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;

-- show long running queries
SELECT pid, now() - pg_stat_activity.query_start AS duration, query, state
FROM pg_stat_activity
WHERE (now() - pg_stat_activity.query_start) > interval '20 seconds';

-- 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 schemaname as table_schema,
       relname as table_name,
       pg_size_pretty(pg_total_relation_size(relid)) as total_size,
       pg_size_pretty(pg_relation_size(relid)) as data_size,
       pg_size_pretty(pg_total_relation_size(relid) - pg_relation_size(relid)) 
        as external_size
from pg_catalog.pg_statio_user_tables
order by pg_total_relation_size(relid) desc,
         pg_relation_size(relid) 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

-- drop a database
$ dropdb existingdb

-- create a database
$ createdb newdb

-- drop all connections
psql -U username -d thedb -c "SELECT pg_terminate_backend(pg_stat_activity.pid) FROM pg_stat_activity WHERE datname = current_database() AND pid <> pg_backend_pid();"