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  • What's the best practice for async APIs that return futures on Scala?

    - by Maurício Linhares
    I have started a project to write an async PostgreSQL driver on Scala and to be async, I need to accept callbacks and use futures, but then accepting a callback and a future makes the code cumbersome because you always have to send a callback even if it is useless. Here's a test: "insert a row in the database" in { withHandler { (handler, future) => future.get(5, TimeUnit.SECONDS) handler.sendQuery( this.create ){ query => }.get( 5, TimeUnit.SECONDS ) handler.sendQuery( this.insert ){ query => }.get( 5, TimeUnit.SECONDS ).rowsAffected === 1 } } Sending the empty callback is horrible but I couldn't find a way to make it optional or anything like that, so right now I don't have a lot of ideas on how this external API should look like. It could be something like: handler.sendQuery( this.create ).addListener { query => println(query) } But then again, I'm not sure how people are organizing API's in this regard. Providing examples in other projects would also be great.

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  • Is it a bad practice to store large files (10 MB) in a database?

    - by B Seven
    I am currently creating a web application that allows users to store and share files, 1 MB - 10 MB in size. It seems to me that storing the files in a database will significantly slow down database access. Is this a valid concern? Is it better to store the files in the file system and save the file name and path in the database? Are there any best practices related to storing files when working with a database? I am working in PHP and MySQL for this project, but is the issue the same for most environments (Ruby on Rails, PHP, .NET) and databases (MySQL, PostgreSQL).

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  • Why is the console hanging randomly?

    - by Josh M.
    Ubuntu 10.10 Server x64 installed as Virtual Box VM. Fresh install plus postgresql and tomcat6 installed via aptitude. Rebooted the server and now when I run some command the console hangs. For instance, I run "sudo shutdown now" and then nothing happens but I am not returned to the prompt. I hit CTRL+C and nothing happens except ^C appears on the following line. I can type whatever and it will show up inline. I switch to tty2 and try to login and I only get as far as [username][enter] and that console hangs. One other thing - after "sudo reboot" the console appears to hang (just like above) when shutting down tomcat6. Any idea what's going on or what I should check? Thanks!

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  • How to improve performance of ubuntu server 10.04 for my dms system?

    - by prasanna
    I will be using one of the dms (document management system) which is java + jackrabbit + postgresql + jboss + openoffice based on ubuntu server 10.04. this is the only application i will running on my server. i want to speed up the performance of the system for this. can you give me tips for improvements of ubuntu server? can i change any settings which give fast system performance. My application will be used concurrently by around 70 - 80 people. We have total 600 users. they will constanly upload , download the files in dms. i am going to use dedicated dell server with minimum 4 gb of RAM. i appreciate help. thanks and regards, Prasanna

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  • SQLite with two python processes accessing it: one reading, one writing

    - by BBnyc
    I'm developing a small system with two components: one polls data from an internet resource and translates it into sql data to persist it locally; the second one reads that sql data from the local instance and serves it via json and a restful api. I was originally planning to persist the data with postgresql, but because the application will have a very low-volume of data to store and traffic to serve, I thought that was overkill. Is SQLite up to the job? I love the idea of the small footprint and no need to maintain yet another sql server for this one task, but am concerned about concurrency. It seems that with write ahead logging enabled, concurrently reading and writing a SQLite database can happen without locking either process out of the database. Can a single SQLite instance sustain two concurrent processes accessing it, if only one reads and the other writes? I started writing the code but was wondering if this is a misapplication of SQLite.

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  • Developing a live video-streaming website

    - by cawecoy
    I'm a computer science student and know a little about some technology to start developing my website, like PHP, RubyOnRails and Python, and MySQL and PostgreSQL for Database. I need to know what are the best (secure, stable, low-price, etc) to get started, based on my business information: My website will be a live video-streaming one, similar to livestream.com We need to provide a secure service for our customers. They need to have a page to create and configure their own Live-Streaming-Videos, get statistics, etc. We work with Wowza Media Server ruuning on an Apache Server In addition, I would like to know some good practices for this kind of website development, as I am new to this. Thanks in advance!

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  • Habanero

    - by csharp-source.net
    An Enterprise Application Framework for .Net that is ideally suited for developing applications in an agile manner. The framework is used for producing an application from the data layer through to the front-end. Free open source under the LGPL license, it includes ORM, code generation and runtime UI generation to create one application for the desktop & web. Features: * ORM: Map database tables to objects in code * Persist property values to and from the database * Define all mapping in a single XML file * Switch between database vendors with one setting * Support for MySQL, MS Sql Server, MS Access, Oracle, PostgreSQL, SQLite, Firebird * FireStarter GUI class definitions xml manager * Generate user interfaces and map properties to controls * Develop for both desktop (with Windows Forms) and web (with Gizmox' Visual WebGUI) * Generate new projects and code files * Generate UI forms from templates * Reverse engineer class definitions from existing databases * Support variable data sources, including an in-memory database. Ships with Firestarter a free database reverse engineering, Domain Modelling and Code Generator.

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  • Breaking 1NF to model subset constraints. Does this sound sane?

    - by Chris Travers
    My first question here. Appologize if it is in the wrong forum but this seems pretty conceptual. I am looking at doing something that goes against conventional wisdom and want to get some feedback as to whether this is totally insane or will result in problems, so critique away! I am on PostgreSQL 9.1 but may be moving to 9.2 for this part of this project. To re-iterate: Does it seem sane to break 1NF in this way? I am not looking for debugging code so much as where people see problems that this might lead. The Problem In double entry accounting, financial transactions are journal entries with an arbitrary number of lines. Each line has either a left value (debit) or a right value (credit) which can be modelled as a single value with negatives as debits and positives as credits or vice versa. The sum of all debits and credits must equal zero (so if we go with a single amount field, sum(amount) must equal zero for each financial journal entry). SQL-based databases, pretty much required for this sort of work, have no way to express this sort of constraint natively and so any approach to enforcing it in the database seems rather complex. The Write Model The journal entries are append only. There is a possibility we will add a delete model but it will be subject to a different set of restrictions and so is not applicable here. If and when we allow deletes, we will probably do them using a simple ON DELETE CASCADE designation on the foreign key, and require that deletes go through a dedicated stored procedure which can enforce the other constraints. So inserts and selects have to be accommodated but updates and deletes do not for this task. My Proposed Solution My proposed solution is to break first normal form and model constraints on arrays of tuples, with a trigger that breaks the rows out into another table. CREATE TABLE journal_line ( entry_id bigserial primary key, account_id int not null references account(id), journal_entry_id bigint not null, -- adding references later amount numeric not null ); I would then add "table methods" to extract debits and credits for reporting purposes: CREATE OR REPLACE FUNCTION debits(journal_line) RETURNS numeric LANGUAGE sql IMMUTABLE AS $$ SELECT CASE WHEN $1.amount < 0 THEN $1.amount * -1 ELSE NULL END; $$; CREATE OR REPLACE FUNCTION credits(journal_line) RETURNS numeric LANGUAGE sql IMMUTABLE AS $$ SELECT CASE WHEN $1.amount > 0 THEN $1.amount ELSE NULL END; $$; Then the journal entry table (simplified for this example): CREATE TABLE journal_entry ( entry_id bigserial primary key, -- no natural keys :-( journal_id int not null references journal(id), date_posted date not null, reference text not null, description text not null, journal_lines journal_line[] not null ); Then a table method and and check constraints: CREATE OR REPLACE FUNCTION running_total(journal_entry) returns numeric language sql immutable as $$ SELECT sum(amount) FROM unnest($1.journal_lines); $$; ALTER TABLE journal_entry ADD CONSTRAINT CHECK (((journal_entry.running_total) = 0)); ALTER TABLE journal_line ADD FOREIGN KEY journal_entry_id REFERENCES journal_entry(entry_id); And finally we'd have a breakout trigger: CREATE OR REPLACE FUNCTION je_breakout() RETURNS TRIGGER LANGUAGE PLPGSQL AS $$ BEGIN IF TG_OP = 'INSERT' THEN INSERT INTO journal_line (journal_entry_id, account_id, amount) SELECT NEW.id, account_id, amount FROM unnest(NEW.journal_lines); RETURN NEW; ELSE RAISE EXCEPTION 'Operation Not Allowed'; END IF; END; $$; And finally CREATE TRIGGER AFTER INSERT OR UPDATE OR DELETE ON journal_entry FOR EACH ROW EXECUTE_PROCEDURE je_breaout(); Of course the example above is simplified. There will be a status table that will track approval status allowing for separation of duties, etc. However the goal here is to prevent unbalanced transactions. Any feedback? Does this sound entirely insane? Standard Solutions? In getting to this point I have to say I have looked at four different current ERP solutions to this problems: Represent every line item as a debit and a credit against different accounts. Use of foreign keys against the line item table to enforce an eventual running total of 0 Use of constraint triggers in PostgreSQL Forcing all validation here solely through the app logic. My concerns are that #1 is pretty limiting and very hard to audit internally. It's not programmer transparent and so it strikes me as being difficult to work with in the future. The second strikes me as being very complex and required a series of contraints and foreign keys against self to make work, and therefore it strikes me as complex, hard to sort out at least in my mind, and thus hard to work with. The fourth could be done as we force all access through stored procedures anyway and this is the most common solution (have the app total things up and throw an error otherwise). However, I think proof that a constraint is followed is superior to test cases, and so the question becomes whether this in fact generates insert anomilies rather than solving them. If this is a solved problem it isn't the case that everyone agrees on the solution....

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  • System Slow After Uprading Ubuntu

    - by Aragon N
    i have an ubuntu network machine which has release of 10.04.1 LTS Lucid. on this system i have apache, postgresql and django. for some app. development i have to install php and php-curl... due to being on network, i have exported wmvare machine to internet and firstly i have upgraded system and then install php5 packages on it. After all replacing it with its old place, i have considered that the new system query is some slow according to another. Old system query time : 140 ms New system query time : 9.11 s i have checked /etc/network interface and it seems there is no problem. i have checked /etc/resolv.conf and it seems ok i have checked /etc/nsswitch.conf and only host section is different from old one which old system has hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4 and then i have checked time host -t A services.myapp.com and i got real 0m0.355s user 0m0.010s sys 0m0.020s and now what can i have to check for boosting my system as before?

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  • What steps to take in resolving/fixing/optimizing a long boot, with possible looping errors as the culprit

    - by Tchalvak
    So my boot time has been slowing and slowing as time has gone on... I am running a number of services (e.g. apache/mysql, postgresql), but it has seen a drastic slowing lately, while I've only been applying updates as normal. I happened to check out my /var/log/boot.log and it is spammed with many lines of this: init: upstart-udev-bridge main process (2738) terminated with status 1 init: upstart-udev-bridge main process ended, respawning I wasn't able to find any solutions to that issue in google, or much talk of it at all, and I'm not really certain that error is the problem, but it is the only lead that I have. What steps should I go through to diagnose boot problems/a slow bootup?

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  • How can I distribute a unique database already in production?

    - by JVerstry
    Let's assume a successful web Spring application running on a MySQL or PostgreSQL database. The traffic is becoming so high and the amount of data is becoming so big that a distributed database solution needs to be implemented to address scalability issue. Let's also assume this application is using Hibernate and the data access layer is cleanly separated with DAOs. Ideally, one should be able to add or remove databases easily. A failback solution is welcome too. What would be the best strategy to scale this database? Is it possible to minimize sharding code (Shard) in the application?

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  • Enhanced LINQ to SQL Compatible ORM Solution from Devart

    Devart has recently announced the release of LinqConnect - an enhanced LINQ to SQL compatible ORM solution with extended functionality, support for SQL Server, Oracle, MySQL, PostgreSQL, and SQLite, its own visual model designer, seamlessly integrating to Visual Studio, and SQL monitoring tool. LinqConnect allows you to quickly create mapping model and generate data access layer code for your application, greatly decreasing development time and eliminating the need to work over routine tasks. It...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • Greatly Enhanced LINQ Capabilities in Devart ADO.NET Data Providers

    Devart has recently announced the release of dotConnect products for Oracle, MySQL, PostgreSQL, and SQLite - ADO.NET providers that offer Entity Framework support, LINQ to SQL support, and contain an ORM model designer for developing LINQ to SQL and EF models based on different database engines. New dotConnect ADO.NET Providers offer advanced LinqConnect ORM solution (formerly known as Devart LINQ support) closely compatible with Microsoft LINQ to SQL and having its own advanced features. Devart...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • Alternative to | more to display error results page by page

    - by Lane
    The command psql -d template_postgis2 -f /usr/share/postgresql/9.1/contrib/postgis-2.1/postgis.sql returns a list of errors that is too long to be displayed by scrolling up to the beginning of the error. I tried the same command with "| more" and "| less" added up at the end of the command but it does not display the message page by page as it should. I also tried to put the output in a file with "> file.txt" but I do not get in this new file what is displayed on the screen!! I don't understand why. I guess i can't do this with a psql command?? Is there any other way to get all the error message? Thanks for your help!

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  • Open source login solution

    - by David
    Authentication is such a general problem, which most websites have to implement. There are a few commercial solutions, but all lack sufficient functionality to customize the registration process. Therefore, I am looking for an open-source alternative. I am using PHP and with PostgreSQL as database, but as far as I understand one could utilize authentication solutions using other technologies and integrate them into our site in various ways. Therefore, I am looking for such solutions in any technology apart from those requiring Microsoft infrastructure... I would prefer Open Source solution, which have already implemented the following features: Has password recovery procedure Username is the email address of the user Has "Remember me" functionailty (meaning that the user is logged in automatically without seeing the login page) email address verification Google has gotten me nowhere on this and neither a search on this site...

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  • Faut-il en finir avec la mode NoSQL ? Ou est-ce plus qu'une simple mode passagère ?

    Faut-il en finir avec la mode NoSQL ? Ou est-ce plus qu'une simple mode passagère ? La question est volontairement provocante. Elle est posée, en des termes encore plus crus, par Ted Dziuba dans un billet intitulé « I Can't Wait for NoSQL to Die ». « Certains ingénieurs pensent que l'évolutivité et l'architecture sont la solution [de tous les problèmes]. C'est comme cela qu'est né le mouvement NoSQL », y écrit-il. « L'idée développée avec NoSQL est que toutes les bases de données relationnelles, telles que MySQL et PostgreSQL, sont caduques et que les bases de données fondées sur des documents ou les bases de données sans schéma représentent l'avenir». ...

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  • Visual Studio 2010 RC and Entity Framework 4 RC Support in the New Version of ADO.NET Data Providers

    Devart has recently announced the release of dotConnect products for Oracle, MySQL, PostgreSQL, and SQLite - ADO.NET providers that offer Entity Framework support, LINQ to SQL support, and contain an ORM model designer for developing LINQ to SQL and EF models based on different database engines. New dotConnect ADO.NET providers offer complete support for Visual Studio 2010 Release Candidate and Entity Framework 4 Release Candidate. Entity Developer 2.80, a designer for modeling and code generation...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • How to enable a Web portal-based enterprise platform on different domains and hosts without customization [on hold]

    - by S.Jalali
    At Coscend, a cloud and communications software product company, we have built a Web portal-based collaboration platform that we like to host on five different Windows- and Linux-based servers in different hosting environments that run Web servers. Each of these Windows and Linux servers has a different host name and domain name (and IP address). Our team would appreciate your guidance on: (1) Is there a way to implement this Web portal-based platform on these Linux and Windows servers without customizing the host name, domain name and IP address for each individual instance? (2) Is there a way to create some variables using JavaScript for host name and domain name and call them from the different implementations? If a reference to the host/domain names occurs on hundreds of our pages, the variables or objects would replace that. (3) This is part of making these JavaScript modules portable and re-usable for different environments and instances. The portal is written in JavaScript that is embedded in HTML5 and padded with CSS3. Other technologies include Flash, Flex, PostgreSQL and MySQL.

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  • How hard it will be for the programmer to learn MS SSRS adn SSIS [closed]

    - by user75380
    I have a programming background in php/python/java for 5 years and I know MySQL and PostgreSQL. Currently in our company the MSQL Business Intelligence person is leaving his job in 4 months. I am thinking of trying to go to his place, at least try as I want to move in Business Intelligence field in SSRS and SSIS. I just want to know that is it possible for me to get my head around those things in 4 months because I have no idea how they work and how hard it will be for me to pick up those things. Can I do that? I just want to know from experienced people if I can move towards that field? At least how should I start? In my area there are shortages of person, so once I know the stuff I can get into junior jobs easily but I want to know from experienced people.

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  • Sortie de la version 0.8 du serveur de mapping D2RQ supportant SPARQL 1.1 et de nouvelles bases relationnelles

    Nouvelle version de D2RQ Aujourd'hui est sortie la nouvelle version 0.8 du serveur de mapping D2RQ. L'outil recommande au minimum Java 5 pour fonctionner et est disponible sur son site officiel. D2RQ permet d'exposer des données relationnelles contenues dans des SGBD classiques (MySQL, Oracle, PostgreSQL, SQL Server, etc.) en tant que données liées sur le Web de données. D2RQ a pris son envol depuis environ trois semaines avec la forte participation au projet du groupe pharmaceutique UCB. La société biopharmaceutique UCB est axée sur la découverte et le...

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  • What makes Java so suitable for writing NoSQL Databases

    - by good_computer
    Looking at this page that aggregates the current NoSQL landscape, one can see that the majority of these projects are written in Java. Databases are complex systems software dealing with the file system, and so C/C++ would be a better choice than Java for this. (that's my thinking which might be flawed) Secondly, databases deal with transferring large amounts of data from disk to RAM -- which they call a working set. The JVM takes non-trivial amount of RAM for it's own purpose -- so it would be more efficient to use a platform that leaves lots of memory for data instead of hogging it for its own operations. The major relational databases are ALL written in C/C++ MySQL C, C++ Oracle Assembler, C, C++ SQL Server C++ PostgreSQL C SQLite C So what makes Java so popular in NoSQL world.

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  • Using QTDesigner with PyQT and Python 2.6

    - by PyNewbie27
    Hi. I'm fairly new to Python and trying to work with the latest versions of QTDesigner, PyQT 4.7 and QT4.7 (I downloaded the whole package from PyQT4.7 website). I can't figure out how to make QTDesigner integrate closely with Python: ie. If I select "Form" View Code in QTDesigners menu, it errors saying "Unable to launch C:/Python26/Lib/site-packages/PyQT4/bin\uic." If I look in that directory there is a pyuic.py but not "uic". From searching online it seems this doesn't exist because it's expecting a C++ install instead of the python version. Is there anyway to make QTDesigner use/call pyuic.py to generate the code, then open an IDE or text editor of my choice to show me the PYTHON code generated by the QTDesigner-PyUIC chain? I'd like Designer to integrate closely with python, so I can make custom slots/signals in Designer while designing, then tweak the python code directly in my IDE later. If it is not possible to code directly inside QTDesigner using python, does that mean I have to hand code my programs entire UI directly in my PythonIDE? Using Designer directly would seemingly be nearly very very nice for a newbie such as myself, since I can see what properties each widget has and visually edit them while still learning the QT syntax without constantly having to use web resources to see what properties each widget should have and helps with boilerplate code generation, and what their defaults are, etc. I've googled and nobody seems to be using QTDesigner and Python in this manner together. It seems most are either handcoding all the QT code in their Python IDE of choice, or have found an obvious/easy method of doing what I want, therefore not really producing up to date tutorials on making this work together. Please enlighten me if you can. Thanks in advance for your time. Please include any suggestions you might have to a newbie trying to use Python with QT and QTDesigner. Thank you.

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  • ASP: Updating an image's IMAGEURL within a REPEATER

    - by Django Reinhardt
    Hi, I hope someone can help me. It's a pretty newbie question, I'm afraid. I have an image inside a repeater, and I would like to change its IMAGEURL based on parameter that's being passed to it. <asp:Repeater ID="Repeater" runat="server"> <HeaderTemplate> <asp:Image ID="imgType" runat="server" /> </HeaderTemplate> <ItemTemplate> <%# Eval("DisplayName")%> </ItemTemplate> <SeparatorTemplate> <hr /> </SeparatorTemplate> </asp:Repeater> There is a SWITCH statement in the code behind that is altering the IMAGEURL depending on what's being passed to it. Inevitably, however, the images ID ("imgType") is not visible to the SWITCH statement (presumably because it's inside a REPEATER). Any suggestions on the best way to implement this would be greatly appreciated. Sorry for such a newbie question. Thanks!

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  • NHibernate CreateSqlQuery and object graph

    - by magellings
    Hello I'm a newbie to NHibernate. I'd like to make one sql query to the database using joins to my three tables. I have an Application with many Roles with many Users. I'm trying to get NHibernate to properly form the object graph starting with the Application object. For example, if I have 10 application records, I want 10 application objects and then those objects have their roles which have their users. What I'm getting however resembles a Cartesian product in which I have as many Application objects as total User records. I've looked into this quite a bit and am not sure if it is possible to form the application hierarchy correctly. I can only get the flattened objects to come back. It seems "maybe" possible as in my research I've read about "grouped joins" and "hierarchical output" with an upcoming LINQ to NHibernate release. Again though I'm a newbie. [Update Based on Frans comment in Ayende's post here I'm guessing what I want to do is not possible http://ayende.com/Blog/archive/2008/12/01/solving-the-select-n1-problem.aspx ] Thanks for you time in advance. Session.CreateSQLQuery(@"SELECT a.ID, a.InternalName, r.ID, r.ApplicationID, r.Name, u.UserID, u.RoleID FROM dbo.[Application] a JOIN dbo.[Roles] r ON a.ID = r.ApplicationID JOIN dbo.[UserRoleXRef] u ON u.RoleID = r.ID") .AddEntity("app", typeof(RightsBasedSecurityApplication)) .AddJoin("role", "app.Roles") .AddJoin("user", "role.RightsUsers") .List<RightsBasedSecurityApplication>().AsQueryable();

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  • How do I protect the trunk from hapless newbies?

    - by Michael Haren
    A coworker relayed the following problem, let's say it's fictional to protect the guilty: A team of 5-10 works on a project which is issue-driven. That is, the typical flow goes like this: a chunk of work (bug, enhancement, etc.) is created as an issue in the issue tracker The issue is assigned to a developer The developer resolves the issue and commits their code changes to the trunk At release time, the frozen, and heavily tested trunk or release branch or whatever is built in release mode and released The problem he's having is that a couple newbies made several bad commits that weren't caught due to an unfortunate chain of events. This was followed by a bad release with a rollback or flurry of hot fixes. One idea we're toying with: Revoke commit access to the trunk for newbies and make them develop on a per-developer branch (we're using SVN): Good: newbies are isolated and can't hurt others Good: committers merge newbie branches with the trunk frequently Good: this enforces rigid code reviews Bad: this is burdensome on the committers (but there's probably no way around it since the code needs reviewed!) Bad: it might make traceability of trunk changes a little tougher since the reviewer would be doing the commit--not too sure on this. Update: Thank you, everyone, for your valuable input. I have concluded that this is far less a code/coder problem than I first presented. The root of the issue is that the release procedure failed to capture and test some poor quality changes to the trunk. Plugging that hole is most important. Relying on the false assumption that code in the trunk is "good" is not the solution. Once that hole--testing--is plugged, mistakes by everyone--newbie or senior--will be caught properly and dealt with accordingly. Next, a greater emphasis on code reviews and mentorship (probably driven by some systematic changes to encourage it) will go a long way toward improving code quality. With those two fixes in place, I don't think something as rigid or draconian as what I proposed above is necessary. Thanks!

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