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repmgrd: catch cases where more than one node has initiated voting

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The node(s) with higher ID will "yield", leaving the decision making
up to the node with the lower ID.

This happens very rarely, usually when the random delay is close
enough on two or mode nodes that vote initiation is simultaneous.
This commit is contained in:
Ian Barwick
2017-07-18 17:04:24 +09:00
parent 248525ccba
commit 6e270b2faf
4 changed files with 93 additions and 29 deletions
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67
repmgrd-physical.c
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@@ -680,7 +680,7 @@ do_primary_failover(void)
/* attempt to initiate voting process */
ElectionResult election_result = do_election();
/* XXX add pre-event notification here */
/* TODO add pre-event notification here */
failover_state = FAILOVER_STATE_UNKNOWN;
log_debug("election result: %s", _print_election_result(election_result));
@@ -702,13 +702,7 @@ do_primary_failover(void)
log_info(_("I am the candidate but did not get all votes; will now determine the best candidate"));
/* reset node list */
get_active_sibling_node_records(local_conn,
local_node_info.node_id,
upstream_node_info.node_id,
&standby_nodes);
/* standby_nodes is in the state created by do_election() */
best_candidate = poll_best_candidate(&standby_nodes);
/*
@@ -1220,12 +1214,14 @@ poll_best_candidate(NodeInfoList *standby_nodes)
NodeInfoListCell *cell;
t_node_info *best_candidate = &local_node_info;
// XXX ensure standby_nodes is set correctly
/*
* we need to definitively decide the best candidate, as in some corner
* cases we could end up with two candidate nodes, so they should each
* come to the same conclusion
* come to the same conclusion.
*
* XXX check there are no cases where the standby node's LSN is
* not set
*/
for (cell = standby_nodes->head; cell; cell = cell->next)
{
@@ -1248,9 +1244,17 @@ poll_best_candidate(NodeInfoList *standby_nodes)
log_debug("node %i has lower node_id, now best candidate", cell->node_info->node_id);
best_candidate = cell->node_info;
}
if (cell->node_info->conn != NULL && PQstatus(upstream_conn) == CONNECTION_OK)
{
PQfinish(cell->node_info->conn);
cell->node_info->conn = NULL;
}
}
log_info(_("best candidate is %i"), best_candidate->node_id);
log_info(_("best candidate is node %s (node ID: %i)"),
best_candidate->node_name,
best_candidate->node_id);
return best_candidate;
}
@@ -1653,23 +1657,51 @@ do_election(void)
for (cell = standby_nodes.head; cell; cell = cell->next)
{
VoteRequestResult vote_result;
log_debug("checking node %i...", cell->node_info->node_id);
/* ignore unreachable nodes */
if (cell->node_info->node_status != NODE_STATUS_UP)
continue;
votes_for_me += request_vote(cell->node_info->conn,
&local_node_info,
cell->node_info,
electoral_term);
vote_result = request_vote(cell->node_info->conn,
&local_node_info,
cell->node_info,
electoral_term);
switch (vote_result)
{
case VR_VOTE_REFUSED:
if (cell->node_info->node_id < local_node_info.node_id)
{
log_debug(_("node %i refused vote, their ID is lower, yielding"),
cell->node_info->node_id);
PQfinish(cell->node_info->conn);
cell->node_info->conn = NULL;
clear_node_info_list(&standby_nodes);
reset_node_voting_status();
log_debug("other node is candidate, returning NOT CANDIDATE");
return ELECTION_NOT_CANDIDATE;
}
log_debug(_("no vote recevied from %i, our ID is lower, not yielding"),
cell->node_info->node_id);
break;
case VR_POSITIVE_VOTE:
votes_for_me += 1;
break;
case VR_NEGATIVE_VOTE:
break;
}
if (cell->node_info->last_wal_receive_lsn > local_node_info.last_wal_receive_lsn)
{
/* register if another node is ahead of us */
other_node_is_ahead = true;
}
PQfinish(cell->node_info->conn);
cell->node_info->conn = NULL;
}
/* vote for myself, but only if I believe no-one else is ahead */
@@ -1722,4 +1754,3 @@ close_connections_physical()
}
}