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Meta: Simplified System Catalog for PostgreSQL

Overview

System catalogs are great, because they provide a data-centric view into the database's structure. PostgreSQL has two system catalogs, pg_catalog and information_schema, but each have some drawbacks. pg_catalog mirrors PostgreSQL's internal structure, and centers around oid, object identifiers that aren't intended for "above the hood" developers to know or care about. information_schema is part of the SQL standard, and is filled with many views and columns that don't match PostgreSQL's terminology or features.

The goals with meta is to provide an "above the hood" system catalog for PostgreSQL that is normalized and uses common names for views and columns.

Features:

  • Meta System catalog: ~30 views (full list) that, under the hood, query and synthesize pg_catalog and information_schema
  • Meta-identifiers: A set of composite types that encapsulate variables necessary to identify PostgreSQL objects (tables, columns, casts, types, etc.) by name, and serve as "soft" primary keys to the views above. See meta-identifiers for more.
  • Catalog triggers: Optional meta_triggers extension, which adds INSERT/UPDATE triggers on the catalog's views. These triggers make it possible to do DDL statements (e.g. CREATE TABLE ...) with an DML statement (e.g. insert into meta.table (name) values('foo')), similar to a schema diff and migration tool but with a data-centric approach.

Status:

  • The catalog is still evolving. The goal is to mirror PostgreSQL's architecture completely and accurately, but we're still figuring out "where to draw the lines".
  • Most common PostgreSQL features are covered, but PostgreSQL is very large, and 100% coverage is not complete.
  • Not every feature has read/write triggers

Install

Install the extension into PostgreSQL's extension/ directory:

cd meta/
make
sudo make install

From a PostgreSQL shell, install the hstore extension in schema public.

CREATE EXTENSION hstore SCHEMA public;

Finally, install the meta extension:

CREATE EXTENSION meta;

Optionally, install the meta_triggers extension, to make views updatable.

Documentation

Meta-Identifiers Type System

See identifiers.

System Catalog

The system catalog contains the following views:

  • cast
  • column
  • connection
  • constraint_check
  • constraint_unique
  • extension
  • foreign_column
  • foreign_data_wrapper
  • foreign_key
  • foreign_server
  • foreign_table
  • function
  • function_parameter
  • operator
  • policy
  • policy_role
  • relation
  • relation_column
  • role
  • role_inheritance
  • schema
  • sequence
  • table
  • table_privilege
  • trigger
  • type
  • view

meta schema diagram