CartoDB user table

A "cartodb" user table is a table with a well-known set of fields and a well-known set of triggers attached on.

The fields are:

• cartodb_id, a numerical primary key of serial type
• created_at, timestamp with timezone not null default now()
• updated_at, timestamp with timezone not null default now()
• the_geom, geometry, GiST indexed
• the_geom_webmercator, geometry, GiST indexed

The triggers are (can change in the future):

• cache_checkpoint before modifying statement invalidates varnish (wrong to be before?)
• track_updates after modifying statement updates cdb_tablemetadata
• test_quota before changing statement to forbid if overquota
• test_quota_per_row before changing row to forbod if overquota (checked on a probabilistic basis)
• update_the_geom_webmercator before insert or update row to maintain the_geom_webmercator
• update_updated_at_trigger before update row to maintain updated_at