Changing default number of prefetch batches to -1 (i.e. Autotune).

PiperOrigin-RevId: 329318576

research/object_detection/protos/input_reader.proto

@@ -72,7 +72,7 @@ message InputReader {
   // to a small constant and increment linearly until the improvements become
   // marginal or you exceed your cpu memory budget. Setting this to -1,
   // automatically tunes this value for you.
-  optional int32 num_prefetch_batches = 20 [default = 2];
+  optional int32 num_prefetch_batches = 20 [default = -1];
 
   // Maximum number of records to keep in reader queue.
   optional uint32 queue_capacity = 3 [default = 2000, deprecated = true];