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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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43
dbutils.c
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@@ -2622,7 +2622,8 @@ get_voting_status(PGconn *conn)
return voting_status;
}
int
VoteRequestResult
request_vote(PGconn *conn, t_node_info *this_node, t_node_info *other_node, int electoral_term)
{
PQExpBufferData query;
@@ -2648,8 +2649,36 @@ request_vote(PGconn *conn, t_node_info *this_node, t_node_info *other_node, int
/* check for NULL */
if (PQgetisnull(res, 0, 0))
{
log_debug("XXX NULL returned by repmgr.request_vote()");
return 0;
PQclear(res);
log_debug("NULL returned by repmgr.request_vote()");
/*
* get the node's last receive location anyway
* TODO: have repmgr.request_vote() return two values
*/
initPQExpBuffer(&query);
appendPQExpBuffer(
&query,
#if (PG_VERSION_NUM >= 100000)
"SELECT pg_catalog.pg_last_wal_receive_lsn()");
#else
"SELECT pg_catalog.pg_last_xlog_receive_location()");
#endif
res = PQexec(conn, query.data);
termPQExpBuffer(&query);
if (PQresultStatus(res) == PGRES_TUPLES_OK)
{
other_node->last_wal_receive_lsn = parse_lsn(PQgetvalue(res, 0, 0));
}
PQclear(res);
return VR_VOTE_REFUSED;
}
other_node->last_wal_receive_lsn = parse_lsn(PQgetvalue(res, 0, 0));
@@ -2664,7 +2693,7 @@ request_vote(PGconn *conn, t_node_info *this_node, t_node_info *other_node, int
if (lsn_diff > 0)
{
log_debug("local node is ahead");
return 1;
return VR_POSITIVE_VOTE;
}
@@ -2672,7 +2701,7 @@ request_vote(PGconn *conn, t_node_info *this_node, t_node_info *other_node, int
if (lsn_diff < 0)
{
log_debug("other node is ahead");
return 0;
return VR_NEGATIVE_VOTE;
}
/* tiebreak */
@@ -2681,12 +2710,12 @@ request_vote(PGconn *conn, t_node_info *this_node, t_node_info *other_node, int
if (this_node->priority < other_node->priority)
{
log_debug("other node has higher priority");
return 0;
return VR_NEGATIVE_VOTE;
}
/* still tiebreak - we're the candidate, so we win */
log_debug("win by default");
return 1;
return VR_POSITIVE_VOTE;
}