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"
 	"encoding/hex"
 	"github.com/golang/protobuf/proto"
 	"github.com/google/uuid"
 	"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
 }

 // 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)
 }

 type revData struct {
 	Children map[string][]string
 	Config   string
 }

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

 	if pair, _ := pr.kvStore.Get(pr.GetHash()); pair != nil && skipOnExist {
 		log.Debugw("revision-config-already-exists", log.Fields{"hash": pr.GetHash()})
 		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.GetHash(), blob); err != nil {
 			log.Warnw("problem-storing-revision-config",
 				log.Fields{"error": err, "hash": pr.GetHash(), "data": pr.GetConfig().Data})
 		} else {
 			log.Debugw("storing-revision-config",
 				log.Fields{"hash": pr.GetHash(), "data": pr.GetConfig().Data})
 			pr.isStored = true
 		}
 	}
 }

 func (pr *PersistedRevision) SetupWatch(key string) {
 	if pr.events == nil {
 		pr.events = make(chan *kvstore.Event)

 		log.Debugw("setting-watch", log.Fields{"key": key})

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

 		pr.isWatched = true

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

 func (pr *PersistedRevision) updateInMemory(data interface{}) {
 	var pac *proxyAccessControl
 	var pathLock string

 	//
 	// If a proxy exists for this revision, use it to lock access to the path
 	// and prevent simultaneous updates to the object in memory
 	//
 	if pr.GetNode().GetProxy() != nil {
 		log.Debugw("update-in-memory--reserve-and-lock", log.Fields{"key": pr.GetHash(), "path": pathLock})
 		pathLock, _ = pr.GetNode().GetProxy().parseForControlledPath(pr.GetNode().GetProxy().getFullPath())
 		pac = PAC().ReservePath(pr.GetNode().GetProxy().getFullPath(), pr.GetNode().GetProxy(), pathLock)
 		pac.SetProxy(pr.GetNode().GetProxy())
 		pac.lock()

 		defer log.Debugw("update-in-memory--release-and-unlock", log.Fields{"key": pr.GetHash(), "path": pathLock})
 		defer pac.unlock()
 		defer PAC().ReleasePath(pathLock)
 	}

 	//
 	// Update the object in memory through a transaction
 	// This will allow for the object to be subsequently merged with any changes
 	// that might have occurred in memory
 	//

 	log.Debugw("update-in-memory--custom-transaction", log.Fields{"key": pr.GetHash()})

 	// Prepare the transaction
 	branch := pr.GetBranch()
 	latest := branch.GetLatest()
 	txidBin, _ := uuid.New().MarshalBinary()
 	txid := hex.EncodeToString(txidBin)[:12]

 	makeBranch := func(node *node) *Branch {
 		return node.MakeBranch(txid)
 	}

 	// Apply the update in a transaction branch
 	updatedRev := latest.GetNode().Update("", data, false, txid, makeBranch)
 	updatedRev.SetHash(latest.GetHash())

 	// Merge the transaction branch in memory
 	if mergedRev, _ := latest.GetNode().MergeBranch(txid, false); mergedRev != nil {
 		branch.SetLatest(mergedRev)
 	}

 	// The transaction branch must be deleted to free-up memory
 	//latest.GetNode().GetRoot().DeleteTxBranch(txid)
 }

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

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

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

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

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

 				if dataPair, err := pr.kvStore.Get(pr.GetHash()); err != nil || dataPair == nil {
 					log.Errorw("update-in-memory--key-retrieval-failed", log.Fields{"key": pr.GetHash(), "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(), "error": err})
 					} else {
 						pr.updateInMemory(data.Interface())
 					}
 				}

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

 	log.Debugw("exiting-watch", log.Fields{"key": pr.GetHash()})
 }

 func (pr *PersistedRevision) LoadFromPersistence(path string, txid string) []Revision {
 	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 {
 			var children []Revision
 			children = make([]Revision, len(rev.GetChildren(name)))
 			copy(children, rev.GetChildren(name))
 			existChildMap := make(map[string]int)
 			for i, child := range rev.GetChildren(name) {
 				existChildMap[child.GetHash()] = i
 			}

 			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(
 						"loading-from-persistence--failed-to-unmarshal",
 						log.Fields{"path": path, "txid": txid, "error": err},
 					)
 				} else if field.Key != "" {
 					var key reflect.Value
 					var keyValue interface{}
 					var keyStr string

 					if path == "" {
 						// e.g. /logical_devices --> path="" name=logical_devices key=""
 						_, key = GetAttributeValue(data.Interface(), field.Key, 0)
 						keyStr = key.String()

 					} else {
 						// e.g.
 						// /logical_devices/abcde --> path="abcde" name=logical_devices
 						// /logical_devices/abcde/image_downloads --> path="abcde/image_downloads" name=logical_devices

 						partition := strings.SplitN(path, "/", 2)
 						key := partition[0]
 						if len(partition) < 2 {
 							path = ""
 						} else {
 							path = partition[1]
 						}
 						keyValue = field.KeyFromStr(key)
 						keyStr = keyValue.(string)

 						if idx, childRev := rev.GetBranch().Node.findRevByKey(children, field.Key, keyValue); childRev != nil {
 							// Key is memory, continue recursing path
 							if newChildRev := childRev.LoadFromPersistence(path, txid); newChildRev != nil {
 								children[idx] = newChildRev[0]

 								rev := rev.UpdateChildren(name, rev.GetChildren(name), rev.GetBranch())
 								rev.GetBranch().Node.makeLatest(rev.GetBranch(), rev, nil)

 								response = append(response, newChildRev[0])
 								continue
 							}
 						}
 					}

 					childRev := rev.GetBranch().Node.MakeNode(data.Interface(), txid).Latest(txid)
 					childRev.SetHash(name + "/" + keyStr)

 					// Do not process a child that is already in memory
 					if _, childExists := existChildMap[childRev.GetHash()]; !childExists {
 						// Create watch for <component>/<key>
 						childRev.SetupWatch(childRev.GetHash())

 						children = append(children, childRev)
 						rev = rev.UpdateChildren(name, children, rev.GetBranch())

 						rev.GetBranch().Node.makeLatest(rev.GetBranch(), rev, nil)
 					}
 					response = append(response, childRev)
 					continue
 				}
 			}
 		}
 	}

 	return response
 }

 // 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,
 	}

 	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,
 	}

 	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,
 	}

 	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) {
 	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 includeConfig {
 				if err := pr.kvStore.Delete(pr.GetConfig().Hash); err != nil {
 					log.Errorw("failed-to-remove-revision-config", log.Fields{"hash": pr.GetConfig().Hash, "error": err.Error()})
 				}
 			}

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

 			if pr.isWatched {
 				pr.kvStore.DeleteWatch(pr.GetHash(), pr.events)
 				pr.isWatched = 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)
 }
	/*
	* 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"
	"encoding/hex"
	"github.com/golang/protobuf/proto"
	"github.com/google/uuid"
	"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
	}

	// 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)
	}

	type revData struct {
	Children map[string][]string
	Config string
	}

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

	if pair, _ := pr.kvStore.Get(pr.GetHash()); pair != nil && skipOnExist {
	log.Debugw("revision-config-already-exists", log.Fields{"hash": pr.GetHash()})
	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.GetHash(), blob); err != nil {
	log.Warnw("problem-storing-revision-config",
	log.Fields{"error": err, "hash": pr.GetHash(), "data": pr.GetConfig().Data})
	} else {
	log.Debugw("storing-revision-config",
	log.Fields{"hash": pr.GetHash(), "data": pr.GetConfig().Data})
	pr.isStored = true
	}
	}
	}

	func (pr *PersistedRevision) SetupWatch(key string) {
	if pr.events == nil {
	pr.events = make(chan *kvstore.Event)

	log.Debugw("setting-watch", log.Fields{"key": key})

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

	pr.isWatched = true

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

	func (pr *PersistedRevision) updateInMemory(data interface{}) {
	var pac *proxyAccessControl
	var pathLock string

	//
	// If a proxy exists for this revision, use it to lock access to the path
	// and prevent simultaneous updates to the object in memory
	//
	if pr.GetNode().GetProxy() != nil {
	log.Debugw("update-in-memory--reserve-and-lock", log.Fields{"key": pr.GetHash(), "path": pathLock})
	pathLock, _ = pr.GetNode().GetProxy().parseForControlledPath(pr.GetNode().GetProxy().getFullPath())
	pac = PAC().ReservePath(pr.GetNode().GetProxy().getFullPath(), pr.GetNode().GetProxy(), pathLock)
	pac.SetProxy(pr.GetNode().GetProxy())
	pac.lock()

	defer log.Debugw("update-in-memory--release-and-unlock", log.Fields{"key": pr.GetHash(), "path": pathLock})
	defer pac.unlock()
	defer PAC().ReleasePath(pathLock)
	}

	//
	// Update the object in memory through a transaction
	// This will allow for the object to be subsequently merged with any changes
	// that might have occurred in memory
	//

	log.Debugw("update-in-memory--custom-transaction", log.Fields{"key": pr.GetHash()})

	// Prepare the transaction
	branch := pr.GetBranch()
	latest := branch.GetLatest()
	txidBin, _ := uuid.New().MarshalBinary()
	txid := hex.EncodeToString(txidBin)[:12]

	makeBranch := func(node node) Branch {
	return node.MakeBranch(txid)
	}

	// Apply the update in a transaction branch
	updatedRev := latest.GetNode().Update("", data, false, txid, makeBranch)
	updatedRev.SetHash(latest.GetHash())

	// Merge the transaction branch in memory
	if mergedRev, _ := latest.GetNode().MergeBranch(txid, false); mergedRev != nil {
	branch.SetLatest(mergedRev)
	}

	// The transaction branch must be deleted to free-up memory
	//latest.GetNode().GetRoot().DeleteTxBranch(txid)
	}

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

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

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

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

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

	if dataPair, err := pr.kvStore.Get(pr.GetHash()); err != nil \|\| dataPair == nil {
	log.Errorw("update-in-memory--key-retrieval-failed", log.Fields{"key": pr.GetHash(), "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(), "error": err})
	} else {
	pr.updateInMemory(data.Interface())
	}
	}

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

	log.Debugw("exiting-watch", log.Fields{"key": pr.GetHash()})
	}

	func (pr *PersistedRevision) LoadFromPersistence(path string, txid string) []Revision {
	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 {
	var children []Revision
	children = make([]Revision, len(rev.GetChildren(name)))
	copy(children, rev.GetChildren(name))
	existChildMap := make(map[string]int)
	for i, child := range rev.GetChildren(name) {
	existChildMap[child.GetHash()] = i
	}

	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(
	"loading-from-persistence--failed-to-unmarshal",
	log.Fields{"path": path, "txid": txid, "error": err},
	)
	} else if field.Key != "" {
	var key reflect.Value
	var keyValue interface{}
	var keyStr string

	if path == "" {
	// e.g. /logical_devices --> path="" name=logical_devices key=""
	_, key = GetAttributeValue(data.Interface(), field.Key, 0)
	keyStr = key.String()

	} else {
	// e.g.
	// /logical_devices/abcde --> path="abcde" name=logical_devices
	// /logical_devices/abcde/image_downloads --> path="abcde/image_downloads" name=logical_devices

	partition := strings.SplitN(path, "/", 2)
	key := partition[0]
	if len(partition) < 2 {
	path = ""
	} else {
	path = partition[1]
	}
	keyValue = field.KeyFromStr(key)
	keyStr = keyValue.(string)

	if idx, childRev := rev.GetBranch().Node.findRevByKey(children, field.Key, keyValue); childRev != nil {
	// Key is memory, continue recursing path
	if newChildRev := childRev.LoadFromPersistence(path, txid); newChildRev != nil {
	children[idx] = newChildRev[0]

	rev := rev.UpdateChildren(name, rev.GetChildren(name), rev.GetBranch())
	rev.GetBranch().Node.makeLatest(rev.GetBranch(), rev, nil)

	response = append(response, newChildRev[0])
	continue
	}
	}
	}

	childRev := rev.GetBranch().Node.MakeNode(data.Interface(), txid).Latest(txid)
	childRev.SetHash(name + "/" + keyStr)

	// Do not process a child that is already in memory
	if _, childExists := existChildMap[childRev.GetHash()]; !childExists {
	// Create watch for <component>/<key>
	childRev.SetupWatch(childRev.GetHash())

	children = append(children, childRev)
	rev = rev.UpdateChildren(name, children, rev.GetBranch())

	rev.GetBranch().Node.makeLatest(rev.GetBranch(), rev, nil)
	}
	response = append(response, childRev)
	continue
	}
	}
	}
	}

	return response
	}

	// 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,
	}

	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,
	}

	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,
	}

	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) {
	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 includeConfig {
	if err := pr.kvStore.Delete(pr.GetConfig().Hash); err != nil {
	log.Errorw("failed-to-remove-revision-config", log.Fields{"hash": pr.GetConfig().Hash, "error": err.Error()})
	}
	}

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

	if pr.isWatched {
	pr.kvStore.DeleteWatch(pr.GetHash(), pr.events)
	pr.isWatched = 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)
	}