nufaylr/postgres-cheatsheet.md

## postgres-cheatsheet.md

      
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              postgres-cheatsheet.md
            
          
    PSQL

Magic words:
psql -U postgres
Some interesting flags (to see all, use -h):

-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 *.*

\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

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__.

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


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


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

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

Tools


pg-top: top for PG. sudo apt-get install ptop + pg_top
Unix-like reverse search in psql:

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