Merge pull request #222 from Shopify/backport-topo-throttler-watch-fix-to-v18

Backport: Throttler: keep watching topo even on error (vitessio#18223)

Author: brendar

go/vt/srvtopo/server.go

@@ -42,6 +42,9 @@ type Server interface {
 	// GetSrvKeyspace returns the SrvKeyspace for a cell/keyspace.
 	GetSrvKeyspace(ctx context.Context, cell, keyspace string) (*topodatapb.SrvKeyspace, error)
 
+	// WatchSrvKeyspace starts watching the SrvKeyspace object for changes. The callback function is called upon change.
+	// The callback function should return `true` if it wishes to continue watching for further changes, or `false` if it
+	// is done and wants to stop watching.
 	WatchSrvKeyspace(ctx context.Context, cell, keyspace string, callback func(*topodatapb.SrvKeyspace, error) bool)
 
 	// WatchSrvVSchema starts watching the SrvVSchema object for

go/vt/vttablet/tabletserver/throttle/throttler.go

@@ -319,7 +319,7 @@ func (throttler *Throttler) WatchSrvKeyspaceCallback(srvks *topodatapb.SrvKeyspa
 		if !topo.IsErrType(err, topo.Interrupted) && !errors.Is(err, context.Canceled) {
 			log.Errorf("WatchSrvKeyspaceCallback error: %v", err)
 		}
-		return false
+		return true
 	}
 	throttlerConfig := throttler.normalizeThrottlerConfig(srvks.ThrottlerConfig)