Previously the check verifying that a node has connected to its upstream
merely assumed the presence of a record in pg_stat_replication indicates
a successful replication connection. However the record may contain a
state other than "streaming", typically "startup" (which will occur when
a node has diverged from its upstream and will therefore never
transition to "streaming"), which needs to be taken into account when
considering the state of the replication connection to avoid false
positives.
We have a --downstream option to check for attached nodes, but it
would be useful to have a corresponding --upstream option too.
A following patch will adapt the behaviour of this option when executed
on the primary node.
This is mainly useful for the --data-directory-config option, which
requires permission to read pg_settings to verify that the data
directory configured in "repmgr.conf" matches the data directory
actually in use.
If pg_settings read permission is not available, repmgr will fall
back to a simple check that the data directory configured in
"repmgr.conf" is a valid PostgreSQL directory. This is not entirely
foolproof, as it's possible PostgreSQL could be using a different
data directory.
In a few places, replication connections are generated from the
parameters used by existing connections. This has resulted in a
number of similar blocks of code which do more-or-less the same
thing almost but not quite identically. In two cases, the code
omitted to set "dbname=replication", which can cause problems
in some contexts.
These code blocks have now been consolidated into standardized
functions.
This also resolves the issue addressed by GitHub #619.
Within a PostgreSQL data directory, all files should have the same
ownership as the data directory itself. PostgreSQL itself expects
this, and ownership of files by another user is likely to cause
problems.
In PostgreSQL 11 or earlier, if "recovery.conf" cannot be moved
by PostgreSQL (because e.g. it is owned by root), it will not be
possible to promote the standby to primary.
In PostgreSQL 12 and later, if "postgresql.auto.conf" on the demotion
candidate (current primary) has incorrect ownership (e.g. owned by
root), repmgr will very likely not be able to modify this file and
write the replication configuration required for the node to rejoin
the cluster as a standby.
Checks added to catch both cases before a switchover is executed.
From PostgreSQL 10, a member of the default roles "pg_monitor" and/or
"pg_read_all_settings" can read pg_settings without requiring superuser
privileges.
Previously, a hint was being emitted about making the repmgr user a
member of one of those groups, but no check for membership was being
made, meaning the check could only be run by a superuser.
This enables us to better determine whether a node is definitively
attached, definitively not attached, or if it was not possible to
determine the attached state.
If the WAL receiver has been temporarily disabled, we don't want to
wait for it to start up as it may not be able to at that point; we do
however need to reset "wal_retrieve_retry_interval".
This is intended to ensure that all nodes have a constant LSN while
making the failover decision.
This feature is experimental and needs to be explicitly enabled with the
configuration file option "standby_disconnect_on_failover".
Note enabling this option will result in a delay in the failover decision
until the WAL receiver is disconnected on all nodes.
We only want to check the status of physical replication slots
to determine whether a streaming replication standby has become
detached and there is therefore a risk of uncontrolled WAL buildup
on the local node.
It's not feasible to second-guess the state of logical replication
slots.
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.
Eventually we'll want to have this contain the optional replication
info contained in the t_node_info struct, which should then contain a
pointer to a ReplInfo struct.
If the rejoin target is not in recovery, but not registered as primary
(we detect this by attempting to connect to the registered primary)
we abort and suggest fixing the repmgr metadata first.
