Cheat sheet Postgres

PSQL

Magic words:

psql -U postgres

Some interesting flags (to see all, use -h or --help depending on your psql version):

• -E: will describe the underlaying queries of the \ commands (cool for learning!)

• -l: psql will list all databases and then exit (useful if the user you connect with doesn't has a default database, like at AWS RDS)

Most \d commands support additional param of __schema__.name__ and accept wildcards like *.*

• \?: Show help (list of available commands with an explanation)

• \q: Quit/Exit

• \c __database__: Connect to a database

• \d __table__: Show table definition (columns, etc.) including triggers

• \d+ __table__: More detailed table definition including description and physical disk size

• \l: List databases

• \dy: List events

• \df: List functions

• \di: List indexes

• \dn: List schemas

• \dt *.*: List tables from all schemas (if *.* is omitted will only show SEARCH_PATH ones)

• \dT+: List all data types

• \dv: List views

• \dx: List all extensions installed

• \df+ __function__ : Show function SQL code.

• \x: Pretty-format query results instead of the not-so-useful ASCII tables

• \copy (SELECT * FROM __table_name__) TO 'file_path_and_name.csv' WITH CSV: Export a table as CSV

• \des+: List all foreign servers

• \dE[S+]: List all foreign tables

• \! __bash_command__: execute __bash_command__ (e.g. \! ls)

User Related:

• \du: List users

• \du __username__: List a username if present.

• create role __test1__: Create a role with an existing username.

• create role __test2__ noinherit login password __passsword__;: Create a role with username and password.

• set role __test__;: Change role for current session to __test__.

• grant __test2__ to __test1__;: Allow __test1__ to set its role as __test2__.

• \deu+: List all user mapping on server

Configuration

• Service management commands:

sudo service postgresql stop
sudo service postgresql start
sudo service postgresql restart

• Changing verbosity & querying Postgres log: 1) First edit the config file, set a decent verbosity, save and restart postgres:

sudo vim /etc/postgresql/9.3/main/postgresql.conf

# Uncomment/Change inside:
log_min_messages = debug5
log_min_error_statement = debug5
log_min_duration_statement = -1

sudo service postgresql restart

1. Now you will get tons of details of every statement, error, and even background tasks like VACUUMs

tail -f /var/log/postgresql/postgresql-9.3-main.log

1. How to add user who executed a PG statement to log (editing postgresql.conf):

log_line_prefix = '%t %u %d %a '

• Check Extensions enabled in postgres: SELECT * FROM pg_extension;

• Show available extensions: SELECT * FROM pg_available_extension_versions;

Create command

There are many CREATE choices, like CREATE DATABASE __database_name__, CREATE TABLE __table_name__ ... Parameters differ but can be checked at the official documentation.

Handy queries

• SELECT * FROM pg_proc WHERE proname='__procedurename__': List procedure/function

• SELECT * FROM pg_views WHERE viewname='__viewname__';: List view (including the definition)

• SELECT pg_size_pretty(pg_total_relation_size('__table_name__'));: Show DB table space in use

• SELECT pg_size_pretty(pg_database_size('__database_name__'));: Show DB space in use

• show statement_timeout;: Show current user's statement timeout

• SELECT * FROM pg_indexes WHERE tablename='__table_name__' AND schemaname='__schema_name__';: Show table indexes

• Get all indexes from all tables of a schema:

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,
    pg_namespace n
WHERE
   t.oid = ix.indrelid
   AND i.oid = ix.indexrelid
   AND a.attrelid = t.oid
   AND a.attnum = ANY(ix.indkey)
   AND t.relnamespace = n.oid
    AND n.nspname = 'kartones'
ORDER BY
   t.relname,
   i.relname

• Execution data:

  • Queries being executed at a certain DB:

SELECT datname, application_name, pid, backend_start, query_start, state_change, state, query 
  FROM pg_stat_activity 
  WHERE datname='__database_name__';

• Get all queries from all dbs waiting for data (might be hung):

SELECT * FROM pg_stat_activity WHERE waiting='t'

• Currently running queries with process pid:

SELECT 
  pg_stat_get_backend_pid(s.backendid) AS procpid, 
  pg_stat_get_backend_activity(s.backendid) AS current_query
FROM (SELECT pg_stat_get_backend_idset() AS backendid) AS s;

• Get Connections by Database: SELECT datname, numbackends FROM pg_stat_database;

Casting:

• CAST (column AS type) or column::type

• '__table_name__'::regclass::oid: Get oid having a table name

Query analysis:

• EXPLAIN __query__: see the query plan for the given query

• EXPLAIN ANALYZE __query__: see and execute the query plan for the given query

• ANALYZE [__table__]: collect statistics

Generating random data (source):

• INSERT INTO some_table (a_float_value) SELECT random() * 100000 FROM generate_series(1, 1000000) i;

Get sizes of tables, indexes and full DBs:

select current_database() as database,
  pg_size_pretty(total_database_size) as total_database_size,
  schema_name,
  table_name,
  pg_size_pretty(total_table_size) as total_table_size,
  pg_size_pretty(table_size) as table_size,
  pg_size_pretty(index_size) as index_size
  from ( select table_name,
          table_schema as schema_name,
          pg_database_size(current_database()) as total_database_size,
          pg_total_relation_size(table_name) as total_table_size,
          pg_relation_size(table_name) as table_size,
          pg_indexes_size(table_name) as index_size
          from information_schema.tables
          where table_schema=current_schema() and table_name like 'table_%'
          order by total_table_size
      ) as sizes;

• COPY command: Import/export from CSV to tables:

COPY table_name [ ( column_name [, ...] ) ]
FROM { 'filename' | STDIN }
[ [ WITH ] ( option [, ...] ) ]

COPY { table_name [ ( column_name [, ...] ) ] | ( query ) }
TO { 'filename' | STDOUT }
[ [ WITH ] ( option [, ...] ) ]

• List all grants for a specific user

SELECT table_catalog, table_schema, table_name, privilege_type
FROM   information_schema.table_privileges
WHERE  grantee = 'user_to_check' ORDER BY table_name;

• List all assigned user roles

SELECT
    r.rolname,
    r.rolsuper,
    r.rolinherit,
    r.rolcreaterole,
    r.rolcreatedb,
    r.rolcanlogin,
    r.rolconnlimit,
    r.rolvaliduntil,
    ARRAY(SELECT b.rolname
      FROM pg_catalog.pg_auth_members m
      JOIN pg_catalog.pg_roles b ON (m.roleid = b.oid)
      WHERE m.member = r.oid) as memberof, 
    r.rolreplication
FROM pg_catalog.pg_roles r
ORDER BY 1;

• Check permissions in a table:

SELECT grantee, privilege_type
FROM information_schema.role_table_grants
WHERE table_name='name-of-the-table';

• Kill all Connections:

SELECT pg_terminate_backend(pg_stat_activity.pid)
FROM pg_stat_activity
WHERE datname = current_database() AND pid <> pg_backend_pid();

Keyboard shortcuts

• CTRL + R: reverse-i-search

Tools

• ptop and pg_top: top for PG. Available on the APT repository from apt.postgresql.org.

• pg_activity: Command line tool for PostgreSQL server activity monitoring.

• Unix-like reverse search in psql:

$ echo "bind "^R" em-inc-search-prev" > $HOME/.editrc
$ source $HOME/.editrc

• Show IP of the DB Instance: SELECT inet_server_addr();

• File to save PostgreSQL credentials and permissions (format: hostname:port:database:username:password): chmod 600 ~/.pgpass

• Collect statistics of a database (useful to improve speed after a Database Upgrade as previous query plans are deleted): ANALYZE VERBOSE;

• To obtain the CREATE TABLE query of a table, any visual GUI like pgAdmin allows to easily, but else you can use pg_dump, e.g.: pg_dump -t '<schema>.<table>' --schema-only <database> (source)

Resources & Documentation

• Postgres Weekly newsletter: The best way IMHO to keep up to date with PG news

• 100 psql Tips: Name says all, lots of useful tips!

• PostgreSQL Exercises: An awesome resource to learn to learn SQL, teaching you with simple examples in a great visual way. Highly recommended.

• A Performance Cheat Sheet for PostgreSQL: Great explanations of EXPLAIN, EXPLAIN ANALYZE, VACUUM, configuration parameters and more. Quite interesting if you need to tune-up a postgres setup.

• annotated.conf: Annotations of all 269 postgresql.conf settings for PostgreSQL 10.

• psql -c "\l+" -H -q postgres > out.html: Generate a html report of your databases (source: Daniel Westermann)