The Postgres system columns are documented in Chapter 5. Data Definition > 5.4. System Columns.
That page mentions that
oid values “are 32-bit quantities”. And that page says the same about transaction identifiers. So I will assume that means
cmax are all 32-bit integers.
But that leaves the
ctid system column.
The physical location of the row version within its table. Note that although the ctid can be used to locate the row version very quickly, a row's ctid will change if it is updated or moved by VACUUM FULL. Therefore ctid is useless as a long-term row identifier. The OID, or even better a user-defined serial number, should be used to identify logical rows.
➡ What is the data type of the
Specifically I am interested in version Postgres 10.3, but if it has changed over past versions, that would be good to know.