XID as a 12 byte (bytea) unique indexed Postgres column

[nkev]

In my Postgres 9.6+ tables, I want to use an xid as a unique indexed column and also sometimes as primary key or foreign key column too. Is it more performant to store it as a 20 character string or 12 byte binary? I initially thought binary would be more efficient, but this article suggests otherwise.

Does anyone have any experience using a bytea as a primary key? If so, is it more efficient to use the default bytea hex format or the older bytea escape format?

[feikesteenbergen]

If so, is it more efficient to use the default bytea hex format or the older bytea escape format?

As far as I know, the escape and hex options only apply to how to represent the bytea value (input/output), it does not concern itself with the on-disk format, so efficiency of storage is a non-issue.
See also:
https://www.postgresql.org/docs/current/static/datatype-binary.html

a 20 character string or 12 byte binary

You'll lose 8 bytes storage per row, so for storage efficiency, bytea(12) beats text(20).

=# select pg_column_size(repeat('c', '20')), pg_column_size(convert_to(repeat('c', 12), 'UTF8'));
 pg_column_size | pg_column_size
----------------+----------------
             24 |             16

Is it more performant

Perhaps you can benchmark your suggested schema yourself, as for my (simple) setup I don't see a significant enough difference.

On the whole, I prefer text if it is text, and bytea if it is binary (encrypted values for example).