db/model/persisted_revision.go - voltha-go - Gitiles

 /*
  * Copyright 2018-present Open Networking Foundation

  * 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 model

 import (
 	"bytes"
 	"compress/gzip"
 	"github.com/golang/protobuf/proto"
 	"github.com/opencord/voltha-go/common/log"
 	"github.com/opencord/voltha-go/db/kvstore"
 	"reflect"
 	"runtime/debug"
 	"strings"
 	"sync"
 )

 // PersistedRevision holds information of revision meant to be saved in a persistent storage
 type PersistedRevision struct {
 	Revision
 	Compress bool

 	events    chan *kvstore.Event `json:"-"`
 	kvStore   *Backend            `json:"-"`
 	mutex     sync.RWMutex        `json:"-"`
 	isStored  bool
 	isWatched bool
 }

 type watchCache struct {
 	Cache sync.Map
 }

 var watchCacheInstance *watchCache
 var watchCacheOne sync.Once

 func Watches() *watchCache {
 	watchCacheOne.Do(func() {
 		watchCacheInstance = &watchCache{Cache: sync.Map{}}
 	})
 	return watchCacheInstance
 }

 // NewPersistedRevision creates a new instance of a PersistentRevision structure
 func NewPersistedRevision(branch *Branch, data interface{}, children map[string][]Revision) Revision {
 	pr := &PersistedRevision{}
 	pr.kvStore = branch.Node.GetRoot().KvStore
 	pr.Revision = NewNonPersistedRevision(nil, branch, data, children)
 	return pr
 }

 // Finalize is responsible of saving the revision in the persistent storage
 func (pr *PersistedRevision) Finalize(skipOnExist bool) {
 	pr.store(skipOnExist)
 }

 func (pr *PersistedRevision) store(skipOnExist bool) {
 	if pr.GetBranch().Txid != "" {
 		return
 	}

 	if pair, _ := pr.kvStore.Get(pr.GetName()); pair != nil && skipOnExist {
 		log.Debugw("revision-config-already-exists", log.Fields{"hash": pr.GetHash(), "name": pr.GetName()})
 		return
 	}

 	if blob, err := proto.Marshal(pr.GetConfig().Data.(proto.Message)); err != nil {
 		// TODO report error
 	} else {
 		if pr.Compress {
 			var b bytes.Buffer
 			w := gzip.NewWriter(&b)
 			w.Write(blob)
 			w.Close()
 			blob = b.Bytes()
 		}

 		if err := pr.kvStore.Put(pr.GetName(), blob); err != nil {
 			log.Warnw("problem-storing-revision-config",
 				log.Fields{"error": err, "hash": pr.GetHash(), "name": pr.GetName(), "data": pr.GetConfig().Data})
 		} else {
 			log.Debugw("storing-revision-config", log.Fields{"hash": pr.GetHash(), "name": pr.GetName(), "data": pr.GetConfig().Data})
 			pr.isStored = true
 		}
 	}
 }

 func (pr *PersistedRevision) SetupWatch(key string) {
 	if key == "" {
 		log.Debugw("ignoring-watch", log.Fields{"key": key, "revision-hash": pr.GetHash(), "stack": string(debug.Stack())})
 		return
 	}

 	if _, exists := Watches().Cache.LoadOrStore(key+"-"+pr.GetHash(), struct{}{}); exists {
 		return
 	}

 	if pr.events == nil {
 		pr.events = make(chan *kvstore.Event)

 		log.Debugw("setting-watch-channel", log.Fields{"key": key, "revision-hash": pr.GetHash(), "stack": string(debug.Stack())})

 		pr.SetName(key)
 		pr.events = pr.kvStore.CreateWatch(key)
 	}

 	if !pr.isWatched {
 		pr.isWatched = true

 		log.Debugw("setting-watch-routine", log.Fields{"key": key, "revision-hash": pr.GetHash(), "stack": string(debug.Stack())})

 		// Start watching
 		go pr.startWatching()
 	}
 }

 func (pr *PersistedRevision) startWatching() {
 	log.Debugw("starting-watch", log.Fields{"key": pr.GetHash(), "stack": string(debug.Stack())})

 StopWatchLoop:
 	for {
 		if pr.IsDiscarded() {
 			break StopWatchLoop
 		}

 		select {
 		case event, ok := <-pr.events:
 			if !ok {
 				log.Errorw("event-channel-failure: stopping watch loop", log.Fields{"key": pr.GetHash(), "watch": pr.GetName()})
 				break StopWatchLoop
 			}

 			log.Debugw("received-event", log.Fields{"type": event.EventType, "watch": pr.GetName()})

 			switch event.EventType {
 			case kvstore.DELETE:
 				log.Debugw("delete-from-memory", log.Fields{"key": pr.GetHash(), "watch": pr.GetName()})
 				pr.Revision.Drop("", true)
 				break StopWatchLoop

 			case kvstore.PUT:
 				log.Debugw("update-in-memory", log.Fields{"key": pr.GetHash(), "watch": pr.GetName()})

 				if dataPair, err := pr.kvStore.Get(pr.GetName()); err != nil || dataPair == nil {
 					log.Errorw("update-in-memory--key-retrieval-failed", log.Fields{"key": pr.GetHash(), "watch": pr.GetName(), "error": err})
 				} else {
 					data := reflect.New(reflect.TypeOf(pr.GetData()).Elem())

 					if err := proto.Unmarshal(dataPair.Value.([]byte), data.Interface().(proto.Message)); err != nil {
 						log.Errorw("update-in-memory--unmarshal-failed", log.Fields{"key": pr.GetHash(), "watch": pr.GetName(), "error": err})
 					} else {
 						if pr.GetNode().GetProxy() != nil {
 							pr.LoadFromPersistence(pr.GetNode().GetProxy().getFullPath(), "")
 						}
 					}
 				}

 			default:
 				log.Debugw("unhandled-event", log.Fields{"key": pr.GetHash(), "watch": pr.GetName(), "type": event.EventType})
 			}
 		}
 	}

 	Watches().Cache.Delete(pr.GetName() + "-" + pr.GetHash())

 	log.Debugw("exiting-watch", log.Fields{"key": pr.GetHash(), "watch": pr.GetName(), "stack": string(debug.Stack())})
 }

 // UpdateData modifies the information in the data model and saves it in the persistent storage
 func (pr *PersistedRevision) UpdateData(data interface{}, branch *Branch) Revision {
 	log.Debugw("updating-persisted-data", log.Fields{"hash": pr.GetHash()})

 	newNPR := pr.Revision.UpdateData(data, branch)

 	newPR := &PersistedRevision{
 		Revision: newNPR,
 		Compress: pr.Compress,
 		kvStore:  pr.kvStore,
 		events:   pr.events,
 	}

 	if newPR.GetHash() != pr.GetHash() {
 		newPR.isWatched = false
 		newPR.isStored = false
 		pr.Drop(branch.Txid, false)
 		newPR.SetupWatch(newPR.GetName())
 	} else {
 		newPR.isWatched = true
 		newPR.isStored = true
 	}

 	return newPR
 }

 // UpdateChildren modifies the children of a revision and of a specific component and saves it in the persistent storage
 func (pr *PersistedRevision) UpdateChildren(name string, children []Revision, branch *Branch) Revision {
 	log.Debugw("updating-persisted-children", log.Fields{"hash": pr.GetHash()})

 	newNPR := pr.Revision.UpdateChildren(name, children, branch)

 	newPR := &PersistedRevision{
 		Revision: newNPR,
 		Compress: pr.Compress,
 		kvStore:  pr.kvStore,
 		events:   pr.events,
 	}

 	if newPR.GetHash() != pr.GetHash() {
 		newPR.isWatched = false
 		newPR.isStored = false
 		pr.Drop(branch.Txid, false)
 		newPR.SetupWatch(newPR.GetName())
 	} else {
 		newPR.isWatched = true
 		newPR.isStored = true
 	}

 	return newPR
 }

 // UpdateAllChildren modifies the children for all components of a revision and saves it in the peristent storage
 func (pr *PersistedRevision) UpdateAllChildren(children map[string][]Revision, branch *Branch) Revision {
 	log.Debugw("updating-all-persisted-children", log.Fields{"hash": pr.GetHash()})

 	newNPR := pr.Revision.UpdateAllChildren(children, branch)

 	newPR := &PersistedRevision{
 		Revision: newNPR,
 		Compress: pr.Compress,
 		kvStore:  pr.kvStore,
 		events:   pr.events,
 	}

 	if newPR.GetHash() != pr.GetHash() {
 		newPR.isWatched = false
 		newPR.isStored = false
 		pr.Drop(branch.Txid, false)
 		newPR.SetupWatch(newPR.GetName())
 	} else {
 		newPR.isWatched = true
 		newPR.isStored = true
 	}

 	return newPR
 }

 // Drop takes care of eliminating a revision hash that is no longer needed
 // and its associated config when required
 func (pr *PersistedRevision) Drop(txid string, includeConfig bool) {
 	pr.Revision.Drop(txid, includeConfig)
 }

 // Drop takes care of eliminating a revision hash that is no longer needed
 // and its associated config when required
 func (pr *PersistedRevision) StorageDrop(txid string, includeConfig bool) {
 	log.Debugw("dropping-revision",
 		log.Fields{"txid": txid, "hash": pr.GetHash(), "config-hash": pr.GetConfig().Hash, "stack": string(debug.Stack())})

 	pr.mutex.Lock()
 	defer pr.mutex.Unlock()
 	if pr.kvStore != nil && txid == "" {
 		if pr.isStored {
 			if pr.isWatched {
 				pr.kvStore.DeleteWatch(pr.GetName(), pr.events)
 				pr.isWatched = false
 			}

 			if err := pr.kvStore.Delete(pr.GetName()); err != nil {
 				log.Errorw("failed-to-remove-revision", log.Fields{"hash": pr.GetHash(), "error": err.Error()})
 			} else {
 				pr.isStored = false
 			}
 		}

 	} else {
 		if includeConfig {
 			log.Debugw("attempted-to-remove-transacted-revision-config", log.Fields{"hash": pr.GetConfig().Hash, "txid": txid})
 		}
 		log.Debugw("attempted-to-remove-transacted-revision", log.Fields{"hash": pr.GetHash(), "txid": txid})
 	}

 	pr.Revision.Drop(txid, includeConfig)
 }

 // verifyPersistedEntry validates if the provided data is available or not in memory and applies updates as required
 func (pr *PersistedRevision) verifyPersistedEntry(data interface{}, typeName string, keyName string, keyValue string, txid string) (response Revision) {
 	rev := pr

 	children := make([]Revision, len(rev.GetBranch().GetLatest().GetChildren(typeName)))
 	copy(children, rev.GetBranch().GetLatest().GetChildren(typeName))

 	// Verify if the revision contains a child that matches that key
 	if childIdx, childRev := rev.GetNode().findRevByKey(rev.GetBranch().GetLatest().GetChildren(typeName), keyName, keyValue); childRev != nil {
 		// A child matching the provided key exists in memory
 		// Verify if the data differs to what was retrieved from persistence
 		if childRev.GetData().(proto.Message).String() != data.(proto.Message).String() {
 			log.Debugw("verify-persisted-entry--data-is-different", log.Fields{
 				"key":  childRev.GetHash(),
 				"name": childRev.GetName(),
 			})

 			// Data has changed; replace the child entry and update the parent revision
 			updatedChildRev := childRev.UpdateData(data, childRev.GetBranch())
 			updatedChildRev.SetupWatch(updatedChildRev.GetName())
 			childRev.Drop(txid, false)

 			if childIdx >= 0 {
 				children[childIdx] = updatedChildRev
 			} else {
 				children = append(children, updatedChildRev)
 			}

 			rev.GetBranch().LatestLock.Lock()
 			updatedRev := rev.UpdateChildren(typeName, children, rev.GetBranch())
 			rev.GetBranch().Node.makeLatest(rev.GetBranch(), updatedRev, nil)
 			rev.GetBranch().LatestLock.Unlock()

 			// Drop the previous child revision
 			rev.GetBranch().Node.Latest().ChildDrop(typeName, childRev.GetHash())

 			if updatedChildRev != nil {
 				log.Debugw("verify-persisted-entry--adding-child", log.Fields{
 					"key":  updatedChildRev.GetHash(),
 					"name": updatedChildRev.GetName(),
 				})
 				response = updatedChildRev
 			}
 		} else {
 			// Data is the same. Continue to the next entry
 			log.Debugw("verify-persisted-entry--same-data", log.Fields{
 				"key":  childRev.GetHash(),
 				"name": childRev.GetName(),
 			})
 			if childRev != nil {
 				log.Debugw("verify-persisted-entry--keeping-child", log.Fields{
 					"key":  childRev.GetHash(),
 					"name": childRev.GetName(),
 				})
 				response = childRev
 			}
 		}
 	} else {
 		// There is no available child with that key value.
 		// Create a new child and update the parent revision.
 		log.Debugw("verify-persisted-entry--no-such-entry", log.Fields{
 			"key":  keyValue,
 			"name": typeName,
 		})

 		// Construct a new child node with the retrieved persistence data
 		childRev = rev.GetBranch().Node.MakeNode(data, txid).Latest(txid)

 		// We need to start watching this entry for future changes
 		childRev.SetName(typeName + "/" + keyValue)

 		// Add the child to the parent revision
 		rev.GetBranch().LatestLock.Lock()
 		children = append(children, childRev)
 		updatedRev := rev.GetBranch().Node.Latest().UpdateChildren(typeName, children, rev.GetBranch())
 		childRev.SetupWatch(childRev.GetName())

 		//rev.GetBranch().Node.Latest().Drop(txid, false)
 		rev.GetBranch().Node.makeLatest(rev.GetBranch(), updatedRev, nil)
 		rev.GetBranch().LatestLock.Unlock()

 		// Child entry is valid and can be included in the response object
 		if childRev != nil {
 			log.Debugw("verify-persisted-entry--adding-child", log.Fields{
 				"key":  childRev.GetHash(),
 				"name": childRev.GetName(),
 			})
 			response = childRev
 		}
 	}

 	return response
 }

 // LoadFromPersistence retrieves data from kv store at the specified location and refreshes the memory
 // by adding missing entries, updating changed entries and ignoring unchanged ones
 func (pr *PersistedRevision) LoadFromPersistence(path string, txid string) []Revision {
 	pr.mutex.Lock()
 	defer pr.mutex.Unlock()

 	log.Debugw("loading-from-persistence", log.Fields{"path": path, "txid": txid})

 	var response []Revision
 	var rev Revision

 	rev = pr

 	if pr.kvStore != nil && path != "" {
 		blobMap, _ := pr.kvStore.List(path)

 		partition := strings.SplitN(path, "/", 2)
 		name := partition[0]

 		if len(partition) < 2 {
 			path = ""
 		} else {
 			path = partition[1]
 		}

 		field := ChildrenFields(rev.GetBranch().Node.Type)[name]

 		if field != nil && field.IsContainer {
 			log.Debugw("load-from-persistence--start-blobs", log.Fields{
 				"path": path,
 				"name": name,
 				"size": len(blobMap),
 			})

 			for _, blob := range blobMap {
 				output := blob.Value.([]byte)

 				data := reflect.New(field.ClassType.Elem())

 				if err := proto.Unmarshal(output, data.Interface().(proto.Message)); err != nil {
 					log.Errorw("load-from-persistence--failed-to-unmarshal", log.Fields{
 						"path":  path,
 						"txid":  txid,
 						"error": err,
 					})
 				} else if path == "" {
 					if field.Key != "" {
 						// Retrieve the key identifier value from the data structure
 						// based on the field's key attribute
 						_, key := GetAttributeValue(data.Interface(), field.Key, 0)

 						if entry := pr.verifyPersistedEntry(data.Interface(), name, field.Key, key.String(), txid); entry != nil {
 							response = append(response, entry)
 						}
 					}

 				} else if field.Key != "" {
 					// The request is for a specific entry/id
 					partition := strings.SplitN(path, "/", 2)
 					key := partition[0]
 					if len(partition) < 2 {
 						path = ""
 					} else {
 						path = partition[1]
 					}
 					keyValue := field.KeyFromStr(key)

 					if entry := pr.verifyPersistedEntry(data.Interface(), name, field.Key, keyValue.(string), txid); entry != nil {
 						response = append(response, entry)
 					}
 				}
 			}

 			log.Debugw("load-from-persistence--end-blobs", log.Fields{"path": path, "name": name})
 		} else {
 			log.Debugw("load-from-persistence--cannot-process-field", log.Fields{
 				"type": rev.GetBranch().Node.Type,
 				"name": name,
 			})
 		}
 	}

 	return response
 }
	/*
	* Copyright 2018-present Open Networking Foundation

	* 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 model

	import (
	"bytes"
	"compress/gzip"
	"github.com/golang/protobuf/proto"
	"github.com/opencord/voltha-go/common/log"
	"github.com/opencord/voltha-go/db/kvstore"
	"reflect"
	"runtime/debug"
	"strings"
	"sync"
	)

	// PersistedRevision holds information of revision meant to be saved in a persistent storage
	type PersistedRevision struct {
	Revision
	Compress bool

	events chan *kvstore.Event `json:"-"`
	kvStore *Backend `json:"-"`
	mutex sync.RWMutex `json:"-"`
	isStored bool
	isWatched bool
	}

	type watchCache struct {
	Cache sync.Map
	}

	var watchCacheInstance *watchCache
	var watchCacheOne sync.Once

	func Watches() *watchCache {
	watchCacheOne.Do(func() {
	watchCacheInstance = &watchCache{Cache: sync.Map{}}
	})
	return watchCacheInstance
	}

	// NewPersistedRevision creates a new instance of a PersistentRevision structure
	func NewPersistedRevision(branch *Branch, data interface{}, children map[string][]Revision) Revision {
	pr := &PersistedRevision{}
	pr.kvStore = branch.Node.GetRoot().KvStore
	pr.Revision = NewNonPersistedRevision(nil, branch, data, children)
	return pr
	}

	// Finalize is responsible of saving the revision in the persistent storage
	func (pr *PersistedRevision) Finalize(skipOnExist bool) {
	pr.store(skipOnExist)
	}

	func (pr *PersistedRevision) store(skipOnExist bool) {
	if pr.GetBranch().Txid != "" {
	return
	}

	if pair, _ := pr.kvStore.Get(pr.GetName()); pair != nil && skipOnExist {
	log.Debugw("revision-config-already-exists", log.Fields{"hash": pr.GetHash(), "name": pr.GetName()})
	return
	}

	if blob, err := proto.Marshal(pr.GetConfig().Data.(proto.Message)); err != nil {
	// TODO report error
	} else {
	if pr.Compress {
	var b bytes.Buffer
	w := gzip.NewWriter(&b)
	w.Write(blob)
	w.Close()
	blob = b.Bytes()
	}

	if err := pr.kvStore.Put(pr.GetName(), blob); err != nil {
	log.Warnw("problem-storing-revision-config",
	log.Fields{"error": err, "hash": pr.GetHash(), "name": pr.GetName(), "data": pr.GetConfig().Data})
	} else {
	log.Debugw("storing-revision-config", log.Fields{"hash": pr.GetHash(), "name": pr.GetName(), "data": pr.GetConfig().Data})
	pr.isStored = true
	}
	}
	}

	func (pr *PersistedRevision) SetupWatch(key string) {
	if key == "" {
	log.Debugw("ignoring-watch", log.Fields{"key": key, "revision-hash": pr.GetHash(), "stack": string(debug.Stack())})
	return
	}

	if _, exists := Watches().Cache.LoadOrStore(key+"-"+pr.GetHash(), struct{}{}); exists {
	return
	}

	if pr.events == nil {
	pr.events = make(chan *kvstore.Event)

	log.Debugw("setting-watch-channel", log.Fields{"key": key, "revision-hash": pr.GetHash(), "stack": string(debug.Stack())})

	pr.SetName(key)
	pr.events = pr.kvStore.CreateWatch(key)
	}

	if !pr.isWatched {
	pr.isWatched = true

	log.Debugw("setting-watch-routine", log.Fields{"key": key, "revision-hash": pr.GetHash(), "stack": string(debug.Stack())})

	// Start watching
	go pr.startWatching()
	}
	}

	func (pr *PersistedRevision) startWatching() {
	log.Debugw("starting-watch", log.Fields{"key": pr.GetHash(), "stack": string(debug.Stack())})

	StopWatchLoop:
	for {
	if pr.IsDiscarded() {
	break StopWatchLoop
	}

	select {
	case event, ok := <-pr.events:
	if !ok {
	log.Errorw("event-channel-failure: stopping watch loop", log.Fields{"key": pr.GetHash(), "watch": pr.GetName()})
	break StopWatchLoop
	}

	log.Debugw("received-event", log.Fields{"type": event.EventType, "watch": pr.GetName()})

	switch event.EventType {
	case kvstore.DELETE:
	log.Debugw("delete-from-memory", log.Fields{"key": pr.GetHash(), "watch": pr.GetName()})
	pr.Revision.Drop("", true)
	break StopWatchLoop

	case kvstore.PUT:
	log.Debugw("update-in-memory", log.Fields{"key": pr.GetHash(), "watch": pr.GetName()})

	if dataPair, err := pr.kvStore.Get(pr.GetName()); err != nil \|\| dataPair == nil {
	log.Errorw("update-in-memory--key-retrieval-failed", log.Fields{"key": pr.GetHash(), "watch": pr.GetName(), "error": err})
	} else {
	data := reflect.New(reflect.TypeOf(pr.GetData()).Elem())

	if err := proto.Unmarshal(dataPair.Value.([]byte), data.Interface().(proto.Message)); err != nil {
	log.Errorw("update-in-memory--unmarshal-failed", log.Fields{"key": pr.GetHash(), "watch": pr.GetName(), "error": err})
	} else {
	if pr.GetNode().GetProxy() != nil {
	pr.LoadFromPersistence(pr.GetNode().GetProxy().getFullPath(), "")
	}
	}
	}

	default:
	log.Debugw("unhandled-event", log.Fields{"key": pr.GetHash(), "watch": pr.GetName(), "type": event.EventType})
	}
	}
	}

	Watches().Cache.Delete(pr.GetName() + "-" + pr.GetHash())

	log.Debugw("exiting-watch", log.Fields{"key": pr.GetHash(), "watch": pr.GetName(), "stack": string(debug.Stack())})
	}

	// UpdateData modifies the information in the data model and saves it in the persistent storage
	func (pr PersistedRevision) UpdateData(data interface{}, branch Branch) Revision {
	log.Debugw("updating-persisted-data", log.Fields{"hash": pr.GetHash()})

	newNPR := pr.Revision.UpdateData(data, branch)

	newPR := &PersistedRevision{
	Revision: newNPR,
	Compress: pr.Compress,
	kvStore: pr.kvStore,
	events: pr.events,
	}

	if newPR.GetHash() != pr.GetHash() {
	newPR.isWatched = false
	newPR.isStored = false
	pr.Drop(branch.Txid, false)
	newPR.SetupWatch(newPR.GetName())
	} else {
	newPR.isWatched = true
	newPR.isStored = true
	}

	return newPR
	}

	// UpdateChildren modifies the children of a revision and of a specific component and saves it in the persistent storage
	func (pr PersistedRevision) UpdateChildren(name string, children []Revision, branch Branch) Revision {
	log.Debugw("updating-persisted-children", log.Fields{"hash": pr.GetHash()})

	newNPR := pr.Revision.UpdateChildren(name, children, branch)

	newPR := &PersistedRevision{
	Revision: newNPR,
	Compress: pr.Compress,
	kvStore: pr.kvStore,
	events: pr.events,
	}

	if newPR.GetHash() != pr.GetHash() {
	newPR.isWatched = false
	newPR.isStored = false
	pr.Drop(branch.Txid, false)
	newPR.SetupWatch(newPR.GetName())
	} else {
	newPR.isWatched = true
	newPR.isStored = true
	}

	return newPR
	}

	// UpdateAllChildren modifies the children for all components of a revision and saves it in the peristent storage
	func (pr PersistedRevision) UpdateAllChildren(children map[string][]Revision, branch Branch) Revision {
	log.Debugw("updating-all-persisted-children", log.Fields{"hash": pr.GetHash()})

	newNPR := pr.Revision.UpdateAllChildren(children, branch)

	newPR := &PersistedRevision{
	Revision: newNPR,
	Compress: pr.Compress,
	kvStore: pr.kvStore,
	events: pr.events,
	}

	if newPR.GetHash() != pr.GetHash() {
	newPR.isWatched = false
	newPR.isStored = false
	pr.Drop(branch.Txid, false)
	newPR.SetupWatch(newPR.GetName())
	} else {
	newPR.isWatched = true
	newPR.isStored = true
	}

	return newPR
	}

	// Drop takes care of eliminating a revision hash that is no longer needed
	// and its associated config when required
	func (pr *PersistedRevision) Drop(txid string, includeConfig bool) {
	pr.Revision.Drop(txid, includeConfig)
	}

	// Drop takes care of eliminating a revision hash that is no longer needed
	// and its associated config when required
	func (pr *PersistedRevision) StorageDrop(txid string, includeConfig bool) {
	log.Debugw("dropping-revision",
	log.Fields{"txid": txid, "hash": pr.GetHash(), "config-hash": pr.GetConfig().Hash, "stack": string(debug.Stack())})

	pr.mutex.Lock()
	defer pr.mutex.Unlock()
	if pr.kvStore != nil && txid == "" {
	if pr.isStored {
	if pr.isWatched {
	pr.kvStore.DeleteWatch(pr.GetName(), pr.events)
	pr.isWatched = false
	}

	if err := pr.kvStore.Delete(pr.GetName()); err != nil {
	log.Errorw("failed-to-remove-revision", log.Fields{"hash": pr.GetHash(), "error": err.Error()})
	} else {
	pr.isStored = false
	}
	}

	} else {
	if includeConfig {
	log.Debugw("attempted-to-remove-transacted-revision-config", log.Fields{"hash": pr.GetConfig().Hash, "txid": txid})
	}
	log.Debugw("attempted-to-remove-transacted-revision", log.Fields{"hash": pr.GetHash(), "txid": txid})
	}

	pr.Revision.Drop(txid, includeConfig)
	}

	// verifyPersistedEntry validates if the provided data is available or not in memory and applies updates as required
	func (pr *PersistedRevision) verifyPersistedEntry(data interface{}, typeName string, keyName string, keyValue string, txid string) (response Revision) {
	rev := pr

	children := make([]Revision, len(rev.GetBranch().GetLatest().GetChildren(typeName)))
	copy(children, rev.GetBranch().GetLatest().GetChildren(typeName))

	// Verify if the revision contains a child that matches that key
	if childIdx, childRev := rev.GetNode().findRevByKey(rev.GetBranch().GetLatest().GetChildren(typeName), keyName, keyValue); childRev != nil {
	// A child matching the provided key exists in memory
	// Verify if the data differs to what was retrieved from persistence
	if childRev.GetData().(proto.Message).String() != data.(proto.Message).String() {
	log.Debugw("verify-persisted-entry--data-is-different", log.Fields{
	"key": childRev.GetHash(),
	"name": childRev.GetName(),
	})

	// Data has changed; replace the child entry and update the parent revision
	updatedChildRev := childRev.UpdateData(data, childRev.GetBranch())
	updatedChildRev.SetupWatch(updatedChildRev.GetName())
	childRev.Drop(txid, false)

	if childIdx >= 0 {
	children[childIdx] = updatedChildRev
	} else {
	children = append(children, updatedChildRev)
	}

	rev.GetBranch().LatestLock.Lock()
	updatedRev := rev.UpdateChildren(typeName, children, rev.GetBranch())
	rev.GetBranch().Node.makeLatest(rev.GetBranch(), updatedRev, nil)
	rev.GetBranch().LatestLock.Unlock()

	// Drop the previous child revision
	rev.GetBranch().Node.Latest().ChildDrop(typeName, childRev.GetHash())

	if updatedChildRev != nil {
	log.Debugw("verify-persisted-entry--adding-child", log.Fields{
	"key": updatedChildRev.GetHash(),
	"name": updatedChildRev.GetName(),
	})
	response = updatedChildRev
	}
	} else {
	// Data is the same. Continue to the next entry
	log.Debugw("verify-persisted-entry--same-data", log.Fields{
	"key": childRev.GetHash(),
	"name": childRev.GetName(),
	})
	if childRev != nil {
	log.Debugw("verify-persisted-entry--keeping-child", log.Fields{
	"key": childRev.GetHash(),
	"name": childRev.GetName(),
	})
	response = childRev
	}
	}
	} else {
	// There is no available child with that key value.
	// Create a new child and update the parent revision.
	log.Debugw("verify-persisted-entry--no-such-entry", log.Fields{
	"key": keyValue,
	"name": typeName,
	})

	// Construct a new child node with the retrieved persistence data
	childRev = rev.GetBranch().Node.MakeNode(data, txid).Latest(txid)

	// We need to start watching this entry for future changes
	childRev.SetName(typeName + "/" + keyValue)

	// Add the child to the parent revision
	rev.GetBranch().LatestLock.Lock()
	children = append(children, childRev)
	updatedRev := rev.GetBranch().Node.Latest().UpdateChildren(typeName, children, rev.GetBranch())
	childRev.SetupWatch(childRev.GetName())

	//rev.GetBranch().Node.Latest().Drop(txid, false)
	rev.GetBranch().Node.makeLatest(rev.GetBranch(), updatedRev, nil)
	rev.GetBranch().LatestLock.Unlock()

	// Child entry is valid and can be included in the response object
	if childRev != nil {
	log.Debugw("verify-persisted-entry--adding-child", log.Fields{
	"key": childRev.GetHash(),
	"name": childRev.GetName(),
	})
	response = childRev
	}
	}

	return response
	}

	// LoadFromPersistence retrieves data from kv store at the specified location and refreshes the memory
	// by adding missing entries, updating changed entries and ignoring unchanged ones
	func (pr *PersistedRevision) LoadFromPersistence(path string, txid string) []Revision {
	pr.mutex.Lock()
	defer pr.mutex.Unlock()

	log.Debugw("loading-from-persistence", log.Fields{"path": path, "txid": txid})

	var response []Revision
	var rev Revision

	rev = pr

	if pr.kvStore != nil && path != "" {
	blobMap, _ := pr.kvStore.List(path)

	partition := strings.SplitN(path, "/", 2)
	name := partition[0]

	if len(partition) < 2 {
	path = ""
	} else {
	path = partition[1]
	}

	field := ChildrenFields(rev.GetBranch().Node.Type)[name]

	if field != nil && field.IsContainer {
	log.Debugw("load-from-persistence--start-blobs", log.Fields{
	"path": path,
	"name": name,
	"size": len(blobMap),
	})

	for _, blob := range blobMap {
	output := blob.Value.([]byte)

	data := reflect.New(field.ClassType.Elem())

	if err := proto.Unmarshal(output, data.Interface().(proto.Message)); err != nil {
	log.Errorw("load-from-persistence--failed-to-unmarshal", log.Fields{
	"path": path,
	"txid": txid,
	"error": err,
	})
	} else if path == "" {
	if field.Key != "" {
	// Retrieve the key identifier value from the data structure
	// based on the field's key attribute
	_, key := GetAttributeValue(data.Interface(), field.Key, 0)

	if entry := pr.verifyPersistedEntry(data.Interface(), name, field.Key, key.String(), txid); entry != nil {
	response = append(response, entry)
	}
	}

	} else if field.Key != "" {
	// The request is for a specific entry/id
	partition := strings.SplitN(path, "/", 2)
	key := partition[0]
	if len(partition) < 2 {
	path = ""
	} else {
	path = partition[1]
	}
	keyValue := field.KeyFromStr(key)

	if entry := pr.verifyPersistedEntry(data.Interface(), name, field.Key, keyValue.(string), txid); entry != nil {
	response = append(response, entry)
	}
	}
	}

	log.Debugw("load-from-persistence--end-blobs", log.Fields{"path": path, "name": name})
	} else {
	log.Debugw("load-from-persistence--cannot-process-field", log.Fields{
	"type": rev.GetBranch().Node.Type,
	"name": name,
	})
	}
	}

	return response
	}