This is for backbranches to prevent them running against newer
PostgreSQL versions with which they are not compatible, for example
4.4.x with PostgreSQL 12 and later.
Check the demotion candidate's registered repmgr.conf file can be found.
If the configuration file has been deleted or moved, previously the
resulting error message would have been a confusing reference to
an incorrectly configured data directory; by explicitly checking for the
expected configuration file, we can make troubleshooting easier.
Original patch by laixiong <yin.zhb@gmail.com> (GitHub #615), modified
by Ian Barwick.
Handle corner case where standby (demotion candidate) doesn't
attach during the main check cycle, but does at the final check,
where we'll want to mark the operation as successful.
There were some corner cases where "repmgr standby switchover"
would erroneously report a successful switchover, even if the
demotion candidate had not reattached to the promotion candidate.
Also improve the logging in various places to make it clearer
what is happening on which node.
Make the code previously only used by "standby follow" generally
available - we'll want to use this from "node rejoin" as well.
While we're at it, when reporting failure due to lack of free
replication slots, report the current value of "max_replication_slots".
Usually repmgrd requires the parameters "promote_command" and
"follow_command" to be present in the configuration file. These are
not required if "failover=manual", but the configuration sanity check
following receipt of SIGHUP was not checking that.
Addresses issue reported in GitHub #614.
An attempt will be made to delete an existing replication slot on the
old upstream node (this is important during e.g. a switchover operation
or when attaching a cascaded standby to a new upstream). However if the
standby is currently attached to the follow target node anyway, the
replication slot should never be deleted.
Enable operations which create or drop replication slots to be carried
out with the minimum necessary user permissions, i.e. a user with the
REPLICATION attribute.
This can be the repmgr user, or a dedicated replication user.
In the latter case, if the dedicated replication user is only
permitted to make replication connections, the streaming
replication protocol is used to create/drop slots.
Implements part of GitHub #536.
