Try next host after a "cannot connect now" failure.

tglsfdc · tglsfdc · commit c1d589571c49 · 2021-01-11T14:12:31.000-05:00
If a server returns ERRCODE_CANNOT_CONNECT_NOW, try the next host, if multiple host names have been provided. This allows dealing gracefully with standby servers that might not be in hot standby mode yet. In the wake of the preceding commit, it might be plausible to retry many more error cases than we do now, but I (tgl) am hesitant to move too aggressively on that --- it's not clear it'd be desirable for cases such as bad-password, for example. But this case seems safe enough. Hubert Zhang, reviewed by Takayuki Tsunakawa Discussion: https://postgr.es/m/BN6PR05MB3492948E4FD76C156E747E8BC9160@BN6PR05MB3492.namprd05.prod.outlook.com
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
@@ -3315,6 +3315,20 @@ PQconnectPoll(PGconn *conn)
 					/* OK, we read the message; mark data consumed */
 					conn->inStart = conn->inCursor;
 
+					/*
+					 * If error is "cannot connect now", try the next host if
+					 * any (but we don't want to consider additional addresses
+					 * for this host, nor is there much point in changing SSL
+					 * or GSS mode).  This is helpful when dealing with
+					 * standby servers that might not be in hot-standby state.
+					 */
+					if (strcmp(conn->last_sqlstate,
+							   ERRCODE_CANNOT_CONNECT_NOW) == 0)
+					{
+						conn->try_next_host = true;
+						goto keep_going;
+					}
+
 					/* Check to see if we should mention pgpassfile */
 					pgpassfileWarning(conn);
 
