doc: add docs for age(xid) and mxid_age(xid)
Reported-by: David Rowley
Discussion: https://postgr.es/m/CAKJS1f_OQpz7rpe-KJmskVxbU06buiXbfonxG3JLB+nGCJ5E=g@mail.gmail.com
Backpatch-through: 16
Branch
------
REL_16_STABLE
Details
-------
https://git.postgresql.org/pg/commitdiff/7471230cc697fec3dc3c4094aa81469c02fa53c6
Modified Files
--------------
doc/src/sgml/func.sgml | 28 ++++++++++++++++++++++++++++
1 file changed, 28 insertions(+)