// by user
SELECT (table_schema || '.' || table_name) AS table, string_agg(privilege_type, ', ') AS privileges
FROM information_schema.role_table_grants
WHERE grantee='user_name'
GROUP BY (table_schema || '.' || table_name);

// by table
SELECT grantee, string_agg(privilege_type, ', ') AS privileges
FROM information_schema.role_table_grants
WHERE table_name='table_name'
GROUP BY grantee;

SELECT pg_database.datname, pg_database_size(pg_database.datname), pg_size_pretty(pg_database_size(pg_database.datname)) 
FROM pg_database 
ORDER BY pg_database_size DESC;

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;

or

SELECT nspname || '.' || relname AS "relation", T.spcname, pg_size_pretty(pg_relation_size(C.oid)) AS "size", 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) 
LEFT JOIN pg_tablespace T ON (T.oid = C.reltablespace) 
WHERE nspname NOT IN ('pg_catalog', 'information_schema') 
ORDER BY pg_total_relation_size(C.oid) DESC

1.CREATE ROLE xxx LOGIN PASSWORD 'yyy';

2.GRANT CONNECT ON DATABASE mydb TO xxx;

3.GRANT USAGE ON SCHEMA my_schema | public TO xxx;

4.GRANT SELECT ON ALL TABLES IN SCHEMA my_schema | public TO xxx;

SELECT bl.pid AS src_pid, a.usename AS src_user, ka.query AS src_stmt, now() - ka.query_start AS src_duration, kl.pid AS blk_pid, 
       ka.usename AS blk_user, a.query AS blk_stmt, now() - a.query_start  AS blk_duration  
FROM  pg_locks bl 
JOIN pg_stat_activity a ON a.pid = bl.pid 
JOIN pg_locks kl ON kl.transactionid = bl.transactionid AND kl.pid != bl.pid 
JOIN pg_stat_activity ka ON ka.pid = kl.pid  
WHERE NOT bl.granted;