mvcc: add HashByRev to kv.go

HashByRev computes the hash of all MVCC keys up to a given revision.

mvcc/kv.go

@@ -107,10 +107,12 @@ type KV interface {
 	// Write creates a write transaction.
 	Write() TxnWrite
 
-	// Hash retrieves the hash of KV state and revision.
-	// This method is designed for consistency checking purposes.
+	// Hash computes the hash of the KV's backend.
 	Hash() (hash uint32, revision int64, err error)
 
+	// HashByRev computes the hash of all MVCC revisions up to a given revision.
+	HashByRev(rev int64) (hash uint32, revision int64, compactRev int64, err error)
+
 	// Compact frees all superseded keys with revisions less than rev.
 	Compact(rev int64) (<-chan struct{}, error)
 

mvcc/kvstore.go

@@ -17,6 +17,7 @@ package mvcc
 import (
 	"encoding/binary"
 	"errors"
+	"hash/crc32"
 	"math"
 	"sync"
 	"sync/atomic"
@@ -44,6 +45,8 @@ var (
 	ErrClosed    = errors.New("mvcc: closed")
 
 	plog = capnslog.NewPackageLogger("github.com/coreos/etcd", "mvcc")
+
+	emptyKeep = make(map[revision]struct{})
 )
 
 const (
@@ -98,6 +101,12 @@ type store struct {
 	fifoSched schedule.Scheduler
 
 	stopc chan struct{}
+
+	// keepMu protects keep
+	keepMu sync.RWMutex
+	// keep contains all revisions <= compactMainRev to be kept for the
+	// ongoing compaction; nil otherwise.
+	keep map[revision]struct{}
 }
 
 // NewStore returns a new store. It is useful to create a store inside
@@ -160,6 +169,63 @@ func (s *store) Hash() (hash uint32, revision int64, err error) {
 	return h, s.currentRev, err
 }
 
+func (s *store) HashByRev(rev int64) (hash uint32, currentRev int64, compactRev int64, err error) {
+	s.mu.Lock()
+	s.revMu.RLock()
+	compactRev, currentRev = s.compactMainRev, s.currentRev
+	s.revMu.RUnlock()
+
+	if rev > 0 && rev <= compactRev {
+		s.mu.Unlock()
+		return 0, 0, compactRev, ErrCompacted
+	} else if rev > 0 && rev > currentRev {
+		s.mu.Unlock()
+		return 0, currentRev, 0, ErrFutureRev
+	}
+
+	s.keepMu.Lock()
+	if s.keep == nil {
+		// ForceCommit ensures that txnRead begins after backend
+		// has committed all the changes from the prev completed compaction.
+		s.b.ForceCommit()
+		s.keep = emptyKeep
+	}
+	keep := s.keep
+	s.keepMu.Unlock()
+
+	tx := s.b.ReadTx()
+	tx.Lock()
+	defer tx.Unlock()
+	s.mu.Unlock()
+
+	if rev == 0 {
+		rev = currentRev
+	}
+
+	upper := revision{main: rev + 1}
+	lower := revision{main: compactRev + 1}
+	h := crc32.New(crc32.MakeTable(crc32.Castagnoli))
+
+	h.Write(keyBucketName)
+	err = tx.UnsafeForEach(keyBucketName, func(k, v []byte) error {
+		kr := bytesToRev(k)
+		if !upper.GreaterThan(kr) {
+			return nil
+		}
+		// skip revisions that are scheduled for deletion
+		// due to compacting; don't skip if there isn't one.
+		if lower.GreaterThan(kr) && len(keep) > 0 {
+			if _, ok := keep[kr]; !ok {
+				return nil
+			}
+		}
+		h.Write(k)
+		h.Write(v)
+		return nil
+	})
+	return h.Sum32(), currentRev, compactRev, err
+}
+
 func (s *store) Compact(rev int64) (<-chan struct{}, error) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
@@ -191,6 +257,9 @@ func (s *store) Compact(rev int64) (<-chan struct{}, error) {
 	s.b.ForceCommit()
 
 	keep := s.kvindex.Compact(rev)
+	s.keepMu.Lock()
+	s.keep = keep
+	s.keepMu.Unlock()
 	ch := make(chan struct{})
 	var j = func(ctx context.Context) {
 		if ctx.Err() != nil {
@@ -202,6 +271,9 @@ func (s *store) Compact(rev int64) (<-chan struct{}, error) {
 			return
 		}
 		close(ch)
+		s.keepMu.Lock()
+		s.keep = nil
+		s.keepMu.Unlock()
 	}
 
 	s.fifoSched.Schedule(j)