If replay is paused, we can't be really sure that more WAL will be received
between the check and the promote operation, which would risk the promote
operation not taking place during the switchover (it would happen
as soon as WAL replay is resumed and pending WAL is replayed).
Therefore we simply quit with an informative slew of messages and
leave the user to sort it out.
GitHub #540.
In some circumstances, e.g. while performing a switchover, it is essential
that repmgrd does not take any kind of failover action, as this will put
the cluster into an incorrect state.
Previously it was necessary to stop repmgrd on all nodes (or at least
those nodes which repmgrd would consider as promotion candidates), however
this is a cumbersome and potentially risk-prone operation, particularly if the
replication cluster contains more than a couple of servers.
To prevent this issue from occurring, this patch introduces the ability
to "pause" repmgrd on all nodes wth a single command ("repmgr daemon pause")
which notifies repmgrd not to take any failover action until the node
is "unpaused" ("repmgr daemon unpause").
"repmgr daemon status" provides an overview of each node and whether repmgrd
is running, and if so whether it is paused.
"repmgr standby switchover" has been modified to automatically pause repmgrd
while carrying out the switchover.
See documentation for further details.
Previously repmgr would first check that a replication can be made
from the demotion candidate to the promotion candidate, however it's
preferable to sanity-check the number of available walsenders first,
to provide a more useful error message.
Previously repmgr was relying on whatever command was configured to
start PostgreSQL to determine whether the node being rejoined had
started correctly. However it's preferable to actively poll the upstream
to confirm it has restarted and actually attached as a standby before
confirming success of the "node rejoin" action.
This can be overridden with the -W/--no-wait option.
(Note that for consistency with other PostgreSQL utilities, the
short form of the --wait option is now "-w"; this is currently
only used in "repmgr standby follow".)
Also update "repmgr node rejoin" documentation with a list of supported
options, and add some useful index entries for "pg_rewind".
Implements GitHub #415.
pg_rewind is not part of the core distribution for those, but we
provided support in repmgr 3.3 so should extend it to repmgr 4.
Note that there is no check in place whether the pg_rewind binary
exists, so it's up to the user to ensure it's present.
Addresses GitHub #413.
During a switchover operation, once the demoted primary has been restarted
as a standby, repmgr attempts to reconnect to verify its status and drop
any redundant replication slots. However it's possible the standby may still
be in the startup phase, so poll for "standby_reconnect_timeout" seconds
before giving up.
Addresses GitHub #408.
When executing a command on a remote server, repmgr expects the remote binary
to be in the same location as the local binary. It's reasonable to assume
repmgr will be deployed in a unified environment; if not, the onus is on the
user to ensure repmgr can find the remote binary, e.g. by creating appropriate
symlinks.
Addresses query in GitHub #406.
