PostgreSQL command line cheatsheet

postgres-cheatsheet.md

PSQL

Magic words:

psql -U postgres

If run with -E flag, it will describe the underlaying queries of the \ commands (cool for learning!).

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

• \q: Quit/Exit
• \c __database__: Connect to a database
• \d __table__: Show table definition including triggers
• \dt *.*: List tables from all schemas (if *.* is omitted will only show SEARCH_PATH ones)
• \l: List databases
• \dn: List schemas
• \df: List functions
• \dv: List views
• \df+ __function : Show function SQL code.
• \x: Pretty-format query results instead of the not-so-useful ASCII tables

You can have unix-like reverse search in psql:

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

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

2. 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

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

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

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;

Casting:

• CAST (column AS type) or column::type
• '__table_name__'::regclass::oid: Get oid having a table name

Backup

Create a backup for desired database and table

pg_dump -Uusername dbname -t desired_table --schema-only

Tools

• pg-top: top for PG. sudo apt-get install ptop + pg_top