Related
I'm building online examination system and i want to use accdb for database. My question is will accdb allow multiple students to read the test from the database?
not clear what you mean by on-line? Do you mean you are building a web based applcation of some sort?
Access does allow multiple users to work against the database at the same time. This typically means that you split the database into a front end (application part) and the back end - a accDB with just the tables.
And you can use the access database (engine) to drive data for a web site. However, you don't and can't use VBA or the access forms for this purpose.
Since you ONLY useing the tables and not anything else releated to Access when you build such a on-line system? Then in most cases, little if any reason exists to use the access data engine, since any of the business code and UI will be built with different tools then Access. And every web site hosting these days offers MySQL, or SQL server or some other database.
These other database systems are far more approcilate and work better with multi-user operations.
So, keep in mind when you use the term "Access", you are talking about two parts:
The data base engine - (ACE, or previous called JET). This data engine (like most database engines) does not provide any UI, reporting or anything, but is just a system to hold the tables and data. You then write the web based "on-line" software with asp.net, or whatever technology stack that you are familier with.
The 2nd part of access is the so called IDE (integrated development enviroment). That part of access lets you write code, build forms, and build reports. However, that part is not web based, and thus using the term "on-line" does not really apply here. Access IDE when used is strictly 100% desktop only.
In fact, often, if you need a multi-user applcation, we often will build + use MS-Access to build that windows desktop software, but will still choose to use a server based database system like SQL server or mySQL.
So, access alone does not really give rise to a "on-line" system, and that would require that you adopt a set of web based development tools.
So this can't be a new problem.
We are developing a solution making use of an open source CRM (SuiteCRM). Our solution will require quite a lot of customisation both in CRM configuration and custom code. We will have 4 or 5 developers with any one of them making required configuration changes to the CRM. The CRM manages it's own DB and dynamically modifies the schema and configuration data without even notifying the developer in question that this has been done.
Unmanaged we will end up with 4 or 5 different versions of the database to merge.
Liquibase may be an option, but filtering out test data from schema and config changes might be a nightmare.
I thought I would reach out and see if anyone has come across this kind of problem before.
Once method is to have your developers create/update database dumps into the root of your project before committing there changes to a CVS repository.
I'm currently developing a small WPF application using a file database (SQLCe).
Since I'm near release of the product and I've had no experience with setup and deployment I would like to hear your thoughts around this subject.
The application is small and the updates that I will make is minor database changes (such as alter tables, columns etc.) and dll updates.
I've tried to play around with ClickOnce deployment but I don't understand how updates to a database should be handled.
On the other hand a standard Setup and Deployment project feels rather complex for just a couple of database updates and dll replacements?
Which one of these two "tools" would you recommend for my given scenario?
Are there any best practises or other tools that can ease the setup and deployment work?
Cheers!
Try NSIS http://nsis.sourceforge.net/. It's a good tool and allows for custom update programs to be written quite easily. This would be able to handle all of the .dll replacements and is very suited for this type of deployment.
In terms of the database updates; if you’re going to be writing scripts to update the data base tables, you will need to consider how you’re going to connect to the local instance of the data base to run the scripts against the DB. The more automated the solution, you may want to consider an application to look up the location of the DB and execute the scripts at the run time of the NSIS script being run.
Small overhead, with a lot of flexibility.
There has been some discussion on the SO community wiki about whether database objects should be version controlled. However, I haven't seen much discussion about the best-practices for creating a build-automation process for database objects.
This has been a contentious point of discussion for my team - particularly since developers and DBAs often have different goals, approaches, and concerns when evaluating the benefits and risks of an automation approach to database deployment.
I would like to hear some ideas from the SO community about what practices have been effective in the real world.
I realize that it is somewhat subjective which practices are really best, but I think a good dialog about what work could be helpful to many folks.
Here are some of my teaser questions about areas of concern in this topic. These are not meant to be a definitive list - rather a starting point for people to help understand what I'm looking for.
Should both test and production environments be built from source control?
Should both be built using automation - or should production by built by copying objects from a stable, finalized test environment?
How do you deal with potential differences between test and production environments in deployment scripts?
How do you test that the deployment scripts will work as effectively against production as they do in test?
What types of objects should be version controlled?
Just code (procedures, packages, triggers, java, etc)?
Indexes?
Constraints?
Table Definitions?
Table Change Scripts? (eg. ALTER scripts)
Everything?
Which types of objects shouldn't be version controlled?
Sequences?
Grants?
User Accounts?
How should database objects be organized in your SCM repository?
How do you deal with one-time things like conversion scripts or ALTER scripts?
How do you deal with retiring objects from the database?
Who should be responsible for promoting objects from development to test level?
How do you coordinate changes from multiple developers?
How do you deal with branching for database objects used by multiple systems?
What exceptions, if any, can be reasonable made to this process?
Security issues?
Data with de-identification concerns?
Scripts that can't be fully automated?
How can you make the process resilient and enforceable?
To developer error?
To unexpected environmental issues?
For disaster recovery?
How do you convince decision makers that the benefits of DB-SCM truly justify the cost?
Anecdotal evidence?
Industry research?
Industry best-practice recommendations?
Appeals to recognized authorities?
Cost/Benefit analysis?
Who should "own" database objects in this model?
Developers?
DBAs?
Data Analysts?
More than one?
Here are some some answers to your questions:
Should both test and production environments be built from source control? YES
Should both be built using automation - or should production by built by copying objects from a stable, finalized test environment?
Automation for both. Do NOT copy data between the environments
How do you deal with potential differences between test and production environments in deployment scripts?
Use templates, so that actually you would produce different set of scripts for each environment (ex. references to external systems, linked databases, etc)
How do you test that the deployment scripts will work as effectively against production as they do in test?
You test them on pre-production environment: test deployment on exact copy of production environment (database and potentially other systems)
What types of objects should be version controlled?
Just code (procedures, packages, triggers, java, etc)?
Indexes?
Constraints?
Table Definitions?
Table Change Scripts? (eg. ALTER scripts)
Everything?
Everything, and:
Do not forget static data (lookup lists etc), so you do not need to copy ANY data between environments
Keep only current version of the database scripts (version controlled, of course), and
Store ALTER scripts: 1 BIG script (or directory of scripts named liked 001_AlterXXX.sql, so that running them in natural sort order will upgrade from version A to B)
Which types of objects shouldn't be version controlled?
Sequences?
Grants?
User Accounts?
see 2. If your users/roles (or technical user names) are different between environments, you can still script them using templates (see 1.)
How should database objects be organized in your SCM repository?
How do you deal with one-time things like conversion scripts or ALTER scripts?
see 2.
How do you deal with retiring objects from the database?
deleted from DB, removed from source control trunk/tip
Who should be responsible for promoting objects from development to test level?
dev/test/release schedule
How do you coordinate changes from multiple developers?
try NOT to create a separate database for each developer. you use source-control, right? in this case developers change the database and check-in the scripts. to be completely safe, re-create the database from the scripts during nightly build
How do you deal with branching for database objects used by multiple systems?
tough one: try to avoid at all costs.
What exceptions, if any, can be reasonable made to this process?
Security issues?
do not store passwords for test/prod. you may allow it for dev, especially if you have automated daily/nightly DB rebuilds
Data with de-identification concerns?
Scripts that can't be fully automated?
document and store with the release info/ALTER script
How can you make the process resilient and enforceable?
To developer error?
tested with daily build from scratch, and compare the results to the incremental upgrade (from version A to B using ALTER). compare both resulting schema and static data
To unexpected environmental issues?
use version control and backups
compare the PROD database schema to what you think it is, especially before deployment. SuperDuperCool DBA may have fixed a bug that was never in your ticket system :)
For disaster recovery?
How do you convince decision makers that the benefits of DB-SCM truly justify the cost?
Anecdotal evidence?
Industry research?
Industry best-practice recommendations?
Appeals to recognized authorities?
Cost/Benefit analysis?
if developers and DBAs agree, you do not need to convince anyone, I think (Unless you need money to buy a software like a dbGhost for MSSQL)
Who should "own" database objects in this model?
Developers?
DBAs?
Data Analysts?
More than one?
Usually DBAs approve the model (before check-in or after as part of code review). They definitely own performance related objects. But in general the team own it [and employer, of course :)]
I treat the SQL as source-code when possible
If I can write it in standard's compliant SQL then it generally goes in a file in my source control. The file will define as much as possible such as SPs, Table CREATE statements.
I also include dummy data for testing in source control:
proj/sql/setup_db.sql
proj/sql/dummy_data.sql
proj/sql/mssql_specific.sql
proj/sql/mysql_specific.sql
And then I abstract out all my SQL queries so that I can build the entire project for MySQL, Oracle, MSSQL or anything else.
Build and test automation uses these build-scripts as they are as important as the app source and tests everything from integrity through triggers, procedures and logging.
We use continuous integration via TeamCity. At each checkin to source control, the database and all the test data is re-built from scratch, then the code, then the unit tests are run against the code. If you're using a code-generation tool like CodeSmith, it can also be placed into your build process to generate your data access layer fresh with each build, making sure that all your layers "match up" and do not produce errors due to mismatched SP parameters or missing columns.
Each build has its own collection of SQL scripts that are stored in the $project\SQL\ directory in source control, assigned a numerical prefix and executed in order. That way, we're practicing our deployment procedure at every build.
Depending on the lookup table, most of our lookup values are also stored in scripts and run to make sure the configuration data is what we expect for, say, "reason_codes" or "country_codes". This way we can make a lookup data change in dev, test it out and then "promote" it through QA and production, instead of using a tool to modify lookup values in production, which can be dangerous for uptime.
We also create a set of "rollback" scripts that undo our database changes, in case a build to production goes screwy. You can test the rollback scripts by running them, then re-running the unit tests for the build one version below yours, after its deployment scripts run.
+1 for Liquibase:
LiquiBase is an open source (LGPL), database-independent library for tracking, managing and applying database changes. It is built on a simple premise: All database changes (structure and data) are stored in an XML-based descriptive manner and checked into source control.
The good point, that DML changes are stored semantically, not just diff, so that you could track the purpose of the changes.
It could be combined with GIT version control for better interaction. I'm going to configure our dev-prod enviroment to try it out.
Also you could use Maven, Ant build systems for building production code from scripts.
Tha minus is that LiquiBase doesnt integrate into widespread SQL IDE's and you should do basic operations yourself.
In adddition to this you could use DBUnit for DB testing - this tool allows data generation scripts to be used for testing your production env with cleanup aftewards.
IMHO:
Store DML in files so that you could
version them.
Automate schema build process from
source control.
For testing purposes developer could
use local DB builded from
source control via build system +
load testing Data with scripts, or
DBUnit scripts (from Source
Control).
LiquiBase allows you to provide "run
sequence" of scripts to respect
dependences.
There should be DBA team that checks master
brunch with ALL changes
before production use. I mean they
check trunk/branch from other DBA's
before committing into MASTER trunk.
So that master is always consistent
and production ready.
We faced all mentioned problems with code changes, merging, rewriting in our billing production database. This topic is great for discovering all that stuff.
By asking "teaser questions" you seem to be more interested in a discussion than someone's opinion of final answers. The active (>2500 members) mailing list agileDatabases has addressed many of these questions and is, in my experience, a sophisticated and civil forum for this kind of discussion.
I basically agree with every answer given by van. Fore more insight, my baseline for database management is K. Scott Allen series (a must read, IMHO. And Jeff's opinion too it seems).
Database objects can always be rebuilt from scratch by launching a single SQL file (that can itself call other SQL files) : Create.sql. This can include static data insertion (lists...).
The SQL scripts are parameterized so that no environment-dependent and/or sensitive information is stored in plain files.
I use a custom batch file to launch Create.sql : Create.cmd. Its goal is mainly to check for pre-requisites (tools, environment variables...) and send parameters to the SQL script. It can also bulk-load static data from CSV files for performance issues.
Typically, system user credentials would be passed as a parameter to the Create.cmd file.
IMHO, dynamic data loading should require another step, depending on your environment. Developers will want to load their database with test, junk or no data at all, while at the other end production managers will want to load production data. I would consider storing test data in source control as well (to ease unit testing, for instance).
Once the first version of the database has been put into production, you will need not only build scripts (mainly for developers), but also upgrade scripts (based on the same principles) :
There must be a way to retrieve the version from the database (I use a stored procedure, but a table would do as well).
Before releasing a new version, I create an Upgrade.sql file (that can call other ones) that allows upgrading version N-1 to version N (N being the version being released). I store this script under a folder named N-1.
I have a batch file that does the upgrade : Upgrade.cmd. It can retrieve the current version (CV) of the database via a simple SELECT statement, launch the Upgrade.sql script stored under the CV folder, and loop until no folder is found. This way, you can automatically upgrade from, say, N-3 to N.
Problems with this are :
It is difficult to automatically compare database schemas, depending on database vendors. This can lead to incomplete upgrade scripts.
Every change to the production environment (usually by DBAs for performance tuning) should find its way to the source control as well. To make sure of this, it is usually possible to log every modification to the database via a trigger. This log is reset after every upgrade.
More ideally, though, DBA initiated changes should be part of the release/upgrade process when possible.
As to what kind of database objects do you want to have under source control ? Well, I would say as much as possible, but not more ;-) If you want to create users with passwords, get them a default password (login/login, practical for unit testing purposes), and make the password change a manual operation. This happens a lot with Oracle where schemas are also users...
We have our Silverlight project with MSSQL database in Git version control. The easiest way is to make sure you've got a slimmed down database (content wise), and do a complete dump from f.e. Visual Studio. Then you can do 'sqlcmd' from your build script to recreate the database on each dev machine.
For deployment this is not possible since the databases are too large: that's the main reason for having them in a database in the first place.
I strongly believe that a DB should be part of source control and to a large degree part of the build process. If it is in source control then I have the same coding safe guards when writing a stored procedure in SQL as I do when writing a class in C#. I do this by including a DB scripts directory under my source tree. This script directory doesn't necessarily have one file for one object in the database. That would be a pain in the butt! I develop in my db just a I would in my code project. Then when I am ready to check in I do a diff between the last version of my database and the current one I am working on. I use SQL Compare for this and it generates a script of all the changes. This script is then saved to my db_update directory with a specific naming convention 1234_TasksCompletedInThisIteration where the number is the next number in the set of scripts already there, and the name describes what is being done in this check in. I do this this way because as part of my build process I start with a fresh database that is then built up programatically using the scripts in this directory. I wrote a custom NAnt task that iterates through each script executing its contents on the bare db. Obviously if I need some data to go into the db then I have data insert scripts too. This has many benefits too it. One, all of my stuff is versioned. Two, each build is a fresh build which means that there won't be any sneaky stuff eking its way into my development process (such as dirty data that causes oddities in the system). Three, when a new guy is added to the dev team, they simply need to get latest and their local dev is built for them on the fly. Four, I can run test cases (I didn't call it a "unit test"!) on my database as the state of the database is reset with each build (meaning I can test my repositories without worrying about adding test data to the db).
This is not for everyone.
This is not for every project. I usually work on green field projects which allows me this convenience!
Rather than get into white tower arguments, here's a solution that has worked very well for me on real world problems.
Building a database from scratch can be summarised as managing sql scripts.
DBdeploy is a tool that will check the current state of a database - e.g. what scripts have been previously run against it, what scripts are available to be run and therefore what scripts are needed to be run.
It will then collate all the needed scripts together and run them. It then records which scripts have been run.
It's not the prettiest tool or the most complex - but with careful management it can work very well. It's open source and easily extensible. Once the running of the scripts is handled nicely adding some extra components such as a shell script that checks out the latest scripts and runs dbdeploy against a particular instance is easily achieved.
See a good introduction here:
http://code.google.com/p/dbdeploy/wiki/GettingStarted
You might find that Liquibase handles a lot of what you're looking for.
Every developer should have their own local database, and use source code control to publish to the team. My solution is here : http://dbsourcetools.codeplex.com/
Have fun,
- Nathan
In a corporate development environment writing mostly administrative software, should every developer use their own database instance, or should they use a central database instance during development? What are the advantages and disadvantages of each approach? What about other environments and other products?
If you all share the same database, you might have some issues if someone make a structure change to the database and that the code is not "Synchronized" with it.
I highly recommend one DB per developer for the only reason that you don't want to do "write" test to see someone else override you right after. A simple exemple? You try to display product for a website. Everything works until all the products disappear. Problem? Another developer decided to play with the "Active" flag of the product to test something else. In cases like that, a transaction might not even work. End of the story, you spend time debugging for someone else action.
I highly recommend replicating the staging database to the developer database once in a while to synchronize the structure (or better, have a tool to rebuild a database from scratch).
Of course, we require scripts for changes to the database and EVERYTHING is in a Source Control.
The days when database environments should be scarce are long gone. I'm writing this posting on a XW9300 with 5x15k SCSI disks in it. This machine will run a substantial ETL job in a fairly reasonable length of time and (in mid-2007) cost me about £1,700 on ebay including the disks. From a developer's perspective, especially on database centric projects like data warehousing, the line between a developer and a DBA is quite blurred. As I write this I am building a partition management framework for a SQL Server 2005 data warehouse.
Developers should have one or more development databases of their own for (IMO) these reasons:
Requires people to keep stored procedures, patch scripts and schema definition files in source control. Applying the patches can be automated to a fairly large extent. There are even tools such as Redgate SQL Compare Pro that do much of the grunt work for this.
Encourages an application architecture that facilitates easy configuration management and deployment, as people have to deploy onto their own workstations. Many deployment wrinkles will get sorted out long before they hit production or people even realise they could have gone wrong.
Avoids developers tripping up on each other's work. On something like a data warehouse where people are working with ETL code this is an even bigger win.
It encourages a degree of responsibility as developers have to learn basic database administration. This also eliminates a lot of the requirements for operational support staff and some of the dev-vs. ops friction.
If you have your own database, there are no gatekeepers obstructing experimentation or other work on it. The politics around managing 'servers' disappear as there are no 'servers'.
This is a productivity win in an any environment with significant incumbent bureaucracy.
For small data volumes an ordinary PC is fast enough for this. Developer editions or licencing are available for most if not all database management systems and will run on a desktop O/S. If you're working with Linux or Unix this is even less of an issue. For larger data volumes, up to and including most MIS applications, a workstation like an HP XW9400 or Lenovo D10 can be outfitted with 5 15k disks for less than the cost of a lot of professional development tooling. (Yes, I know it's dual licence, but a commercial all-platform licence for QT is about £4000 a seat).
A machine like this will run an ETL process with 10's to 100's of millions of rows faster than you might think.
It facilitates setting up more than one environment for smoke testing or reconciliation purposes. As you have complete control over the machine, you have quite a lot of scope for mocking up conditions in a production environment. For example, I once made a simple emulator for Control-M by just bodging some of its runtime scripts.
Where you have this level of control and transparency over the environment you can produce a fairly robustly tested deployment process which does quite a lot to eliminate opportunities for finger-pointing in production deployment.
I've seen small teams working with 14 environments, and had 7 active on a workstation at the same time. On database heavy work such as ETL, where you're with with whole tables, working in a single dev environment is a recipe for time wastage or spending your time walking on eggshells.
Also, you can use single user development licences for database platforms, which can save you the cost of the workstations just in database licencing. Most developer licences (Microsoft and OTN are a couple of examples I'm familiar with) will let you use the system on a single workstation for a single developer free or for a nominal price.
Conversely, licencing terms on shared development servers are often somewhat murky and I've seen vendors try to shake customers down for licencing on dev servers on more than one occasion.
Each of our developers has a fully functional database. Changes are scripted and source controlled like any other code.
Ideally, yes, each developer should have a "sandbox" development environment, so they can test their code even before deploying it to a shared testing/staging environment.
Each developer's environment should run scripted tests that reset the database to a known state. This is impossible to do in a shared environment.
The cost of giving each developer their own instance is less than the cost of the chaos resulting from multiple developers trying to test volatile changes together in a shared environment.
On the other hand, in many IT shops the system uses complex infrastructure, involving multiple application servers or multiple physical nodes. Then the economics change; it's less expensive for people to cooperate and avoid stepping on each other's work than it would be to replicate it for each developer. Especially true if you integrate expensive third-party systems that don't give you licenses for multiple development environments.
So the answer is yes and no. :-) Do give each developer their own environment if that environment can be reproduced inexpensively.
My recommendation is to have 2 levels of development environment:
Each developer has their own personal development system, with its own dp, web servers, etc. This allows them to code against a known setup, write automated (system level) tests that initialize their database and systems to a known state, etc.
The development integration environment is shared by all developers and used to make sure everything is working together as expected before handing it off to QA. Code is checked out from source control and installed there, and there's only a single instance of any servers (db or otherwise).
This question hints at what a developer needs to do his/her job. Certainly a private DB instance should be provided. Equally important, I would make sure that the DB is the same product/version as what you intend to deploy to. Don't develop on MySQL 6.x and deploy to MySQL 5.x. (This goes for app servers, and web servers as well!)
Having a developer DB doesn't necessarily ean you need it hosted on your local machine. You could have a central DBMS host machine with all dev dbs located on it. The pros are the garauntee that you develop against the target DB. Less overhead on dev boxes, more space/horsepower for beefy IDEs and app servers. The cons are single point of failure for all devs. (The DBMS server goes down nobody can work.) Lack of dev exposure to setting up and administering the DBMS. Devs cannot experiment as easily with upcoming DB releases or alternate DB choices to solve tough problems.
Some of the pros can be cons and vice-versa depending on your organization and structure. Maybe you don't want devs administering the DBMS. Maybe you do plan to support varying DB platforms. The decision boils down to your organization as well as your target platform choices. If you plan to target a variety of DB/OS/app server combinations then each dev should not only have their own DB but should work in a unique combination. (MySQL/Tomcat/OSX for one DB2/Jetty/Linux for another Postegres/Geronimo/WinXP for a 3rd, etc.) If you setup an ASP (Application Service Provider) type shop on an iSeries on the other hand then of course you'll likely have a central host with all dev dbmses still each dev should have at least a separate db instance to allow structural changes to schema.
I have an instance of SQLServer Development Edition installed locally. We have a QA DB server, as well as multiple production servers. All development and integration testing is done using my local server (or other developers local servers). New releases are staged to the QA server. Each release, after acceptance by the customer, is put into production.
Since I mostly do web development, I use the web server bundled with VS2008 for development and local test, then publish the web app to a QA web server hosted on a VM. Once accepted by the customer, it is published to one of several different production web servers -- some virtual, some not, depending on the application.
My department at my company only has limited development environments, purely because of cost of support and hardware. We have a couple of environments which are based on t-1 nightly refreshes from production, and some static ones.
Ideally, everyone should have their own, but in many cases, this is going to be impractical when the following are true:
you have a large number of developers needing resources (our department has maybe 80)
each developer needs multiple resources (typically i use 4-5 different dbs each day)
up to date data is important (you just cant refresh them fast enough)
In these cases, shared instances and good communication are whats needed.
One advantage to one database per developer, each developer has a snapshot of their own data in a "known" state.
I like the idea of using a local version when a developer must be isolated - developing a schema change, performance testing, setting up specific scenarios, etc...
At other times use the shared version as to insure everything is in sync with each other.
I think there's a terminology problem here. It's been a while since I've worn my DBA hat (golly gee, almost 10 years) - so someone else can chime in and correct me.
I think everyone is in agreement that each developer should have his own sandbox schema set.
In MySQL and Sybase/MS SQLServer, each database engine can support multiple databases. Each database is (normally) fully independent of the other database. So you can have one database engine instance, and give each developer his database space to do as he wish. the only problem is if the developers are using tempdb -- there can be collisions there (I think -- this you will need to look up). Just be careful that cross-database queries with fixed database names are not used.
In Oracle, the database engine instance is tied to a particular schema set. If you have multiple developers on the same engine, they are all pointing to the same tables. In this case, yes, you will need to run multiple instances.
Each of our developers has a local database. We store the create script AND a dump of the "standard data" in our SVN repo. We have an extensive set of tests that must pass against this test data. We also have a "sandbox" database that is available for people to put data in that they want shared into the standard data. This works well for us and allows us to let developers modify their local copies of data to test things, but we control what gets passed to other developers. We also strictly control schema changes, so we don't encounter the problems that someone else mentioned.
It really depends on the nature of your application. If yours is a client-server architecture in a distributed environment, it is best to have a central database that everyone uses. If the product gives users an environment with local database instances, you can use that. It is best if your development mirrors the real world environment as closely as possible.
It is also dependent on what stage of development you are in. Probably in the early stages, you dont want to get bogged down by connectivity, network and distributed environment issues and just want to be up and running. In such a case, you can start with a database instance-per-user model before switching to the central model as the product reaches some level of maturity.
In my company we tend to copy the entire DB when working on non-trivial new features. The reasoning there is disk space is cheap, whereas accidental data loss (even if it's test data) isn't.
I've worked in both types of development environments. Personally, I prefer to have my own DB/app server. However, there may be some advantages to using a shared infrastructure for development.
The main one is that a shared environment more closely resembles a real-world scenario: you are more likely to uncover problems with locking or transactions when all developers share a DB. Giving each developer their own DB may lead to "it works on my DB" syndrome.
However, if you need to apply and test schema changes or optimisations, then I can see problems in this sort of set-up.
Maybe a compromise solution would work best: all developers share infrastructure, and if someone needs to test schema changes, they create their own temporary DB instance (maybe there is one just sitting there for this purpose?) until they are happy to commit the new schema to source control.
You do have your entire schema (and test data) in source control, right? Right???
I like the compromise solution (all developers share infrastructure, and if someone needs to test schema changes, they create their own temporary DB instance (maybe there is one just sitting there for this purpose?) until they are happy to commit the new schema to source control.)
One DB per developer. No question. But the issue really is how to script entire databases, "control data", and version them. My solution is here : http://dbsourcetools.codeplex.com/
Have fun. - Nathan.
The database schemas should be held in source control and developers should own the changesets checked in for code and db together. Prior to checkin the developer should be working on his own database. After checkin, an automated build (eg: on checkin, nightly, etc), should update a central integrated db, along with the apps themselves.
At developer instance level the data loaded should be appropriate for unit testing, at least. At integrated level, the shared db should hold data also appropriate for testing, but should not rely on production replication - this is just a slack substitute for managed test data.
In my experience the only reason that developers opt for a shared db is that they believe that developing and running on recent production data is somehow 'real' and means that they can put less effort into testing. They prefer to tread on each others toes and put up with a shared db that slowly corrupts before the next production refresh than write and manage proper tests. It's this kind of management practice that gives the IT world the poor reputation to deliver that it currently has.
I'd suggest to use one instance of the database. You don't want your database to be a moving target.