back_up_postgresql should create separate dump files for each database

[mgedmin]

back_up_postgresql now uses pg_dumpall and dumps everything into a single file.

I'd prefer to have separate dump files for each database.

[mgedmin]

pg_dumpall works by emitting commands to re-create roles, tablespaces, and empty databases, then invoking pg_dump for each database. This means that while each database will be internally consistent, the snapshots of different databases might not be exactly in-sync.
-- http://www.postgresql.org/docs/9.1/static/backup-dump.html

So basically I want sql files for the roles/tablespaces, and then a dump file for each DB. Hmm. pg_dumpall takes -g/--globals-only ("Dump only global objects (roles and tablespaces), no databases."). Good! But I'm a bit unsure about parsing psql -l with shell...

[mgedmin]

Perhaps we should also make it possible for the user to specify a desired dump format? Some of them sound quite interesting (directory with a file per table, or a tar of the above).

[mgedmin]

Uh, it should be documented that back_up_postgresql only does it for the default cluster (you can have multiple clusters, running different PostgreSQL versions, and OS upgrades often leave it that way!)

[mgedmin]

I've changed my mind on dump formats:

pg_restore: [archiver] unsupported version (1.13) in file header

SQL is portable; efficient binary formats from random PostgreSQL versions are apparently not. (This was a dump create with pg_dump -Fc on 9.4, pg_restore was version 10.5.)