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 keys 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 	// Compact frees all superseded keys with revisions less than rev.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"
@@ -98,11 +99,15 @@ type store struct {
 	fifoSched schedule.Scheduler
 
 	stopc chan struct{}
+
+	compactc chan struct{}
 }
 
 // NewStore returns a new store. It is useful to create a store inside
 // mvcc pkg. It should only be used for testing externally.
 func NewStore(b backend.Backend, le lease.Lessor, ig ConsistentIndexGetter) *store {
+	closedc := make(chan struct{})
+	close(closedc)
 	s := &store{
 		b:       b,
 		ig:      ig,
@@ -116,7 +121,8 @@ func NewStore(b backend.Backend, le lease.Lessor, ig ConsistentIndexGetter) *sto
 		bytesBuf8: make([]byte, 8),
 		fifoSched: schedule.NewFIFOScheduler(),
 
-		stopc: make(chan struct{}),
+		stopc:    make(chan struct{}),
+		compactc: closedc,
 	}
 	s.ReadView = &readView{s}
 	s.WriteView = &writeView{s}
@@ -160,6 +166,56 @@ 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) {
+	readTx := s.b.ReadTx()
+	for {
+		s.mu.RLock()
+		compactRev = s.compactMainRev
+		currentRev = s.currentRev
+		compactc := s.compactc
+		s.mu.RUnlock()
+		if rev > 0 && rev < compactRev {
+			return 0, 0, compactRev, ErrCompacted
+		} else if rev > 0 && rev > currentRev {
+			return 0, currentRev, 0, ErrFutureRev
+		}
+		select {
+		case <-compactc:
+		case <-s.stopc:
+			return 0, 0, 0, ErrClosed
+		}
+		s.mu.Lock()
+		if s.compactc == compactc {
+			s.b.ForceCommit()
+			currentRev = s.currentRev
+			compactRev = s.compactMainRev
+			readTx.Lock()
+			defer readTx.Unlock()
+			s.mu.Unlock()
+			break
+		}
+		s.mu.Unlock()
+	}
+
+	if rev == 0 {
+		rev = currentRev
+	}
+	upper := revision{main: rev + 1}
+	h := crc32.New(crc32.MakeTable(crc32.Castagnoli))
+
+	h.Write(keyBucketName)
+	err = readTx.UnsafeForEach(keyBucketName, func(k, v []byte) error {
+		if !upper.GreaterThan(bytesToRev(k)) {
+			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()
@@ -192,6 +248,7 @@ func (s *store) Compact(rev int64) (<-chan struct{}, error) {
 
 	keep := s.kvindex.Compact(rev)
 	ch := make(chan struct{})
+	s.compactc = ch
 	var j = func(ctx context.Context) {
 		if ctx.Err() != nil {
 			s.compactBarrier(ctx, ch)