This is a new bug in PG12. When you have a database with an OID above
INT32_MAX (signed), then pg_basebackup fails thus:
pg_basebackup: error: could not get write-ahead log end position from
server: ERROR: value "3000000000" is out of range for type integer
The cause appears to be commit 6b9e875f7286d8535bff7955e5aa3602e188e436.
A possible fix is attached. An alternative to using
OidInputFunctionCall() would be exporting something like oidin_subr().
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Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services