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• Windows.Forms.Timer instance and UI threads

  - by David Rutten

  I have a custom control whose primary purpose is to draw data. I want to add a ScheduleUpdate(int milliSeconds) method to the control which will force an update X milliseconds from now. Since this is all GUI land, I should be using a Windows.Forms.Timer, but how does this timer instance know which thread it belongs to? What if ScheduleUpdate() is called from a non-UI thread? Should I construct the timer in the Control constructor? Or perhaps the Load event? Or is it safe to postpone construction until I'm inside ScheduleUpdate()? I know there are some very similar questions about this already, but I don't have a Timer component on my control, I'm constructing it on a when-it's-needed basis.

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• Transactional isolation level needed for safely incrementing ids

  - by Knut Arne Vedaa

  I'm writing a small piece of software that is to insert records into a database used by a commercial application. The unique primary keys (ids) in the relevant table(s) are sequential, but does not seem to be set to "auto increment". Thus, I assume, I will have to find the largest id, increment it and use that value for the record I'm inserting. In pseudo-code for brevity: id = select max(id) from some_table id++ insert into some_table values(id, othervalues...) Now, if another thread started the same transaction before the first one finished its insert, you would get two identical ids and a failure when trying to insert the last one. You could check for that failure and retry, but a simpler solution might be setting an isolation level on the transaction. For this, would I need SERIALIZABLE or a lower level? Additionally, is this, generally, a sound way of solving the problem? Are the any other ways of doing it?

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• What are the prerequisites for learning embedded systems programming ?

  - by WarDoGG

  I have completed my graduation in Computer engineering. We had some basic electronics courses in Digital signal processing, Information theory etc but my primary field is Programming. However, i was looking to get into Embedded sytems programming with NO knowledge of how it is done. However, i am very keen on going into this field. My questions : what are the languages used to program embedded system programs ? Will i be able to learn without having any basics in electronics ? any other prerequisites that i should know ?

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• php, mySQL - how to create a table?

  - by user296516

  Hi guys, I have written a code that should check weather there is a table called imei.$addimei and, if not, create it... $userdatabase = mysqli_connect('localhost', 'root', 'marina', 'imei'); ... $result = mysqli_query($userdatabase, "SELECT * FROM imei".$addimei."" ); if ( !$result ) { echo('creating table...'); /// if no such table, make one! mysql_query ( $userdatabase, 'CREATE TABLE imei'.$addimei.'( ID int NOT NULL AUTO_INCREMENT, PRIMARY KEY(ID), EVENT varchar(15), TIME varchar(25), FLD1 varchar(35), FLD2 varchar(35), IP varchar(25), )' ); } Yet the CREATE TABLE somehow doesn't seem to work. Warning: mysql_query() expects parameter 1 to be string, object given in C:\xampp\xampp\htdocs\mobi\mainmenu.php on line 564 Any idea's what wrong? Thanks!

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• What resources will help me understand the fundamentals of Relational Database Systems.

  - by Rachel

  This are few of the fundamental database questions which has always given me trouble. I have tried using google and wiki but I somehow I miss out on understanding the functionality rather than terminology. If possible would really appreciate if someone can share more insights on this questions using some visual representative examples. What is a key? A candidate key? A primary key? An alternate key? A foreign key? What is an index and how does it help your database? What are the data types available and when to use which ones?

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• How to select all parents of a node in a hierarchical mysql table?

  - by Ehsan Khodarahmi

  I have a MySQL table that represents data for a tree GUI component, here's the structure of my table: treeTable ( id INT NOT NULL PRIMARY KEY, parentId INT, name VARCHAR(255) ); parentId is a self-referencing foreign key. Now I want to write a stored procedure which gets a node id and returns a result set that contains that node and all of its parents. For example, suppose that my table has filled with this data: 1, null, 'root' 2, 1 , 'level_1' 3, 2 , 'level_2' Now I want to get all parent nodes of node 3 (nodes 1 and 2) and return a result set that contains all tree records. Can anybody help me please?

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• PostgreSQL - disabling constraints

  - by azp74

  I have a table with approx 5 million rows which has a fk constraint referencing the primary key of another table (also approx 5 million rows). I need to delete about 75000 rows from both tables. I know that if I try doing this with the fk constraint enabled it's going to take an unacceptable amount of time. Coming from an Oracle background my first thought was to disable the constraint, do the delete & then reenable the constraint. PostGres appears to let me disable constraint triggers if I am a super user (I'm not, but I am logging in as the user that owns/created the objects) but that doesn't seem to be quite what I want. The other option is to drop the constraint and then reinstate it. I'm worried that rebuilding the constraint is going to take ages given the size of my tables. Any thoughts?

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• how I delete a row in a table in Joomla?

  - by Sara

  I have a table id h_id t_id 1 3 1 2 3 2 3 3 3 4 4 2 5 4 3 id is the primary key. I have not created a JTable for this table. Now I want to delete rows by h_id. Are there any method like which I can use without writing a sql DELETE query? $db = JFactory::getDBO(); $row =& $this->getTable('tablename'); $row->delete($pk); Any better solution will be greatly appreciated.

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• Cross-compiling a Python script on Linux into a Windows executable

  - by Chinmay Kanchi

  I have a Python script that I'd like to compile into a Windows executable. Now, py2exe works fine from Windows, but I'd like to be able to run this from Linux. I do have Windows on my development machine, but Linux is my primary dev platform and I'm getting kind of sick of rebooting into Windows just to create the .exe. Any ideas? PS: I am aware that py2exe doesn't exactly compile the python file as much as package your script with the Python interpreter. But either way, the result is that you don't need Python installed to run the script.

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• What stage of normalization is this? (moving repeating data into separate table)

  - by Sergio

  Hi There, I have noticed that when designing a database I tend to shift any repeating sets of data into a separate table. For example, say I had a table of people, with each person living in a state. I would then move these repeating states into a separate table and reference them with foreign keys. However, what if I was not storing any more data about states. I would then have a table with StateID and State in. Is this action correct? State is dependant on the primary key of the users table, so does shifting it into its own table help with anything? Thanks,

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• Clustered index dilemma - ID or sort?

  - by richardtallent

  I have a table with two very important fields: id INT identity(1,1) PRIMARY KEY identifiersortcode VARCHAR(900) My app always sorts and pages search results in the UI based on identifiersortcode, but all table joins (and they are legion) are on the id field. (Aside: yes, the sort code really is that long. There's a strong BL reason.) Also, due to O/RM use, most SELECT statements are going to pull almost every column. Currently, the clustered index is on id, but I'm wondering if the TOP / ORDER BY portion of most queries would make identifiersortcode a more attractive option as the clustered key, even considering all of the table joins going on. Inserts on the table and changes to the identifiersortcode are limited enough that changing my clustered index would be a problem for insert/update operations. Trying to make the sort code's non-clustered index a covering index (using INCLUDE) is not a good option. There are a number of large columns, and some of them have a lot of update activity.

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• Error messages for model validation using data annotations

  - by oneBelizean

  Given the follow classes: using System.ComponentModel.DataAnnotations; public class Book{ public Contact PrimaryContact{get; set;} public Contact SecondaryContact{get; set;} [Required(ErrorMessage="Book name is required")] public string Name{get; set;} } public class Contact{ [Required(ErrorMessage="Name is required")] public string Name{get; set;} } Is there a clean way I can give a distinct error message for each instance of Contact in Book using DataAnnotations? For example, if the name was missing from the PrimaryContact instance the error would read "primary contact name is required". My current solution is to create a validation service that checks the model state for field errors then remove said errors and add them back using the specific language I'd like.

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• SharePoint thinks new Server is offline?

  - by emalamisura

  I added an index server to the topology, and tried to switch it from the front end to the index server but for some reason I get an exception every time in Central Admin saying the server is offline. I checked everything... IIS is running and is serving out correctly The App Pool Identity is valid I restarted IIS I restarted the Indexing server I had a wierd problem when installing SP2 for SharePoint, (WSS sp2 installed fine) where it got stuck and "Upgrading SharePoint Products and Technologies" and I had to run the following command to get it to continue: psconfig -cmd upgrade -inplace b2b -wait -force After that it said it succeeded with no errors... The only thing I haven't done is reboot the Primary server cause I have to do it in off hours, but I want to make sure I have covered all my other bases first...Any ideas?

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• Store data for songs MySQL DB

  - by Johan

  I'm storing a huge set of songs in a MySQL database. This is what I store in the 'songs' table: CREATE TABLE `songs` ( `song_id` int(10) unsigned NOT NULL auto_increment, `song_artist` varchar(255) NOT NULL, `song_track` varchar(255) NOT NULL, `song_mix` varchar(255) NOT NULL, `song_title` text NOT NULL, `song_hash` varchar(40) NOT NULL, `song_addtime` int(10) unsigned NOT NULL, `song_source` text NOT NULL, `song_file` varchar(255) NOT NULL, PRIMARY KEY (`song_id`) ) ENGINE=MyISAM AUTO_INCREMENT=1857 DEFAULT CHARSET=latin1 Now I'd like to keep track of how many plays each song has, and other song-specific data that relates to the song. I don't want to keep adding fields to the 'songs' table for this. How can I store song related data a more efficient way? What's the best practice here?

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• Does DB2 have an "insert or update" statement?

  - by Mikael Eriksson

  From my code (Java) I want to ensure that a row exists in the database (DB2) after my code is executed. My code now does a select and if no result is returned it does an insert. I really don't like this code since it exposes me to concurrency issuses when running in a multi-threaded environment. What I would like to do is to put this logic in DB2 instead of in my Java code. Does DB2 have an "insert-or-update" statement? Or anything like it that I can use? For example: insertupdate into mytable values ('myid') Another way of doing it would probably be to allways do the insert and catch "SQL-code -803 primary key already exists", but I would like to avoid that if possible.

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• Compare values for audit trail

  - by kagaku

  I'm attempting to develop an audit trail/tracking solution for an existing database written in PLSQL/PHP - however I'm still unsure as of yet on an easy (to implement and maintain) solution for tracking changes to fields/values. For instance, the project tracking portion of the DB APP tracks over 200 fields and ideally I'd like a nice way to show a history of changes, such as: 5/10/2010 - Project 435232 updated by John Doe Changed Project Name (Old: Test Project; New: Super Test Project) Changed Submission Date (Old: 5/10/2010; New: 5/11/2010) Changed Description (Old: This is an example!; New: This is a test example) Essentially for each field (db column) it would output a new line to show the old/new values. So far my current idea is saving the current version of the data to a temporary table, updating the primary table with the new data then loading each row into an array and doing an array compare to determine the differences. This seems a bit convoluted, and if there is an easier method I'd love to know it. Any ideas or suggestions are much appreciated!

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• Replace into equivalent for postgresql and then autoincrementing an int

  - by Mohamed Ikal Al-Jabir

  Okay no seriously, if a postgresql guru can help out I'm just getting started. Basically what I want is a simple table like such: CREATE TABLE schema.searches ( search_id serial NOT NULL, search_query character varying(255), search_count integer DEFAULT 1, CONSTRAINT pkey_search_id PRIMARY KEY (search_id) ) WITH ( OIDS=FALSE ); I need something like REPLACE INTO for mysql. I don't know if I have to write my own procedure or something? Basically: check if the query already exists if so, just add 1 to the count it not, add it to the db I can do this in my php code but I'd rather all that be done in postgres C engine Thanks for helping

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• Weighted Average with LINQ

  - by jsmith

  My goal is to get a weighted average from one table, based on another tables primary key. Example Data: Table1 Key WEIGHTED_AVERAGE 0200 0 Table2 ForeignKey LENGTH PCR 0200 105 52 0200 105 60 0200 105 54 0200 105 -1 0200 47 55 I need to get a weighted average based on the length of a segment and I need to ignore values of -1. I know how to do this in SQL, but my goal is to do this in LINQ. It looks something like this in SQL: SELECT Sum(t2.PCR*t2.LENGTH)/Sum(t2.LENGTH) AS WEIGHTED_AVERAGE FROM Table1 t1, Table2 t2 WHERE t2.PCR <> -1 AND t2.ForeinKey = t1.Key; I am still pretty new to LINQ, and having a hard time figuring out how I would translate this. The result weighted average should come out to roughly 55.3. Thank you.

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• Scripting window positioning in OS X

  - by Matt Trent

  My primary computing setup is a macbook pro with a large external monitor. I'm looking for a convenient way of moving a number of the windows of open programs from the laptop screen to the external monitor when I plug it in. I've seen a few partial scripts for accomplishing this, but nothing comprehensive. Ideally I'd like to specify the laptop screen location and external monitor location for each window and be able to toggle between them. Is anyone aware of any existing utility or Applscripts that can perform this?

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• Single HTML Table from multiple MySQL tables

  - by David Chouinard

  Hi! I've been struggling for a while with this one; I'll try to explain it here as simply as possible. Consider this MySQL table: +----------+-----------+---------+--------+ |status_id |session_id |pilot_id |present | +----------+-----------+---------+--------+ |1 |61 |901 |1 | |2 |63 |901 |1 | |3 |62 |901 |0 | |4 |62 |902 |1 | |5 |63 |903 |1 | +----------+-----------+---------+--------+ Both session_id and pilot_id are foreign keys making reference to a primary key in another table. The same pilot_id can be associated with different session_id, but every pilot_id-session_id combination is unique. I need to make an HTML table (in PHP) that would display the data like this: +----------+---------+---------+---------+ | |61 |62 |63 | +----------+---------+---------+---------+ |901 |X | |X | |902 | |X | | |903 | | |X | +----------+---------+---------+---------+ Hence, rows are pilot_id and columns are session_id. When a pilot_id-session_id combination has a present value of 1, the corresponding cell should be checked. (ie. when the row-combination is zero or the combination does not exist in the MySQL table, nothing should appear in the HTML table) Phew. Any ideas? Thanks!

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• Inserting multiple types into an SQLite database with Python

  - by mankoff

  I'm trying to create an SQLite 3 database from Python. I have a few types I'd like to insert into each record: A float, and then 3 groups of n floats, currently a tuple but could be an array or list.. I'm not well-enough versed in Python to understand all the differences. My problem is the INSERT statement. DAS = 12345 lats = (42,43,44,45) lons = (10,11,12,13) times = (1,2,3,4,5,6,7,8,9) import sqlite3 connection = sqlite3.connect("test.db") cursor = connection.cursor() cursor.execute( "create table foo(DAS LONG PRIMARY KEY,lats real(4),lons real(4), times real(9) )" ) I'm not sure what comes next. Something along the lines of: cmd = 'INSERT into foo values (?,?,?,?), ..." cursor.execute(cmd) How should I best build the SQL insert command given this data?

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• Dynamically determining table name given field name in SQL server

  - by Salman A

  Strange situation: I am trying to remove some hard coding from my code. There is a situation where I have a field, lets say "CityID", and using this information, I want to find out which table contains a primary key called CityID. Logically, you'd say that it's probably a table called "City" but it's not... that table is called "Cities". There are some other inconsistencies in database naming hence I can never be sure if removing the string "ID" and finding out the plural will be sufficient. Note: Once I figure out that CityID refers to a table called Cities, I will perform a join to replace CityID with city name on the fly. I will appreciate if someonw can also tell me how to find out the first varchar field in a table given its name.

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• Custom validation works in development but not in unit test

  - by Geolev

  I want to validate that at least one of two columns have a value in my model. I found somewhere on the web that I could create a custom validator as follows: # Check for the presence of one or another field: # :validates_presence_of_at_least_one_field :last_name, :company_name - would require either last_name or company_name to be filled in # also works with arrays # :validates_presence_of_at_least_one_field :email, [:name, :address, :city, :state] - would require email or a mailing type address module ActiveRecord module Validations module ClassMethods def validates_presence_of_at_least_one_field(*attr_names) msg = attr_names.collect {|a| a.is_a?(Array) ? " ( #{a.join(", ")} ) " : a.to_s}.join(", ") + "can't all be blank. At least one field must be filled in." configuration = { :on => :save, :message => msg } configuration.update(attr_names.extract_options!) send(validation_method(configuration[:on]), configuration) do |record| found = false attr_names.each do |a| a = [a] unless a.is_a?(Array) found = true a.each do |attr| value = record.respond_to?(attr.to_s) ? record.send(attr.to_s) : record[attr.to_s] found = !value.blank? end break if found end record.errors.add_to_base(configuration[:message]) unless found end end end end end I put this in a file called lib/acs_validator.rb in my project and added "require 'acs_validator'" to my environment.rb. This does exactly what I want. It works perfectly when I manually test it in the development environment but when I write a unit test it breaks my test environment. This is my unit test: require 'test_helper' class CustomerTest < ActiveSupport::TestCase # Replace this with your real tests. test "the truth" do assert true end test "customer not valid" do puts "customer not valid" customer = Customer.new assert !customer.valid? assert customer.errors.invalid?(:subdomain) assert_equal "Company Name and Last Name can't both be blank.", customer.errors.on(:contact_lname) end end This is my model: class Customer < ActiveRecord::Base validates_presence_of :subdomain validates_presence_of_at_least_one_field :customer_company_name, :contact_lname, :message => "Company Name and Last Name can't both be blank." has_one :service_plan end When I run the unit test, I get the following error: DEPRECATION WARNING: Rake tasks in vendor/plugins/admin_data/tasks, vendor/plugins/admin_data/tasks, and vendor/plugins/admin_data/tasks are deprecated. Use lib/tasks instead. (called from /usr/lib/ruby/gems/1.8/gems/rails-2.3.8/lib/tasks/rails.rb:10) Couldn't drop acs_test : #<ActiveRecord::StatementInvalid: PGError: ERROR: database "acs_test" is being accessed by other users DETAIL: There are 1 other session(s) using the database. : DROP DATABASE IF EXISTS "acs_test"> acs_test already exists NOTICE: CREATE TABLE will create implicit sequence "customers_id_seq" for serial column "customers.id" NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "customers_pkey" for table "customers" NOTICE: CREATE TABLE will create implicit sequence "service_plans_id_seq" for serial column "service_plans.id" NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "service_plans_pkey" for table "service_plans" /usr/bin/ruby1.8 -I"lib:test" "/usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake/rake_test_loader.rb" "test/unit/customer_test.rb" "test/unit/service_plan_test.rb" "test/unit/helpers/dashboard_helper_test.rb" "test/unit/helpers/customers_helper_test.rb" "test/unit/helpers/service_plans_helper_test.rb" /usr/lib/ruby/gems/1.8/gems/activerecord-2.3.8/lib/active_record/base.rb:1994:in `method_missing_without_paginate': undefined method `validates_presence_of_at_least_one_field' for #<Class:0xb7076bd0> (NoMethodError) from /usr/lib/ruby/gems/1.8/gems/will_paginate-2.3.12/lib/will_paginate/finder.rb:170:in `method_missing' from /home/george/projects/advancedcomfortcs/app/models/customer.rb:3 from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:31:in `gem_original_require' from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:31:in `require' from /usr/lib/ruby/gems/1.8/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:158:in `require' from /usr/lib/ruby/gems/1.8/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:265:in `require_or_load' from /usr/lib/ruby/gems/1.8/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:224:in `depend_on' from /usr/lib/ruby/gems/1.8/gems/activesupport-2.3.8/lib/active_support/dependencies.rb:136:in `require_dependency' from /usr/lib/ruby/gems/1.8/gems/rails-2.3.8/lib/initializer.rb:414:in `load_application_classes' from /usr/lib/ruby/gems/1.8/gems/rails-2.3.8/lib/initializer.rb:413:in `each' from /usr/lib/ruby/gems/1.8/gems/rails-2.3.8/lib/initializer.rb:413:in `load_application_classes' from /usr/lib/ruby/gems/1.8/gems/rails-2.3.8/lib/initializer.rb:411:in `each' from /usr/lib/ruby/gems/1.8/gems/rails-2.3.8/lib/initializer.rb:411:in `load_application_classes' from /usr/lib/ruby/gems/1.8/gems/rails-2.3.8/lib/initializer.rb:197:in `process' from /usr/lib/ruby/gems/1.8/gems/rails-2.3.8/lib/initializer.rb:113:in `send' from /usr/lib/ruby/gems/1.8/gems/rails-2.3.8/lib/initializer.rb:113:in `run' from /home/george/projects/advancedcomfortcs/config/environment.rb:9 from ./test/test_helper.rb:2:in `require' from ./test/test_helper.rb:2 from ./test/unit/customer_test.rb:1:in `require' from ./test/unit/customer_test.rb:1 from /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake/rake_test_loader.rb:5:in `load' from /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake/rake_test_loader.rb:5 from /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake/rake_test_loader.rb:5:in `each' from /usr/lib/ruby/gems/1.8/gems/rake-0.8.7/lib/rake/rake_test_loader.rb:5 rake aborted! Command failed with status (1): [/usr/bin/ruby1.8 -I"lib:test" "/usr/lib/ru...] (See full trace by running task with --trace) It seems to have stepped on will_paginate somehow. Does anyone have any suggestions? Is there another way to do the validation I'm attempting to do? Thanks, George

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• Software to find dependencys in a database that not have them as restrictions

  - by Tomas Friden

  I have a database in SQL server 2005 that originaly comes fom an old mainframe. All relations was set in the surrounding software and there are non i the database. I need to find the relations, not by field name but by actual contence in the registers. (as suggestions, I realize I'l have to check them up) It would be nice with some extras, like finding motherless posts etc. but not a primary demand. There are some 200 registers with max 2 000 000 posts in any register. Does any one know of a software that can help me with this? The software I can find presuposes that relations are set in the database :(

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• Subversion for version control

  - by Gabriel Parenza

  Hi, I am working on an application whose primary purpose would be to provide source control management. My idea is to use to SVNKit for file check-out and check-in. However, while working with SVNKit, I realised it does not have the speed I was looking for. For instance, whenever developers create a ChangeRequest, which can encompass change in 3-40 files, I have to create a directory structure distributed across 32 folders. Doing so takes around 50 seconds, Another instance is that after creating change request developers can add files to the request. Copying even a single file from Trunk to branch takes around 6-7 secs. My question is has anyone had experience like this and what did you do to improve the performance? Moreover, is my approach correct? NOTE: I am using "http" protocol and can't use "svn" protocol.

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