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  • When is porting data from MySQL to CouchDB NOT advisable? Seeking cautionary tales

    - by dan
    I've dabbled in CouchDB and I have pretty good MySQL experience. I've also created one production application that uses both. I like MySQL but I've run into scaling/concurrency issues with MySQL that CouchDB advertises itself as a general solution for. The problem is that I have MySQL based applications that are pretty huge, and I don't really know whether it would be a good idea or not to try to port them over to a CouchDB datastore. I don't want to put in a lot of time and effort only to find out that my application is really not a good fit for CouchDB. Is there any sort of informed consensus on when porting a MySQL based app to CouchDB is NOT advisable? Any cautionary tales? I think CouchDB is really cool and want to use it more. I'd also like to know ahead of time what specific types of data querying scenarios CouchDB is really not good for, or if CouchDB can really replace MySQL for all the applications I create going forward.

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  • Prevent duplicate rows with all non-unique columns (only with MySQL)?

    - by letseatfood
    Ho do I prevent a duplicate row from being created in a table with two columns, neither of which are unique? And can this be done using MySQL only, or does it require checks with my PHP script? Here is the CREATE query for the table in question (two other tables exist, users and roles): CREATE TABLE users_roles ( user_id INT(100) NOT NULL, role_id INT(100) NOT NULL, FOREIGN KEY (user_id) REFERENCES users(user_id), FOREIGN KEY (role_id) REFERENCES roles(role_id) ) ENGINE = INNODB; I would like the following query, if executed more than once, to throw an error: INSERT INTO users_roles (user_id, role_id) VALUES (1, 2); Please do not recommend bitmasks as an answer. Thanks!

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  • Can't fill a column of NULLs with actual values by making an association to the proper values in the

    - by UkraineTrain
    I have a table with separate columns for months, days and a varchar column for 6 hour increments for each day ('12AM', '6AM', '12PM', '6PM'). There's also a column that's supposed to have calculated numeric values for each of those 6 hour increments. These calculated values come from some reference table. This reference table contains values for each day for several months broken down by hour where each hour has its own column. So, basically, I have to add the values for each 6 hour increment. I have no idea how to associate the correct values in the reference table to those 6 hour increments. I will really appreciate any help on this.

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  • how to restore very large .bak file (180 GB) in SQL Server 2008

    - by Umutos
    Hello! I have a verly large .bak file (180 GB) which was stored in Microsoft SQL Server 2008 and I have to restore it. I first installed Microsoft SQL Server 2008 Express and tried to restore it in MS SQL management studio express but it didn't work because there is a size limit. Does anybody know a method how i can restore the file? Its the first time I work with Microsoft SQL and I have no clue what to do. Its really urgend and I would be really helpful for any help! Thanks a lot! Umutos

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  • Get information from various sources

    - by Francesc
    Hi. I'm developing an app that has to get some information from various sources (APIs and RSS) and display it to the user in near real-time. What's the best way to get it: 1.Have a cron job to update them all accounts every 12h, and when a user is requesting one, update that account, save it to the DB and show it to the user? 2.Have a cron job to update them all accounts every 6h, and when a user is requesting one, update the account and showing it to the user without saving it to the DB? What's the best way to get it? What's faster? And what's the most scallable?

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  • How do I avoid a race condition in my Rails app?

    - by Cathal
    Hi, I have a really simple Rails application that allows users to register their attendance on a set of courses. The ActiveRecord models are as follows: class Course < ActiveRecord::Base has_many :scheduled_runs ... end class ScheduledRun < ActiveRecord::Base belongs_to :course has_many :attendances has_many :attendees, :through => :attendances ... end class Attendance < ActiveRecord::Base belongs_to :user belongs_to :scheduled_run, :counter_cache => true ... end class User < ActiveRecord::Base has_many :attendances has_many :registered_courses, :through => :attendances, :source => :scheduled_run end A ScheduledRun instance has a finite number of places available, and once the limit is reached, no more attendances can be accepted. def full? attendances_count == capacity end attendances_count is a counter cache column holding the number of attendance associations created for a particular ScheduledRun record. My problem is that I don't fully know the correct way to ensure that a race condition doesn't occur when 1 or more people attempt to register for the last available place on a course at the same time. My Attendance controller looks like this: class AttendancesController < ApplicationController before_filter :load_scheduled_run before_filter :load_user, :only => :create def new @user = User.new end def create unless @user.valid? render :action => 'new' end @attendance = @user.attendances.build(:scheduled_run_id => params[:scheduled_run_id]) if @attendance.save flash[:notice] = "Successfully created attendance." redirect_to root_url else render :action => 'new' end end protected def load_scheduled_run @run = ScheduledRun.find(params[:scheduled_run_id]) end def load_user @user = User.create_new_or_load_existing(params[:user]) end end As you can see, it doesn't take into account where the ScheduledRun instance has already reached capacity. Any help on this would be greatly appreciated.

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  • Referencing surrogate key

    - by Arman
    I have a table that has an autoincrement surrogate key. I want to use it as a foreign key of my other table. The thing is, I cant figure out how I can reference it to that table, because it is nearly impossible to determine what I have to reference(the actual value of the surrogate key). Please be noted that what I am trying to do is adding a tuple/record through my program(outside the dbms). The process is: Add a new record in Table1 and generate an autoincrement key. Update Add a new record in Table2 and reference its foreign key to the primary key of Table1. Update My question is : HOW do I store the foreign key if I didnt know what is it?

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  • How to find the entity with the greatest primary key?

    - by simpatico
    I've an entity LearningUnit that has an int primary key. Actually, it has nothing more. Entity Concept has the following relationship with it: @ManyToOne @Size(min=1,max=7) private LearningUnit learningUnit; In a constructor of Concept I need to retrieve the LearningUnit with the greatest primary key. If no LearningUnit exists yet I instantiate one. I then set this.learningUnit to the retrieved/instantied. Finally, I call the empty constructor of Concept in a try-catch block, to have the entitymanager do the cardinality check. If an exception is thrown (I expect one in the case that already another 7 Concepts are referring to the same LearningUnit. In that case, I case instantiate a new LearningUnit with a new greater primary key. Please, also point out, if any, clear pitfalls in my outlined algorithm above.

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  • Fluent nHibernate - How to map a non-key column on a junction table?

    - by The Matt
    Taking an example that is provided on the Fluent nHibernate website, I need to extend it slightly: I need to add a 'Quantity' column to the StoreProduct table. How would I map this using nHibernate? An example mapping is provided for the given scenario above, but I'm not sure how I would get the Quantity column to map to a property on the Product class: public class StoreMap : ClassMap<Store> { public StoreMap() { Id(x => x.Id); Map(x => x.Name); HasMany(x => x.Employee) .Inverse() .Cascade.All(); HasManyToMany(x => x.Products) .Cascade.All() .Table("StoreProduct"); } }

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  • Processing large recordsets in Rails

    - by japancheese
    Hello, I'm trying to perform a daily operation on a larger than normal dataset (2m+ records). However, Rails seems to take a very long time performing operations on such a dataset. Operations like Dataset.all.each do |data| ... end take a very long time to complete (I assume this is because it can't fit all the items into memory at once, right?). Does anyone have any strategies on how I could handle this situation? I know SQL would probably speed up the process, but I'm looking to use the Rails environment as I can do many more complicated things to the data than I can with just SQL statements.

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  • Use DataContext to create schema in an existing blank database file?

    - by jdk
    With a DataContext and a blank file-based database that already exists, is it possible to write the Data Context classes (i.e. the ones I added to the designer) to create the db schema? With a data context I only see the abilities to either: create a new database file and have its structure created at the same time, or to populate data into an existing database having preexisting schema. I'm looking for a hybrid solution between those two worlds. Update 1: My proof that a preexisting db is not compatible with the Data Context CreateDatabase() operation is this error Database 'C:...\App_Data\IntermediateData.mdf' already exists. Choose a different database name. based on this code using (IntermediateClassesDataContext intermediateContext = new IntermediateClassesDataContext(_getIntermediateConn())) { intermediateContext.CreateDatabase(); }

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  • If I take a large datatype. Will it affect performance in sql server

    - by Shantanu Gupta
    If i takes larger datatype where i know i should have taken datatype that was sufficient for possible values that i will insert into a table will affect any performance in sql server in terms of speed or any other way. eg. IsActive (0,1,2,3) not more than 3 in any case. I know i must take tinyint but due to some reasons consider it as compulsion, i am taking every numeric field as bigint and every character field as nVarchar(Max) Please give statistics if possible, to let me try to overcoming that compulsion. I need some solid analysis that can really make someone rethink before taking any datatype.

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  • Using a variable derived from a drop-down list as the column name in a select statement ... Access DB

    - by user1459698
    I'm working with the world's worst DB that was already here so don't blame me for that. So, here's what I have so far ... module = txtModule.value presstype = txtPressType.value SQL_query = "SELECT * FROM tbl_spareparts WHERE '"& module &"' <> '""' AND '"& module &"' = '"& presstype &"' AND Manufacturer = '"& txtsrch.value &"' ORDER BY SAP_Part_No" Set rsData = conn.Execute(SQL_query) This brings up the following SQL statement: SELECT * FROM tbl_spareparts WHERE 'Banyan_Module' <> '"' AND 'Banyan_Module' = 'PB' AND Manufacturer = 'Tester' ORDER BY SAP_Part_No Is there any way I can use the module variable as a column name - obviously the ''s around the column name are causing an error. This is really bothering me. BTW, I'm writing this in VBScript inside a .HTA application page as it has to run locally on tech PCs. Thanks. R.

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  • How to use multiple identity numbers in one table?

    - by vincer
    I have an web application that creates printable forms, these forms have a unique number on them, the problem is I have 2 forms that separate numbers need to be created for them. ie) Form1- Numbered 2000000-2999999 Form2- Numbered 3000000-3999999 dbo.test2 - is my form information table Tsel - is my autoinc table for the 3000000 series numbers Tadv - is my autoinc table for the 2000000 series numbers What I have done is create 2 tables with just autoinc row (one for 2000000 series numbers and one for 3000000 series numbers), I then created a trigger to add a record to the coresponding table, read back the autoinc number and add it to my table that stores the form information including the just created autoinc number for the right series of forms. Although it does work, I'm concerned that the numbers will get messed up under load. I'm not sure the @@IDENTITY will always return the right value when many people are using the system. (I cannot have duplicates and I need to use the numbering form show above. See code below. ** TRIGGER ** CREATE TRIGGER MAKEANID2 ON dbo.test2 AFTER INSERT AS SET NOCOUNT ON declare @someid int declare @someid2 int declare @startfrom int declare @test1 varchar(10) select @someid=@@IDENTITY select @test1 = (Select name1 from test2 where sysid = @someid ) if @test1 = 'select' begin insert into Tsel Default values select @someid2 = @@IDENTITY end if @test1 = 'adv' begin insert into Tadv Default values select @someid2 = @@IDENTITY end update test2 set name2=(@someid2) where sysid = @someid SET NOCOUNT OFF

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  • Phantom activity on MySQL

    - by LoveMeSomeCode
    This is probably just my total lack of MySQL expertise, but is it typical to see lots of phantom activity on a MySQL instance via phpMyAdmin? I have a shared hosting plan through Lithium, and when I log in through the phpMyAdmin console and click on the 'Status' tab, it's showing crazy high numbers for queries. Within an hour of activating my account I had 1 million queries. At first I thought this was them setting things up, but the number is climbing constantly, averaging 170/second. I've got a support ticket in with Lithium, but I thought I'd ask here if this were a MySQL/shared host thing, because I had the same thing happen with a shared hosting plan through Joyent.

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  • Create new table with Wordpress API

    - by Fire G
    I'm trying to create a new plugin to track popular posts based on views and I have everything done and ready to go, but I can't seem to create a new table using the Wordpress API (I can do it with standard PHP or with phpMyAdmin, but I want this plugin to be self-sufficient). I've tried several ways ($wpdb-query, $wpdb-get_results, dbDelta) but none of them will create the new table. function create_table(){ global $wpdb; $tablename = $wpdb->prefix.'popular_by_views'; $ppbv_table = $wpdb->get_results("SHOW TABLES LIKE '".$tablename."'" , ARRAY_N); if(is_null($ppbv_table)){ $create_table_sql = "CREATE TABLE '".$tablename."' ( 'id' BIGINT(50) NOT NULL AUTO_INCREMENT, 'url' VARCHAR(255) NOT NULL, 'views' BIGINT(50) NOT NULL, PRIMARY KEY ('id'), UNIQUE ('id') );"; $wpdb->show_errors(); $wpdb->flush(); if(is_null($wpdb->get_results("SHOW TABLES LIKE '".$tablename."'" , ARRAY_N))) echo 'crap, the SQL failed.'; } else echo 'table already exists, nothing left to do.';}

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  • mysql circular dependency in foreign key constraints

    - by Flavius
    Given the schema: What I need is having every user_identities.belongs_to reference an users.id. At the same time, every users has a primary_identity as shown in the picture. However when I try to add this reference with ON DELETE NO ACTION ON UPDATE NO ACTION, MySQL says #1452 - Cannot add or update a child row: a foreign key constraint fails (yap.#sql-a3b_1bf, CONSTRAINT #sql-a3b_1bf_ibfk_1 FOREIGN KEY (belongs_to) REFERENCES users (id) ON DELETE NO ACTION ON UPDATE NO ACTION) I suspect this is due to the circular dependency, but how could I solve it (and maintain referential integrity)?

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  • Alter multiple tables' columns length

    - by gdoron
    So, we just found out that 254 tables in our Oracle DBMS have one column named "Foo" with the wrong length- Number(10) instead of Number(3). That foo column is a part from the PK of the tables. Those tables have other tables with forigen keys to it. What I did is: backed-up the table with a temp table. Disabled the forigen keys to the table. Disabled the PK with the foo column. Nulled the foo column for all the rows. Restored all the above But now we found out it's not just couple of tables but 254 tables. Is there an easy way, (or at least easier than this) to alter the columns length? P.S. I have DBA permissions.

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  • sqlserver how to set job priority

    - by Buzz
    Is there any way to set one job priority higher then other, In my case there are two jobs those are working on same set of tables,first JOB-A which is running every 12 hr and other JOB-B is every 10 minutes , i think at some time when they run simultaneously JOB-B is getting in to deadlock and get failed, i google the topic and found sqlgoverner is helpful in such cases does anyone know how to resolve?

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