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• Database for Python Twisted

  - by Will

  There's an API for Twisted apps to talk to a database in a scalable way: twisted.enterprise.dbapi The confusing thing is, which database to pick? The database will have a Twisted app that is mostly making inserts and updates and relatively few selects, and then other strictly-read-only clients that are accessing the database directly making selects. (The read-only users are not necessarily selecting the data that the Twisted app is inserting; its not as though the database is being used as a message-queue) My understanding - which I'd like corrected/adviced - is that: Postgres is a great DB, but all the Python bindings - and there is a confusing maze of them - are abandonware There is psycopg2, but that makes a lot of noise about doing its own connection-pooling and things; does this co-exist gracefully/usefully/transparently with the Twisted async database connection pooling and such? SQLLite is a great database for little things but if used in a multi-user way it does whole-database locking, so performance would suck in the usage pattern I envisage MySQL - after the Oracle takeover, who'd want to adopt it now or adopt a fork? Is there anything else out there?

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• Show progress during a long Ajax call

  - by kousen

  I have a simple web site (http://www.kousenit.com/twitterfollowervalue) that computes a quantity based on a person's Twitter followers. Since the Twitter API only returns followers 100 at a time, a complete process may involve lots of calls. At the moment, I have an Ajax call to a method that runs the Twitter loop. The method looks like (Groovy): def updateFollowers() { def slurper = new XmlSlurper() followers = [] def next = -1 while (next) { def url = "http://api.twitter.com/1/statuses/followers.xml?id=$id&cursor=$next" def response = slurper.parse(url) response.users.user.each { u -> followers << new TwitterUser(... process data ...) } next = response.next_cursor.toBigInteger() } return followers } This is invoked from a controller called renderTTFV.groovy. I call the controller via an Ajax call using the prototype library: On my web page, in the header section (JavaScript): function displayTTFV() { new Ajax.Updater('ttfv','renderTTFV.groovy', {}); } and there's a div in the body of the page that updates when the call is complete. Everything is working, but the updateFollowers method can take a fair amount of time. Is there some way I could return a progress value? For example, I'd like to update the web page on every iteration. I know ahead of time how many iterations there will be. I just can't figure out a way to update the page in the middle of that loop. Any suggestions would be appreciated.

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• WPF Notify changes on object

  - by Erik Z

  I have a gridview were I define some columns, like this... <GridViewColumn.CellTemplate> <DataTemplate> <TextBlock Text="{Binding MyProp}" /> </DataTemplate> </GridViewColumn.CellTemplate> I bind my gridview to a collection and implemts INotifyPropertyChanged in the property MyProp. This works well and any changes of MyProp are reflected to the gridview. If I add another column that is bound to the object itself I dont get any notifications/updates. My code... <GridViewColumn.CellTemplate> <DataTemplate> <TextBlock Text="{Binding Converter={StaticResource myConverter}}"/> </DataTemplate> </GridViewColumn.CellTemplate> I think I need something like INotifyPropertyChanged for the object but I have no idea how to do this. Any suggestions?

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• ASP.NET retrieve Average CPU Usage

  - by Sam

  Last night I did a load test on a site. I found that one of my shared caches is a bottleneck. I'm using a ReaderWriterLockSlim to control the updates of the data. Unfortunately at one point there are ~200 requests trying to update the data at approximately the same time. This also coincided with CPU usage spikes. The data being updated is in the ASP.NET Cache. What I'd like to do is if the CPU usage is around 75%, I'd like to just skip the cache and hit the database on another machine. My problem is that I don't know how expensive it is to create a new performance counter to check the cpu usage. Also, if I would probably like the average cpu usage over the last 2 or 3 seconds. However, I can't sit there and calculate the cpu time as that would take longer than it's taking to update the cache currently. Is there an easy way to get the average CPU usage? Are there any drawbacks to this? I'm also considering totaling the wait count for the lock and then at a certain threshold switch over to the database. The concern I had with this approach would be that changing hardware might allow more locks with less of a strain on the system. And also finding the right balance for the threshold would be cumbersome and it doesn't take into account any other load on the machine. But it's a simple approach, and simple is 99% of the time better.

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• Speeding up inner-joins and subqueries while restricting row size and table membership

  - by hiffy

  I'm developing an rss feed reader that uses a bayesian filter to filter out boring blog posts. The Stream table is meant to act as a FIFO buffer from which the webapp will consume 'entries'. I use it to store the temporary relationship between entries, users and bayesian filter classifications. After a user marks an entry as read, it will be added to the metadata table (so that a user isn't presented with material they have already read), and deleted from the stream table. Every three minutes, a background process will repopulate the Stream table with new entries (i.e. whenever the daemon adds new entries after the checks the rss feeds for updates). Problem: The query I came up with is hella slow. More importantly, the Stream table only needs to hold one hundred unread entries at a time; it'll reduce duplication, make processing faster and give me some flexibility with how I display the entries. The query (takes about 9 seconds on 3600 items with no indexes): insert into stream(entry_id, user_id) select entries.id, subscriptions_users.user_id from entries inner join subscriptions_users on subscriptions_users.subscription_id = entries.subscription_id where subscriptions_users.user_id = 1 and entries.id not in (select entry_id from metadata where metadata.user_id = 1) and entries.id not in (select entry_id from stream where user_id = 1); The query explained: insert into stream all of the entries from a user's subscription list (subscriptions_users) that the user has not read (i.e. do not exist in metadata) and which do not already exist in the stream. Attempted solution: adding limit 100 to the end speeds up the query considerably, but upon repeated executions will keep on adding a different set of 100 entries that do not already exist in the table (with each successful query taking longer and longer). This is close but not quite what I wanted to do. Does anyone have any advice (nosql?) or know a more efficient way of composing the query?

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• Long running transactions with Spring and Hibernate?

  - by jimbokun

  The underlying problem I want to solve is running a task that generates several temporary tables in MySQL, which need to stay around long enough to fetch results from Java after they are created. Because of the size of the data involved, the task must be completed in batches. Each batch is a call to a stored procedure called through JDBC. The entire process can take half an hour or more for a large data set. To ensure access to the temporary tables, I run the entire task, start to finish, in a single Spring transaction with a TransactionCallbackWithoutResult. Otherwise, I could get a different connection that does not have access to the temporary tables (this would happen occasionally before I wrapped everything in a transaction). This worked fine in my development environment. However, in production I got the following exception: java.sql.SQLException: Lock wait timeout exceeded; try restarting transaction This happened when a different task tried to access some of the same tables during the execution of my long running transaction. What confuses me is that the long running transaction only inserts or updates into temporary tables. All access to non-temporary tables are selects only. From what documentation I can find, the default Spring transaction isolation level should not cause MySQL to block in this case. So my first question, is this the right approach? Can I ensure that I repeatedly get the same connection through a Hibernate template without a long running transaction? If the long running transaction approach is the correct one, what should I check in terms of isolation levels? Is my understanding correct that the default isolation level in Spring/MySQL transactions should not lock tables that are only accessed through selects? What can I do to debug which tables are causing the conflict, and prevent those tables from being locked by the transaction?

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• Can it be done in a more elegant way with the Swing Timer?

  - by Roman

  Bellow is the code for the simplest GUI countdown. Can the same be done in a shorter and more elegant way with the usage of the Swing timer? import javax.swing.JFrame; import javax.swing.JLabel; import javax.swing.SwingUtilities; public class CountdownNew { static JLabel label; // Method which defines the appearance of the window. public static void showGUI() { JFrame frame = new JFrame("Simple Countdown"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); label = new JLabel("Some Text"); frame.add(label); frame.pack(); frame.setVisible(true); } // Define a new thread in which the countdown is counting down. public static Thread counter = new Thread() { public void run() { for (int i=10; i>0; i=i-1) { updateGUI(i,label); try {Thread.sleep(1000);} catch(InterruptedException e) {}; } } }; // A method which updates GUI (sets a new value of JLabel). private static void updateGUI(final int i, final JLabel label) { SwingUtilities.invokeLater( new Runnable() { public void run() { label.setText("You have " + i + " seconds."); } } ); } public static void main(String[] args) { SwingUtilities.invokeLater(new Runnable() { public void run() { showGUI(); counter.start(); } }); } }

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• Nhibernate fires SQL commands

  - by Chris

  Hi all, when updating an entity A, NHibernate also send an SQL update command for some other entity B. A and B are not related. Just before saving entity A, the parent of entity B is loaded via a SQLQuery. Then, when accessed, B is lazy loaded (part of a collection). If I save entity A an update statement for entity B is generated as well. How can that be, that when saving an entity, another entity loaded before but is not related to the entity saved, is updated as well?! Can I somehow track where the update comes from? Btw. I am using an save event listener. Could it be that this is always triggered for entity loaded, even though they are not saved explicitly? public class EntitySaveEventListener : NHibernate.Event.Default.DefaultSaveEventListener { protected override object PerformSaveOrUpdate(SaveOrUpdateEvent e) { //auditing return base.PerformSaveOrUpdate(e); } } Update (sorry for providing not enough info): I tracked it down a bit. A select stateement on a entity called address is executed (is it lazy loaded by a parent). Then I create a new entity called Request. Right before saving this entity a session flush is called which updates the address, even though I did not call save or update on the address. Address is a collection within Request. <class name="Request" table="Request"> <bag name="addresses" access="field" cascade="all-delete-orphan" where="IsDeleted = 0"> <key column="RequestId"/> <one-to-many class="Address"/> </bag> ... // address is fetched only NHibernate.SQL: 2010-02-17 11:47:21,306 [21] DEBUG NHibernate.SQL [(null)] - SELECT addresses0_.RequestId as ServiceP8_3_, .... // session flushed here // address is updated NHibernate.SQL: 2010-02-17 11:47:34,306 [21] DEBUG NHibernate.SQL [(null)] - Batch commands: command 0:UPDATE Address SET Street = @p0, ..... Would the address be updated automatically when it is manipulated somehow even though it is not explicitly saved via it's parent (cascade)?

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• Section or group name 'cachingConfiguration' is already defined - but where?

  - by Richard Ev

  On Windows XP I am working on a .NET 3.5 web app that's a combination of WebForms and MVC2 (The WebForms parts are legacy, and being migrated to MVC). When I run this from VS2008 using the ASP.NET web server everything works as expected. However, when I host the app in IIS and try to use it, I see the following error Section or group name 'cachingConfiguration' is already defined. Updates to this may only occur at the configuration level where it is defined. Source Error: Line 24: </sectionGroup> Line 25: <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net"/> Line 26: <section name="cachingConfiguration" type="Microsoft.Practices.EnterpriseLibrary.Caching.Configuration.CacheManagerSettings,Microsoft.Practices.EnterpriseLibrary.Caching, Version=4.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" /> Line 27: </configSections> Line 28: Sure enough, if I remove the offending line (line 26 in the error message) from my web.config then the app runs correctly. However, I really need to find out where the duplicate definition of this is. It's nowhere in my solution. Where else could it be?

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• NSTimer to smooth out playback position

  - by Michael

  I have an audio player and I want to show the current time of the the playback. I'm using a custom play class. The app downloads the mp3 to a file then plays from the file when 5% has been downloaded. I have a progress view update as the file plays and update a label on each call to the progress view. However, this is jerky... sometimes even going backward a digit or two. I was considering using an NSTimer to smooth things out. I would be fired every second to a method and pass the percentage played figure to the method then update the label. First, does this seem reasonable? Second, how do I pass the percentage (a float) over to the target of the timer. Right now I am putting the percent played into a dictionary but this seems less than optimal. This is what is called update the progress bar: -(void)updateAudioProgress:(Percentage)percent { audio = percent; if (!seekChanging) slider.value = percent; NSMutableDictionary *myDictionary = [[NSMutableDictionary alloc] init]; [myDictionary setValue:[NSNumber numberWithFloat:percent] forKey:@"myPercent"]; [NSTimer scheduledTimerWithTimeInterval:5 target:self selector:@selector(myTimerMethod:) userInfo:myDictionary repeats:YES]; [myDictionary release]; } This is called first after 5 seconds but then updates each time the method is called. As always, comments and pointers appreciated.

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• Clustered index - multi-part vs single-part index and effects of inserts/deletes

  - by Anssssss

  This question is about what happens with the reorganizing of data in a clustered index when an insert is done. I assume that it should be more expensive to do inserts on a table which has a clustered index than one that does not because reorganizing the data in a clustered index involves changing the physical layout of the data on the disk. I'm not sure how to phrase my question except through an example I came across at work. Assume there is a table (Junk) and there are two queries that are done on the table, the first query searches by Name and the second query searches by Name and Something. As I'm working on the database I discovered that the table has been created with two indexes, one to support each query, like so: --drop table Junk1 CREATE TABLE Junk1 ( Name char(5), Something char(5), WhoCares int ) CREATE CLUSTERED INDEX IX_Name ON Junk1 ( Name ) CREATE NONCLUSTERED INDEX IX_Name_Something ON Junk1 ( Name, Something ) Now when I looked at the two indexes, it seems that IX_Name is redundant since IX_Name_Something can be used by any query that desires to search by Name. So I would eliminate IX_Name and make IX_Name_Something the clustered index instead: --drop table Junk2 CREATE TABLE Junk2 ( Name char(5), Something char(5), WhoCares int ) CREATE CLUSTERED INDEX IX_Name_Something ON Junk2 ( Name, Something ) Someone suggested that the first indexing scheme should be kept since it would result in more efficient inserts/deletes (assume that there is no need to worry about updates for Name and Something). Would that make sense? I think the second indexing method would be better since it means one less index needs to be maintained. I would appreciate any insight into this specific example or directing me to more info on maintenance of clustered indexes.

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• Convert string to variable in Javascript

  - by waiwai933

  Is there any way to convert a string to a variable in Javascript? Right now, what I have is a script that updates data based on the values of the select box: <script type="text/javascript"> var a = new Array(); a[0] = 'Name'; a[1] = 'Description'; var b = new Array(); b[0] = 'Name 2'; b[1] = 'Description 2'; function changeSystem(){ var selectedAccount=document.getElementById('selected_option').value; document.getElementById('name').innerHTML = selectedAccount[0]; document.getElementById('description').innerHTML = selectedAccount[1]; } </script> <form method="POST"> <select onchange="changeSystem()" id="selected_option"> <option>A</option> <option>B</option> </select> </form> <span id="name"></span><br> <span id="description"></span><br> selectedAccount is the string of the chosen element in <select>. However, for it to access the array, it needs to be a variable, i.e. a[0] instead of 'a'[0]. What solutions are there to this?

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• Encapsulate update method inside of object or have method which accepts an object to update

  - by Tom

  Hi, I actually have 2 questions related to each other: I have an object (class) called, say MyClass which holds data from my database. Currently I have a list of these objects ( List < MyClass ) that resides in a singleton in a "communal area". I feel it's easier to manage the data this way and I fail to see how passing a class around from object to object is beneficial over a singleton (I would be happy if someone can tell me why). Anyway, the data may change in the database from outside my program and so I have to update the data every so often. To update the list of the MyClass I have a method called say, Update, written in another class which accepts a list of MyClass. This updates all the instances of MyClass in the list. However would it be better instead to encapulate the Update() method inside the MyClass object, so instead I would say foreach(MyClass obj in MyClassList) { obj.update(); } What is a better implementation and why? The update method requires a XML reader. I have written an XML reader class which is basically a wrapper over the standard XML reader the language natively provides which provides application specific data collection. Should the XML reader class be in anyway in the "inheritance path" of the MyClass object - the MyClass objects inherits from the XML reader because it uses a few methods. I can't see why it should. I don't like the idea of declaring an instance of the XML Reader class inside of MyClass and an MyClass object is meant to be a simple "record" from the database and I feel giving it loads of methods, other object instances is a bit messy. Perhaps my XML reader class should be static but C#'s native XMLReader isn't static.? Any comments would be greatly appreciated Thanks Thomas

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• Canvas scroll animation not working correctly

  - by pedalpete

  I'm building a gantt chart style timeline using html canvas element. I am currently attempting to add the functionality which allows the user to click a next/prev button to have the gantt chart scroll to display earlier or later times. The way I am doing this is to have a span.adjustTime where the id holds a value in seconds for the time to be adjusted (eg 86400 for one day). I am trying to animate the scrolling so it looks like a scroll, rather than jumping ahead by one day. I have a small problem in my timing calculation, but the script below is not animating, but rather jumping directly to the final time. I do have the draw function running on a separate setInterval which updates every second, so I'm hoping it isn't an issue of conflicting timers on the same function on the same element and data. jQuery('span.adjustTime').click(function() { var adjustBy = parseInt(jQuery(this).attr('id').replace('a', '')); var data = jQuery('img#logo').data(); for(var m = 1; m >= 30; m++) { gantt.startUnixTime = gantt.startUnixTime + (adjustBy * (m * 0.001)); var moveTimer = setTimeout(function() { draw(document.getElementById('gantt'), data, gantt); }, 1000); if (m == 30) { clearTimeout(moveTimer); } } });

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• Updating Data through Objects

  - by Chacha102

  So, lets say I have a record: $record = new Record(); and lets say I assign some data to that record: $record->setName("SomeBobJoePerson"); How do I get that into the database. Do I..... A) Have the module do it. class Record{ public function __construct(DatabaseConnection $database) { $this->database = $database; } public function setName($name) { $this->database->query("query stuff here"); $this->name = $name; } } B) Run through the modules at the end of the script class Record{ private $changed = false; public function __construct(array $data=array()) { $this->data = $data; } public function setName($name) { $this->data['name'] = $name; $this->changed = true; } public function isChanged() { return $this->changed; } public function toArray() { return $this->array; } } class Updater { public function update(array $records) { foreach($records as $record) { if($record->isChanged()) { $this->updateRecord($record->toArray()); } } } public function updateRecord(){ // updates stuff } }

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• How to deploy a number of disparate project types?

  - by niteice

  This question is similar to http://stackoverflow.com/questions/1900269/whats-the-best-way-to-deploy-an-executable-process-on-a-web-server. The situation is this: I'm developing a product that needs to be deployed to a web server. It consists of 4 website projects, a background service, a couple of command-line tools, and two assemblies shared by all of these components. Now, I also happen to administer the server that this product will be deployed on. So I'm familiar with everything that may need to be done to perform an update: Copy website files Replace the service binary Install updated components in the GAC Configure IIS Update database schema After some research it seems that, to reduce deployment time and to be able to let the other sysadmins handle deployment, I want to deploy all of these as an MSI, except that I don't know a thing about installers. I know VS can generate web deployment projects, but where do I go from there? Being able to simply click Next a few times on an installer is my goal for deploying updates. It would also be nice to modularize it, so for example, I could distribute the four websites among multiple servers and have everything appear as individual components in the installer, and as one entity in Add/Remove Programs. Is all of this too much to ask in a single package?

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• Update database settings in properties file in Spring

  - by mvg

  Hi all, I am trying to create a Database Manager page which shows the database details on page load and updates the database settings when the user press submit I followed this tutorial and set the database settings in properties file. I managed to update the database settings in properties file programmatically. When I retrieved the database settings using the following code DriverManagerDataSource databaseSource = (DriverManagerDataSource)context.getBean("dataSource"); databaseSource.getUsername(); I managed to get the old value and unable to get the new value This is the mapping in applicationContext.xml file <bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"> <property name="location"> <value>classpath:/bundle/database.properties</value> </property> </bean> <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource"> <property name="driverClassName" value="${jdbc.driverClassName}" /> <property name="url" value="${jdbc.url}" /> <property name="username" value="${jdbc.username}" /> <property name="password" value="${jdbc.password}" /> </bean> I checked the properties file and found it to be updated with the latest input. What am I missing? Thanks in advance P.S I am using JSF1.2 with Spring 3 Update Just making my requirement simple. I am creating a setparate dbsettings page, so that when user wishes to connect to different database he/she can just enter the details in dbsettings page and connect

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• Attaching event on the fly with prototype

  - by andreas

  Hi, I've been scratching my head over this for an hour... I have a list of todo which has done button on each item. Every time a user clicks on that, it's supposed to do an Ajax call to the server, calling the marking function then updates the whole list. The problem I'm facing is that the new list has done buttons as well on each item. And it doesn't attach the click event anymore after first update. How do you attach an event handler on newly updated element with prototype? Note: I've passed evalScripts: true to the updater wrapper initial event handler attach <script type="text/javascript"> document.observe('dom:loaded', function() { $$('.todo-done a').each(function(a) { $(a).observe('click', function(e) { var todoId = $(this).readAttribute('href').substr(1); new Ajax.Updater('todo-list', $.utils.getPath('/todos/ajax_mark/done'), { onComplete: function() { $.utils.updateList({evalScripts: true}); } }); }); }) }); </script> updateList: <script type="text/javascript"> var Utils = Class.create({ updateList: function(options) { if(typeof options == 'undefined') { options = {}; } new Ajax.Updater('todo-list', $.utils.getPath('/todos/ajax_get'), $H(options).merge({ onComplete: function() { $first = $('todo-list').down(); $first.hide(); Effect.Appear($first, {duration: 0.7}); new Effect.Pulsate($('todo-list').down(), {pulses: 1, duration: 0.4, queue: 'end'}); } }) ); } }) $.utils = new Utils('globals'); </script> any help is very much appreciated, thank you :)

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• how can I save/keep-in-sync an in-memory graph of objects with the database?

  - by Greg

  Question - What is a good best practice approach for how can I save/keep-in-sync an jn-memory graph of objects with the database? Background: That is say I have the classes Node and Relationship, and the application is building up a graph of related objects using these classes. There might be 1000 nodes with various relationships between them. The application needs to query the structure hence an in-memory approach is good for performance no doubt (e.g. traverse the graph from Node X to find the root parents) The graph does need to be persisted however into a database with tables NODES and RELATIONSHIPS. Therefore what is a good best practice approach for how can I save/keep-in-sync an jn-memory graph of objects with the database? Ideal requirements would include: build up changes in-memory and then 'save' afterwards (mandatory) when saving, apply updates to database in correct order to avoid hitting any database constraints (mandatory) keep persistence mechanism separate from model, for ease in changing persistence layer if needed, e.g. don't just wrap an ADO.net DataRow in the Node and Relationship classes (desirable) mechanism for doing optimistic locking (desirable) Or is the overhead of all this for a smallish application just not worth it and I should just hit the database each time for everything? (assuming the response times were acceptable) [would still like to avoid if not too much extra overhead to remain somewhat scalable re performance]

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• Using SVN post-commit hook to update only files that have been commited

  - by fondie

  I am using an SVN repository for my web development work. I have a development site set up which holds a checkout of the repository. I have set up an SVN post-commit hook so that whenever a commit is made to the repository the development site is updated: cd /home/www/dev_ssl /usr/bin/svn up This works fine but due to the size of the repository the updates take a long time (approx. 3 minutes) which is rather frustrating when making regular commits. What I'd like is to change the post-commit hook to only update those files/directories that have been committed but I don't know how to go about doing this. Updating the "lowest common directory" would probably be the best solution, e.g. If committing the follow files: /branches/feature_x/images/logo.jpg /branches/feature_x/css/screen.css It would update the directory: /branches/feature_x/ Can anyone help me create a solution that achieves this please? Thanks! Update: The repository and development site are located on the same server so network issues shouldn't be involved. CPU usage is very low, and I/O should be ok (it's running on hi-spec dedicated server) The development site is approx. 7.5GB in size and contains approx. 600,000 items, this is mainly due to having multiple branches/tags

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• Guid Primary /Foreign Key dilemma SQL Server

  - by Xience

  Hi guys, I am faced with the dilemma of changing my primary keys from int identities to Guid. I'll put my problem straight up. It's a typical Retail management app, with POS and back office functionality. Has about 100 tables. The database synchronizes with other databases and receives/ sends new data. Most tables don't have frequent inserts, updates or select statements executing on them. However, some do have frequent inserts and selects on them, eg. products and orders tables. Some tables have upto 4 foreign keys in them. If i changed my primary keys from 'int' to 'Guid', would there be a performance issue when inserting or querying data from tables that have many foreign keys. I know people have said that indexes will be fragmented and 16 bytes is an issue. Space wouldn't be an issue in my case and apparently index fragmentation can also be taken care of using 'NEWSEQUENTIALID()' function. Can someone tell me, from there experience, if Guid will be problematic in tables with many foreign keys. I'll be much appreciative of your thoughts on it...

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• Comparing two images from the clipboard class

  - by VeXe

  In a C# winform app. I'm writing a Clipboard log manager that logs test to a log file, (everytime a Ctrl+c/x is pressed the copied/cut text gets appended to the file) I also did the same for images, that is, if you press "prtScreen", the screen shot you took will also go to a folder. I do that by using a timer, inside I have something which 'looks' like this: if (Clipboard.ContainsImage()) { if (IsClipboardUpdated()) { LogData(); UpdateLastClipboardData(); } } This is how the rest of the methods look like: public void UpdateLastClipboardData() { // ... other updates LastClipboardImage = Clipboard.GetImage(); } // This is how I determine if there's a new image in the clipboard... public bool IsClipboardUpdated() { return (LastClipboardImage != Clipboard.GetImage()); } public void LogData() { Clipboard.GetImage().Save(ImagesLogFolder + "\\Image" + now_hours + "_" + now_mins + "_" + now_secs + ".jpg"); } The problem is: inside the update method, "LastClipboardImage != Clipboard.GetImage()" is always returning true! I even did the following inside the update method: Image img1 = Clipboard.GetImage(); Image img2 = Clipboard.GetImage(); Image img3 = img2; bool b1 = img1 == img2; // this returned false. WHY?? bool b2 = img3 == img2; // this returned true. Makes sense. Please help, the comparison isn't working... why?

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• Python's asyncore to periodically send data using a variable timeout. Is there a better way?

  - by Nick Sonneveld

  I wanted to write a server that a client could connect to and receive periodic updates without having to poll. The problem I have experienced with asyncore is that if you do not return true when dispatcher.writable() is called, you have to wait until after the asyncore.loop has timed out (default is 30s). The two ways I have tried to work around this is 1) reduce timeout to a low value or 2) query connections for when they will next update and generate an adequate timeout value. However if you refer to 'Select Law' in 'man 2 select_tut', it states, "You should always try to use select() without a timeout." Is there a better way to do this? Twisted maybe? I wanted to try and avoid extra threads. I'll include the variable timeout example here: #!/usr/bin/python import time import socket import asyncore # in seconds UPDATE_PERIOD = 4.0 class Channel(asyncore.dispatcher): def __init__(self, sock, sck_map): asyncore.dispatcher.__init__(self, sock=sock, map=sck_map) self.last_update = 0.0 # should update immediately self.send_buf = '' self.recv_buf = '' def writable(self): return len(self.send_buf) > 0 def handle_write(self): nbytes = self.send(self.send_buf) self.send_buf = self.send_buf[nbytes:] def handle_read(self): print 'read' print 'recv:', self.recv(4096) def handle_close(self): print 'close' self.close() # added for variable timeout def update(self): if time.time() >= self.next_update(): self.send_buf += 'hello %f\n'%(time.time()) self.last_update = time.time() def next_update(self): return self.last_update + UPDATE_PERIOD class Server(asyncore.dispatcher): def __init__(self, port, sck_map): asyncore.dispatcher.__init__(self, map=sck_map) self.port = port self.sck_map = sck_map self.create_socket(socket.AF_INET, socket.SOCK_STREAM) self.bind( ("", port)) self.listen(16) print "listening on port", self.port def handle_accept(self): (conn, addr) = self.accept() Channel(sock=conn, sck_map=self.sck_map) # added for variable timeout def update(self): pass def next_update(self): return None sck_map = {} server = Server(9090, sck_map) while True: next_update = time.time() + 30.0 for c in sck_map.values(): c.update() # <-- fill write buffers n = c.next_update() #print 'n:',n if n is not None: next_update = min(next_update, n) _timeout = max(0.1, next_update - time.time()) asyncore.loop(timeout=_timeout, count=1, map=sck_map)

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• asyncore callbacks launching threads... ok to do?

  - by sbartell

  I'm unfamiliar with asyncore, and have very limited knowledge of asynchronous programming except for a few intro to twisted tutorials. I am most familiar with threads and use them in all my apps. One particular app uses a couchdb database as its interface. This involves longpolling the db looking for changes and updates. The module I use for couchdb is couchdbkit. It uses an asyncore loop to watch for these changes and send them to a callback. So, I figure from this callback is where I launch my worker threads. It seems a bit crude to mix asynchronous and threaded programming. I really like couchdbkit, but would rather not introduce issues into my program. So, my question is, is it safe to fire threads from an async callback? Here's some code... {{{ def dispatch(change): global jobs, db_url # jobs is my queue db = Database(db_url) work_order = db.get(change['id']) # change is an id to the document that changed. # i need to get the actual document (workorder) worker = Worker(work_order, db) # fire the thread jobs.append[worker] worker.start() return main() . . . consumer.wait(cb=dispatch, since=update_seq, timeout=10000) #wait constains the asyncloop. }}}

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• Using SetParent to steal the main window of another process but keeping the message loops separate

  - by insta

  Background: My coworker and I are maintaining a million-line legacy application we inherited. Its frontend is written in VB6, and as we're devoting almost all of our resources to converting it to C#, we are looking for quick & dirty solutions to our specific problem. The application behaves in a plugin-ish manner. There are up to 20ish separate ActiveX controls that can be loaded at once in a grid-style layout. The problem is that the ActiveX controls do all of their processing on their own UI thread, and as a lot of it is blocking waiting on network access, the UI gets very soupy. When our hosting C# app loads these controls, it becomes unresponsive because of how many controls are chewing up UI resources doing nothing. To top it off, the controls are fragile and will crash at the slightest provocation. When they are hosted in the main C# app, it creates serious instability. The best my coworker and I have come up with so far is starting a process per ActiveX control. This process, which we call the proxy, is another winforms app. It uses named pipes to communicate with the hosting process. The hosting process creates a window, loads an ActiveX control of our choice (via some reflections & AxHost magic), and tells the main process what its window handle is via the named pipe. The main process uses a combination of SetParent, and SetWindowPos to move the proxy application into itself to emulate a plugin. Size updates are sent via the named pipe. This works well enough until the ActiveX application does some sort of lengthy process and we click around on the main window while it's working. For awhile the main window is responsive, but eventually it becomes unresponsive as the child window waits for its UI thread. How can we keep the child windows on their own complete thread while still getting the benefits of SetParent? (please let me know if anything isn't clear!)

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