Useful PostgreSQL Queries and Commands

postgres_queries_and_commands.sql

-- show running queries (pre 9.2)
SELECT procpid, age(clock_timestamp(), query_start), usename, current_query 
FROM pg_stat_activity 
WHERE current_query != '<IDLE>' AND current_query NOT ILIKE '%pg_stat_activity%' 
ORDER BY query_start desc;

-- show running queries (9.2)
SELECT pid, age(clock_timestamp(), query_start), usename, query 
FROM pg_stat_activity 
WHERE query != '<IDLE>' AND query NOT ILIKE '%pg_stat_activity%' 
ORDER BY query_start desc;

-- kill running query
SELECT pg_cancel_backend(procpid);

-- kill idle query
SELECT pg_terminate_backend(procpid);

-- vacuum command
VACUUM (VERBOSE, ANALYZE);

-- all database users
select * from pg_stat_activity where current_query not like '<%';

-- all databases and their sizes
select * from pg_user;

-- all tables and their size, with/without indexes
select datname, pg_size_pretty(pg_database_size(datname))
from pg_database
order by pg_database_size(datname) desc;

-- cache hit rates (should not be less than 0.99)
SELECT sum(heap_blks_read) as heap_read, sum(heap_blks_hit)  as heap_hit, (sum(heap_blks_hit) - sum(heap_blks_read)) / sum(heap_blks_hit) as ratio
FROM pg_statio_user_tables;

-- table index usage rates (should not be less than 0.99)
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 
ORDER BY n_live_tup DESC;

-- how many indexes are in cache
SELECT sum(idx_blks_read) as idx_read, sum(idx_blks_hit)  as idx_hit, (sum(idx_blks_hit) - sum(idx_blks_read)) / sum(idx_blks_hit) as ratio
FROM pg_statio_user_indexes;

-- Dump database on remote host to file
$ pg_dump -U username -h hostname databasename > dump.sql

-- Import dump into existing database
$ psql -d newdb -f dump.sql

• How to show all blocked queries

SELECT pid, 
       usename, 
       pg_blocking_pids(pid) as blocked_by, 
       query as blocked_query
FROM pg_stat_activity
WHERE cardinality(pg_blocking_pids(pid)) > 0

• How to terminate a blocked query

SELECT pg_cancel_backend(a.pid), pg_terminate_backend(a.pid)

• How to terminate all blocked queries

SELECT pg_cancel_backend(a.pid), pg_terminate_backend(a.pid)
FROM (
    SELECT pid, 
       usename, 
       pg_blocking_pids(pid) as blocked_by, 
       query as blocked_query
    FROM pg_stat_activity
    WHERE cardinality(pg_blocking_pids(pid)) > 0) a

• How to grant schema permissions to a user that belongs to a group transformer

grant usage on schema <schema> to group transformer;
grant select on all tables in schema <schema> to group transformer;
alter default privileges for user <user> in schema <schema> grant select on tables to group transformer;