introduce new scorch index builder (#1282)

The purpose of the index builder is to better support
use cases where one would like to index a set of data,
not search it during the build, ensure the resulting file
is in an efficient optimized state, and then support
opening this index read-only to serve queries.

Useful implementation details:

Only an Index() method is offered, meaning you do not control
the batch size.  The builder will group data into batches
using a configurable 'batchSize' parameter (default 1000)

All of these batches are persisted as segments into a temp
location.  You can control this using 'buildPathPrefix', or
it will default to a system temp location.

You must call Close() after indexing all data.  This will
flush the last batch, and begin merging segments.  The
builder will attempt to merge several segments at once. This
is configurable with the 'mergeMax' setting, which defaults
to 10.  Merging continues until there is only 1 segment
remaining.

At this point, the final segment is moved to the final
location (as specified by the original builder constructor).
The root.bolt is created, pointing to the segment, and
the remaining bleve index wrapping is completed.

builder.go

@@ -0,0 +1,94 @@
+//  Copyright (c) 2019 Couchbase, Inc.
+//
+// Licensed 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 bleve
+
+import (
+	"encoding/json"
+	"fmt"
+
+	"github.com/blevesearch/bleve/document"
+	"github.com/blevesearch/bleve/index"
+	"github.com/blevesearch/bleve/index/scorch"
+	"github.com/blevesearch/bleve/mapping"
+)
+
+type builderImpl struct {
+	b index.IndexBuilder
+	m mapping.IndexMapping
+}
+
+func (b *builderImpl) Index(id string, data interface{}) error {
+	if id == "" {
+		return ErrorEmptyID
+	}
+
+	doc := document.NewDocument(id)
+	err := b.m.MapDocument(doc, data)
+	if err != nil {
+		return err
+	}
+	err = b.b.Index(doc)
+	return err
+}
+
+func (b *builderImpl) Close() error {
+	return b.b.Close()
+}
+
+func newBuilder(path string, mapping mapping.IndexMapping, config map[string]interface{}) (Builder, error) {
+	if path == "" {
+		return nil, fmt.Errorf("builder requires path")
+	}
+
+	err := mapping.Validate()
+	if err != nil {
+		return nil, err
+	}
+
+	if config == nil {
+		config = map[string]interface{}{}
+	}
+
+	// the builder does not have an API to interact with internal storage
+	// however we can pass k/v pairs through the config
+	mappingBytes, err := json.Marshal(mapping)
+	if err != nil {
+		return nil, err
+	}
+	config["internal"] = map[string][]byte{
+		string(mappingInternalKey): mappingBytes,
+	}
+
+	// do not use real config, as these are options for the builder,
+	// not the resulting index
+	meta := newIndexMeta(scorch.Name, scorch.Name, map[string]interface{}{})
+	err = meta.Save(path)
+	if err != nil {
+		return nil, err
+	}
+
+	config["path"] = indexStorePath(path)
+
+	b, err := scorch.NewBuilder(config)
+	if err != nil {
+		return nil, err
+	}
+	rv := &builderImpl{
+		b: b,
+		m: mapping,
+	}
+
+	return rv, nil
+}

builder_test.go

@@ -0,0 +1,89 @@
+//  Copyright (c) 2019 Couchbase, Inc.
+//
+// Licensed 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 bleve
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"testing"
+)
+
+func TestBuilder(t *testing.T) {
+	tmpDir, err := ioutil.TempDir("", "bleve-scorch-builder-test")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer func() {
+		err = os.RemoveAll(tmpDir)
+		if err != nil {
+			t.Fatalf("error cleaning up test index")
+		}
+	}()
+
+	conf := map[string]interface{}{
+		"batchSize": 2,
+		"mergeMax":  2,
+	}
+	b, err := NewBuilder(tmpDir, NewIndexMapping(), conf)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	for i := 0; i < 10; i++ {
+		doc := map[string]interface{}{
+			"name": "hello",
+		}
+		err = b.Index(fmt.Sprintf("%d", i), doc)
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	err = b.Close()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	idx, err := Open(tmpDir)
+	if err != nil {
+		t.Fatalf("error opening index: %v", err)
+	}
+	defer func() {
+		err = idx.Close()
+		if err != nil {
+			t.Errorf("error closing index: %v", err)
+		}
+	}()
+
+	docCount, err := idx.DocCount()
+	if err != nil {
+		t.Errorf("error checking doc count: %v", err)
+	}
+	if docCount != 10 {
+		t.Errorf("expected doc count to be 10, got %d", docCount)
+	}
+
+	q := NewTermQuery("hello")
+	q.SetField("name")
+	req := NewSearchRequest(q)
+	res, err := idx.Search(req)
+	if err != nil {
+		t.Errorf("error searching index: %v", err)
+	}
+	if res.Total != 10 {
+		t.Errorf("expected 10 search hits, got %d", res.Total)
+	}
+}

index.go

@@ -293,3 +293,17 @@ func Open(path string) (Index, error) {
 func OpenUsing(path string, runtimeConfig map[string]interface{}) (Index, error) {
 	return openIndexUsing(path, runtimeConfig)
 }
+
+// Builder is a limited interface, used to build indexes in an offline mode.
+// Items cannot be updated or deleted, and the caller MUST ensure a document is
+// indexed only once.
+type Builder interface {
+	Index(id string, data interface{}) error
+	Close() error
+}
+
+// NewBuilder creates a builder, which will build an index at the specified path,
+// using the specified mapping and options.
+func NewBuilder(path string, mapping mapping.IndexMapping, config map[string]interface{}) (Builder, error) {
+	return newBuilder(path, mapping, config)
+}

index/index.go

@@ -367,3 +367,10 @@ type OptimizableContext interface {
 type DocValueReader interface {
 	VisitDocValues(id IndexInternalID, visitor DocumentFieldTermVisitor) error
 }
+
+// IndexBuilder is an interface supported by some index schemes
+// to allow direct write-only index building
+type IndexBuilder interface {
+	Index(doc *document.Document) error
+	Close() error
+}