Tables

Unsafe alternative

Dropping a table is unsafe if the table has foreign keys to other tables:

DROP TABLE my_table;

When dropping a table for each foreign key the database must check if there are any row in the referenced table that will violate the constraint.

This can take a lot of time depending if the referenced table is optimised for querying or not (i.e. don't have an index) also will require an ACCESS EXCLUSIVE lock on the referenced table.

Safe alternative

To safely drop the table it's better first drop each foreign key one by one using the technique describe in How to obtain a lock safely for a migration and then drop the table as last operation.