sentinel: fix check for same reported vs spec sync standbys

When electing a new master we are swapping the new master uid with the old
master uid in the syncstandbys slice. This could end with an unordered slice in
the spec that will make the sentinel fail the check that the reported standbys
are the same of the spec one blocking any future syncstandby update.

Since the reported order is not a problem just check that the syncstandbys are
the same regardless of their order.

We'll keep the sorting to avoid unneeded updates to synchronous_standby_names by
the keeper.

cmd/sentinel/cmd/sentinel.go

@@ -304,8 +304,6 @@ func (s *Sentinel) updateKeepersStatus(cd *cluster.ClusterData, keepersInfo clus
 			db.Status.TimelinesHistory = dbs.TimelinesHistory
 			db.Status.PGParameters = cluster.PGParameters(dbs.PGParameters)
 
-			// Sort synchronousStandbys so we can compare the slice regardless of its order
-			sort.Sort(sort.StringSlice(dbs.SynchronousStandbys))
 			db.Status.SynchronousStandbys = dbs.SynchronousStandbys
 
 			db.Status.OlderWalFile = dbs.OlderWalFile
@@ -1074,6 +1072,11 @@ func (s *Sentinel) updateCluster(cd *cluster.ClusterData, pis cluster.ProxiesInf
 				if len(newMasterDB.Spec.SynchronousStandbys) == 0 {
 					newMasterDB.Spec.ExternalSynchronousStandbys = []string{fakeStandbyName}
 				}
+
+				// Just sort to always have them in the same order and avoid
+				// unneeded updates to synchronous_standby_names by the keeper.
+				sort.Sort(sort.StringSlice(newMasterDB.Spec.SynchronousStandbys))
+				sort.Sort(sort.StringSlice(newMasterDB.Spec.ExternalSynchronousStandbys))
 			} else {
 				newMasterDB.Spec.SynchronousReplication = false
 				newMasterDB.Spec.SynchronousStandbys = nil
@@ -1189,7 +1192,7 @@ func (s *Sentinel) updateCluster(cd *cluster.ClusterData, pis cluster.ProxiesInf
 					// this way, when we have to choose a new master we are sure
 					// that there're no intermediate changes between the
 					// reported standbys and the required ones.
-					if !util.CompareStringSlice(masterDB.Status.SynchronousStandbys, masterDB.Spec.SynchronousStandbys) {
+					if !util.CompareStringSliceNoOrder(masterDB.Status.SynchronousStandbys, masterDB.Spec.SynchronousStandbys) {
 						log.Infof("won't update masterDB required synchronous standby since the latest master reported synchronous standbys are different from the db spec ones", "reported", curMasterDB.Status.SynchronousStandbys, "spec", curMasterDB.Spec.SynchronousStandbys)
 					} else {
 						addFakeStandby := false
@@ -1338,10 +1341,10 @@ func (s *Sentinel) updateCluster(cd *cluster.ClusterData, pis cluster.ProxiesInf
 							masterDB.Spec.ExternalSynchronousStandbys = append(masterDB.Spec.ExternalSynchronousStandbys, fakeStandbyName)
 						}
 
-						// Sort synchronousStandbys so we can compare the slice regardless of its order
+						// Just sort to always have them in the same order and avoid
+						// unneeded updates to synchronous_standby_names by the keeper.
 						sort.Sort(sort.StringSlice(masterDB.Spec.SynchronousStandbys))
 						sort.Sort(sort.StringSlice(masterDB.Spec.ExternalSynchronousStandbys))
-
 					}
 				} else {
 					masterDB.Spec.SynchronousReplication = false