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"
 	"context"
 	"reflect"
 	"strings"
 	"sync"

 	"github.com/golang/protobuf/proto"
 	"github.com/google/uuid"
 	"github.com/opencord/voltha-lib-go/v3/pkg/db"
 	"github.com/opencord/voltha-lib-go/v3/pkg/db/kvstore"
 	"github.com/opencord/voltha-lib-go/v3/pkg/log"
 )

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

 	events       chan *kvstore.Event
 	kvStore      *db.Backend
 	mutex        sync.RWMutex
 	versionMutex sync.RWMutex
 	Version      int64
 	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.Version = 1
 	pr.Revision = NewNonPersistedRevision(nil, branch, data, children)
 	return pr
 }

 func (pr *PersistedRevision) getVersion() int64 {
 	pr.versionMutex.RLock()
 	defer pr.versionMutex.RUnlock()
 	return pr.Version
 }

 func (pr *PersistedRevision) setVersion(version int64) {
 	pr.versionMutex.Lock()
 	defer pr.versionMutex.Unlock()
 	pr.Version = version
 }

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

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

 	log.Debugw("ready-to-store-revision", log.Fields{"hash": pr.GetHash(), "name": pr.GetName(), "data": pr.GetData()})

 	// clone the revision data to avoid any race conditions with processes
 	// accessing the same data
 	cloned := proto.Clone(pr.GetConfig().Data.(proto.Message))

 	if blob, err := proto.Marshal(cloned); err != nil {
 		log.Errorw("problem-to-marshal", log.Fields{"error": err, "hash": pr.GetHash(), "name": pr.GetName(), "data": pr.GetData()})
 	} else {
 		if pr.Compress {
 			var b bytes.Buffer
 			w := gzip.NewWriter(&b)
 			if _, err := w.Write(blob); err != nil {
 				log.Errorw("Unable to write a compressed form of p to the underlying io.Writer.", log.Fields{"error": err})
 			}
 			w.Close()
 			blob = b.Bytes()
 		}

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

 // SetupWatch -
 func (pr *PersistedRevision) SetupWatch(ctx context.Context, key string) {
 	if key == "" {
 		log.Debugw("ignoring-watch", log.Fields{"key": key, "revision-hash": pr.GetHash()})
 		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()})

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

 	if !pr.isWatched {
 		pr.isWatched = true

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

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

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

 StopWatchLoop:
 	for {
 		latestRev := pr.GetBranch().GetLatest()
 		event, ok := <-pr.events
 		if !ok {
 			log.Errorw("event-channel-failure: stopping watch loop", log.Fields{"key": latestRev.GetHash(), "watch": latestRev.GetName()})
 			break StopWatchLoop
 		}
 		log.Debugw("received-event", log.Fields{"type": event.EventType, "watch": latestRev.GetName()})

 		switch event.EventType {
 		case kvstore.DELETE:
 			log.Debugw("delete-from-memory", log.Fields{"key": latestRev.GetHash(), "watch": latestRev.GetName()})

 			// Remove reference from cache
 			getRevCache().Delete(latestRev.GetName())

 			// Remove reference from parent
 			parent := pr.GetBranch().Node.GetRoot()
 			parent.GetBranch(NONE).Latest.ChildDropByName(latestRev.GetName())

 			break StopWatchLoop

 		case kvstore.PUT:
 			log.Debugw("update-in-memory", log.Fields{"key": latestRev.GetHash(), "watch": latestRev.GetName()})
 			if latestRev.getVersion() >= event.Version {
 				log.Debugw("skipping-matching-or-older-revision", log.Fields{
 					"watch":          latestRev.GetName(),
 					"watch-version":  event.Version,
 					"latest-version": latestRev.getVersion(),
 				})
 				continue
 			} else {
 				log.Debugw("watch-revision-is-newer", log.Fields{
 					"watch":          latestRev.GetName(),
 					"watch-version":  event.Version,
 					"latest-version": latestRev.getVersion(),
 				})
 			}

 			data := reflect.New(reflect.TypeOf(latestRev.GetData()).Elem())

 			if err := proto.Unmarshal(event.Value.([]byte), data.Interface().(proto.Message)); err != nil {
 				log.Errorw("failed-to-unmarshal-watch-data", log.Fields{"key": latestRev.GetHash(), "watch": latestRev.GetName(), "error": err})
 			} else {
 				log.Debugw("un-marshaled-watch-data", log.Fields{"key": latestRev.GetHash(), "watch": latestRev.GetName(), "data": data.Interface()})

 				var pathLock string

 				// The watch reported new persistence data.
 				// Construct an object that will be used to update the memory
 				blobs := make(map[string]*kvstore.KVPair)
 				key, _ := kvstore.ToString(event.Key)
 				blobs[key] = &kvstore.KVPair{
 					Key:     key,
 					Value:   event.Value,
 					Session: "",
 					Lease:   0,
 					Version: event.Version,
 				}

 				if latestRev.getNode().GetProxy() != nil {
 					//
 					// 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 the proxy already has a request in progress, then there is no need to process the watch
 					if latestRev.getNode().GetProxy().GetOperation() != ProxyNone {
 						log.Debugw("operation-in-progress", log.Fields{
 							"key":       latestRev.GetHash(),
 							"path":      latestRev.getNode().GetProxy().getFullPath(),
 							"operation": latestRev.getNode().GetProxy().operation.String(),
 						})
 						continue
 					}

 					pathLock, _ = latestRev.getNode().GetProxy().parseForControlledPath(latestRev.getNode().GetProxy().getFullPath())

 					// Reserve the path to prevent others to modify while we reload from persistence
 					if _, err = latestRev.getNode().GetProxy().getRoot().KvStore.Client.Reserve(ctx, pathLock+"_", uuid.New().String(), ReservationTTL); err != nil {
 						log.Errorw("Unable to acquire a key and set it to a given value", log.Fields{"error": err})
 					}
 					latestRev.getNode().GetProxy().SetOperation(ProxyWatch)

 					// Load changes and apply to memory
 					if _, err = latestRev.LoadFromPersistence(ctx, latestRev.GetName(), "", blobs); err != nil {
 						log.Errorw("Unable to refresh the memory by adding missing entries", log.Fields{"error": err})
 					}

 					// Release path
 					if err = latestRev.getNode().GetProxy().getRoot().KvStore.Client.ReleaseReservation(ctx, pathLock+"_"); err != nil {
 						log.Errorw("Unable to release reservation for a specific key", log.Fields{"error": err})
 					}
 				} else {
 					// This block should be reached only if coming from a non-proxied request
 					log.Debugw("revision-with-no-proxy", log.Fields{"key": latestRev.GetHash(), "watch": latestRev.GetName()})

 					// Load changes and apply to memory
 					if _, err = latestRev.LoadFromPersistence(ctx, latestRev.GetName(), "", blobs); err != nil {
 						log.Errorw("Unable to refresh the memory by adding missing entries", log.Fields{"error": err})
 					}
 				}
 			}

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

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

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

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

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

 	newPR := &PersistedRevision{
 		Revision:  newNPR,
 		Compress:  pr.Compress,
 		kvStore:   pr.kvStore,
 		events:    pr.events,
 		Version:   pr.getVersion(),
 		isWatched: pr.isWatched,
 	}

 	if newPR.GetHash() != pr.GetHash() {
 		newPR.isStored = false
 		pr.Drop(branch.Txid, false)
 		pr.Drop(branch.Txid, false)
 	} else {
 		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(ctx context.Context, name string, children []Revision, branch *Branch) Revision {
 	log.Debugw("updating-persisted-children", log.Fields{"hash": pr.GetHash()})

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

 	newPR := &PersistedRevision{
 		Revision:  newNPR,
 		Compress:  pr.Compress,
 		kvStore:   pr.kvStore,
 		events:    pr.events,
 		Version:   pr.getVersion(),
 		isWatched: pr.isWatched,
 	}

 	if newPR.GetHash() != pr.GetHash() {
 		newPR.isStored = false
 		pr.Drop(branch.Txid, false)
 	} else {
 		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(ctx context.Context, children map[string][]Revision, branch *Branch) Revision {
 	log.Debugw("updating-all-persisted-children", log.Fields{"hash": pr.GetHash()})

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

 	newPR := &PersistedRevision{
 		Revision:  newNPR,
 		Compress:  pr.Compress,
 		kvStore:   pr.kvStore,
 		events:    pr.events,
 		Version:   pr.getVersion(),
 		isWatched: pr.isWatched,
 	}

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

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

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

 		if err := pr.kvStore.Delete(ctx, 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(ctx context.Context, data interface{}, typeName string, keyName string,
 	keyValue string, txid string, version int64) (response Revision) {
 	// Parent which holds the current node entry
 	parent := pr.GetBranch().Node.GetRoot()

 	// Get a copy of the parent's children
 	children := make([]Revision, len(parent.GetBranch(NONE).Latest.GetChildren(typeName)))
 	copy(children, parent.GetBranch(NONE).Latest.GetChildren(typeName))

 	// Verify if a child with the provided key value can be found
 	if childIdx, childRev := pr.getNode().findRevByKey(children, keyName, keyValue); childRev != nil {
 		// A child matching the provided key exists in memory
 		// Verify if the data differs from what was retrieved from persistence
 		// Also check if we are treating a newer revision of the data or not
 		if childRev.GetData().(proto.Message).String() != data.(proto.Message).String() && childRev.getVersion() < version {
 			log.Debugw("revision-data-is-different", log.Fields{
 				"key":               childRev.GetHash(),
 				"name":              childRev.GetName(),
 				"data":              childRev.GetData(),
 				"in-memory-version": childRev.getVersion(),
 				"persisted-version": version,
 			})

 			//
 			// Data has changed; replace the child entry and update the parent revision
 			//

 			// BEGIN Lock child -- prevent any incoming changes
 			childRev.GetBranch().LatestLock.Lock()

 			// Update child
 			updatedChildRev := childRev.UpdateData(ctx, data, childRev.GetBranch())

 			updatedChildRev.getNode().SetProxy(childRev.getNode().GetProxy())
 			updatedChildRev.SetupWatch(ctx, updatedChildRev.GetName())
 			updatedChildRev.SetLastUpdate()
 			updatedChildRev.(*PersistedRevision).setVersion(version)

 			// Update cache
 			getRevCache().Set(updatedChildRev.GetName(), updatedChildRev)
 			childRev.Drop(txid, false)

 			childRev.GetBranch().LatestLock.Unlock()
 			// END lock child

 			// Update child entry
 			children[childIdx] = updatedChildRev

 			// BEGIN lock parent -- Update parent
 			parent.GetBranch(NONE).LatestLock.Lock()

 			updatedRev := parent.GetBranch(NONE).GetLatest().UpdateChildren(ctx, typeName, children, parent.GetBranch(NONE))
 			parent.GetBranch(NONE).Node.makeLatest(parent.GetBranch(NONE), updatedRev, nil)

 			parent.GetBranch(NONE).LatestLock.Unlock()
 			// END lock parent

 			// Drop the previous child revision
 			parent.GetBranch(NONE).Latest.ChildDrop(typeName, childRev.GetHash())

 			if updatedChildRev != nil {
 				log.Debugw("verify-persisted-entry--adding-child", log.Fields{
 					"key":  updatedChildRev.GetHash(),
 					"name": updatedChildRev.GetName(),
 					"data": updatedChildRev.GetData(),
 				})
 				response = updatedChildRev
 			}
 		} else {
 			log.Debugw("keeping-revision-data", log.Fields{
 				"key":                 childRev.GetHash(),
 				"name":                childRev.GetName(),
 				"data":                childRev.GetData(),
 				"in-memory-version":   childRev.getVersion(),
 				"persistence-version": version,
 			})

 			// Update timestamp to reflect when it was last read and to reset tracked timeout
 			childRev.SetLastUpdate()
 			if childRev.getVersion() < version {
 				childRev.(*PersistedRevision).setVersion(version)
 			}
 			getRevCache().Set(childRev.GetName(), childRev)
 			response = childRev
 		}

 	} else {
 		// There is no available child with that key value.
 		// Create a new child and update the parent revision.
 		log.Debugw("no-such-revision-entry", log.Fields{
 			"key":     keyValue,
 			"name":    typeName,
 			"data":    data,
 			"version": version,
 		})

 		// BEGIN child lock
 		pr.GetBranch().LatestLock.Lock()

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

 		// We need to start watching this entry for future changes
 		childRev.SetName(typeName + "/" + keyValue)
 		childRev.SetupWatch(ctx, childRev.GetName())
 		childRev.(*PersistedRevision).setVersion(version)

 		// Add entry to cache
 		getRevCache().Set(childRev.GetName(), childRev)

 		pr.GetBranch().LatestLock.Unlock()
 		// END child lock

 		//
 		// Add the child to the parent revision
 		//

 		// BEGIN parent lock
 		parent.GetBranch(NONE).LatestLock.Lock()
 		children = append(children, childRev)
 		updatedRev := parent.GetBranch(NONE).GetLatest().UpdateChildren(ctx, typeName, children, parent.GetBranch(NONE))
 		updatedRev.getNode().SetProxy(parent.GetBranch(NONE).Node.GetProxy())
 		parent.GetBranch(NONE).Node.makeLatest(parent.GetBranch(NONE), updatedRev, nil)
 		parent.GetBranch(NONE).LatestLock.Unlock()
 		// END parent lock

 		// Child entry is valid and can be included in the response object
 		if childRev != nil {
 			log.Debugw("adding-revision-to-response", log.Fields{
 				"key":  childRev.GetHash(),
 				"name": childRev.GetName(),
 				"data": childRev.GetData(),
 			})
 			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(ctx context.Context, path string, txid string, blobs map[string]*kvstore.KVPair) ([]Revision, error) {
 	pr.mutex.Lock()
 	defer pr.mutex.Unlock()

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

 	var response []Revision
 	var err error

 	for strings.HasPrefix(path, "/") {
 		path = path[1:]
 	}

 	if pr.kvStore != nil && path != "" {
 		if len(blobs) == 0 {
 			log.Debugw("retrieve-from-kv", log.Fields{"path": path, "txid": txid})

 			if blobs, err = pr.kvStore.List(ctx, path); err != nil {
 				log.Errorw("failed-to-retrieve-data-from-kvstore", log.Fields{"error": err})
 				return nil, err
 			}
 		}

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

 		var nodeType interface{}
 		if len(partition) < 2 {
 			path = ""
 			nodeType = pr.GetBranch().Node.Type
 		} else {
 			path = partition[1]
 			nodeType = pr.GetBranch().Node.GetRoot().Type
 		}

 		field := ChildrenFields(nodeType)[name]

 		if field != nil && field.IsContainer {
 			log.Debugw("parsing-data-blobs", log.Fields{
 				"path": path,
 				"name": name,
 				"size": len(blobs),
 			})

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

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

 				if err := proto.Unmarshal(output, data.Interface().(proto.Message)); err != nil {
 					log.Errorw("failed-to-unmarshal", log.Fields{
 						"path":  path,
 						"txid":  txid,
 						"error": err,
 					})
 				} else if path == "" {
 					if field.Key != "" {
 						log.Debugw("no-path-with-container-key", log.Fields{
 							"path": path,
 							"txid": txid,
 							"data": data.Interface(),
 						})

 						// 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(ctx, data.Interface(), name, field.Key, key.String(), txid, blob.Version); entry != nil {
 							response = append(response, entry)
 						}
 					} else {
 						log.Debugw("path-with-no-container-key", log.Fields{
 							"path": path,
 							"txid": txid,
 							"data": data.Interface(),
 						})
 					}

 				} else if field.Key != "" {
 					log.Debugw("path-with-container-key", log.Fields{
 						"path": path,
 						"txid": txid,
 						"data": data.Interface(),
 					})
 					// 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(ctx, data.Interface(), name, field.Key, keyValue.(string), txid, blob.Version); entry != nil {
 						response = append(response, entry)
 					}
 				}
 			}

 			log.Debugw("no-more-data-blobs", log.Fields{"path": path, "name": name})
 		} else {
 			log.Debugw("cannot-process-field", log.Fields{
 				"type": pr.GetBranch().Node.Type,
 				"name": name,
 			})
 		}
 	}

 	return response, nil
 }
	/*
	* 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"
	"context"
	"reflect"
	"strings"
	"sync"

	"github.com/golang/protobuf/proto"
	"github.com/google/uuid"
	"github.com/opencord/voltha-lib-go/v3/pkg/db"
	"github.com/opencord/voltha-lib-go/v3/pkg/db/kvstore"
	"github.com/opencord/voltha-lib-go/v3/pkg/log"
	)

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

	events chan *kvstore.Event
	kvStore *db.Backend
	mutex sync.RWMutex
	versionMutex sync.RWMutex
	Version int64
	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.Version = 1
	pr.Revision = NewNonPersistedRevision(nil, branch, data, children)
	return pr
	}

	func (pr *PersistedRevision) getVersion() int64 {
	pr.versionMutex.RLock()
	defer pr.versionMutex.RUnlock()
	return pr.Version
	}

	func (pr *PersistedRevision) setVersion(version int64) {
	pr.versionMutex.Lock()
	defer pr.versionMutex.Unlock()
	pr.Version = version
	}

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

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

	log.Debugw("ready-to-store-revision", log.Fields{"hash": pr.GetHash(), "name": pr.GetName(), "data": pr.GetData()})

	// clone the revision data to avoid any race conditions with processes
	// accessing the same data
	cloned := proto.Clone(pr.GetConfig().Data.(proto.Message))

	if blob, err := proto.Marshal(cloned); err != nil {
	log.Errorw("problem-to-marshal", log.Fields{"error": err, "hash": pr.GetHash(), "name": pr.GetName(), "data": pr.GetData()})
	} else {
	if pr.Compress {
	var b bytes.Buffer
	w := gzip.NewWriter(&b)
	if _, err := w.Write(blob); err != nil {
	log.Errorw("Unable to write a compressed form of p to the underlying io.Writer.", log.Fields{"error": err})
	}
	w.Close()
	blob = b.Bytes()
	}

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

	// SetupWatch -
	func (pr *PersistedRevision) SetupWatch(ctx context.Context, key string) {
	if key == "" {
	log.Debugw("ignoring-watch", log.Fields{"key": key, "revision-hash": pr.GetHash()})
	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()})

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

	if !pr.isWatched {
	pr.isWatched = true

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

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

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

	StopWatchLoop:
	for {
	latestRev := pr.GetBranch().GetLatest()
	event, ok := <-pr.events
	if !ok {
	log.Errorw("event-channel-failure: stopping watch loop", log.Fields{"key": latestRev.GetHash(), "watch": latestRev.GetName()})
	break StopWatchLoop
	}
	log.Debugw("received-event", log.Fields{"type": event.EventType, "watch": latestRev.GetName()})

	switch event.EventType {
	case kvstore.DELETE:
	log.Debugw("delete-from-memory", log.Fields{"key": latestRev.GetHash(), "watch": latestRev.GetName()})

	// Remove reference from cache
	getRevCache().Delete(latestRev.GetName())

	// Remove reference from parent
	parent := pr.GetBranch().Node.GetRoot()
	parent.GetBranch(NONE).Latest.ChildDropByName(latestRev.GetName())

	break StopWatchLoop

	case kvstore.PUT:
	log.Debugw("update-in-memory", log.Fields{"key": latestRev.GetHash(), "watch": latestRev.GetName()})
	if latestRev.getVersion() >= event.Version {
	log.Debugw("skipping-matching-or-older-revision", log.Fields{
	"watch": latestRev.GetName(),
	"watch-version": event.Version,
	"latest-version": latestRev.getVersion(),
	})
	continue
	} else {
	log.Debugw("watch-revision-is-newer", log.Fields{
	"watch": latestRev.GetName(),
	"watch-version": event.Version,
	"latest-version": latestRev.getVersion(),
	})
	}

	data := reflect.New(reflect.TypeOf(latestRev.GetData()).Elem())

	if err := proto.Unmarshal(event.Value.([]byte), data.Interface().(proto.Message)); err != nil {
	log.Errorw("failed-to-unmarshal-watch-data", log.Fields{"key": latestRev.GetHash(), "watch": latestRev.GetName(), "error": err})
	} else {
	log.Debugw("un-marshaled-watch-data", log.Fields{"key": latestRev.GetHash(), "watch": latestRev.GetName(), "data": data.Interface()})

	var pathLock string

	// The watch reported new persistence data.
	// Construct an object that will be used to update the memory
	blobs := make(map[string]*kvstore.KVPair)
	key, _ := kvstore.ToString(event.Key)
	blobs[key] = &kvstore.KVPair{
	Key: key,
	Value: event.Value,
	Session: "",
	Lease: 0,
	Version: event.Version,
	}

	if latestRev.getNode().GetProxy() != nil {
	//
	// 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 the proxy already has a request in progress, then there is no need to process the watch
	if latestRev.getNode().GetProxy().GetOperation() != ProxyNone {
	log.Debugw("operation-in-progress", log.Fields{
	"key": latestRev.GetHash(),
	"path": latestRev.getNode().GetProxy().getFullPath(),
	"operation": latestRev.getNode().GetProxy().operation.String(),
	})
	continue
	}

	pathLock, _ = latestRev.getNode().GetProxy().parseForControlledPath(latestRev.getNode().GetProxy().getFullPath())

	// Reserve the path to prevent others to modify while we reload from persistence
	if _, err = latestRev.getNode().GetProxy().getRoot().KvStore.Client.Reserve(ctx, pathLock+"_", uuid.New().String(), ReservationTTL); err != nil {
	log.Errorw("Unable to acquire a key and set it to a given value", log.Fields{"error": err})
	}
	latestRev.getNode().GetProxy().SetOperation(ProxyWatch)

	// Load changes and apply to memory
	if _, err = latestRev.LoadFromPersistence(ctx, latestRev.GetName(), "", blobs); err != nil {
	log.Errorw("Unable to refresh the memory by adding missing entries", log.Fields{"error": err})
	}

	// Release path
	if err = latestRev.getNode().GetProxy().getRoot().KvStore.Client.ReleaseReservation(ctx, pathLock+"_"); err != nil {
	log.Errorw("Unable to release reservation for a specific key", log.Fields{"error": err})
	}
	} else {
	// This block should be reached only if coming from a non-proxied request
	log.Debugw("revision-with-no-proxy", log.Fields{"key": latestRev.GetHash(), "watch": latestRev.GetName()})

	// Load changes and apply to memory
	if _, err = latestRev.LoadFromPersistence(ctx, latestRev.GetName(), "", blobs); err != nil {
	log.Errorw("Unable to refresh the memory by adding missing entries", log.Fields{"error": err})
	}
	}
	}

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

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

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

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

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

	newPR := &PersistedRevision{
	Revision: newNPR,
	Compress: pr.Compress,
	kvStore: pr.kvStore,
	events: pr.events,
	Version: pr.getVersion(),
	isWatched: pr.isWatched,
	}

	if newPR.GetHash() != pr.GetHash() {
	newPR.isStored = false
	pr.Drop(branch.Txid, false)
	pr.Drop(branch.Txid, false)
	} else {
	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(ctx context.Context, name string, children []Revision, branch Branch) Revision {
	log.Debugw("updating-persisted-children", log.Fields{"hash": pr.GetHash()})

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

	newPR := &PersistedRevision{
	Revision: newNPR,
	Compress: pr.Compress,
	kvStore: pr.kvStore,
	events: pr.events,
	Version: pr.getVersion(),
	isWatched: pr.isWatched,
	}

	if newPR.GetHash() != pr.GetHash() {
	newPR.isStored = false
	pr.Drop(branch.Txid, false)
	} else {
	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(ctx context.Context, children map[string][]Revision, branch Branch) Revision {
	log.Debugw("updating-all-persisted-children", log.Fields{"hash": pr.GetHash()})

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

	newPR := &PersistedRevision{
	Revision: newNPR,
	Compress: pr.Compress,
	kvStore: pr.kvStore,
	events: pr.events,
	Version: pr.getVersion(),
	isWatched: pr.isWatched,
	}

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

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

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

	if err := pr.kvStore.Delete(ctx, 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(ctx context.Context, data interface{}, typeName string, keyName string,
	keyValue string, txid string, version int64) (response Revision) {
	// Parent which holds the current node entry
	parent := pr.GetBranch().Node.GetRoot()

	// Get a copy of the parent's children
	children := make([]Revision, len(parent.GetBranch(NONE).Latest.GetChildren(typeName)))
	copy(children, parent.GetBranch(NONE).Latest.GetChildren(typeName))

	// Verify if a child with the provided key value can be found
	if childIdx, childRev := pr.getNode().findRevByKey(children, keyName, keyValue); childRev != nil {
	// A child matching the provided key exists in memory
	// Verify if the data differs from what was retrieved from persistence
	// Also check if we are treating a newer revision of the data or not
	if childRev.GetData().(proto.Message).String() != data.(proto.Message).String() && childRev.getVersion() < version {
	log.Debugw("revision-data-is-different", log.Fields{
	"key": childRev.GetHash(),
	"name": childRev.GetName(),
	"data": childRev.GetData(),
	"in-memory-version": childRev.getVersion(),
	"persisted-version": version,
	})

	//
	// Data has changed; replace the child entry and update the parent revision
	//

	// BEGIN Lock child -- prevent any incoming changes
	childRev.GetBranch().LatestLock.Lock()

	// Update child
	updatedChildRev := childRev.UpdateData(ctx, data, childRev.GetBranch())

	updatedChildRev.getNode().SetProxy(childRev.getNode().GetProxy())
	updatedChildRev.SetupWatch(ctx, updatedChildRev.GetName())
	updatedChildRev.SetLastUpdate()
	updatedChildRev.(*PersistedRevision).setVersion(version)

	// Update cache
	getRevCache().Set(updatedChildRev.GetName(), updatedChildRev)
	childRev.Drop(txid, false)

	childRev.GetBranch().LatestLock.Unlock()
	// END lock child

	// Update child entry
	children[childIdx] = updatedChildRev

	// BEGIN lock parent -- Update parent
	parent.GetBranch(NONE).LatestLock.Lock()

	updatedRev := parent.GetBranch(NONE).GetLatest().UpdateChildren(ctx, typeName, children, parent.GetBranch(NONE))
	parent.GetBranch(NONE).Node.makeLatest(parent.GetBranch(NONE), updatedRev, nil)

	parent.GetBranch(NONE).LatestLock.Unlock()
	// END lock parent

	// Drop the previous child revision
	parent.GetBranch(NONE).Latest.ChildDrop(typeName, childRev.GetHash())

	if updatedChildRev != nil {
	log.Debugw("verify-persisted-entry--adding-child", log.Fields{
	"key": updatedChildRev.GetHash(),
	"name": updatedChildRev.GetName(),
	"data": updatedChildRev.GetData(),
	})
	response = updatedChildRev
	}
	} else {
	log.Debugw("keeping-revision-data", log.Fields{
	"key": childRev.GetHash(),
	"name": childRev.GetName(),
	"data": childRev.GetData(),
	"in-memory-version": childRev.getVersion(),
	"persistence-version": version,
	})

	// Update timestamp to reflect when it was last read and to reset tracked timeout
	childRev.SetLastUpdate()
	if childRev.getVersion() < version {
	childRev.(*PersistedRevision).setVersion(version)
	}
	getRevCache().Set(childRev.GetName(), childRev)
	response = childRev
	}

	} else {
	// There is no available child with that key value.
	// Create a new child and update the parent revision.
	log.Debugw("no-such-revision-entry", log.Fields{
	"key": keyValue,
	"name": typeName,
	"data": data,
	"version": version,
	})

	// BEGIN child lock
	pr.GetBranch().LatestLock.Lock()

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

	// We need to start watching this entry for future changes
	childRev.SetName(typeName + "/" + keyValue)
	childRev.SetupWatch(ctx, childRev.GetName())
	childRev.(*PersistedRevision).setVersion(version)

	// Add entry to cache
	getRevCache().Set(childRev.GetName(), childRev)

	pr.GetBranch().LatestLock.Unlock()
	// END child lock

	//
	// Add the child to the parent revision
	//

	// BEGIN parent lock
	parent.GetBranch(NONE).LatestLock.Lock()
	children = append(children, childRev)
	updatedRev := parent.GetBranch(NONE).GetLatest().UpdateChildren(ctx, typeName, children, parent.GetBranch(NONE))
	updatedRev.getNode().SetProxy(parent.GetBranch(NONE).Node.GetProxy())
	parent.GetBranch(NONE).Node.makeLatest(parent.GetBranch(NONE), updatedRev, nil)
	parent.GetBranch(NONE).LatestLock.Unlock()
	// END parent lock

	// Child entry is valid and can be included in the response object
	if childRev != nil {
	log.Debugw("adding-revision-to-response", log.Fields{
	"key": childRev.GetHash(),
	"name": childRev.GetName(),
	"data": childRev.GetData(),
	})
	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(ctx context.Context, path string, txid string, blobs map[string]kvstore.KVPair) ([]Revision, error) {
	pr.mutex.Lock()
	defer pr.mutex.Unlock()

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

	var response []Revision
	var err error

	for strings.HasPrefix(path, "/") {
	path = path[1:]
	}

	if pr.kvStore != nil && path != "" {
	if len(blobs) == 0 {
	log.Debugw("retrieve-from-kv", log.Fields{"path": path, "txid": txid})

	if blobs, err = pr.kvStore.List(ctx, path); err != nil {
	log.Errorw("failed-to-retrieve-data-from-kvstore", log.Fields{"error": err})
	return nil, err
	}
	}

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

	var nodeType interface{}
	if len(partition) < 2 {
	path = ""
	nodeType = pr.GetBranch().Node.Type
	} else {
	path = partition[1]
	nodeType = pr.GetBranch().Node.GetRoot().Type
	}

	field := ChildrenFields(nodeType)[name]

	if field != nil && field.IsContainer {
	log.Debugw("parsing-data-blobs", log.Fields{
	"path": path,
	"name": name,
	"size": len(blobs),
	})

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

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

	if err := proto.Unmarshal(output, data.Interface().(proto.Message)); err != nil {
	log.Errorw("failed-to-unmarshal", log.Fields{
	"path": path,
	"txid": txid,
	"error": err,
	})
	} else if path == "" {
	if field.Key != "" {
	log.Debugw("no-path-with-container-key", log.Fields{
	"path": path,
	"txid": txid,
	"data": data.Interface(),
	})

	// 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(ctx, data.Interface(), name, field.Key, key.String(), txid, blob.Version); entry != nil {
	response = append(response, entry)
	}
	} else {
	log.Debugw("path-with-no-container-key", log.Fields{
	"path": path,
	"txid": txid,
	"data": data.Interface(),
	})
	}

	} else if field.Key != "" {
	log.Debugw("path-with-container-key", log.Fields{
	"path": path,
	"txid": txid,
	"data": data.Interface(),
	})
	// 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(ctx, data.Interface(), name, field.Key, keyValue.(string), txid, blob.Version); entry != nil {
	response = append(response, entry)
	}
	}
	}

	log.Debugw("no-more-data-blobs", log.Fields{"path": path, "name": name})
	} else {
	log.Debugw("cannot-process-field", log.Fields{
	"type": pr.GetBranch().Node.Type,
	"name": name,
	})
	}
	}

	return response, nil
	}