This involves mainly abstracting the functions which copy
and create records from repmgr.c to dbutils.c, as they need
to be shared between repmgr and repmgrd.
Per issue noted here:
https://groups.google.com/forum/#!topic/repmgr/v5nu1Xwf6X0
Sometimes it's desirable to re-sync a "stale" data directory
on a standby, rather than start from scratch with pg_basebackup().
This re-adds the rsync code from the 2.x series, with some
modifications.
TODO: tablespace support.
Attempt to attach to the next available upstream node, otherwise
quit monitoring. We'll need to add further options for failover
scenarios, including attempting to attach to another node,
shutting down the server completely etc.
To handle cascaded replication we're going to have to keep track
of each node's upstream node. Also enumerate the node type
("primary", "standby" or "witness") and mark if active.
Use the reported `server_version_num` integer for version number
detection and comparison. This makes it easier to set an arbitrary
minimum supported version (rather than "9.0 or later") as well
as future-proofing for 10.x and later.
wait_connection_availability() did take at least 2 seconds per call in
the old incarnation. Now we may finish a call without any sleep at all
when the result is already ready at the time called
Because PQcancel() establish a new synchronous connection to the
database, if it fails it means something wrong has happenned with
master. So instead of just ignore the failure, CancelQuery() now
reports a failure condition so we can detect master's death in
that situation.
This is very important specially when only postmaster crashes but
other children/backend connections are still there. Because the
children connection won't fail and CancelQuery() failure is our
only indication of something wrong happenning.
Currently we just ignore the PQcancel() failure which leads us to
a situation in which we just loop forever
trying to cancel the async query.
Reported by: Martin Euser <martin.euser@nl.abnamro.com>
Problem analyzed and bug spotted by: Andres Freund <andres@2ndquadrant.com>
Patch by: Jaime Casanova <jaime@2ndquadrant.com>
to find the master.
This was a micro optimization based on the fact that all commands that
needed to detect the master were executed from the standby but now that
we have CLUSTER level commands that is not true anymore
