slack-19.0: backport v22 VTOrc optimizations, part 2 (#613)

* `vtorc`: remove duplicate instance read from backend (vitessio#17834)

Signed-off-by: Tim Vaillancourt <tim@timvaillancourt.com>

* `vtorc`: add index for `inst.ReadInstanceClusterAttributes` table scan

Signed-off-by: Tim Vaillancourt <tim@timvaillancourt.com>

---------

Signed-off-by: Tim Vaillancourt <tim@timvaillancourt.com>

Author: timvaillancourt

go/vt/vtorc/db/generate_base.go

@@ -118,6 +118,9 @@ CREATE INDEX last_checked_idx_database_instance ON database_instance(last_checke
 CREATE INDEX last_seen_idx_database_instance ON database_instance(last_seen)
 	`,
 	`
+CREATE INDEX hostname_port_database_instance ON database_instance(hostname, port)
+	`,
+	`
 DROP TABLE IF EXISTS audit
 `,
 	`

go/vt/vtorc/inst/instance_dao.go

@@ -204,7 +204,7 @@ func ReadTopologyInstanceBufferable(tabletAlias string, latency *stopwatch.Named
 		goto Cleanup
 	}
 
-	fs, err = fullStatus(tabletAlias)
+	fs, err = fullStatus(tablet)
 	if err != nil {
 		goto Cleanup
 	}

go/vt/vtorc/inst/tablet_dao.go

@@ -44,11 +44,7 @@ func InitializeTMC() tmclient.TabletManagerClient {
 }
 
 // fullStatus gets the full status of the MySQL running in vttablet.
-func fullStatus(tabletAlias string) (*replicationdatapb.FullStatus, error) {
-	tablet, err := ReadTablet(tabletAlias)
-	if err != nil {
-		return nil, err
-	}
+func fullStatus(tablet *topodatapb.Tablet) (*replicationdatapb.FullStatus, error) {
 	tmcCtx, tmcCancel := context.WithTimeout(context.Background(), topo.RemoteOperationTimeout)
 	defer tmcCancel()
 	return tmc.FullStatus(tmcCtx, tablet)