Golang DB.Get方法代碼示例

// GetTableDescriptor retrieves a table descriptor directly from the KV layer.
func GetTableDescriptor(kvDB *client.DB, database string, table string) *TableDescriptor {
	dbNameKey := MakeNameMetadataKey(keys.RootNamespaceID, database)
	gr, err := kvDB.Get(dbNameKey)
	if err != nil {
		panic(err)
	}
	if !gr.Exists() {
		panic("database missing")
	}
	dbDescID := ID(gr.ValueInt())

	tableNameKey := MakeNameMetadataKey(dbDescID, table)
	gr, err = kvDB.Get(tableNameKey)
	if err != nil {
		panic(err)
	}
	if !gr.Exists() {
		panic("table missing")
	}

	descKey := MakeDescMetadataKey(ID(gr.ValueInt()))
	desc := &Descriptor{}
	if err := kvDB.GetProto(descKey, desc); err != nil {
		panic("proto missing")
	}
	return desc.GetTable()
}

// concurrentIncrements starts two Goroutines in parallel, both of which
// read the integers stored at the other's key and add it onto their own.
// It is checked that the outcome is serializable, i.e. exactly one of the
// two Goroutines (the later write) sees the previous write by the other.
func concurrentIncrements(db *client.DB, t *testing.T) {
	// wgStart waits for all transactions to line up, wgEnd has the main
	// function wait for them to finish.
	var wgStart, wgEnd sync.WaitGroup
	wgStart.Add(2 + 1)
	wgEnd.Add(2)

	for i := 0; i < 2; i++ {
		go func(i int) {
			// Read the other key, write key i.
			readKey := []byte(fmt.Sprintf(testUser+"/value-%d", (i+1)%2))
			writeKey := []byte(fmt.Sprintf(testUser+"/value-%d", i))
			defer wgEnd.Done()
			wgStart.Done()
			// Wait until the other goroutines are running.
			wgStart.Wait()

			if pErr := db.Txn(func(txn *client.Txn) *roachpb.Error {
				txn.SetDebugName(fmt.Sprintf("test-%d", i), 0)

				// Retrieve the other key.
				gr, pErr := txn.Get(readKey)
				if pErr != nil {
					return pErr
				}

				otherValue := int64(0)
				if gr.Value != nil {
					otherValue = gr.ValueInt()
				}

				_, pErr = txn.Inc(writeKey, 1+otherValue)
				return pErr
			}); pErr != nil {
				t.Error(pErr)
			}
		}(i)
	}

	// Kick the goroutines loose.
	wgStart.Done()
	// Wait for the goroutines to finish.
	wgEnd.Wait()
	// Verify that both keys contain something and, more importantly, that
	// one key actually contains the value of the first writer and not only
	// its own.
	total := int64(0)
	results := []int64(nil)
	for i := 0; i < 2; i++ {
		readKey := []byte(fmt.Sprintf(testUser+"/value-%d", i))
		gr, pErr := db.Get(readKey)
		if pErr != nil {
			t.Fatal(pErr)
		}
		if gr.Value == nil {
			t.Fatalf("unexpected empty key: %s=%v", readKey, gr.Value)
		}
		total += gr.ValueInt()
		results = append(results, gr.ValueInt())
	}

	// First writer should have 1, second one 2
	if total != 3 {
		t.Fatalf("got unserializable values %v", results)
	}
}

// concurrentIncrements starts two Goroutines in parallel, both of which
// read the integers stored at the other's key and add it onto their own.
// It is checked that the outcome is serializable, i.e. exactly one of the
// two Goroutines (the later write) sees the previous write by the other.
// The isMultiphase option runs the transaction in multiple phases recreating
// the transaction from the transaction protobuf returned from the server.
func concurrentIncrements(db *client.DB, t *testing.T, isMultiphase bool) {
	// wgStart waits for all transactions to line up, wgEnd has the main
	// function wait for them to finish.
	var wgStart, wgEnd sync.WaitGroup
	wgStart.Add(2 + 1)
	wgEnd.Add(2)

	for i := 0; i < 2; i++ {
		go func(i int) {
			// Read the other key, write key i.
			readKey := []byte(fmt.Sprintf(testUser+"/value-%d", (i+1)%2))
			writeKey := []byte(fmt.Sprintf(testUser+"/value-%d", i))
			defer wgEnd.Done()
			wgStart.Done()
			// Wait until the other goroutines are running.
			wgStart.Wait()

			if isMultiphase {
				applyInc := func(txn *client.Txn) (error, proto.Transaction) {
					txn.SetDebugName(fmt.Sprintf("test-%d", i))
					b := client.Batch{}
					// Retrieve the other key.
					b.Get(readKey)
					if err := txn.Run(&b); err != nil {
						return err, txn.GetState()
					}
					otherValue := int64(0)
					gr := b.Results[0].Rows[0]
					if gr.Value != nil {
						otherValue = gr.ValueInt()
					}
					// New txn.
					txn = db.ReconstructTxn(txn.GetState())
					// Write our key.
					b = client.Batch{}
					b.Inc(writeKey, 1+otherValue)
					if err := txn.Run(&b); err != nil {
						return err, txn.GetState()
					}
					// New txn.
					txn = db.ReconstructTxn(txn.GetState())
					err := txn.Commit(&client.Batch{})
					return err, txn.GetState()
				}
				for r := retry.Start(client.DefaultTxnRetryOptions); r.Next(); {
					txn := db.ReconstructTxn(proto.Transaction{})
					if err, txnProto := applyInc(txn); err != nil {
						// New txn.
						txn = db.ReconstructTxn(txnProto)
						if err := txn.Rollback(); err != nil {
							t.Error(err)
						} else {
							// retry
							continue
						}
					}
					// exit retry
					break
				}
			} else {
				if err := db.Txn(func(txn *client.Txn) error {
					txn.SetDebugName(fmt.Sprintf("test-%d", i))

					// Retrieve the other key.
					gr, err := txn.Get(readKey)
					if err != nil {
						return err
					}

					otherValue := int64(0)
					if gr.Value != nil {
						otherValue = gr.ValueInt()
					}

					_, err = txn.Inc(writeKey, 1+otherValue)
					return err
				}); err != nil {
					t.Error(err)
				}
			}
		}(i)
	}

	// Kick the goroutines loose.
	wgStart.Done()
	// Wait for the goroutines to finish.
	wgEnd.Wait()
	// Verify that both keys contain something and, more importantly, that
	// one key actually contains the value of the first writer and not only
	// its own.
	total := int64(0)
	results := []int64(nil)
	for i := 0; i < 2; i++ {
		readKey := []byte(fmt.Sprintf(testUser+"/value-%d", i))
//.........這裏部分代碼省略.........