To write out the last query as a CSV file:
\g (format=csv) foo.csv
To show the last query in extended mode (without changing the setting):
\gx
To run a query that generates SQL, then run that SQL:
-- Index every column in the table:
SELECT format('CREATE INDEX ON table (%I)', i)
FROM pg_attribute
WHERE attrelid = 'products'::regclass
AND attnum > 0
ORDER BY attnum
\gexec
Find the worst tables for full table scans:
SELECT relname,
100 * idx_scan / (seq_scan + idx_scan) percent_of_times_index_used,
n_live_tup rows_in_table
FROM pg_stat_user_tables
WHERE seq_scan + idx_scan > 0
ORDER BY n_live_tup DESC;
Find the worst tables for missed cache rate:
SELECT relname, heap_blks_read, heap_blks_hit,
round(heap_blks_hit::numeric/(heap_blks_hit + heap_blks_read), 3)
FROM pg_statio_user_tables
WHERE heap_blks_read > 0
ORDER BY 4
LIMIT 25;
Find the worst tables for missed cache rate on indexes:
SELECT relname, idx_blks_read, idx_blks_hit,
round(idx_blks_hit::numeric/(idx_blks_hit + idx_blks_read), 3)
FROM pg_statio_user_tables
WHERE idx_blks_read > 0
ORDER BY 4
LIMIT 25;
Find the overall cache hit rate (should be 99%+):
SELECT sum(heap_blks_read) as heap_read,
sum(heap_blks_hit) as heap_hit,
sum(heap_blks_hit) / (sum(heap_blks_hit) + sum(heap_blks_read)) as ratio
FROM pg_statio_user_tables;
Find the biggest tables from the current database:
SELECT nspname || '.' || relname AS "relation",
pg_size_pretty(pg_relation_size(C.oid)) AS "size"
FROM pg_class C
LEFT JOIN pg_namespace N ON (N.oid = C.relnamespace)
WHERE nspname NOT IN ('pg_catalog', 'information_schema')
ORDER BY pg_relation_size(C.oid) DESC
Find tables with lots of dead tuples:
SELECT relname, n_live_tup, n_dead_tup,
last_vacuum, last_autovacuum, last_analyze, last_autoanalyze,
vacuum_count, autovacuum_count, analyze_count, autoanalyze_count
FROM pg_stat_all_tables
ORDER BY n_dead_tup DESC LIMIT 20;
regexp_matches(string, pattern)
Unforunately this returns a setof text[] with all the matches found. If you just want one, you can do this:
SELECT (regexp_matches(col, 'foo(bar)'))[1] FROM baz
Show the current transaction isolation level:
SELECT current_setting('transaction_isolation');
To start a new Rails project:
sudo su - postgres -c psql <<-EOQ CREATE USER foo WITH PASSWORD 'bar'; ALTER USER foo CREATEDB; EOQ rake db:create db:migrate
To write to a file:
\o filename
Like a <> b but accounting for nulls:
a IS DISTINCT FROM b
Find the current queries:
SELECT datname,procpid,current_query FROM pg_stat_activity;
or in 9.3:
SELECT datname, pid, state, waiting, query, query_start FROM pg_stat_activity ORDER BY query_start;
or in 9.6:
SELECT datname, pid, state, wait_event, query, query_start FROM pg_stat_activity ORDER BY query_start;
Show the current locks:
SELECT locktype,
database,
relation::regclass,
page,
tuple,
virtualxid,
transactionid,
classid,
objid,
objsubid,
virtualtransaction,
pid,
mode,
granted
FROM pg_locks
ORDER BY pid
;
Show the blocked/blocking pids and queries:
SELECT blocked_locks.pid AS blocked_pid,
blocked_activity.usename AS blocked_user,
blocking_locks.pid AS blocking_pid,
blocking_activity.usename AS blocking_user,
blocked_activity.query AS blocked_statement,
blocking_activity.query AS current_statement_in_blocking_process
FROM pg_catalog.pg_locks blocked_locks
JOIN pg_catalog.pg_stat_activity blocked_activity ON blocked_activity.pid = blocked_locks.pid
JOIN pg_catalog.pg_locks blocking_locks
ON blocking_locks.locktype = blocked_locks.locktype
AND blocking_locks.DATABASE IS NOT DISTINCT FROM blocked_locks.DATABASE
AND blocking_locks.relation IS NOT DISTINCT FROM blocked_locks.relation
AND blocking_locks.page IS NOT DISTINCT FROM blocked_locks.page
AND blocking_locks.tuple IS NOT DISTINCT FROM blocked_locks.tuple
AND blocking_locks.virtualxid IS NOT DISTINCT FROM blocked_locks.virtualxid
AND blocking_locks.transactionid IS NOT DISTINCT FROM blocked_locks.transactionid
AND blocking_locks.classid IS NOT DISTINCT FROM blocked_locks.classid
AND blocking_locks.objid IS NOT DISTINCT FROM blocked_locks.objid
AND blocking_locks.objsubid IS NOT DISTINCT FROM blocked_locks.objsubid
AND blocking_locks.pid != blocked_locks.pid
JOIN pg_catalog.pg_stat_activity blocking_activity ON blocking_activity.pid = blocking_locks.pid
WHERE NOT blocked_locks.GRANTED
Kill a query:
SELECT pg_cancel_backend(12345);
To get the number of years between two dates:
SELECT extract(year from age(now(), '2014-01-01'));
NOT:
SELECT extract(year from now() - '2014-01-01');
Set or overwrite an hstore key/value:
UPDATE hstore_test SET data = data || '"key4"=>"some value"'::hstore UPDATE hstore_test SET data = data || hstore(ARRAY['key4', 'some value'])
master (10.0.1.1)
In postgresql.conf:
wal_level = hot_standby max_wal_senders = 3 checkpoint_segments = 8 wal_keep_segments = 8 archive_mode = on archive_command = 'rsync -aq -e "ssh -o StrictHostKeyChecking=no" %p 10.0.1.2:/var/lib/postgresql/9.3/archive/%f' archive_timeout = 3600
slave (10.0.1.2)
In postgresql.conf:
hot_standby = on
Has a recovery.conf file at e.g. /var/lib/postgresql/9.3/main/recovery.conf:
standby_mode = 'on' primary_conninfo = 'host=10.0.1.1 port=5432 user=postgres' trigger_file = '/var/lib/postgresql/9.3/main/trigger' # Shell command to execute an archived segment of WAL file series. # Required for archive recovery if streaming replication falls behind too far. restore_command = 'cp /var/lib/postgresql/9.3/archive/%f %p' archive_cleanup_command = '/usr/lib/postgresql/9.3/bin/pg_archivecleanup /var/lib/postgresql/9.3/archive/ %r'
failover
Just create a trigger file on the slave, e.g.:
touch /var/lib/postgresql/9.3/main/trigger
Get a CSV file:
COPY ( ... ) TO '/tmp/foo.csv' WITH CSV HEADER
See default permissions for a user:
\\ddp
Grant default permissions to a user (so they get the same permissions on future-created tables and views):
ALTER DEFAULT PRIVILEGES IN SCHEMA public GRANT SELECT ON TABLES TO the_user;
You can use \l to list privileges on each database.
You'll see lines like db_user=CTc/postgres and =c/postgres. The name before the equals sign is the user with those privileges. If there is no name, it means the special PUBLIC role, which is everyone. The name after the slash is who granted the privileges.
To see the permissions on a given table: \z table_name. Or \dp for all tables/views/sequences.
The letters mean (https://www.postgresql.org/docs/9.5/static/sql-grant.html):
Also for other objects (functions and schemas), you'll see:
Note that neither command shows default privileges, unlike
SELECT grantee, privilege_type FROM information_schema.role_table_grants WHERE table_name = 'foo'
This is an interesting summary also: https://www.postgresql.org/message-id/20120703014228.11c82a45%40james.intern
On a Mac using Peter Eisentraut's Postgres formulae, use pex to install extensions. For example:
pex -g /opt/homebrew/Cellar/postgresql@14/14.9/bin/pg_config install postgis
And you can solve lots of compilation errors with the tricks from https://gist.github.com/skissane/0487c097872a7f6d0dcc9bcd120c2ccd
Use PGCLUSTER to select which postgres you want. E.g. PGCLUSTER=12/main pg_dump .... Personally I like to hack my pg_config too so I can easily build & install extensions against old versions for Postgres: https://stackoverflow.com/a/43403193/122087