Change timeline field of IDENTIFY_SYSTEM to int8
It was int4, but in the other replication commands, timelines are
returned as int8.
Reviewed-by: Nathan Bossart <nathandbossart@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/
7e4fdbdc-699c-4cd0-115d-
fb78a957fc22@enterprisedb.com