list of schema with sizes (relative and absolute) in a PostgreSQL database

Question

I\'m looking for a query that returns a result of the form for any database (see example below supposing total space used by the database is 40GB)

schema | si         


        

Answer 1

Better solution:

WITH 

schemas AS (
SELECT schemaname as name, sum(pg_relation_size(quote_ident(schemaname) || '.' || quote_ident(tablename)))::bigint as size FROM pg_tables
GROUP BY schemaname
),

db AS (
SELECT pg_database_size(current_database()) AS size
)

SELECT schemas.name, 
       pg_size_pretty(schemas.size) as absolute_size,
       schemas.size::float / (SELECT size FROM db)  * 100 as relative_size
FROM schemas;

The accepted answer solves the described problem, but the suggested query is not efficient. You can do EXPLAIN to see the difference:

EXPLAIN WITH 

schemas AS (
SELECT schemaname as name, sum(pg_relation_size(quote_ident(schemaname) || '.' || quote_ident(tablename)))::bigint as size FROM pg_tables
GROUP BY schemaname
),

db AS (SELECT pg_database_size(current_database()) AS size)

SELECT schemas.name, 
       pg_size_pretty(schemas.size) as absolute_size,
       schemas.size::float / (SELECT size FROM db)  * 100 as relative_size
FROM schemas;

                                                 QUERY PLAN
------------------------------------------------------------------------------------------------------------
 CTE Scan on schemas  (cost=47100.79..47634.34 rows=16417 width=104)
   CTE schemas
     ->  Finalize HashAggregate  (cost=46854.50..47100.76 rows=16417 width=72)
           Group Key: n.nspname
           ->  Gather  (cost=43119.63..46608.25 rows=32834 width=96)
                 Workers Planned: 2
                 ->  Partial HashAggregate  (cost=42119.63..42324.85 rows=16417 width=96)
                       Group Key: n.nspname
                       ->  Hash Left Join  (cost=744.38..39763.93 rows=94228 width=128)
                             Hash Cond: (c.relnamespace = n.oid)
                             ->  Parallel Seq Scan on pg_class c  (cost=0.00..38772.14 rows=94228 width=72)
                                   Filter: (relkind = ANY ('{r,p}'::"char"[]))
                             ->  Hash  (cost=539.17..539.17 rows=16417 width=68)
                                   ->  Seq Scan on pg_namespace n  (cost=0.00..539.17 rows=16417 width=68)
   CTE db
     ->  Result  (cost=0.00..0.01 rows=1 width=8)
   InitPlan 3 (returns $3)
     ->  CTE Scan on db  (cost=0.00..0.02 rows=1 width=8)

vs

EXPLAIN SELECT schema_name, 
       pg_size_pretty(sum(table_size)::bigint),
       (sum(table_size) / pg_database_size(current_database())) * 100
FROM (
  SELECT pg_catalog.pg_namespace.nspname as schema_name,
         pg_relation_size(pg_catalog.pg_class.oid) as table_size
  FROM   pg_catalog.pg_class
     JOIN pg_catalog.pg_namespace ON relnamespace = pg_catalog.pg_namespace.oid
) t
GROUP BY schema_name
ORDER BY schema_name; 

                                       QUERY PLAN
-------------------------------------------------------------------------------------------
 GroupAggregate  (cost=283636.24..334759.75 rows=1202906 width=128)
   Group Key: pg_namespace.nspname
   ->  Sort  (cost=283636.24..286643.51 rows=1202906 width=72)
         Sort Key: pg_namespace.nspname
         ->  Hash Join  (cost=744.38..51446.15 rows=1202906 width=72)
               Hash Cond: (pg_class.relnamespace = pg_namespace.oid)
               ->  Seq Scan on pg_class  (cost=0.00..44536.06 rows=1202906 width=8)
               ->  Hash  (cost=539.17..539.17 rows=16417 width=68)
                     ->  Seq Scan on pg_namespace  (cost=0.00..539.17 rows=16417 width=68)