// beginCmd waits for any overlapping, already-executing commands via
// the command queue and adds itself to the queue to gate follow-on
// commands which overlap its key range. This method will block if
// there are any overlapping commands already in the queue. Returns
// the command queue insertion key, to be supplied to subsequent
// invocation of endCmd().
func (r *Range) beginCmd(header *proto.RequestHeader, readOnly bool) interface{} {
r.Lock()
var wg sync.WaitGroup
r.cmdQ.GetWait(header.Key, header.EndKey, readOnly, &wg)
cmdKey := r.cmdQ.Add(header.Key, header.EndKey, readOnly)
r.Unlock()
wg.Wait()
// Update the incoming timestamp if unset. Wait until after any
// preceding command(s) for key range are complete so that the node
// clock has been updated to the high water mark of any commands
// which might overlap this one in effect.
if header.Timestamp.Equal(proto.ZeroTimestamp) {
header.Timestamp = r.rm.Clock().Now()
}
return cmdKey
}
// TestTxnPutOutOfOrder tests a case where a put operation of an older
// timestamp comes after a put operation of a newer timestamp in a
// txn. The test ensures such an out-of-order put succeeds and
// overrides an old value. The test uses a "Writer" and a "Reader"
// to reproduce an out-of-order put.
//
// 1) The Writer executes a put operation and writes a write intent with
// time T in a txn.
// 2) Before the Writer's txn is committed, the Reader sends a high priority
// get operation with time T+100. This pushes the Writer txn timestamp to
// T+100 and triggers the restart of the Writer's txn. The original
// write intent timestamp is also updated to T+100.
// 3) The Writer starts a new epoch of the txn, but before it writes, the
// Reader sends another high priority get operation with time T+200. This
// pushes the Writer txn timestamp to T+200 to trigger a restart of the
// Writer txn. The Writer will not actually restart until it tries to commit
// the current epoch of the transaction. The Reader updates the timestamp of
// the write intent to T+200. The test deliberately fails the Reader get
// operation, and cockroach doesn't update its read timestamp cache.
// 4) The Writer executes the put operation again. This put operation comes
// out-of-order since its timestamp is T+100, while the intent timestamp
// updated at Step 3 is T+200.
// 5) The put operation overrides the old value using timestamp T+100.
// 6) When the Writer attempts to commit its txn, the txn will be restarted
// again at a new epoch timestamp T+200, which will finally succeed.
func TestTxnPutOutOfOrder(t *testing.T) {
defer leaktest.AfterTest(t)
key := "key"
// Set up a filter to so that the get operation at Step 3 will return an error.
var numGets int32
storage.TestingCommandFilter = func(args proto.Request) error {
if _, ok := args.(*proto.GetRequest); ok &&
args.Header().Key.Equal(proto.Key(key)) &&
args.Header().Txn == nil {
// The Reader executes two get operations, each of which triggers two get requests
// (the first request fails and triggers txn push, and then the second request
// succeeds). Returns an error for the fourth get request to avoid timestamp cache
// update after the third get operation pushes the txn timestamp.
if atomic.AddInt32(&numGets, 1) == 4 {
return util.Errorf("Test")
}
}
return nil
}
defer func() {
storage.TestingCommandFilter = nil
}()
manualClock := hlc.NewManualClock(0)
clock := hlc.NewClock(manualClock.UnixNano)
store, stopper := createTestStoreWithEngine(t,
engine.NewInMem(proto.Attributes{}, 10<<20),
clock,
true,
nil)
defer stopper.Stop()
// Put an initial value.
initVal := []byte("initVal")
err := store.DB().Put(key, initVal)
if err != nil {
t.Fatalf("failed to put: %s", err)
}
waitPut := make(chan struct{})
waitFirstGet := make(chan struct{})
waitTxnRestart := make(chan struct{})
waitSecondGet := make(chan struct{})
waitTxnComplete := make(chan struct{})
// Start the Writer.
go func() {
epoch := -1
// Start a txn that does read-after-write.
// The txn will be restarted twice, and the out-of-order put
// will happen in the second epoch.
if err := store.DB().Txn(func(txn *client.Txn) error {
epoch++
if epoch == 1 {
// Wait until the second get operation is issued.
close(waitTxnRestart)
<-waitSecondGet
}
updatedVal := []byte("updatedVal")
if err := txn.Put(key, updatedVal); err != nil {
return err
}
// Make sure a get will return the value that was just written.
actual, err := txn.Get(key)
if err != nil {
return err
}
if !bytes.Equal(actual.ValueBytes(), updatedVal) {
t.Fatalf("unexpected get result: %s", actual)
}
if epoch == 0 {
// Wait until the first get operation will push the txn timestamp.
close(waitPut)
<-waitFirstGet
}
b := &client.Batch{}
err = txn.Commit(b)
return err
}); err != nil {
t.Fatal(err)
}
if epoch != 2 {
t.Fatalf("unexpected number of txn retries: %d", epoch)
}
close(waitTxnComplete)
}()
<-waitPut
// Start the Reader.
// Advance the clock and send a get operation with higher
// priority to trigger the txn restart.
manualClock.Increment(100)
priority := int32(math.MaxInt32)
requestHeader := proto.RequestHeader{
Key: proto.Key(key),
RaftID: 1,
Replica: proto.Replica{StoreID: store.StoreID()},
UserPriority: &priority,
Timestamp: clock.Now(),
}
getCall := proto.Call{
Args: &proto.GetRequest{
RequestHeader: requestHeader,
},
Reply: &proto.GetResponse{},
}
err = store.ExecuteCmd(context.Background(), getCall)
if err != nil {
t.Fatalf("failed to get: %s", err)
}
// Wait until the writer restarts the txn.
close(waitFirstGet)
<-waitTxnRestart
// Advance the clock and send a get operation again. This time
// we use TestingCommandFilter so that a get operation is not
// processed after the write intent is resolved (to prevent the
// timestamp cache from being updated).
manualClock.Increment(100)
requestHeader.Timestamp = clock.Now()
getCall = proto.Call{
Args: &proto.GetRequest{
RequestHeader: requestHeader,
},
Reply: &proto.GetResponse{},
}
err = store.ExecuteCmd(context.Background(), getCall)
if err == nil {
t.Fatal("unexpected success of get")
}
close(waitSecondGet)
<-waitTxnComplete
}