Rails: Mysql to Postgresql

Precautions

• Review all code that uses the sql GROUP BY. Mysql is liberal with GROUP BY (until 5.7) - it allows you to select a column that is not part of the GROUP BY clause, which is incorrect. Postgresql doesn't allow this.
• Mysql LIKE is case insensitive. Postgresql is case sensitive. If your code depends on case insensitive matching, use ILIKE

Features to use

• Database migrations are transactional in Postgres. This means, if a migration fails, it is rolled back entirely. This is a big win. (Nothing needs to be done to use this. Added just so we can be thankful)
• INET columns - a column type to store IP addresses or versions (to achieve version comparison in db but requires three periods)
• The UUID - if you need ids beyond the INT range or want count obfuscation
• Partial indexes - useful for things like soft-delete. The index considers only the active rows. Results in better/faster indexing