func (db *DistDB) lookupMetadata(metadataKey storage.Key, replicas []storage.Replica) (*storage.RangeLocations, error) {
replica := storage.ChooseRandomReplica(replicas)
if replica == nil {
return nil, util.Errorf("No replica to choose for metadata key: %q", metadataKey)
}
addr, err := db.nodeIDToAddr(replica.NodeID)
if err != nil {
// TODO(harshit): May be retry a different replica.
return nil, err
}
client := rpc.NewClient(addr)
arg := &storage.InternalRangeLookupRequest{
RequestHeader: storage.RequestHeader{
Replica: *replica,
},
Key: metadataKey,
}
var reply storage.InternalRangeLookupResponse
err = client.Call("Node.InternalRangeLookup", arg, &reply)
if err != nil {
return nil, err
}
if reply.Error != nil {
return nil, reply.Error
}
return &reply.Locations, nil
}
// getNode gets an RPC client to the node where the requested
// key is located. The range cache may be updated. The bi-level range
// metadata for the cluster is consulted in the event that the local
// cache doesn't contain range metadata corresponding to the specified
// key.
func (db *DistDB) getNode(key storage.Key) (*rpc.Client, *storage.Replica, error) {
meta2Val, err := db.lookupMeta2(key)
if err != nil {
return nil, nil, err
}
replica := storage.ChooseRandomReplica(meta2Val.Replicas)
if replica == nil {
return nil, nil, util.Errorf("No node found for key: %q", key)
}
addr, err := db.nodeIDToAddr(replica.NodeID)
if err != nil {
// TODO(harshit): May be retry a different replica.
return nil, nil, err
}
return rpc.NewClient(addr), replica, nil
}