PostgreSQL: How to show database size

When you have a large PG database, you may want to find out which tables are consuming the most disk space.
You can easily check this using the following SQL statement from the PostgreSQL wiki.

SELECT nspname || '.' || relname AS "relation",

...

Use this:

SELECT pg_database.datname as "database_name", pg_database_size(pg_database.datname)/1024/1024 AS size_in_mb FROM pg_database ORDER by size_in_mb DESC;

Want to see [database sizes in MySQL](https://makandracards.com/makandra/1447-...

You can check the maximum client Redis database size in Sidekiq with this command.

Sidekiq.redis { |redis| puts redis.info.fetch('maxmemory_human') }
#=> 512.00M

If you just want the maximum database size for a known Redis database ...

There may be reasons to change the locale of your Postgres cluster. A popular one is your development system's locale being used by default (which may be annoying). Here is how to do that.

Beware: By following the steps below, you will drop and r...

PostgreSQL's array data type is pretty useful, but manipulating values of arrays can be awkward because of its syntax.

Consider the following users table which each example below will sta...

When writing Rails migrations to convert a string column to an integer you'd usually say:

change_column :table_name, :column_name, :integer

However, PostgreSQL will complain:

PG::DatatypeMismatch: ERROR:  column "column_name" cannot...

If you want to prevent that two processes run some code at the same time you can use the gem with_advisory_lock.

What happens

1. The thread will wait indefinitely until the lock is acquired.
   ...

Rails understands a :limit options when you create columns in a migration. Its meaning depends on the column type, and sometimes the supplied value.

[The documentation](http://apidock.com/rails/ActiveRecord/ConnectionAdapters/TableDefinition/co...

This is an extract from the linked article. It shows an approach on how to implement encrypted passwords with the AWS Key Management Service (KMS).

For most applications it's enough to use a hashed...

There are many approaches out there how you can import data from a legacy application to a new application. Here is an approach which opens two database connections and uses active record for the legacy system, too:

1. Add you database informati...