// getInternal implements the actual logic of get function.
// The values of multiple versions for the given key should
// be organized as follows:
// ...
// keyA : MVCCMetatata of keyA
// keyA_Timestamp_n : value of version_n
// keyA_Timestamp_n-1 : value of version_n-1
// ...
// keyA_Timestamp_0 : value of version_0
// keyB : MVCCMetadata of keyB
// ...
func (mvcc *MVCC) getInternal(key Key, timestamp proto.Timestamp, txnID []byte) ([]byte, proto.Timestamp, []byte, error) {
meta := &proto.MVCCMetadata{}
ok, err := GetProto(mvcc.engine, key, meta)
if err != nil || !ok {
return nil, proto.Timestamp{}, nil, err
}
// If the read timestamp is greater than the latest one, we can just
// fetch the value without a scan.
if !timestamp.Less(meta.Timestamp) {
if len(meta.TxnID) > 0 && (len(txnID) == 0 || !bytes.Equal(meta.TxnID, txnID)) {
return nil, proto.Timestamp{}, nil, &writeIntentError{TxnID: meta.TxnID}
}
latestKey := mvccEncodeKey(key, meta.Timestamp)
val, err := mvcc.engine.Get(latestKey)
return val, meta.Timestamp, meta.TxnID, err
}
nextKey := mvccEncodeKey(key, timestamp)
// We use the PrefixEndKey(key) as the upper bound for scan.
// If there is no other version after nextKey, it won't return
// the value of the next key.
kvs, err := mvcc.engine.Scan(nextKey, PrefixEndKey(key), 1)
if len(kvs) > 0 {
_, ts, _ := mvccDecodeKey(kvs[0].Key)
return kvs[0].Value, ts, nil, err
}
return nil, proto.Timestamp{}, nil, err
}
// TestCoordinatorHeartbeat verifies periodic heartbeat of the
// transaction record.
func TestCoordinatorHeartbeat(t *testing.T) {
db, _, manual := createTestDB(t)
defer db.Close()
// Set heartbeat interval to 1ms for testing.
db.coordinator.heartbeatInterval = 1 * time.Millisecond
txnID := engine.Key("txn")
<-db.Put(createPutRequest(engine.Key("a"), []byte("value"), txnID))
// Verify 3 heartbeats.
var heartbeatTS proto.Timestamp
for i := 0; i < 3; i++ {
if err := util.IsTrueWithin(func() bool {
ok, txn, err := getTxn(db, engine.MakeKey(engine.KeyLocalTransactionPrefix, txnID))
if !ok || err != nil {
return false
}
// Advance clock by 1ns.
// Locking the coordinator to prevent a data race.
db.coordinator.Lock()
*manual = hlc.ManualClock(*manual + 1)
db.coordinator.Unlock()
if heartbeatTS.Less(*txn.LastHeartbeat) {
heartbeatTS = *txn.LastHeartbeat
return true
}
return false
}, 50*time.Millisecond); err != nil {
t.Error("expected initial heartbeat within 50ms")
}
}
}
// ExampleNewClock shows how to create a new
// hybrid logical clock based on the local machine's
// physical clock. The sanity checks in this example
// will, of course, not fail and the output will be
// the age of the Unix epoch in nanoseconds.
func ExampleNewClock() {
// Initialize a new clock, using the local
// physical clock.
c := NewClock(UnixNano)
// Update the state of the hybrid clock.
s := c.Now()
time.Sleep(50 * time.Nanosecond)
t := proto.Timestamp{WallTime: UnixNano()}
// The sanity checks below will usually never be triggered.
// Timestamp implements the util.Ordered interface.
if s.Less(t) || !t.Less(s) {
log.Fatalf("The later timestamp is smaller than the earlier one")
}
if t.WallTime-s.WallTime > 0 {
log.Fatalf("HLC timestamp %d deviates from physical clock %d", s, t)
}
if s.Logical > 0 {
log.Fatalf("Trivial timestamp has logical component")
}
fmt.Printf("The Unix Epoch is now approximately %dns old.\n", t.WallTime)
}
// Add the specified timestamp to the cache as covering the range of
// keys from start to end. If end is nil, the range covers the start
// key only. txnID is nil for no transaction. readOnly specifies
// whether the command adding this timestamp was read-only or not.
func (tc *TimestampCache) Add(start, end proto.Key, timestamp proto.Timestamp, txnID []byte, readOnly bool) {
// This gives us a memory-efficient end key if end is empty.
if len(end) == 0 {
end = start.Next()
start = end[:len(start)]
}
if tc.latest.Less(timestamp) {
tc.latest = timestamp
}
// Only add to the cache if the timestamp is more recent than the
// low water mark.
if tc.lowWater.Less(timestamp) {
// Check existing, overlapping entries. Remove superseded
// entries or return without adding this entry if necessary.
key := tc.cache.NewKey(start, end)
for _, o := range tc.cache.GetOverlaps(start, end) {
ce := o.Value.(cacheEntry)
if ce.readOnly != readOnly {
continue
}
if o.Key.Contains(key) && !ce.timestamp.Less(timestamp) {
return // don't add this key; there's already a cache entry with >= timestamp.
} else if key.Contains(o.Key) && !timestamp.Less(ce.timestamp) {
tc.cache.Del(o.Key) // delete existing key; this cache entry supersedes.
}
}
ce := cacheEntry{timestamp: timestamp, txnID: txnID, readOnly: readOnly}
tc.cache.Add(key, ce)
}
}
// Get returns the value for the key specified in the request, while
// satisfying the given timestamp condition. The key may be
// arbitrarily encoded; it will be binary-encoded to remove any
// internal null characters. If no value for the key exists, or has
// been deleted, returns nil for value.
//
// The values of multiple versions for the given key should
// be organized as follows:
// ...
// keyA : MVCCMetatata of keyA
// keyA_Timestamp_n : value of version_n
// keyA_Timestamp_n-1 : value of version_n-1
// ...
// keyA_Timestamp_0 : value of version_0
// keyB : MVCCMetadata of keyB
// ...
func (mvcc *MVCC) Get(key Key, timestamp proto.Timestamp, txn *proto.Transaction) (*proto.Value, error) {
binKey := encoding.EncodeBinary(nil, key)
meta := &proto.MVCCMetadata{}
ok, err := GetProto(mvcc.engine, binKey, meta)
if err != nil || !ok {
return nil, err
}
// If the read timestamp is greater than the latest one, we can just
// fetch the value without a scan.
ts := proto.Timestamp{}
var valBytes []byte
if !timestamp.Less(meta.Timestamp) {
if meta.Txn != nil && (txn == nil || !bytes.Equal(meta.Txn.ID, txn.ID)) {
return nil, &writeIntentError{Txn: meta.Txn}
}
latestKey := mvccEncodeKey(binKey, meta.Timestamp)
valBytes, err = mvcc.engine.Get(latestKey)
ts = meta.Timestamp
} else {
nextKey := mvccEncodeKey(binKey, timestamp)
// We use the PrefixEndKey(key) as the upper bound for scan.
// If there is no other version after nextKey, it won't return
// the value of the next key.
kvs, err := mvcc.engine.Scan(nextKey, PrefixEndKey(binKey), 1)
if len(kvs) == 0 {
return nil, err
}
_, ts, _ = mvccDecodeKey(kvs[0].Key)
valBytes = kvs[0].Value
}
if valBytes == nil {
return nil, nil
}
// Unmarshal the mvcc value.
value := &proto.MVCCValue{}
if err := gogoproto.Unmarshal(valBytes, value); err != nil {
return nil, err
}
// Set the timestamp if the value is not nil (i.e. not a deletion tombstone).
if value.Value != nil {
value.Value.Timestamp = &ts
} else if !value.Deleted {
log.Warningf("encountered MVCC value at key %q with a nil proto.Value but with !Deleted: %+v", key, value)
}
return value.Value, nil
}
// TestTxnCoordSenderHeartbeat verifies periodic heartbeat of the
// transaction record.
func TestTxnCoordSenderHeartbeat(t *testing.T) {
defer leaktest.AfterTest(t)
s := createTestDB(t)
defer s.Stop()
defer teardownHeartbeats(s.Sender)
// Set heartbeat interval to 1ms for testing.
s.Sender.heartbeatInterval = 1 * time.Millisecond
initialTxn := newTxn(s.Clock, proto.Key("a"))
call := proto.Call{
Args: createPutRequest(proto.Key("a"), []byte("value"), initialTxn),
Reply: &proto.PutResponse{}}
if err := sendCall(s.Sender, call); err != nil {
t.Fatal(err)
}
*initialTxn = *call.Reply.Header().Txn
// Verify 3 heartbeats.
var heartbeatTS proto.Timestamp
for i := 0; i < 3; i++ {
if err := util.IsTrueWithin(func() bool {
ok, txn, err := getTxn(s.Sender, initialTxn)
if !ok || err != nil {
return false
}
// Advance clock by 1ns.
// Locking the TxnCoordSender to prevent a data race.
s.Sender.Lock()
s.Manual.Increment(1)
s.Sender.Unlock()
if heartbeatTS.Less(*txn.LastHeartbeat) {
heartbeatTS = *txn.LastHeartbeat
return true
}
return false
}, 50*time.Millisecond); err != nil {
t.Error("expected initial heartbeat within 50ms")
}
}
}
// putInternal adds a new timestamped value to the specified key.
// If value is nil, creates a deletion tombstone value.
func (mvcc *MVCC) putInternal(key Key, timestamp proto.Timestamp, value proto.MVCCValue, txn *proto.Transaction) error {
if value.Value != nil && value.Value.Bytes != nil && value.Value.Integer != nil {
return util.Errorf("key %q value contains both a byte slice and an integer value: %+v", key, value)
}
meta := &proto.MVCCMetadata{}
ok, err := GetProto(mvcc.engine, key, meta)
if err != nil {
return err
}
// Use a batch because a put involves multiple writes.
var batch []interface{}
// In case the key metadata exists.
if ok {
// There is an uncommitted write intent and the current Put
// operation does not come from the same transaction.
// This should not happen since range should check the existing
// write intent before executing any Put action at MVCC level.
if meta.Txn != nil && (txn == nil || !bytes.Equal(meta.Txn.ID, txn.ID)) {
return &writeIntentError{Txn: meta.Txn}
}
// We can update the current metadata only if both the timestamp
// and epoch of the new intent are greater than or equal to
// existing. If either of these conditions doesn't hold, it's
// likely the case that an older RPC is arriving out of order.
if !timestamp.Less(meta.Timestamp) && (meta.Txn == nil || txn.Epoch >= meta.Txn.Epoch) {
// If this is an intent and timestamps have changed, need to remove old version.
if meta.Txn != nil && !timestamp.Equal(meta.Timestamp) {
batch = append(batch, BatchDelete(mvccEncodeKey(key, meta.Timestamp)))
}
meta = &proto.MVCCMetadata{Txn: txn, Timestamp: timestamp}
batchPut, err := MakeBatchPutProto(key, meta)
if err != nil {
return err
}
batch = append(batch, batchPut)
} else {
// In case we receive a Put request to update an old version,
// it must be an error since raft should handle any client
// retry from timeout.
return &writeTooOldError{Timestamp: meta.Timestamp, Txn: meta.Txn}
}
} else { // In case the key metadata does not exist yet.
// Create key metadata.
meta = &proto.MVCCMetadata{Txn: txn, Timestamp: timestamp}
batchPut, err := MakeBatchPutProto(key, meta)
if err != nil {
return err
}
batch = append(batch, batchPut)
}
// Make sure to zero the redundant timestamp (timestamp is encoded
// into the key, so don't need it in both places).
if value.Value != nil {
value.Value.Timestamp = nil
}
batchPut, err := MakeBatchPutProto(mvccEncodeKey(key, timestamp), &value)
if err != nil {
return err
}
batch = append(batch, batchPut)
return mvcc.engine.WriteBatch(batch)
}