PL/pgsql functions to compress and decompress PostgreSQL tables using cstore_fdw

compress.sql

-- Compress a table using cstore_fdw
CREATE OR REPLACE FUNCTION compress_table(uncomp_table regclass) RETURNS VOID AS
$BODY$
DECLARE 
	comp_table_name varchar := table_name || '_comp';
BEGIN
	IF EXISTS (SELECT 1 FROM pg_class WHERE oid = table_name AND relkind = 'f') THEN
		RETURN;
	END IF;
	EXECUTE format('CREATE FOREIGN TABLE %I (%s) SERVER cstore_server OPTIONS(compression ''pglz'');', comp_table_name, get_columns_ddl(table_name::varchar));
	EXECUTE format('INSERT INTO %I SELECT * FROM %I', comp_table_name, table_name);
	EXECUTE format('DROP TABLE %I', table_name);
	EXECUTE format('ALTER TABLE %I RENAME TO %s', comp_table_name, table_name::text);
END;
$BODY$
LANGUAGE plpgsql;

-- Turn a a foriegn table into a regular table
CREATE OR REPLACE FUNCTION decompress_table(table_name regclass) RETURNS VOID AS
$BODY$
DECLARE
	uncomp_table_name varchar := table_name || '_uncomp';
BEGIN
	IF EXISTS (SELECT 1 FROM pg_class WHERE oid = table_name AND relkind = 'r') THEN
		RETURN;
	END IF;
	EXECUTE format('CREATE TABLE %I AS SELECT * FROM %I', uncomp_table_name, table_name);
	EXECUTE format('DROP FOREIGN TABLE %I', table_name);
	EXECUTE format('ALTER TABLE %I RENAME TO %I', uncomp_table_name, table_name);
END;
$BODY$
LANGUAGE plpgsql;

-- Adapted from http://stackoverflow.com/questions/2593803/how-to-generate-the-create-table-sql-statement-for-an-existing-table-in-postgr
CREATE OR REPLACE FUNCTION get_columns_ddl(p_table_name varchar)
  RETURNS text AS
$BODY$
DECLARE
    v_table_ddl   text;
    column_record record;
BEGIN
    FOR column_record IN 
        SELECT 
            b.nspname as schema_name,
            b.relname as table_name,
            a.attname as column_name,
            pg_catalog.format_type(a.atttypid, a.atttypmod) as column_type,
            CASE WHEN 
                (SELECT substring(pg_catalog.pg_get_expr(d.adbin, d.adrelid) for 128)
                 FROM pg_catalog.pg_attrdef d
                 WHERE d.adrelid = a.attrelid AND d.adnum = a.attnum AND a.atthasdef) IS NOT NULL THEN
                'DEFAULT '|| (SELECT substring(pg_catalog.pg_get_expr(d.adbin, d.adrelid) for 128)
                              FROM pg_catalog.pg_attrdef d
                              WHERE d.adrelid = a.attrelid AND d.adnum = a.attnum AND a.atthasdef)
            ELSE
                ''
            END as column_default_value,
            CASE WHEN a.attnotnull = true THEN 
                'NOT NULL'
            ELSE
                'NULL'
            END as column_not_null,
            a.attnum as attnum,
            e.max_attnum as max_attnum
        FROM 
            pg_catalog.pg_attribute a
            INNER JOIN 
             (SELECT c.oid,
                n.nspname,
                c.relname
              FROM pg_catalog.pg_class c
                   LEFT JOIN pg_catalog.pg_namespace n ON n.oid = c.relnamespace
              WHERE c.relname ~ ('^('||p_table_name||')$')
                AND pg_catalog.pg_table_is_visible(c.oid)
              ORDER BY 2, 3) b
            ON a.attrelid = b.oid
            INNER JOIN 
             (SELECT 
                  a.attrelid,
                  max(a.attnum) as max_attnum
              FROM pg_catalog.pg_attribute a
              WHERE a.attnum > 0 
                AND NOT a.attisdropped
              GROUP BY a.attrelid) e
            ON a.attrelid=e.attrelid
        WHERE a.attnum > 0 
          AND NOT a.attisdropped
        ORDER BY a.attnum
    LOOP
        IF column_record.attnum = 1 THEN
            v_table_ddl:='';
        ELSE
            v_table_ddl:=v_table_ddl||',';
        END IF;

        IF column_record.attnum <= column_record.max_attnum THEN
            v_table_ddl:=v_table_ddl||chr(10)||
                     '    '||column_record.column_name||' '||column_record.column_type||' '||column_record.column_default_value||' '||column_record.column_not_null;
        END IF;
    END LOOP;

    RETURN v_table_ddl;
END;
$BODY$
  LANGUAGE 'plpgsql';