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snapshot_rollback.go
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/
snapshot_rollback.go
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// Copyright (c) 2017 Couchbase, Inc.
//
// 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 scorch
import (
"fmt"
"log"
"github.com/blevesearch/bleve/index/scorch/segment"
"github.com/boltdb/bolt"
)
type RollbackPoint struct {
epoch uint64
meta map[string][]byte
}
func (r *RollbackPoint) GetInternal(key []byte) []byte {
return r.meta[string(key)]
}
// RollbackPoints returns an array of rollback points available for
// the application to rollback to, with more recent rollback points
// (higher epochs) coming first.
func (s *Scorch) RollbackPoints() ([]*RollbackPoint, error) {
if s.rootBolt == nil {
return nil, fmt.Errorf("RollbackPoints: root is nil")
}
// start a read-only bolt transaction
tx, err := s.rootBolt.Begin(false)
if err != nil {
return nil, fmt.Errorf("RollbackPoints: failed to start" +
" read-only transaction")
}
// read-only bolt transactions to be rolled back
defer func() {
_ = tx.Rollback()
}()
snapshots := tx.Bucket(boltSnapshotsBucket)
if snapshots == nil {
return nil, nil
}
rollbackPoints := []*RollbackPoint{}
c1 := snapshots.Cursor()
for k, _ := c1.Last(); k != nil; k, _ = c1.Prev() {
_, snapshotEpoch, err := segment.DecodeUvarintAscending(k)
if err != nil {
log.Printf("RollbackPoints:"+
" unable to parse segment epoch %x, continuing", k)
continue
}
snapshot := snapshots.Bucket(k)
if snapshot == nil {
log.Printf("RollbackPoints:"+
" snapshot key, but bucket missing %x, continuing", k)
continue
}
meta := map[string][]byte{}
c2 := snapshot.Cursor()
for j, _ := c2.First(); j != nil; j, _ = c2.Next() {
if j[0] == boltInternalKey[0] {
internalBucket := snapshot.Bucket(j)
err = internalBucket.ForEach(func(key []byte, val []byte) error {
copiedVal := append([]byte(nil), val...)
meta[string(key)] = copiedVal
return nil
})
if err != nil {
break
}
}
}
if err != nil {
log.Printf("RollbackPoints:"+
" failed in fetching internal data: %v", err)
continue
}
rollbackPoints = append(rollbackPoints, &RollbackPoint{
epoch: snapshotEpoch,
meta: meta,
})
}
return rollbackPoints, nil
}
// Rollback atomically and durably (if unsafeBatch is unset) brings
// the store back to the point in time as represented by the
// RollbackPoint. Rollback() should only be passed a RollbackPoint
// that came from the same store using the RollbackPoints() API.
func (s *Scorch) Rollback(to *RollbackPoint) error {
if to == nil {
return fmt.Errorf("Rollback: RollbackPoint is nil")
}
if s.rootBolt == nil {
return fmt.Errorf("Rollback: root is nil")
}
revert := &snapshotReversion{}
s.rootLock.Lock()
err := s.rootBolt.View(func(tx *bolt.Tx) error {
snapshots := tx.Bucket(boltSnapshotsBucket)
if snapshots == nil {
return fmt.Errorf("Rollback: no snapshots available")
}
pos := segment.EncodeUvarintAscending(nil, to.epoch)
snapshot := snapshots.Bucket(pos)
if snapshot == nil {
return fmt.Errorf("Rollback: snapshot not found")
}
indexSnapshot, err := s.loadSnapshot(snapshot)
if err != nil {
return fmt.Errorf("Rollback: unable to load snapshot: %v", err)
}
// add segments referenced by loaded index snapshot to the
// ineligibleForRemoval map
for _, segSnap := range indexSnapshot.segment {
filename := zapFileName(segSnap.id)
s.ineligibleForRemoval[filename] = true
}
revert.snapshot = indexSnapshot
revert.applied = make(chan error)
revert.persisted = make(chan error)
return nil
})
s.rootLock.Unlock()
if err != nil {
return err
}
// introduce the reversion
s.revertToSnapshots <- revert
// block until this snapshot is applied
err = <-revert.applied
if err != nil {
return fmt.Errorf("Rollback: failed with err: %v", err)
}
return <-revert.persisted
}