ref: revamp the weight==0 behaviour to avoid touching weights

Author: TPXP

lib/PgSQL_HostGroups_Manager.cpp

@@ -1974,17 +1974,6 @@ PgSQL_SrvC *PgSQL_HGC::get_random_MySrvC(char * gtid_uuid, uint64_t gtid_trxid,
 				}
 			}
 		}
-		if (sum==0 && num_candidates > 0) {
-			proxy_info("No available server in hostgroup %u with weight > 0, but %u candidates found. This is probably due to max_connections reached for all servers. Using candidates with weight 0\n", hid, num_candidates);
-			// Iterate on all candidates and increase their weight
-			for (j=0; j<num_candidates; j++) {
-				mysrvc = mysrvcCandidates[j];
-				// increase the weight of the server
-				mysrvc->weight++;
-				proxy_debug("Increasing weight of server %s:%d to %ld\n", mysrvc->address, mysrvc->port, mysrvc->weight);
-				sum += 1;
-			}
-		}
 		if (sum==0) {
 			// per issue #531 , we try a desperate attempt to bring back online any shunned server
 			// we do this lowering the maximum wait time to 10%
@@ -2044,15 +2033,21 @@ PgSQL_SrvC *PgSQL_HGC::get_random_MySrvC(char * gtid_uuid, uint64_t gtid_trxid,
 				}
 			}
 		}
+		bool use_index_instead_of_weight = false;
 		if (sum==0) {
-			proxy_debug(PROXY_DEBUG_MYSQL_CONNPOOL, 7, "Returning PgSQL_SrvC NULL because no backend ONLINE or with weight\n");
-			if (l>32) {
-				free(mysrvcCandidates);
+			if (num_candidates==0) {
+				proxy_debug(PROXY_DEBUG_MYSQL_CONNPOOL, 7, "Returning PgSQL_SrvC NULL because no backend ONLINE or with weight\n");
+				if (l>32) {
+					free(mysrvcCandidates);
+				}
+	#ifdef TEST_AURORA
+				array_mysrvc_cands += num_candidates;
+	#endif // TEST_AURORA
+				return NULL; // if we reach here, we couldn't find any target
 			}
-#ifdef TEST_AURORA
-			array_mysrvc_cands += num_candidates;
-#endif // TEST_AURORA
-			return NULL; // if we reach here, we couldn't find any target
+			// All servers have weight 0, but we have some candidates - pick a random one (assume they all have weight 1)
+			proxy_info("No available server in hostgroup %u with weight > 0, but %u candidates found. This is probably due to max_connections reached for all servers. Using candidates with weight 0\n", hid, num_candidates);
+			use_index_instead_of_weight = true;
 		}
 
 /*
@@ -2077,7 +2072,7 @@ PgSQL_SrvC *PgSQL_HGC::get_random_MySrvC(char * gtid_uuid, uint64_t gtid_trxid,
 		}
 */
 
-		unsigned int New_sum=sum;
+		unsigned int New_sum=use_index_instead_of_weight ? num_candidates : sum;
 
 		if (New_sum==0) {
 			proxy_debug(PROXY_DEBUG_MYSQL_CONNPOOL, 7, "Returning PgSQL_SrvC NULL because no backend ONLINE or with weight\n");
@@ -2125,7 +2120,7 @@ PgSQL_SrvC *PgSQL_HGC::get_random_MySrvC(char * gtid_uuid, uint64_t gtid_trxid,
 					New_sum = 0;
 					for (j=0; j<num_candidates; j++) {
 						mysrvc = mysrvcCandidates[j];
-						New_sum+=mysrvc->weight;
+						New_sum+=use_index_instead_of_weight ? 1 : mysrvc->weight;
 					}
 				}
 			}
@@ -2143,7 +2138,7 @@ PgSQL_SrvC *PgSQL_HGC::get_random_MySrvC(char * gtid_uuid, uint64_t gtid_trxid,
 
 		for (j=0; j<num_candidates; j++) {
 			mysrvc = mysrvcCandidates[j];
-			New_sum+=mysrvc->weight;
+			New_sum+=use_index_instead_of_weight ? 1 : mysrvc->weight;
 			if (k<=New_sum) {
 				proxy_debug(PROXY_DEBUG_MYSQL_CONNPOOL, 7, "Returning PgSQL_SrvC %p, server %s:%d\n", mysrvc, mysrvc->address, mysrvc->port);
 				if (l>32) {