DB BEST PRACTICES
FOR WEB APPS
Patterns and Tools for Database Versioning, Migration,
Data Loading and Data for Tests
CodeWorks - Atlanta - 9/29/2009

WHO AM I?
Alan Pinstein
@apinstein
apinstein@mac.com
Serial Entrepreneur, current project is Neybor.com
PHP Since 3.0 (~1997), C/C++/Obj-C, Cocoa, etc
PHOCOA PHP Framework http://phocoa.com
On GitHub: http://github.com/apinstein
Atlanta Co-working:
IgnitionAlley.com 151Locust.com

AGENDA
Common DB management problems that cause
frustration and stress
Benefits of formalized solutions
Case Studies
Tools: MP, fixtures, rake, capistrano
Q&A

LIVE Q&A & POLLS
http://codeatl09.eventhive.com/
• Live, crowd-moderated questions & feedback
• Live polls

[production-db] update user set password_md5 = md5(password);
[production-db] alter table user drop column password;

COMMON DB FRUSTRATIONS
Where should I keep track of schema changes?
What changed since last production push?
Did I apply this patch already to this server?
Did I run the migrations on this copy of the app?
Did I run the update script after updating the
schema?
Someone help the new developer set up the project
on his machine...

BENEFITS OF BEST
PRACTICES
Reproducibility
Reduction of complexity and risk
Reduced implementation time for DB changes
Increase in development throughput
Leverage from improvements in third-party tools
Community familiarity with workflows

CASE STUDY: BEFORE
$ vi updates.sql
>> alter table add column foo boolean;
$ git commit updates.sql -m “DB change”
$ ssh production@www0
$ git pull && psql -U production mydb
> i updates.sql
$ echo “” > updates.sql

CASE STUDY: BEFORE
FRAGILE process.
Quickly falls apart with 2+ devs or 2+ servers.
Branches? Fugghetaboutit.

CASE STUDY: AFTER
$ mp -n # create new migration
$ vi migrations/20090723_163051.php
$ mp -m head
$ git commit -a -m “Added new column.”
$ rake db:clone_production
$ rake db:migrate # test on copy of real data
$ cap deploy # push to staging
$ cap production deploy -s tag=staging-2009-09-01.1

CASE STUDY: AFTER
Each DB change encapsulated in a single migration
script
Only code what’s unique to your app
Deployment script automatically runs all necessary
migration scripts on production database
immediately after code deploys
Nothing to remember / eliminates human factor
Easy to test, easy to reproduce

VERSIONS VS MIGRATIONS
schema schema schema
version migration version migration version
1 2 3
A version is the structure of a database at a point in
time
A migration is code that changes the database
structure between versions

SCHEMA VERSIONING
Tracking Blocks of Changes
Sharing Changes With Others
Deploying Changes to Staging & Production

TRACKING
SCHEMA CHANGES
Explicit
Expressing changes as SQL or meta DDLs
Implicit
Schema Diffs

MP: MIGRATIONS FOR PHP
Generic migrations infrastrructure for any project
Open Source (MIT)
http://github.com/apinstein/mp/tree/master
Within 3 weeks, had:
28 public clones
1 fork
8 watchers
GitHub rocks

MP ARCHITECTURE
user: me schema schema
DB Server clean() db: myproj M1->up() version M2->up() version
(no schema) 1 2
M2->down()
clean()

MP SETUP
$ mp -f
MP - The PHP Migrator.
No migrations dir found; initializing migrations directory
at ./migrations.
Current version: 0
$ mp -f -n
Created migration 20090805_201842 at ./migrations/
20090805_201842.php.
$ ls -1 ./migrations
20090801_175831.php
clean.php
version.txt

BASIC USAGE
$ mp -x “pgsql:dbname=myproject;user=me” -m
=> migrates to latest version
TIP: alias myproj-mp=”mp -x ‘pgsql:dbname=myproject;user=me’”
$ myproj-mp -r -m
=> resets to clean, then migrates schema to latest
$ myproj-mp -m redo
=> run down() then up() on current migration
=> useful when developing migrations
$ mp -f -l
20090717_130521: Initial sql code for project
20090717_145424: Add e-commerce subsystem
20090804_145315: Add payment_method columns.

class Migration20090804_145315 extends Migration
{
public function up()
{
$sql = <<<SQL
alter table payment_method
add column account_name text,
add column nickname text,
add column address_id integer,
ADD CONSTRAINT fk_payment_method_address
FOREIGN KEY (address_id)
REFERENCES address(address_id) ON DELETE RESTRICT;
SQL;
$this->migrator->getDbCon()->exec($sql);
}
public function down()
{
$sql = <<<SQL
alter table payment_method
drop column account_name,
drop column nickname,
drop column address_id;
SQL;
$this->migrator->getDbCon()->exec($sql);
}
public function description()
{
return "Add payment_method columns account_name, nickname, and
address_id.";
}
}

MP IN PRACTICE
NEVER edit a migration once it’s been relied upon by
anyone else.
Ideally never edit once pushed to Version Control.
ALWAYS update clean.php to deal with each
migration.
ALWAYS test migrations with redo and clean.
ALWAYS test migrations against a production clone
before deployment.

MP CAVEATS
Post-schema change update scripts that rely on model code at a
certain version can break
Migration A
Adds blog.someFeatureField
Runs model code to copy data from
blog.oldFeatureField to blog.someFeatureField
Migration B
Removes blog.someFeatureField
Migration A will now fail since latest model code no longer
knows about blog.someFeatureField
Branches with migrations that can run out-of-order could be
problematic.

MP CAVEATS
Possible solutions:
Remove migration once it’s run everywhere
Catch errors and fail gracefully
Write upgrade scripts without using model code.

$ php externals/mp/mp -h
migrate usage:
MP CLI
VERSION STORAGE (must use one or the other)
-x --dsn <PDO DSN>
NOTE: if you supply a DSN then mp will automatically store the version number
in your database in a table named public.mp_version.
If you do not supply a dsn then you will need to use the -f flag to tell mp
to use the filesystem for storage of the version.
-f --version-in-file Store the version on the filesystem.
COMMANDS
-r --clean Run clean before doing anything else.
-n --create Create a new migration.
-s --show-version Shows the current version.
-V --set-version <version> Set the current version number maintained by mp to
be <version>. Does not run migrations; used to
initialize mp for an existing system.
-m --migrate <TargetVersion> or 0|up|down|head|redo
* redo is an alias for down + up
-l --list List all migrations in VERSION - DESCRIPTION format
OPTIONS
-v --verbose Verbose messages
-q --quiet Supress all message
-h --help Show this help
-d --dir <MigrationDir>
Default command is "show status".

MP API
$m = new Migrator(array(
Migrator::OPT_PDO_DSN => $dsn,
Migrator::OPT_VERSION_PROVIDER
=> new MigratorVersionProviderDB()
));
$m->clean();
$m->setVersion(‘xxx’);
$m->migrateToVersion(Migrator::VERSION_HEAD);
Easily Integrate with your own framework, app, build system, etc.
When called programmatically your infrastructure is bootstrapped,
so you have access to all of your codebase for grabbing DB
connections, etc.
Optionally supply a delegate, available to clean(), up(), down()

DB BEST PRACTICES
DB Naming Conventions:
Name: project, project_dev, project_staging
User: user
Password: different for each machine
Script to clone production database to local/staging
ssh -C user@host
'pg_dump
--clean --schema-only -U appUser -h 10.0.10.48
myProject'
| psql -U appUser myProject_dev

DATA LOADING - FIXTURES
Example - using WFFixture from phocoa php framework
Declarative, model-aware infrastructure makes setup
of test rigs fast and easy
YAML for readability
Useful for loading real baseline data as well as test
data

BLOG EXAMPLE
Multi-Tenant Blog App
Blog
name
homePageUrl
Post
name
post
status
Comment
email
comment

$fixture = <<<END
Blog:
reasonablyOpinionatedBlog:
name: Reasonably Opinionated
homePageUrl: 'http://reasonablyopinionated.com'
Post:
rant1:
Blog: reasonablyOpinionatedBlog
name: Database Migration is Hard
post: Database Migration is Hard...
status: structureTypeId: <?php BlogStatus::NOT_YET_PUBLISHED ?>
Comment: # to-many
- email: rudecommenter@blah.com
comment: this post sucks
- email: apinstein@mac.com
comment: you suck!
rant2:
Blog: # to-one
name: Some Other Blog
homePageUrl: http://someotherblog.com
name: Cantankerous rant on php 3
post: PHP3 is so old...
status: structureTypeId: <?php BlogStatus::PUBLISHED ?>
END;
$results = WFFixture::WFFixture()->loadFromYaml($fixture);
$this->rant1 = $results['rant1'];

WORKFLOW INTEGRATION
AUTOMATE!!!
Use build tools: phing, rake, capistrano etc

RAKE FOR
DB MANAGEMENT
rake db:backup_production # Backup production DB - for safety before
deployment only
rake db:clone_production # Restore Production DB to Local DB
rake db:create # Create Database
rake db:drop # Drop Database
rake db:export:features # Export all feature data for later reloading.
rake db:export:geographies # Export all geography data for later reloading.
rake db:import:development_data # Load useful data for doing development.
rake db:import:features # Load feature data.
rake db:import:geographies # Load geography data.
rake db:migrate # Migrate to latest db version
rake db:migrate:check # Verify project is already set up for MP.
rake db:migrate:clean # Clean database.
rake db:migrate:head # Update to latest version.
rake db:migrate:rebuild # Rebuild db from clean state and update to
latest version.
rake db:model:rebuild # Rebuild model (reverse om convert-conf) from
existing database state.
rake db:rebuild # Rebuild the entire database, reload baseline
data, and rebuild the propel ORM model.

MP ROADMAP
Support for pinning migrations to specific VCS tags?
Support for manifesting irreversible migrations?

Questions?