Updates the PR to use attribute instead of Env Variable

-Originally AVRO_PARSER_NUM_MINIBATCH was set as an environmental
variable.  Because tensorflow-io rarely uses env vars to fine tune
kernal ops this was changed to an attribute. See comment here:
tensorflow#1283 (comment)

tensorflow_io/core/kernels/avro/parse_avro_kernels.cc

@@ -190,6 +190,7 @@ Status ParseAvro(const AvroParserConfig& config,
 
   // This parameter affects performance in a big and data-dependent way.
   const size_t kMiniBatchSizeBytes = 50000;
+  size_t avro_num_minibatches_;
 
   // Calculate number of minibatches.
   // In main regime make each minibatch around kMiniBatchSizeBytes bytes.
@@ -206,10 +207,9 @@ Status ParseAvro(const AvroParserConfig& config,
         minibatch_bytes = 0;
       }
     }
-    if (const char* n_minibatches =
-            std::getenv("AVRO_PARSER_NUM_MINIBATCHES")) {
-      VLOG(5) << "Overriding num_minibatches with " << n_minibatches;
-      result = std::stoi(n_minibatches);
+    if (avro_num_minibatches_) {
+      VLOG(5) << "Overriding num_minibatches with " << avro_num_minibatches_;
+      result = avro_num_minibatches_;
     }
     // This is to ensure users can control the num minibatches all the way down
     // to size of 1(no parallelism).
@@ -406,6 +406,8 @@ class ParseAvroOp : public OpKernel {
     OP_REQUIRES_OK(ctx, ctx->GetAttr("sparse_types", &sparse_types_));
     OP_REQUIRES_OK(ctx, ctx->GetAttr("dense_types", &dense_types_));
     OP_REQUIRES_OK(ctx, ctx->GetAttr("dense_shapes", &dense_shapes_));
+    OP_REQUIRES_OK(
+        ctx, ctx->GetAttr("avro_num_minibatches", &avro_num_minibatches_));
 
     OP_REQUIRES_OK(ctx, ctx->GetAttr("sparse_keys", &sparse_keys_));
     OP_REQUIRES_OK(ctx, ctx->GetAttr("dense_keys", &dense_keys_));
@@ -419,6 +421,11 @@ class ParseAvroOp : public OpKernel {
           dense_shapes_[d].dims() > 1 && dense_shapes_[d].dim_size(0) == -1;
     }
 
+    // Check that avro_num_minibatches is positive
+    OP_REQUIRES(ctx, avro_num_minibatches_ >= 0,
+                errors::InvalidArgument("Need avro_num_minibatches >= 0, got ",
+                                        avro_num_minibatches_));
+
     string reader_schema_str;
     OP_REQUIRES_OK(ctx, ctx->GetAttr("reader_schema", &reader_schema_str));
 
@@ -513,6 +520,7 @@ class ParseAvroOp : public OpKernel {
   avro::ValidSchema reader_schema_;
   size_t num_dense_;
   size_t num_sparse_;
+  int64 avro_num_minibatches_;
 
  private:
   std::vector<std::pair<string, DataType>> CreateKeysAndTypes() {

tensorflow_io/core/ops/avro_ops.cc

@@ -83,6 +83,7 @@ REGISTER_OP("IO>ParseAvro")
     .Output("sparse_values: sparse_types")
     .Output("sparse_shapes: num_sparse * int64")
     .Output("dense_values: dense_types")
+    .Attr("avro_num_minibatches: int >= 0")
     .Attr("num_sparse: int >= 0")
     .Attr("reader_schema: string")
     .Attr("sparse_keys: list(string) >= 0")
@@ -94,6 +95,7 @@ REGISTER_OP("IO>ParseAvro")
     .SetShapeFn([](shape_inference::InferenceContext* c) {
       size_t num_dense;
       size_t num_sparse;
+      int64 avro_num_minibatches;
       int64 num_sparse_from_user;
       std::vector<DataType> sparse_types;
       std::vector<DataType> dense_types;
@@ -106,6 +108,8 @@ REGISTER_OP("IO>ParseAvro")
       TF_RETURN_IF_ERROR(c->GetAttr("sparse_types", &sparse_types));
       TF_RETURN_IF_ERROR(c->GetAttr("dense_types", &dense_types));
       TF_RETURN_IF_ERROR(c->GetAttr("dense_shapes", &dense_shapes));
+      TF_RETURN_IF_ERROR(
+          c->GetAttr("avro_num_minibatches", &avro_num_minibatches));
 
       TF_RETURN_IF_ERROR(c->GetAttr("sparse_keys", &sparse_keys));
       TF_RETURN_IF_ERROR(c->GetAttr("sparse_ranks", &sparse_ranks));

tensorflow_io/core/python/experimental/parse_avro_ops.py

@@ -130,6 +130,7 @@ def _parse_avro(
     dense_defaults=None,
     dense_shapes=None,
     name=None,
+    avro_num_minibatches=0,
 ):
     """Parses Avro records.
 
@@ -196,6 +197,7 @@ def _parse_avro(
             dense_keys=dense_keys,
             dense_shapes=dense_shapes,
             name=name,
+            avro_num_minibatches=avro_num_minibatches,
         )
 
         (sparse_indices, sparse_values, sparse_shapes, dense_values) = outputs