an 'id' as well as a messages_view table connected with a 'message' field. I want to get the rows in message that are not deleted (comes from messages_view) for a specific 'user'. 'deleted'=1 when the message is deleted. Here is my current SQL Query that just gets the values out of : SELECT * FROM messages WHERE ((m_to=$user_id) OR (m_to=0 AND (m_to_state='' OR m_to_state='$state') AND (m_to_city='' OR m_to_city='$city'))) Here is the layout of my tables: table: messages ---------------------------- id (INT) (auto increment) m_from (INT) <-- Represents a user id (0 = site admin) m_to (INT) <-- Represents a user id (0 = all users) m_to_state (VARCHAR) m_to_city (VARCHAR) table: messages_view ---------------------------- message (INT) <-- Corresponds to messages.id above user (INT) <-- Represents a user id deleted (INT) <-- 1 = deleted

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