=$ create table size_comparison (json_val json, jsonb_val jsonb);
 
=$ with s as materialized ( select 1::int4 as v )
insert into size_comparison select to_json(v), to_jsonb(v) from s;
 
=$ SELECT
    *,
    pg_column_size( json_val ) AS json_size,
    pg_column_size( jsonb_val ) AS jsonb_size
FROM
    size_comparison;
 json_val | jsonb_val | json_size | jsonb_size 
----------+-----------+-----------+------------
 1        | 1         |         2 |         17
(1 row)

=$ create table copy_text_pglz  (v text  compression pglz );
=$ create table copy_json_pglz  (v json  compression pglz );
=$ create table copy_jsonb_pglz (v jsonb compression pglz );
=$ create table copy_text_lz4   (v text  compression lz4 );
=$ create table copy_json_lz4   (v json  compression lz4 );
=$ create table copy_jsonb_lz4  (v jsonb compression lz4 );

=$ SELECT
    test_name,
    length( text_pglz ) AS text_length,
    pg_column_compression( text_pglz ) AS pglz_comp,
    pg_column_size( text_pglz ) AS pglz_size,
    format(
        '%7s %%',
        round( ( 100.0 * pg_column_size( text_pglz ) ) / length( text_pglz ), 2 )
    ) AS pglz_comp,
    pg_column_compression( text_lz4 ) AS lz4_comp,
    pg_column_size( text_lz4 ) AS pglz_size,
    format(
        '%6s %%',
        round( ( 100.0 * pg_column_size( text_lz4 ) ) / length( text_lz4 ), 2 )
    ) AS lz4_comp
FROM
    compression_test
ORDER BY
    text_length;
            test_name            | text_length | pglz_comp | pglz_size | pglz_comp | lz4_comp | pglz_size | lz4_comp 
---------------------------------+-------------+-----------+-----------+-----------+----------+-----------+----------
 random:5                        |           5 | [null]    |         6 |  120.00 % | [null]   |         6 | 120.00 %
 random:505                      |         505 | [null]    |       509 |  100.79 % | [null]   |       509 | 100.79 %
 random:1005                     |        1005 | [null]    |      1005 |  100.00 % | [null]   |      1009 | 100.40 %
 random:1505                     |        1505 | [null]    |      1505 |  100.00 % | [null]   |      1509 | 100.27 %
 legalnotice.html                |        2065 | [null]    |      2071 |  100.29 % | lz4      |      1630 |  78.93 %
 release-prior.html              |        2655 | pglz      |      1214 |   45.73 % | lz4      |      1302 |  49.04 %
 sql-dropuser.html               |        3188 | pglz      |      1462 |   45.86 % | lz4      |      1624 |  50.94 %
 pltcl-procnames.html            |        3670 | pglz      |      1811 |   49.35 % | lz4      |      1970 |  53.68 %
 spi-spi-getvalue.html           |        4216 | pglz      |      1771 |   42.01 % | lz4      |      2020 |  47.91 %
 catalog-pg-db-role-setting.html |        4715 | pglz      |      1811 |   38.41 % | lz4      |      2088 |  44.28 %
 supported-platforms.html        |        5235 | pglz      |      2584 |   49.36 % | lz4      |      2839 |  54.23 %
 datatype-money.html             |        5749 | pglz      |      2814 |   48.95 % | lz4      |      3066 |  53.33 %
 sql-dropsubscription.html       |        6289 | pglz      |      2838 |   45.13 % | lz4      |      3056 |  48.59 %
 pgfreespacemap.html             |        6779 | pglz      |      3134 |   46.23 % | lz4      |      3248 |  47.91 %
(14 rows)