Re: Enum on-disk format

Tom Lane wrote:
> Scott Bailey <artacus(at)comcast(dot)net> writes:
>> I'm trying to better understand the internals of Postgres, and I'm
>> looking at the enum type. The docs say that an enum value is stored on
>> disk as 4 bytes. But enum_send() returns a bytea representing the actual
>> text of the value and not the index of that value. So what step am I
>> missing here?
>
> The wire format isn't necessarily the on-disk format. In this case
> we concluded that the internal OID value wouldn't be of any use to
> clients.
>
>> Also, is there a way to see the raw data for the tuple on a page?
>
> Try contrib/pageinspect, and read
> http://developer.postgresql.org/pgdocs/postgres/storage-page-layout.html
>
> regards, tom lane
>

Thanks Tom that did the trick. The only I/O functions I'm aware of are
send, recv, in and out. What controls converting from/to wire and
on-disk formats? And why is wire format little endian and disk big endian?

And for posterity, here's how to get to the raw tuple data.

SELECT substring(page, lp_off + t_hoff + 1, lp_len - t_hoff) AS tuple_data,
sub.*
FROM (
SELECT (heap_page_items(page)).*, page
FROM (
SELECT get_raw_page('test', 0) page
) s
) sub