find large tables and convert them to compressed tables in Greenplum

gp_zip_tables.sql

Select 
    sum(size) AS total_size_on_disk, 
    sum(size) / (select count(*) from individual) AS per_individual
FROM (
SELECT 
    pg_relation_size(C.oid) AS "size"
  FROM pg_class C
  LEFT JOIN pg_namespace N ON (N.oid = C.relnamespace)
  WHERE 1=1 -- relname in (...)
  ORDER BY pg_relation_size(C.oid) DESC
) table_sizes;


create table xxx_zlib with (appendonly=true, compresstype=zlib, compresslevel=6) as (select * from xxx) distributed by (pkcol1, ...);
drop table xxx;
alter table xxx_zlib rename to xxx;