My question regards PostgreSQL database size.
How can I create new database with fixed size? (e.g. 5 GB)
Once I have created fixed sized PostgreSQL database, how can I resize it ?
As we can read in the comments, there is no direct support in postgresql for this - but you can solve this problem with indirect means, as you can read here: http://bytes.com/topic/postgresql/answers/421532-database-size-limiting
Basically, you have various options to make a separate database instance, or a cluster node, or a partition, and then limit the disk usage on the OS level (f.e. user quotas).
AFAIK in case of a quota exhaust your transactions will be rollbacked, but the db left consistent. But I suggest to doublecheck this before you do some dangerous.