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repmgrd: optionally disconnect WAL receivers during failover

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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.
This commit is contained in:
Ian Barwick
2019-03-01 18:20:44 +09:00
committed by Ian Barwick
parent dd04ebb809
commit 1615353f48
16 changed files with 404 additions and 17 deletions
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90
repmgrd-physical.c
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@@ -87,7 +87,7 @@ static void update_monitoring_history(void);
static void handle_sighup(PGconn **conn, t_server_type server_type);
static const char * format_failover_state(FailoverState failover_state);
static const char *format_failover_state(FailoverState failover_state);
void
@@ -1979,6 +1979,85 @@ do_primary_failover(void)
*/
check_connection(&local_node_info, &local_conn);
/*
* if requested, disable WAL receiver and wait until WAL receivers on all
* sibling nodes are disconnected
*/
if (config_file_options.standby_disconnect_on_failover == true)
{
NodeInfoListCell *cell = NULL;
static NodeInfoList check_sibling_nodes = T_NODE_INFO_LIST_INITIALIZER;
int i;
// XXX make configurable
int sibling_nodes_disconnect_timeout = 30;
bool sibling_node_wal_receiver_connected = false;
disable_wal_receiver(local_conn);
/*
* Loop through all reachable sibling nodes to determine whether
* they have disabled their WAL receivers.
*
* TODO: do_election() also calls get_active_sibling_node_records(),
* consolidate calls if feasible
*
*/
get_active_sibling_node_records(local_conn,
local_node_info.node_id,
local_node_info.upstream_node_id,
&check_sibling_nodes);
for (i = 0; i < sibling_nodes_disconnect_timeout; i++)
{
for (cell = check_sibling_nodes.head; cell; cell = cell->next)
{
pid_t sibling_wal_receiver_pid;
if (cell->node_info->conn == NULL)
cell->node_info->conn = establish_db_connection(cell->node_info->conninfo, false);
sibling_wal_receiver_pid = (pid_t)get_wal_receiver_pid(cell->node_info->conn);
if (sibling_wal_receiver_pid == UNKNOWN_PID)
{
log_warning(_("unable to query WAL receiver PID on node %i"),
cell->node_info->node_id);
}
else if (sibling_wal_receiver_pid > 0)
{
log_info(_("WAL receiver PID on node %i is %i"),
cell->node_info->node_id,
sibling_wal_receiver_pid);
sibling_node_wal_receiver_connected = true;
}
}
if (sibling_node_wal_receiver_connected == false)
{
log_notice(_("WAL receiver disconnected on all sibling nodes"));
break;
}
log_debug("sleeping %i of max %i seconds (\"sibling_nodes_disconnect_timeout\")",
i + 1, sibling_nodes_disconnect_timeout)
sleep(1);
}
if (sibling_node_wal_receiver_connected == true)
{
// XXX what do we do here? abort or continue? make configurable?
log_warning(_("WAL receiver still connected on at least one sibling node"));
}
else
{
log_info(_("WAL receiver disconnected on all %i sibling nodes"),
check_sibling_nodes.node_count);
}
clear_node_info_list(&check_sibling_nodes);
}
/* attempt to initiate voting process */
election_result = do_election();
@@ -1987,6 +2066,13 @@ do_primary_failover(void)
log_debug("election result: %s", _print_election_result(election_result));
/* Reenable WAL receiver, if disabled and node is not the promotion candidate */
if (config_file_options.standby_disconnect_on_failover == true && election_result != ELECTION_WON)
{
// XXX check return value
enable_wal_receiver(local_conn);
}
if (election_result == ELECTION_CANCELLED)
{
log_notice(_("election cancelled"));
@@ -3685,3 +3771,5 @@ handle_sighup(PGconn **conn, t_server_type server_type)
got_SIGHUP = false;
}