How to check disk-usage in specific schema and sum for all schema? pg9+ - postgresql

Question

The documentation about disk-usage have no "fast and simple" clue or information... So is faster to check here.
When I try SELECT pg_relation_filepath(oid), relpages FROM pg_class WHERE relname = 'big' it is working fine... but "big" is not a "public.big", it is a "othername.big", if there are public also, will be ambiguous.
When I try SELECT pg_relation_filepath(oid), relpages FROM pg_class WHERE relname = 'othername.big' not works.
I need to compare disk-usage of tables and to check (or sum) all schema disk-usage.

Answer 1

To get Schema size :
SELECT schemaname, pg_size_pretty(t.taille::bigint) AS taille_table, pg_size_pretty(t.taille_totale::bigint) AS taille_totale_table
FROM (SELECT schemaname,
sum(pg_relation_size(schemaname || '.' || tablename)) AS taille,
sum(pg_total_relation_size(schemaname || '.' || tablename)) AS taille_totale
FROM pg_tables
WHERE relname_exists(tablename,schemaname) -- see note
GROUP BY schemaname) as t ORDER BY taille_totale DESC;
And for Tables by Schema, you can do this :
SELECT schemaname, tablename, tablespace, pg_size_pretty(taille) AS taille_table, pg_size_pretty(taille_totale) AS taille_totale_table
FROM (SELECT *,
pg_relation_size(schemaname || '.' || tablename) AS taille,
pg_total_relation_size(schemaname || '.' || tablename) AS taille_totale
FROM pg_tables) AS tables
WHERE relname_exists(tablename,schemaname) -- see note
ORDER BY taille_totale DESC;
NOTE: to avoid "ERROR: relation 'x.y' does not exist", needs to guard the string before use it, so
use to_regclass(rel_name) in Postgres 9.4+... See https://stackoverflow.com/a/24089729
or use a generic (see "SwissKnife libraries") function for any pg version, as below
CREATE or replace FUNCTION relname_exists(text,text default NULL) RETURNS boolean AS $$
SELECT EXISTS (
SELECT 1
FROM pg_catalog.pg_class c JOIN pg_catalog.pg_namespace n ON n.oid = c.relnamespace,
regexp_split_to_array($1,'\.') t(x) -- not work with quoted names
WHERE CASE
WHEN COALESCE(x[2],'')>'' THEN n.nspname = x[1] AND c.relname = x[2]
WHEN $2 IS NULL THEN n.nspname = 'public' AND c.relname = $1
ELSE n.nspname = $2 AND c.relname = $1
END
)
$$ language SQL IMMUTABLE;

Answer 2

Using pg_class and simplifying layout
Same results as Hervé's queries (that used pg_tables)... Was adapted from https://wiki.postgresql.org/wiki/Disk_Usage
-- -- -- -- --
-- DISK-USAGE
CREATE VIEW pgvw_class_usage AS
SELECT *, pg_size_pretty(table_bytes) AS table_size
FROM (
SELECT nspname , relname, total_bytes
, total_bytes-index_bytes-COALESCE(toast_bytes,0) AS table_bytes
FROM (
SELECT nspname , relname
, 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
) t
ORDER BY 1,2
; -- eg. SELECT * FROM pgvw_class_usage WHERE relname='foo' AND nspname='bar';
CREATE VIEW pgvw_nsclass_usage AS
SELECT *, pg_size_pretty(table_bytes) as table_size
FROM (
SELECT nspname, count(*) as n_tables,
sum(total_bytes) as total_bytes, sum(table_bytes) as table_bytes
FROM pgvw_class_usage
GROUP BY nspname
) t
; -- eg. SELECT * FROM pgvw_nsclass_usage WHERE nspname='bar';
EXAMPLE:
nspname | n_tables | total_bytes | table_bytes | table_size
--------------------+----------+-------------+-------------+------------
bench1 | 8 | 4718592 | 3825664 | 3736 kB
dataset | 4 | 8552448 | 6225920 | 6080 kB
information_schema | 7 | 352256 | 294912 | 288 kB
pg_catalog | 54 | 9003008 | 4734976 | 4624 kB
(4 rows)