add a hack to enable routing to RDONLY tablets for REPLICA queries

Signed-off-by: Michael Demmer <mdemmer@slack-corp.com>

go/vt/vtgate/gateway/discoverygateway.go

@@ -38,18 +38,20 @@ import (
  "vitess.io/vitess/go/vt/vttablet/queryservice"
 
  querypb "vitess.io/vitess/go/vt/proto/query"
+ "vitess.io/vitess/go/vt/proto/topodata"
  topodatapb "vitess.io/vitess/go/vt/proto/topodata"
  vtrpcpb "vitess.io/vitess/go/vt/proto/vtrpc"
  "vitess.io/vitess/go/vt/topo/topoproto"
 )
 
 var (
- cellsToWatch = flag.String("cells_to_watch", "", "comma-separated list of cells for watching tablets")
- tabletFilters flagutil.StringListValue
- refreshInterval = flag.Duration("tablet_refresh_interval", 1*time.Minute, "tablet refresh interval")
- refreshKnownTablets = flag.Bool("tablet_refresh_known_tablets", true, "tablet refresh reloads the tablet address/port map from topo in case it changes")
- topoReadConcurrency = flag.Int("topo_read_concurrency", 32, "concurrent topo reads")
- allowedTabletTypes []topodatapb.TabletType
+ cellsToWatch = flag.String("cells_to_watch", "", "comma-separated list of cells for watching tablets")
+ tabletFilters flagutil.StringListValue
+ refreshInterval = flag.Duration("tablet_refresh_interval", 1*time.Minute, "tablet refresh interval")
+ refreshKnownTablets = flag.Bool("tablet_refresh_known_tablets", true, "tablet refresh reloads the tablet address/port map from topo in case it changes")
+ topoReadConcurrency = flag.Int("topo_read_concurrency", 32, "concurrent topo reads")
+ allowedTabletTypes []topodatapb.TabletType
+ routeReplicaToRdonly = flag.Bool("gateway_route_replica_to_rdonly", false, "route REPLICA queries to RDONLY tablets as well as REPLICA tablets")
 )
 
 const (
@@ -275,6 +277,12 @@ func (dg *discoveryGateway) withRetry(ctx context.Context, target *querypb.Targe
  }
 
  tablets := dg.tsc.GetHealthyTabletStats(target.Keyspace, target.Shard, target.TabletType)
+
+ // temporary hack to enable REPLICA type queries to address both REPLICA tablets and RDONLY tablets
+ if *routeReplicaToRdonly && target.TabletType == topodata.TabletType_REPLICA {
+ tablets = append(tablets, dg.tsc.GetHealthyTabletStats(target.Keyspace, target.Shard, topodata.TabletType_RDONLY)...)
+ }
+
  if len(tablets) == 0 {
  // fail fast if there is no tablet
  err = vterrors.New(vtrpcpb.Code_UNAVAILABLE, "no valid tablet")