v23/syncbase/nosql/database.go - roadmap.go.syncbase - Git at Google

 // Copyright 2015 The Vanadium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package nosql

 import (
 	"sync"
 	"time"

 	wire "v.io/syncbase/v23/services/syncbase/nosql"
 	"v.io/syncbase/v23/syncbase/util"
 	"v.io/v23/context"
 	"v.io/v23/naming"
 	"v.io/v23/security/access"
 	"v.io/v23/services/watch"
 	"v.io/v23/verror"
 	"v.io/x/lib/vlog"
 )

 const (
 	// Wait time before we try to reconnect a broken conflict resolution stream.
 	waitBeforeReconnectInMillis = 2 * time.Second
 	reconnectionCount = "rcc"
 )

 func NewDatabase(parentFullName, relativeName string, schema *Schema) *database {
 	fullName := naming.Join(parentFullName, relativeName)
 	return &database{
 		c:              wire.DatabaseClient(fullName),
 		parentFullName: parentFullName,
 		fullName:       fullName,
 		name:           relativeName,
 		schema:         schema,
 		crState: conflictResolutionState{
 			reconnectWaitTime: waitBeforeReconnectInMillis,
 		},
 	}
 }

 type database struct {
 	c              wire.DatabaseClientMethods
 	parentFullName string
 	fullName       string
 	name           string
 	schema         *Schema
 	crState        conflictResolutionState
 }

 // conflictResolutionState maintains data about the connection of
 // conflict resolution stream with syncbase. It provides a way to disconnect
 // an existing open stream.
 type conflictResolutionState struct {
 	mu                sync.Mutex // guards access to all fields in this struct
 	crContext         *context.T
 	cancelFn          context.CancelFunc
 	isClosed          bool
 	reconnectWaitTime time.Duration
 }

 func (crs *conflictResolutionState) disconnect() {
 	crs.mu.Lock()
 	defer crs.mu.Unlock()
 	crs.isClosed = true
 	crs.cancelFn()
 }

 func (crs *conflictResolutionState) isDisconnected() bool {
 	crs.mu.Lock()
 	defer crs.mu.Unlock()
 	return crs.isClosed
 }

 var _ Database = (*database)(nil)

 // TODO(sadovsky): Validate names before sending RPCs.

 // Name implements Database.Name.
 func (d *database) Name() string {
 	return d.name
 }

 // FullName implements Database.FullName.
 func (d *database) FullName() string {
 	return d.fullName
 }

 // Exists implements Database.Exists.
 func (d *database) Exists(ctx *context.T) (bool, error) {
 	return d.c.Exists(ctx, d.schemaVersion())
 }

 // Table implements Database.Table.
 func (d *database) Table(relativeName string) Table {
 	return newTable(d.fullName, relativeName, d.schemaVersion())
 }

 // ListTables implements Database.ListTables.
 func (d *database) ListTables(ctx *context.T) ([]string, error) {
 	return util.List(ctx, d.fullName)
 }

 // Create implements Database.Create.
 func (d *database) Create(ctx *context.T, perms access.Permissions) error {
 	var schemaMetadata *wire.SchemaMetadata = nil
 	if d.schema != nil {
 		schemaMetadata = &d.schema.Metadata
 	}
 	return d.c.Create(ctx, schemaMetadata, perms)
 }

 // Delete implements Database.Delete.
 func (d *database) Delete(ctx *context.T) error {
 	return d.c.Delete(ctx, d.schemaVersion())
 }

 // CreateTable implements Database.CreateTable.
 func (d *database) CreateTable(ctx *context.T, relativeName string, perms access.Permissions) error {
 	return wire.TableClient(naming.Join(d.fullName, relativeName)).Create(ctx, d.schemaVersion(), perms)
 }

 // DeleteTable implements Database.DeleteTable.
 func (d *database) DeleteTable(ctx *context.T, relativeName string) error {
 	return wire.TableClient(naming.Join(d.fullName, relativeName)).Delete(ctx, d.schemaVersion())
 }

 // Exec implements Database.Exec.
 func (d *database) Exec(ctx *context.T, query string) ([]string, ResultStream, error) {
 	ctx, cancel := context.WithCancel(ctx)
 	call, err := d.c.Exec(ctx, d.schemaVersion(), query)
 	if err != nil {
 		return nil, nil, err
 	}
 	resultStream := newResultStream(cancel, call)
 	// The first row contains headers, pull them off the stream
 	// and return them separately.
 	var headers []string
 	if !resultStream.Advance() {
 		if err = resultStream.Err(); err != nil {
 			// Since there was an error, can't get headers.
 			// Just return the error.
 			return nil, nil, err
 		}
 	}
 	for _, header := range resultStream.Result() {
 		headers = append(headers, header.RawString())
 	}
 	return headers, resultStream, nil
 }

 // BeginBatch implements Database.BeginBatch.
 func (d *database) BeginBatch(ctx *context.T, opts wire.BatchOptions) (BatchDatabase, error) {
 	relativeName, err := d.c.BeginBatch(ctx, d.schemaVersion(), opts)
 	if err != nil {
 		return nil, err
 	}
 	return &batch{database: *NewDatabase(d.parentFullName, relativeName, d.schema)}, nil
 }

 // SetPermissions implements Database.SetPermissions.
 func (d *database) SetPermissions(ctx *context.T, perms access.Permissions, version string) error {
 	return d.c.SetPermissions(ctx, perms, version)
 }

 // GetPermissions implements Database.GetPermissions.
 func (d *database) GetPermissions(ctx *context.T) (perms access.Permissions, version string, err error) {
 	return d.c.GetPermissions(ctx)
 }

 // Watch implements the Database interface.
 func (d *database) Watch(ctx *context.T, table, prefix string, resumeMarker watch.ResumeMarker) (WatchStream, error) {
 	ctx, cancel := context.WithCancel(ctx)
 	call, err := d.c.WatchGlob(ctx, watch.GlobRequest{
 		Pattern:      naming.Join(table, prefix+"*"),
 		ResumeMarker: resumeMarker,
 	})
 	if err != nil {
 		return nil, err
 	}
 	return newWatchStream(cancel, call), nil
 }

 // GetResumeMarker implements the Database interface.
 func (d *database) GetResumeMarker(ctx *context.T) (watch.ResumeMarker, error) {
 	return d.c.GetResumeMarker(ctx)
 }

 // SyncGroup implements Database.SyncGroup.
 func (d *database) SyncGroup(sgName string) SyncGroup {
 	return newSyncGroup(d.fullName, sgName)
 }

 // GetSyncGroupNames implements Database.GetSyncGroupNames.
 func (d *database) GetSyncGroupNames(ctx *context.T) ([]string, error) {
 	return d.c.GetSyncGroupNames(ctx)
 }

 // Blob implements Database.Blob.
 func (d *database) Blob(br wire.BlobRef) Blob {
 	return newBlob(d.fullName, br)
 }

 // CreateBlob implements Database.CreateBlob.
 func (d *database) CreateBlob(ctx *context.T) (Blob, error) {
 	return createBlob(ctx, d.fullName)
 }

 // EnforceSchema implements Database.EnforceSchema.
 func (d *database) EnforceSchema(ctx *context.T) error {
 	var schema *Schema = d.schema
 	if schema == nil {
 		return verror.New(verror.ErrBadState, ctx, "Schema or SchemaMetadata cannot be nil. A valid Schema needs to be used when creating DB handle.")
 	}

 	if schema.Metadata.Version < 0 {
 		return verror.New(verror.ErrBadState, ctx, "Schema version cannot be less than zero.")
 	}

 	if needsResolver(d.schema.Metadata) && d.schema.Resolver == nil {
 		return verror.New(verror.ErrBadState, ctx, "ResolverTypeAppResolves cannot be used in CrRule without providing a ConflictResolver in Schema.")
 	}

 	if _, err := d.upgradeIfOutdated(ctx); err != nil {
 		return err
 	}

 	if d.schema.Resolver == nil {
 		return nil
 	}

 	childCtx, cancelFn := context.WithCancel(ctx)
 	d.crState.crContext = childCtx
 	d.crState.cancelFn = cancelFn

 	go d.establishConflictResolution(childCtx)
 	return nil
 }

 // Close implements Database.Close.
 func (d *database) Close() {
 	d.crState.disconnect()
 }

 func (d *database) upgradeIfOutdated(ctx *context.T) (bool, error) {
 	var schema *Schema = d.schema
 	schemaMgr := d.getSchemaManager()
 	currMeta, err := schemaMgr.getSchemaMetadata(ctx)
 	if err != nil {
 		// If the client app did not set a schema as part of create db
 		// getSchemaMetadata() will return ErrNoExist. If so we set the schema
 		// here.
 		if verror.ErrorID(err) == verror.ErrNoExist.ID {
 			err := schemaMgr.setSchemaMetadata(ctx, schema.Metadata)
 			// The database may not yet exist. If so above call will return
 			// ErrNoExist and we return db without error. If the error
 			// is different then return the error to the caller.
 			if (err != nil) && (verror.ErrorID(err) != verror.ErrNoExist.ID) {
 				return false, err
 			}
 			return false, nil
 		}
 		return false, err
 	}

 	if currMeta.Version >= schema.Metadata.Version {
 		return false, nil
 	}
 	// Call the Upgrader provided by the app to upgrade the schema.
 	//
 	// TODO(jlodhia): disable sync before running Upgrader and reenable
 	// once Upgrader is finished.
 	//
 	// TODO(jlodhia): prevent other processes (local/remote) from accessing
 	// the database while upgrade is in progress.
 	upgradeErr := schema.Upgrader.Run(d, currMeta.Version, schema.Metadata.Version)
 	if upgradeErr != nil {
 		vlog.Error(upgradeErr)
 		return false, upgradeErr
 	}
 	// Update the schema metadata in db to the latest version.
 	metadataErr := schemaMgr.setSchemaMetadata(ctx, schema.Metadata)
 	if metadataErr != nil {
 		vlog.Error(metadataErr)
 		return false, metadataErr
 	}
 	return true, nil
 }

 func (d *database) establishConflictResolution(ctx *context.T) {
 	count := 0
 	for {
 		count++
 		vlog.Infof("Starting a new conflict resolution connection. Re-Connection count: %d", count)
 		childCtx := context.WithValue(ctx, reconnectionCount, count)
 		// listenForConflicts is a blocking method which returns only when the
 		// conflict stream is broken.
 		if err := d.listenForConflicts(childCtx); err != nil {
 			vlog.Errorf("Conflict resolution connection ended with error: %v", err)
 		}

 		// Check if database is closed and if we need to shutdown conflict
 		// resolution.
 		if d.crState.isDisconnected() {
 			vlog.Infof("Shutting down conflict resolution connection.")
 			break
 		}

 		// The connection might have broken because syncbase service went down.
 		// Sleep for a few seconds to allow syncbase to come back up.
 		time.Sleep(d.crState.reconnectWaitTime)
 	}
 }

 func (d *database) listenForConflicts(ctx *context.T) error {
 	resolver, err := d.c.StartConflictResolver(ctx)
 	if err != nil {
 		return err
 	}
 	conflictStream := resolver.RecvStream()
 	resolutionStream := resolver.SendStream()
 	var c *Conflict = &Conflict{}
 	for conflictStream.Advance() {
 		row := conflictStream.Value()
 		addRowToConflict(c, &row)
 		if !row.Continued {
 			resolution := d.schema.Resolver.OnConflict(ctx, c)
 			if err := sendResolution(resolutionStream, resolution); err != nil {
 				return err
 			}
 			c = &Conflict{}  // create a new conflict object for the next batch
 		}
 	}
 	if err := conflictStream.Err(); err != nil {
 		return err
 	}
 	return resolver.Finish()
 }

 // TODO(jlodhia): Should we check if the Resolution received addresses all
 // conflicts in write set?
 func sendResolution(stream interface {
 	Send(item wire.ResolutionInfo) error
 }, resolution Resolution) error {
 	size := len(resolution.ResultSet)
 	count := 0
 	for _, v := range resolution.ResultSet {
 		count++
 		ri := toResolutionInfo(v, count != size)
 		if err := stream.Send(ri); err != nil {
 			vlog.Error("Error while sending resolution")
 			return err
 		}
 	}
 	return nil
 }

 func addRowToConflict(c *Conflict, ci *wire.ConflictInfo) {
 	switch v := ci.Data.(type) {
 	case wire.ConflictDataBatch:
 		if c.Batches == nil {
 			c.Batches = map[uint16]wire.BatchInfo{}
 		}
 		c.Batches[v.Value.Id] = v.Value
 	case wire.ConflictDataRow:
 		rowInfo := v.Value
 		switch op := rowInfo.Op.(type) {
 		case wire.OperationWrite:
 			if c.WriteSet == nil {
 				c.WriteSet = &ConflictRowSet{map[string]ConflictRow{}, map[uint16][]ConflictRow{}}
 			}
 			cr := toConflictRow(op.Value, rowInfo.BatchIds)
 			c.WriteSet.ByKey[cr.Key] = cr
 			for _, bid := range rowInfo.BatchIds {
 				c.WriteSet.ByBatch[bid] = append(c.WriteSet.ByBatch[bid], cr)
 			}
 		case wire.OperationRead:
 			if c.ReadSet == nil {
 				c.ReadSet = &ConflictRowSet{map[string]ConflictRow{}, map[uint16][]ConflictRow{}}
 			}
 			cr := toConflictRow(op.Value, rowInfo.BatchIds)
 			c.ReadSet.ByKey[cr.Key] = cr
 			for _, bid := range rowInfo.BatchIds {
 				c.ReadSet.ByBatch[bid] = append(c.ReadSet.ByBatch[bid], cr)
 			}
 		case wire.OperationScan:
 			if c.ScanSet == nil {
 				c.ScanSet = &ConflictScanSet{map[uint16][]wire.ScanOp{}}
 			}
 			for _, bid := range rowInfo.BatchIds {
 				c.ScanSet.ByBatch[bid] = append(c.ScanSet.ByBatch[bid], op.Value)
 			}
 		}
 	}
 }

 func toConflictRow(op wire.RowOp, batchIds []uint16) ConflictRow {
 	var local, remote, ancestor *Value
 	if op.LocalValue != nil {
 		local = &Value{
 			val:       op.LocalValue.Bytes,
 			WriteTs:   toTime(op.LocalValue.WriteTs),
 			selection: wire.ValueSelectionLocal,
 		}
 	}
 	if op.RemoteValue != nil {
 		remote = &Value{
 			val:       op.RemoteValue.Bytes,
 			WriteTs:   toTime(op.RemoteValue.WriteTs),
 			selection: wire.ValueSelectionRemote,
 		}
 	}
 	if op.AncestorValue != nil {
 		ancestor = &Value{
 			val:       op.AncestorValue.Bytes,
 			WriteTs:   toTime(op.AncestorValue.WriteTs),
 			selection: wire.ValueSelectionOther,
 		}
 	}
 	return ConflictRow{
 		Key:           op.Key,
 		LocalValue:    local,
 		RemoteValue:   remote,
 		AncestorValue: ancestor,
 		BatchIds:      batchIds,
 	}
 }

 // TODO(jlodhia): remove this method once time is stored as time.Time instead
 // of int64
 func toTime(unixNanos int64) time.Time {
 	return time.Unix(
 		unixNanos / 1e9,  // seconds
 		unixNanos % 1e9)  // nanoseconds
 }

 func toResolutionInfo(r ResolvedRow, lastRow bool) wire.ResolutionInfo {
 	sel := wire.ValueSelectionOther
 	resVal := (*wire.Value)(nil)
 	if r.Result != nil {
 		sel = r.Result.selection
 		resVal = &wire.Value{
 			Bytes:   r.Result.val,
 			WriteTs: r.Result.WriteTs.UnixNano(),  // this timestamp is ignored by syncbase
 		}
 	}
 	return wire.ResolutionInfo{
 		Key:       r.Key,
 		Selection: sel,
 		Result:    resVal,
 		Continued: lastRow,
 	}
 }

 func needsResolver(metadata wire.SchemaMetadata) bool {
 	for _, rule := range metadata.Policy.Rules {
 		if rule.Resolver == wire.ResolverTypeAppResolves {
 			return true
 		}
 	}
 	return false
 }

 func (d *database) getSchemaManager() schemaManagerImpl {
 	return newSchemaManager(d.c)
 }

 func (d *database) schemaVersion() int32 {
 	if d.schema == nil {
 		return -1
 	}
 	return d.schema.Metadata.Version
 }
	// Copyright 2015 The Vanadium Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package nosql

	import (
	"sync"
	"time"

	wire "v.io/syncbase/v23/services/syncbase/nosql"
	"v.io/syncbase/v23/syncbase/util"
	"v.io/v23/context"
	"v.io/v23/naming"
	"v.io/v23/security/access"
	"v.io/v23/services/watch"
	"v.io/v23/verror"
	"v.io/x/lib/vlog"
	)

	const (
	// Wait time before we try to reconnect a broken conflict resolution stream.
	waitBeforeReconnectInMillis = 2 * time.Second
	reconnectionCount = "rcc"
	)

	func NewDatabase(parentFullName, relativeName string, schema Schema) database {
	fullName := naming.Join(parentFullName, relativeName)
	return &database{
	c: wire.DatabaseClient(fullName),
	parentFullName: parentFullName,
	fullName: fullName,
	name: relativeName,
	schema: schema,
	crState: conflictResolutionState{
	reconnectWaitTime: waitBeforeReconnectInMillis,
	},
	}
	}

	type database struct {
	c wire.DatabaseClientMethods
	parentFullName string
	fullName string
	name string
	schema *Schema
	crState conflictResolutionState
	}

	// conflictResolutionState maintains data about the connection of
	// conflict resolution stream with syncbase. It provides a way to disconnect
	// an existing open stream.
	type conflictResolutionState struct {
	mu sync.Mutex // guards access to all fields in this struct
	crContext *context.T
	cancelFn context.CancelFunc
	isClosed bool
	reconnectWaitTime time.Duration
	}

	func (crs *conflictResolutionState) disconnect() {
	crs.mu.Lock()
	defer crs.mu.Unlock()
	crs.isClosed = true
	crs.cancelFn()
	}

	func (crs *conflictResolutionState) isDisconnected() bool {
	crs.mu.Lock()
	defer crs.mu.Unlock()
	return crs.isClosed
	}

	var _ Database = (*database)(nil)

	// TODO(sadovsky): Validate names before sending RPCs.

	// Name implements Database.Name.
	func (d *database) Name() string {
	return d.name
	}

	// FullName implements Database.FullName.
	func (d *database) FullName() string {
	return d.fullName
	}

	// Exists implements Database.Exists.
	func (d database) Exists(ctx context.T) (bool, error) {
	return d.c.Exists(ctx, d.schemaVersion())
	}

	// Table implements Database.Table.
	func (d *database) Table(relativeName string) Table {
	return newTable(d.fullName, relativeName, d.schemaVersion())
	}

	// ListTables implements Database.ListTables.
	func (d database) ListTables(ctx context.T) ([]string, error) {
	return util.List(ctx, d.fullName)
	}

	// Create implements Database.Create.
	func (d database) Create(ctx context.T, perms access.Permissions) error {
	var schemaMetadata *wire.SchemaMetadata = nil
	if d.schema != nil {
	schemaMetadata = &d.schema.Metadata
	}
	return d.c.Create(ctx, schemaMetadata, perms)
	}

	// Delete implements Database.Delete.
	func (d database) Delete(ctx context.T) error {
	return d.c.Delete(ctx, d.schemaVersion())
	}

	// CreateTable implements Database.CreateTable.
	func (d database) CreateTable(ctx context.T, relativeName string, perms access.Permissions) error {
	return wire.TableClient(naming.Join(d.fullName, relativeName)).Create(ctx, d.schemaVersion(), perms)
	}

	// DeleteTable implements Database.DeleteTable.
	func (d database) DeleteTable(ctx context.T, relativeName string) error {
	return wire.TableClient(naming.Join(d.fullName, relativeName)).Delete(ctx, d.schemaVersion())
	}

	// Exec implements Database.Exec.
	func (d database) Exec(ctx context.T, query string) ([]string, ResultStream, error) {
	ctx, cancel := context.WithCancel(ctx)
	call, err := d.c.Exec(ctx, d.schemaVersion(), query)
	if err != nil {
	return nil, nil, err
	}
	resultStream := newResultStream(cancel, call)
	// The first row contains headers, pull them off the stream
	// and return them separately.
	var headers []string
	if !resultStream.Advance() {
	if err = resultStream.Err(); err != nil {
	// Since there was an error, can't get headers.
	// Just return the error.
	return nil, nil, err
	}
	}
	for _, header := range resultStream.Result() {
	headers = append(headers, header.RawString())
	}
	return headers, resultStream, nil
	}

	// BeginBatch implements Database.BeginBatch.
	func (d database) BeginBatch(ctx context.T, opts wire.BatchOptions) (BatchDatabase, error) {
	relativeName, err := d.c.BeginBatch(ctx, d.schemaVersion(), opts)
	if err != nil {
	return nil, err
	}
	return &batch{database: *NewDatabase(d.parentFullName, relativeName, d.schema)}, nil
	}

	// SetPermissions implements Database.SetPermissions.
	func (d database) SetPermissions(ctx context.T, perms access.Permissions, version string) error {
	return d.c.SetPermissions(ctx, perms, version)
	}

	// GetPermissions implements Database.GetPermissions.
	func (d database) GetPermissions(ctx context.T) (perms access.Permissions, version string, err error) {
	return d.c.GetPermissions(ctx)
	}

	// Watch implements the Database interface.
	func (d database) Watch(ctx context.T, table, prefix string, resumeMarker watch.ResumeMarker) (WatchStream, error) {
	ctx, cancel := context.WithCancel(ctx)
	call, err := d.c.WatchGlob(ctx, watch.GlobRequest{
	Pattern: naming.Join(table, prefix+"*"),
	ResumeMarker: resumeMarker,
	})
	if err != nil {
	return nil, err
	}
	return newWatchStream(cancel, call), nil
	}

	// GetResumeMarker implements the Database interface.
	func (d database) GetResumeMarker(ctx context.T) (watch.ResumeMarker, error) {
	return d.c.GetResumeMarker(ctx)
	}

	// SyncGroup implements Database.SyncGroup.
	func (d *database) SyncGroup(sgName string) SyncGroup {
	return newSyncGroup(d.fullName, sgName)
	}

	// GetSyncGroupNames implements Database.GetSyncGroupNames.
	func (d database) GetSyncGroupNames(ctx context.T) ([]string, error) {
	return d.c.GetSyncGroupNames(ctx)
	}

	// Blob implements Database.Blob.
	func (d *database) Blob(br wire.BlobRef) Blob {
	return newBlob(d.fullName, br)
	}

	// CreateBlob implements Database.CreateBlob.
	func (d database) CreateBlob(ctx context.T) (Blob, error) {
	return createBlob(ctx, d.fullName)
	}

	// EnforceSchema implements Database.EnforceSchema.
	func (d database) EnforceSchema(ctx context.T) error {
	var schema *Schema = d.schema
	if schema == nil {
	return verror.New(verror.ErrBadState, ctx, "Schema or SchemaMetadata cannot be nil. A valid Schema needs to be used when creating DB handle.")
	}

	if schema.Metadata.Version < 0 {
	return verror.New(verror.ErrBadState, ctx, "Schema version cannot be less than zero.")
	}

	if needsResolver(d.schema.Metadata) && d.schema.Resolver == nil {
	return verror.New(verror.ErrBadState, ctx, "ResolverTypeAppResolves cannot be used in CrRule without providing a ConflictResolver in Schema.")
	}

	if _, err := d.upgradeIfOutdated(ctx); err != nil {
	return err
	}

	if d.schema.Resolver == nil {
	return nil
	}

	childCtx, cancelFn := context.WithCancel(ctx)
	d.crState.crContext = childCtx
	d.crState.cancelFn = cancelFn

	go d.establishConflictResolution(childCtx)
	return nil
	}

	// Close implements Database.Close.
	func (d *database) Close() {
	d.crState.disconnect()
	}

	func (d database) upgradeIfOutdated(ctx context.T) (bool, error) {
	var schema *Schema = d.schema
	schemaMgr := d.getSchemaManager()
	currMeta, err := schemaMgr.getSchemaMetadata(ctx)
	if err != nil {
	// If the client app did not set a schema as part of create db
	// getSchemaMetadata() will return ErrNoExist. If so we set the schema
	// here.
	if verror.ErrorID(err) == verror.ErrNoExist.ID {
	err := schemaMgr.setSchemaMetadata(ctx, schema.Metadata)
	// The database may not yet exist. If so above call will return
	// ErrNoExist and we return db without error. If the error
	// is different then return the error to the caller.
	if (err != nil) && (verror.ErrorID(err) != verror.ErrNoExist.ID) {
	return false, err
	}
	return false, nil
	}
	return false, err
	}

	if currMeta.Version >= schema.Metadata.Version {
	return false, nil
	}
	// Call the Upgrader provided by the app to upgrade the schema.
	//
	// TODO(jlodhia): disable sync before running Upgrader and reenable
	// once Upgrader is finished.
	//
	// TODO(jlodhia): prevent other processes (local/remote) from accessing
	// the database while upgrade is in progress.
	upgradeErr := schema.Upgrader.Run(d, currMeta.Version, schema.Metadata.Version)
	if upgradeErr != nil {
	vlog.Error(upgradeErr)
	return false, upgradeErr
	}
	// Update the schema metadata in db to the latest version.
	metadataErr := schemaMgr.setSchemaMetadata(ctx, schema.Metadata)
	if metadataErr != nil {
	vlog.Error(metadataErr)
	return false, metadataErr
	}
	return true, nil
	}

	func (d database) establishConflictResolution(ctx context.T) {
	count := 0
	for {
	count++
	vlog.Infof("Starting a new conflict resolution connection. Re-Connection count: %d", count)
	childCtx := context.WithValue(ctx, reconnectionCount, count)
	// listenForConflicts is a blocking method which returns only when the
	// conflict stream is broken.
	if err := d.listenForConflicts(childCtx); err != nil {
	vlog.Errorf("Conflict resolution connection ended with error: %v", err)
	}

	// Check if database is closed and if we need to shutdown conflict
	// resolution.
	if d.crState.isDisconnected() {
	vlog.Infof("Shutting down conflict resolution connection.")
	break
	}

	// The connection might have broken because syncbase service went down.
	// Sleep for a few seconds to allow syncbase to come back up.
	time.Sleep(d.crState.reconnectWaitTime)
	}
	}

	func (d database) listenForConflicts(ctx context.T) error {
	resolver, err := d.c.StartConflictResolver(ctx)
	if err != nil {
	return err
	}
	conflictStream := resolver.RecvStream()
	resolutionStream := resolver.SendStream()
	var c *Conflict = &Conflict{}
	for conflictStream.Advance() {
	row := conflictStream.Value()
	addRowToConflict(c, &row)
	if !row.Continued {
	resolution := d.schema.Resolver.OnConflict(ctx, c)
	if err := sendResolution(resolutionStream, resolution); err != nil {
	return err
	}
	c = &Conflict{} // create a new conflict object for the next batch
	}
	}
	if err := conflictStream.Err(); err != nil {
	return err
	}
	return resolver.Finish()
	}

	// TODO(jlodhia): Should we check if the Resolution received addresses all
	// conflicts in write set?
	func sendResolution(stream interface {
	Send(item wire.ResolutionInfo) error
	}, resolution Resolution) error {
	size := len(resolution.ResultSet)
	count := 0
	for _, v := range resolution.ResultSet {
	count++
	ri := toResolutionInfo(v, count != size)
	if err := stream.Send(ri); err != nil {
	vlog.Error("Error while sending resolution")
	return err
	}
	}
	return nil
	}

	func addRowToConflict(c Conflict, ci wire.ConflictInfo) {
	switch v := ci.Data.(type) {
	case wire.ConflictDataBatch:
	if c.Batches == nil {
	c.Batches = map[uint16]wire.BatchInfo{}
	}
	c.Batches[v.Value.Id] = v.Value
	case wire.ConflictDataRow:
	rowInfo := v.Value
	switch op := rowInfo.Op.(type) {
	case wire.OperationWrite:
	if c.WriteSet == nil {
	c.WriteSet = &ConflictRowSet{map[string]ConflictRow{}, map[uint16][]ConflictRow{}}
	}
	cr := toConflictRow(op.Value, rowInfo.BatchIds)
	c.WriteSet.ByKey[cr.Key] = cr
	for _, bid := range rowInfo.BatchIds {
	c.WriteSet.ByBatch[bid] = append(c.WriteSet.ByBatch[bid], cr)
	}
	case wire.OperationRead:
	if c.ReadSet == nil {
	c.ReadSet = &ConflictRowSet{map[string]ConflictRow{}, map[uint16][]ConflictRow{}}
	}
	cr := toConflictRow(op.Value, rowInfo.BatchIds)
	c.ReadSet.ByKey[cr.Key] = cr
	for _, bid := range rowInfo.BatchIds {
	c.ReadSet.ByBatch[bid] = append(c.ReadSet.ByBatch[bid], cr)
	}
	case wire.OperationScan:
	if c.ScanSet == nil {
	c.ScanSet = &ConflictScanSet{map[uint16][]wire.ScanOp{}}
	}
	for _, bid := range rowInfo.BatchIds {
	c.ScanSet.ByBatch[bid] = append(c.ScanSet.ByBatch[bid], op.Value)
	}
	}
	}
	}

	func toConflictRow(op wire.RowOp, batchIds []uint16) ConflictRow {
	var local, remote, ancestor *Value
	if op.LocalValue != nil {
	local = &Value{
	val: op.LocalValue.Bytes,
	WriteTs: toTime(op.LocalValue.WriteTs),
	selection: wire.ValueSelectionLocal,
	}
	}
	if op.RemoteValue != nil {
	remote = &Value{
	val: op.RemoteValue.Bytes,
	WriteTs: toTime(op.RemoteValue.WriteTs),
	selection: wire.ValueSelectionRemote,
	}
	}
	if op.AncestorValue != nil {
	ancestor = &Value{
	val: op.AncestorValue.Bytes,
	WriteTs: toTime(op.AncestorValue.WriteTs),
	selection: wire.ValueSelectionOther,
	}
	}
	return ConflictRow{
	Key: op.Key,
	LocalValue: local,
	RemoteValue: remote,
	AncestorValue: ancestor,
	BatchIds: batchIds,
	}
	}

	// TODO(jlodhia): remove this method once time is stored as time.Time instead
	// of int64
	func toTime(unixNanos int64) time.Time {
	return time.Unix(
	unixNanos / 1e9, // seconds
	unixNanos % 1e9) // nanoseconds
	}

	func toResolutionInfo(r ResolvedRow, lastRow bool) wire.ResolutionInfo {
	sel := wire.ValueSelectionOther
	resVal := (*wire.Value)(nil)
	if r.Result != nil {
	sel = r.Result.selection
	resVal = &wire.Value{
	Bytes: r.Result.val,
	WriteTs: r.Result.WriteTs.UnixNano(), // this timestamp is ignored by syncbase
	}
	}
	return wire.ResolutionInfo{
	Key: r.Key,
	Selection: sel,
	Result: resVal,
	Continued: lastRow,
	}
	}

	func needsResolver(metadata wire.SchemaMetadata) bool {
	for _, rule := range metadata.Policy.Rules {
	if rule.Resolver == wire.ResolverTypeAppResolves {
	return true
	}
	}
	return false
	}

	func (d *database) getSchemaManager() schemaManagerImpl {
	return newSchemaManager(d.c)
	}

	func (d *database) schemaVersion() int32 {
	if d.schema == nil {
	return -1
	}
	return d.schema.Metadata.Version
	}