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cogbk.go
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cogbk.go
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// Licensed to the Apache Software Foundation (ASF) under one or more
// contributor license agreements. See the NOTICE file distributed with
// this work for additional information regarding copyright ownership.
// The ASF licenses this file to You under the Apache License, Version 2.0
// (the "License"); you may not use this file except in compliance with
// the License. You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package graphx
import (
"github.com/apache/beam/sdks/v2/go/pkg/beam/core/graph"
"github.com/apache/beam/sdks/v2/go/pkg/beam/core/graph/coder"
"github.com/apache/beam/sdks/v2/go/pkg/beam/core/runtime/coderx"
"github.com/apache/beam/sdks/v2/go/pkg/beam/core/typex"
"github.com/apache/beam/sdks/v2/go/pkg/beam/core/util/reflectx"
"github.com/apache/beam/sdks/v2/go/pkg/beam/internal/errors"
)
// CoGBK support
//
// TODO(https://github.com/apache/beam/issues/18032): CoGBK is not a supported model primitive, so similarly to other
// SDKs, a translation into GBK is performed to run on portable runners. Due to
// various constraints and to preserve CoGBK as a first-class concept in areas
// such as type-checking and for non-portability runners, the Go translation is
// done by the framework instead of user code.
//
// The basic translation approach is as follows:
//
// In1 : KV<K,X> In2 : KV<K,Y>
// | |
// ------ CoGBK --------
// |
// Out: CoGBK<K,X,Y>
//
// is expanded to a flattened raw union value ("RUV") typed as KV<int,[]byte>:
//
// In1 : KV<K,X> In2 : KV<K,Y>
// | |
// Inject(1) Inject(2)
// | |
// U1: KV<K,RUV> U2: KV<K,RUV>
// | |
// ----- Flatten -------
// |
// U3: KV<K,RUV>
// |
// CoGBK (now a GBK)
// |
// U4: CoGBK<K,RUV>
// |
// Expand
// |
// Out: CoGBK<K,X,Y>
//
// Inject and Expand are system-defined functions. This expansion cannot be
// expressed as Go user code.
const (
URNInject = "beam:go:transform:inject:v1"
URNExpand = "beam:go:transform:expand:v1"
)
// MakeKVUnionCoder returns KV<K,KV<int,[]byte>> for a given CoGBK.
func MakeKVUnionCoder(gbk *graph.MultiEdge) (*coder.Coder, error) {
if gbk.Op != graph.CoGBK {
err := errors.Errorf("expected CoGBK, got %v", gbk)
return nil, errors.WithContext(err, "failed to make KV Union coder")
}
from := gbk.Input[0].From
key := from.Coder.Components[0]
kvCoder, err := makeUnionCoder()
if err != nil {
return nil, errors.Wrapf(err, "failed to make KV Union coder.")
}
return coder.NewKV([]*coder.Coder{key, kvCoder}), nil
}
// MakeGBKUnionCoder returns CoGBK<K,KV<int,[]byte>> for a given CoGBK.
func MakeGBKUnionCoder(gbk *graph.MultiEdge) (*coder.Coder, error) {
if gbk.Op != graph.CoGBK {
err := errors.Errorf("expected CoGBK, got %v", gbk)
return nil, errors.WithContext(err, "failed to make GBK Union coder")
}
from := gbk.Input[0].From
key := from.Coder.Components[0]
kvCoder, err := makeUnionCoder()
if err != nil {
return nil, errors.Wrapf(err, "failed to make GBK Union coder.")
}
return coder.NewCoGBK([]*coder.Coder{key, kvCoder}), nil
}
// makeUnionCoder returns a coder for the raw union value, KV<int,[]byte>. It uses
// varintz instead of the built-in varint to avoid the implicit length-prefixing
// of varint otherwise introduced by Dataflow.
func makeUnionCoder() (*coder.Coder, error) {
c, err := coderx.NewVarIntZ(reflectx.Int)
if err != nil {
return nil, err
}
return coder.NewKV([]*coder.Coder{
{Kind: coder.Custom, T: typex.New(reflectx.Int), Custom: c},
coder.NewBytes(),
}), nil
}