NewUsing persists the provided config to index meta

new method OpenUsing allows user to override values
in the persisted config
example would be opening the index, but using a different
buffer size for leveldb (not actually supported yet, but that
is the idea)
closes #138

index.go

@@ -106,7 +106,7 @@ type Classifier interface {
 // The provided mapping will be used for all
 // Index/Search operations.
 func New(path string, mapping *IndexMapping) (Index, error) {
-	return newIndex(path, mapping)
+	return newIndexUsing(path, mapping, Config.DefaultKVStore, nil)
 }
 
 // NewUsing creates index at the specified path,
@@ -123,5 +123,13 @@ func NewUsing(path string, mapping *IndexMapping, kvstore string, kvconfig map[s
 // Open index at the specified path, must exist.
 // The mapping used when it was created will be used for all Index/Search operations.
 func Open(path string) (Index, error) {
-	return openIndex(path)
+	return openIndexUsing(path, nil)
+}
+
+// OpenUsing opens index at the specified path, must exist.
+// The mapping used when it was created will be used for all Index/Search operations.
+// The provided runtimeConfig can override settings
+// persisted when the kvstore was created.
+func OpenUsing(path string, runtimeConfig map[string]interface{}) (Index, error) {
+	return openIndexUsing(path, runtimeConfig)
 }

index_impl.go

@@ -50,7 +50,7 @@ func newMemIndex(mapping *IndexMapping) (*indexImpl, error) {
 	rv := indexImpl{
 		path:  "",
 		m:     mapping,
-		meta:  newIndexMeta("mem"),
+		meta:  newIndexMeta("mem", nil),
 		stats: &IndexStat{},
 	}
 
@@ -101,10 +101,14 @@ func newIndexUsing(path string, mapping *IndexMapping, kvstore string, kvconfig
 		return newMemIndex(mapping)
 	}
 
+	if kvconfig == nil {
+		kvconfig = map[string]interface{}{}
+	}
+
 	rv := indexImpl{
 		path:  path,
 		m:     mapping,
-		meta:  newIndexMeta(kvstore),
+		meta:  newIndexMeta(kvstore, kvconfig),
 		stats: &IndexStat{},
 	}
 	storeConstructor := registry.KVStoreConstructorByName(rv.meta.Storage)
@@ -116,9 +120,8 @@ func newIndexUsing(path string, mapping *IndexMapping, kvstore string, kvconfig
 	if err != nil {
 		return nil, err
 	}
-	if kvconfig == nil {
-		kvconfig = map[string]interface{}{}
-	}
+	kvconfig["create_if_missing"] = true
+	kvconfig["error_if_exists"] = true
 	kvconfig["path"] = indexStorePath(path)
 
 	// now open the store
@@ -152,15 +155,7 @@ func newIndexUsing(path string, mapping *IndexMapping, kvstore string, kvconfig
 	return &rv, nil
 }
 
-func newIndex(path string, mapping *IndexMapping) (*indexImpl, error) {
-	defaultKVConfig := map[string]interface{}{
-		"create_if_missing": true,
-		"error_if_exists":   true,
-	}
-	return newIndexUsing(path, mapping, Config.DefaultKVStore, defaultKVConfig)
-}
-
-func openIndex(path string) (*indexImpl, error) {
+func openIndexUsing(path string, runtimeConfig map[string]interface{}) (*indexImpl, error) {
 
 	rv := indexImpl{
 		path:  path,
@@ -177,10 +172,16 @@ func openIndex(path string) (*indexImpl, error) {
 		return nil, ErrorUnknownStorageType
 	}
 
-	storeConfig := map[string]interface{}{
-		"path":              indexStorePath(path),
-		"create_if_missing": false,
-		"error_if_exists":   false,
+	storeConfig := rv.meta.Config
+	if storeConfig == nil {
+		storeConfig = map[string]interface{}{}
+	}
+
+	storeConfig["path"] = indexStorePath(path)
+	storeConfig["create_if_missing"] = false
+	storeConfig["error_if_exists"] = false
+	for rck, rcv := range runtimeConfig {
+		storeConfig[rck] = rcv
 	}
 
 	// now open the store

index_meta.go

@@ -18,11 +18,15 @@ import (
 const metaFilename = "index_meta.json"
 
 type indexMeta struct {
-	Storage string `json:"storage"`
+	Storage string                 `json:"storage"`
+	Config  map[string]interface{} `json:"config,omitempty"`
 }
 
-func newIndexMeta(storage string) *indexMeta {
-	return &indexMeta{Storage: storage}
+func newIndexMeta(storage string, config map[string]interface{}) *indexMeta {
+	return &indexMeta{
+		Storage: storage,
+		Config:  config,
+	}
 }
 
 func openIndexMeta(path string) (*indexMeta, error) {