Useful PostgreSQL Queries and Commands

postgres_queries_and_commands.sql

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

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

-- what is running, who is running it, sorted by how long it's been running for
SELECT pid, age(query_start, clock_timestamp()), usename , state, application_name
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;

-- all tables and index sizes over 5mg, plus cumulative total count
SELECT                         
    table_name,
    pg_size_pretty(table_size) AS table_size,
    pg_size_pretty(indexes_size) AS indexes_size,
    pg_size_pretty(total_size) AS total_size,
    sum(total_size) OVER(ORDER BY total_size desc) AS total
FROM (
    SELECT
        table_name,
        pg_table_size(table_name) AS table_size,
        pg_indexes_size(table_name) AS indexes_size,
        pg_total_relation_size(table_name) AS total_size
    FROM (
        SELECT ('"' || table_schema || '"."' || table_name || '"') AS table_name
        FROM information_schema.tables
        WHERE table_schema = 'public'
        
    ) 
    AS all_tables
    where pg_table_size(table_name) > 516096
    ORDER BY total_size DESC
) AS pretty_sizes;


-- 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;

-- which indexes are not used or used rarely

SELECT s.schemaname,
       s.relname AS tablename,
       s.indexrelname AS indexname,
       s.idx_scan,
       pg_relation_size(s.indexrelid) AS index_size
FROM pg_catalog.pg_stat_user_indexes s
   JOIN pg_catalog.pg_index i ON s.indexrelid = i.indexrelid
WHERE s.idx_scan < 1000      -- has never been scanned
  AND 0 <>ALL (i.indkey)  -- no index column is an expression
  AND NOT i.indisunique   -- is not a UNIQUE index
  AND NOT EXISTS          -- does not enforce a constraint
         (SELECT 1 FROM pg_catalog.pg_constraint c
          WHERE c.conindid = s.indexrelid)
ORDER BY pg_relation_size(s.indexrelid) DESC;


-- which indexes are used most to least

SELECT s.schemaname,
       s.relname AS tablename,
       s.indexrelname AS indexname,
       s.idx_scan,
       pg_relation_size(s.indexrelid) AS index_size
FROM pg_catalog.pg_stat_user_indexes s
   JOIN pg_catalog.pg_index i ON s.indexrelid = i.indexrelid
WHERE 0 <>ALL (i.indkey)  -- no index column is an expression
  AND NOT i.indisunique   -- is not a UNIQUE index
  AND NOT EXISTS          -- does not enforce a constraint
         (SELECT 1 FROM pg_catalog.pg_constraint c
          WHERE c.conindid = s.indexrelid)
ORDER BY s.idx_scan DESC;



-- 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