// sendSingleRange gathers and rearranges the replicas, and makes an RPC call.
func (ds *DistSender) sendSingleRange(
ctx context.Context, ba roachpb.BatchRequest, desc *roachpb.RangeDescriptor,
) (*roachpb.BatchResponse, *roachpb.Error) {
// Try to send the call.
replicas := newReplicaSlice(ds.gossip, desc)
// Rearrange the replicas so that those replicas with long common
// prefix of attributes end up first. If there's no prefix, this is a
// no-op.
ds.optimizeReplicaOrder(replicas)
// If this request needs to go to a lease holder and we know who that is, move
// it to the front.
if !(ba.IsReadOnly() && ba.ReadConsistency == roachpb.INCONSISTENT) {
if leaseHolder, ok := ds.leaseHolderCache.Lookup(ctx, desc.RangeID); ok {
if i := replicas.FindReplica(leaseHolder.StoreID); i >= 0 {
replicas.MoveToFront(i)
}
}
}
// TODO(tschottdorf): should serialize the trace here, not higher up.
br, err := ds.sendRPC(ctx, desc.RangeID, replicas, ba)
if err != nil {
return nil, roachpb.NewError(err)
}
// If the reply contains a timestamp, update the local HLC with it.
if br.Error != nil && br.Error.Now != hlc.ZeroTimestamp {
ds.clock.Update(br.Error.Now)
} else if br.Now != hlc.ZeroTimestamp {
ds.clock.Update(br.Now)
}
// Untangle the error from the received response.
pErr := br.Error
br.Error = nil // scrub the response error
return br, pErr
}