.. -*- coding: utf-8; -*-

==========

 Postgres

==========

.. contents::

   :local:

Installing on Debian

====================

Install and create new user and database::

  $ sudo apt-get install postgresql postgresql-client

  $ sudo su - postgres

  % psql

  postgres=# CREATE USER myuser WITH PASSWORD 'mypass';

  postgres=# CREATE DATABASE mydb OWNER myuser;

  postgres=# \q

Connect as user ``mypguser`` to new database::

  $ su - mypguser

  $ psql mypgdatabase

In order to create local host superuser::

  $ sudo su - postgres

  $ createuser --superuser USER

  $ exit

  $ sudo -u USER psql

..

https://wiki.debian.org/PostgreSql

  Debian wiki instructions.

Check version

=============

By SQL query::

  SELECT version();

  SHOW server_version;

  SHOW server_version_num;

From executable::

  $ postgres -V

Check locations

===============

::

  SHOW hba_file;

  SHOW config_file;

Check settings

==============

::

   SELECT name, setting FROM pg_settings;

   SELECT name, current_setting(name), source FROM pg_settings;

Check extensions

================

::

   SELECT * FROM pg_available_extensions;

Set application name

====================

``application_name`` is displayed in ``pg_stat_activity.application_name``.

It can help identify clients of DB. To alter it in current session::

  SET application_name = 'some name';

To show current value::

  SHOW application_name;

Limitations

===========

https://wiki.postgresql.org/wiki/TOAST

  TOAST is a mechanism PostgreSQL uses to keep physical data rows from exceeding the size of a data

  block (typically 8KB).

List privileges

===============

List databases with privileges::

  \l

List schemas with privileges::

  \dn+

List users with privileges::

  \du

List privileges to objects (tables, views, sequences)::

  \dp

  SELECT * FROM information_schema.role_table_grants

  WHERE table_name = 'table_name';

List default privileges::

  \ddp

  SELECT * FROM pg_default_acl;

Grant role options

==================

Show role options and group membership::

  \du

Grant role options::

  ALTER USER me WITH SUPERUSER;

  ALTER USER me WITH CREATEDB CREATEROLE LOGIN;

Revoke role options::

  ALTER USER me WITH NOSUPERUSER;

https://www.postgresql.org/docs/current/sql-createrole.html

  ``CREATE ROLE``.

Granting selects::

  GRANT SELECT ON ALL TABLES IN SCHEMA public TO ro_user;

  GRANT SELECT, INSERT, UPDATE, DELETE ON ALL TABLES IN SCHEMA public TO rw_user;

  GRANT USAGE ON ALL SEQUENCES IN SCHEMA public TO rw_user;

Making read-only role::

  GRANT CONNECT ON DATABASE mydb TO ro;

  GRANT USAGE ON SCHEMA myschema TO ro;

  GRANT SELECT ON TABLE myschema.myt1, myschema.myt2 TO ro;

Granting default privileges for new objects::

  ALTER DEFAULT PRIVILEGES IN SCHEMA myschema GRANT SELECT, INSERT, UPDATE, DELETE ON TABLES TO rw_user;

  ALTER DEFAULT PRIVILEGES IN SCHEMA myschema GRANT ALL ON SEQUENCES TO rw_user;

  ALTER DEFAULT PRIVILEGES IN SCHEMA myschema GRANT EXECUTE ON FUNCTIONS TO rw_user;

Revoke privileges and drop role

===============================

List roles::

  SELECT * FROM pg_roles;

  SELECT oid, rolname FROM pg_roles

  WHERE pg_has_role('xuser', oid, 'member');

Revoke privileges::

  REVOKE ALL PRIVILEGES ON DATABASE mydb FROM xuser;

  REVOKE ALL PRIVILEGES ON SCHEMA myschem FROM xuser;

  REVOKE ALL PRIVILEGES ON ALL TABLES IN SCHEMA myschem FROM xuser;

  REVOKE ALL PRIVILEGES ON ALL SEQUENCES IN SCHEMA myschem FROM xuser;

  do $$

  DECLARE r record;

  begin

      for r in select * from pg_views where schemaname = 'myschem'

      loop

        execute 'revoke all on ' || quote_ident(r.schemaname) ||'.'|| quote_ident(r.viewname) || ' from "xuser"';

      end loop;

  end $$;

To forbid any operations (read/write) without dealing with individual privileges (any pending user

transactions will fail!)::

  REVOKE USAGE ON SCHEMA myschem FROM xuser;

To forbid connection remove privilege from ``public`` role as it inherited by all users and then from user::

  REVOKE CONNECT ON DATABASE mydb FROM public;

  REVOKE CONNECT ON DATABASE mydb FROM xuser;

Role can't be dropped until it owns objects, need to reassign owner::

  REASSIGN OWNED BY xuser TO myuser;

Some objects may left behind role (like default privileges), they can be dropped via::

  DROP OWNED BY xuser;

Remove role::

  DROP ROLE xuser;

Change password

===============

::

   ALTER USER me WITH PASSWORD 'PassWord';

Monitor connections

===================

Current user::

  SELECT current_user;

  SELECT session_user;

Active sessions and queries::

  select * from pg_stat_activity;

  select * from pg_stat_activity

  order by usename;

https://www.postgresql.org/docs/current/monitoring-stats.html

  The Statistics Collector.

Profile queries

===============

Stats on query execution time::

  SELECT * FROM pg_stat_statements;

  SELECT * FROM pg_stat_statements

  ORDER BY calls DESC;

  SELECT * FROM pg_stat_statements

  WHERE query LIKE '%some%'

  ORDER BY calls DESC;

https://www.postgresql.org/docs/current/pgstatstatements.html

  ``pg_stat_statements``.

https://www.postgresql.org/docs/current/indexes-examine.html

  Examining Index Usage.

Reveal execution details::

  EXPLAIN ANALYSE SELECT 1;

  EXPLAIN (TIMING false, COSTS false, ANALYSE) SELECT 1;

  EXPLAIN (TIMING false, COSTS false, BUFFERS false, VERBOSE false, ANALYSE) SELECT 1;

``EXPLAIN ANALYSE`` actually executes a query, if it is destructive enclose the query into a

transaction::

  BEGIN;

  EXPLAIN ANALYZE ...;

  ROLLBACK;

https://www.postgresql.org/docs/11/sql-explain.html

  Syntax of ``EXPLAIN``.

https://www.postgresql.org/docs/11/using-explain.html

  Interpreting results of ``EXPLAIN``.

List databases, schemas and tables

==================================

Default database is ``postgres``.

To list databases and database locales::

  $ psql -U pgadmin -l

or::

  => SELECT datname FROM pg_database WHERE datistemplate = false;

  => \l

To switch databases::

  => \connect NAME

Schemas::

  \dn *

  select schema_name from information_schema.schemata;

  select nspname from pg_catalog.pg_namespace;

To list all tables in the current database::

  \dt

  SELECT table_schema, table_name FROM information_schema.tables ORDER BY table_schema, table_name;

  SELECT * FROM pg_class;

or in all schemas::

  => \dt *.*

List views::

  \dv

List users::

  \du

  \du+

List schemas::

  \dn

List indexes::

  \di

  select * from pg_indexes;

  select * from pg_indexes where schemaname = '...';

  select * from pg_indexes where schemaname = '...' and tablename = '...';

  select * from pg_indexes where schemaname = '...' and indexname = '...';

  select

    t.relname as table_name,

    i.relname as index_name,

    a.attname as column_name

  from

    pg_class t,

    pg_class i,

    pg_index ix,

    pg_attribute a

  where

    t.oid = ix.indrelid

    and i.oid = ix.indexrelid

    and a.attrelid = t.oid

    and a.attnum = ANY(ix.indkey)

    and t.relkind = 'r'

    and t.relname like 'test%'

  order by

    t.relname,

    i.relname;

  select

    t.relname as table_name,

    i.relname as index_name,

    array_to_string(array_agg(a.attname), ', ') as column_names

  from

    pg_class t,

    pg_class i,

    pg_index ix,

    pg_attribute a

  where

    t.oid = ix.indrelid

    and i.oid = ix.indexrelid

    and a.attrelid = t.oid

    and a.attnum = ANY(ix.indkey)

    and t.relkind = 'r'

    and t.relname like 'test%'

  group by

    t.relname,

    i.relname

  order by

    t.relname,

    i.relname;

List index usage::

  SELECT * FROM pg_stat_all_indexes;

  SELECT * FROM pg_stat_all_tables;

  SELECT * FROM pg_stat_user_indexes;

  SELECT * FROM pg_stat_user_tables;

List constraints::

  SELECT * FROM pg_constraint;

  SELECT * FROM pg_constraint WHERE conrelid = (SELECT oid FROM pg_class WHERE relname LIKE 'tblName');

  select * from pg_constraint where conname like '%conName%';

Show constraints and columns to given table::

  select

    c.constraint_name,

    x.table_schema as schema_name, x.table_name, x.column_name,

    y.table_schema as foreign_schema_name, y.table_name as foreign_table_name, y.column_name as foreign_column_name

  from information_schema.referential_constraints c

  join information_schema.key_column_usage x

      on x.constraint_name = c.constraint_name

  join information_schema.key_column_usage y

      on y.ordinal_position = x.position_in_unique_constraint

      and y.constraint_name = c.unique_constraint_name

  where y.table_name = 'sa_pnr'

  order by c.constraint_name, x.ordinal_position

https://www.postgresql.org/docs/current/catalog-pg-constraint.html

  pg_constraint.

https://stackoverflow.com/questions/1152260/postgres-sql-to-list-table-foreign-keys

  List table foreign keys.

List functions::

  \df

List triggers::

  \dy

List misc info::

  select current_database();

  select current_schema();

  select current_user;

  select session_user;

  select current_date;

  select version();

https://www.postgresql.org/docs/current/functions-info.html

  System Information Functions.

Set default schema.

===================

::

  set search_path to NAME;

  set schema 'NAME';

Database, table, index size

===========================

Database size::

  SELECT pg_database_size('geekdb');  -- in bytes

  SELECT pg_size_pretty(pg_database_size('dbname'));

  SELECT datname, pg_database_size(datname) FROM pg_database;

List of databases sizes::

  \l+

  SELECT pg_database_size('mydb');

List tables sizes (and constraints)::

  \d+

Table total size (with indexes)::

  SELECT pg_size_pretty(pg_total_relation_size('schemaname.tablename'));

Table size with TOAST (without indexes)::

  SELECT pg_table_size('schemaname.tablename');

  SELECT pg_size_pretty(pg_relation_size('schemaname.tablename'));

  SELECT pg_relation_size(t.schemaname ||'.'|| t.tablename), t.* FROM pg_tables t ORDER BY 1 DESC;

Largest table in the PostgreSQL database::

  SELECT relname, relpages FROM pg_class ORDER BY relpages DESC;

  SELECT relname, pg_size_pretty(pg_relation_size(p.oid)) FROM pg_class ORDER BY relpages DESC;

Largest tables with TOAST::

  SELECT p.relname, t.relname, pg_size_pretty(pg_relation_size(p.oid)), p.relpages

  FROM pg_class p

  LEFT JOIN pg_class t ON t.reltoastrelid = p.oid

  ORDER BY p.relpages DESC;

Largest TOAST::

  select tbl.relname, toast.relname, toast.relpages

  from pg_class tbl, pg_class toast

  where tbl.reltoastrelid = toast.oid

  order by toast.relpages desc;

Index size::

  SELECT pg_indexes_size('my_ix');

Largest index::

  select pg_relation_size(oid), * from pg_class

  where relkind = 'i'

  order by pg_relation_size(oid) desc;