During work on 64-bit XID patch [1] we found handy to have initdb options to set initial xid/mxid/mxoff values to arbitrary non default values. It helps test different scenarios: related to wraparound, pg_upgrade from 32-bit XID to 64-bit XID, etc.
We realize, this patch can be singled out as an independent patch from the whole patchset in [1] and be useful irrespective of 64-bit XID in cases of testing of wraparound and so on.
In particular, we employed this patch to test recent changes in logical replication of subxacts [2] and found no problems in it near the point of publisher wraparound.
Please share your opinions and reviews are always welcome.
