Find out biggest databases and tables in Postgres

debugging.sql

-- find biggest database
SELECT *, pg_size_pretty(total_bytes) AS total
    , pg_size_pretty(index_bytes) AS INDEX
    , pg_size_pretty(toast_bytes) AS toast
    , pg_size_pretty(table_bytes) AS TABLE
  FROM (
  SELECT *, total_bytes-index_bytes-COALESCE(toast_bytes,0) AS table_bytes FROM (
      SELECT c.oid,nspname AS table_schema, relname AS TABLE_NAME
              , c.reltuples AS row_estimate
              , pg_total_relation_size(c.oid) AS total_bytes
              , pg_indexes_size(c.oid) AS index_bytes
              , pg_total_relation_size(reltoastrelid) AS toast_bytes
          FROM pg_class c
          LEFT JOIN pg_namespace n ON n.oid = c.relnamespace
          WHERE relkind = 'r'
  ) a
) a;

-- get size of a specific database
SELECT pg_size_pretty(pg_database_size('mydatabase'));

-- find biggest tables
SELECT d.datname AS Name,  pg_catalog.pg_get_userbyid(d.datdba) AS Owner,
    CASE WHEN pg_catalog.has_database_privilege(d.datname, 'CONNECT')
        THEN pg_catalog.pg_size_pretty(pg_catalog.pg_database_size(d.datname))
        ELSE 'No Access'
    END AS SIZE
FROM pg_catalog.pg_database d
    ORDER BY
    CASE WHEN pg_catalog.has_database_privilege(d.datname, 'CONNECT')
        THEN pg_catalog.pg_database_size(d.datname)
        ELSE NULL
    END DESC -- nulls first
    LIMIT 20;

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
  LIMIT 20;


SELECT nspname || '.' || relname AS "relation",
    pg_size_pretty(pg_total_relation_size(C.oid)) AS "total_size"
  FROM pg_class C
  LEFT JOIN pg_namespace N ON (N.oid = C.relnamespace)
  WHERE nspname NOT IN ('pg_catalog', 'information_schema')
    AND C.relkind <> 'i'
    AND nspname !~ '^pg_toast'
  ORDER BY pg_total_relation_size(C.oid) DESC
  LIMIT 20;

-- check size of replication slots
SELECT * FROM pg_replication_slots;

SELECT 
  slot_name, 
  database, 
  active,
  pg_xlog_location_diff(pg_current_xlog_insert_location(), restart_lsn) AS retained_bytes 
FROM pg_replication_slots  ;

SELECT pg_drop_replication_slot('name_of_slot_to_remove');