Golang DB.Txn方法代碼示例

// truncateTableInChunks truncates the data of a table in chunks. It deletes a
// range of data for the table, which includes the PK and all indexes.
func truncateTableInChunks(
	ctx context.Context, tableDesc *sqlbase.TableDescriptor, db *client.DB,
) error {
	const chunkSize = TableTruncateChunkSize
	var resume roachpb.Span
	for row, done := 0, false; !done; row += chunkSize {
		resumeAt := resume
		if log.V(2) {
			log.Infof(ctx, "table %s truncate at row: %d, span: %s", tableDesc.Name, row, resume)
		}
		if err := db.Txn(ctx, func(txn *client.Txn) error {
			rd, err := makeRowDeleter(txn, tableDesc, nil, nil, false)
			if err != nil {
				return err
			}
			td := tableDeleter{rd: rd}
			if err := td.init(txn); err != nil {
				return err
			}
			resume, err = td.deleteAllRows(txn.Context, resumeAt, chunkSize)
			return err
		}); err != nil {
			return err
		}
		done = resume.Key == nil
	}
	return nil
}

func (hv *historyVerifier) runTxn(
	txnIdx int,
	priority int32,
	isolation enginepb.IsolationType,
	cmds []*cmd,
	db *client.DB,
	t *testing.T,
) error {
	var retry int
	txnName := fmt.Sprintf("txn %d", txnIdx+1)
	cmdIdx := -1

	err := db.Txn(context.TODO(), func(txn *client.Txn) error {
		// If this is 2nd attempt, and a retry wasn't expected, return a
		// retry error which results in further histories being enumerated.
		if retry++; retry > 1 {
			if !cmds[cmdIdx].expRetry {
				// Propagate retry error to history execution to enumerate all
				// histories where this txn retries at this command.
				return &retryError{txnIdx: txnIdx, cmdIdx: cmdIdx}
			}
			// We're expecting a retry, so just send nil down the done channel.
			cmds[cmdIdx].done(nil)
		}

		txn.SetDebugName(txnName, 0)
		if isolation == enginepb.SNAPSHOT {
			if err := txn.SetIsolation(enginepb.SNAPSHOT); err != nil {
				return err
			}
		}
		txn.InternalSetPriority(priority)

		env := map[string]int64{}
		for cmdIdx+1 < len(cmds) {
			cmdIdx++
			cmds[cmdIdx].env = env
			_, err := hv.runCmd(txn, txnIdx, retry, cmds[cmdIdx], t)
			if err != nil {
				if log.V(1) {
					log.Infof(context.Background(), "%s: failed running %s: %s", txnName, cmds[cmdIdx], err)
				}
				return err
			}
		}
		return nil
	})
	if err != nil {
		for _, c := range cmds[cmdIdx:] {
			c.done(err)
		}
	}
	return err
}

// startTestWriter creates a writer which initiates a sequence of
// transactions, each which writes up to 10 times to random keys with
// random values. If not nil, txnChannel is written to non-blockingly
// every time a new transaction starts.
func startTestWriter(
	db *client.DB,
	i int64,
	valBytes int32,
	wg *sync.WaitGroup,
	retries *int32,
	txnChannel chan struct{},
	done <-chan struct{},
	t *testing.T,
) {
	src := rand.New(rand.NewSource(i))
	defer func() {
		if wg != nil {
			wg.Done()
		}
	}()

	for j := 0; ; j++ {
		select {
		case <-done:
			return
		default:
			first := true
			err := db.Txn(context.TODO(), func(txn *client.Txn) error {
				if first && txnChannel != nil {
					select {
					case txnChannel <- struct{}{}:
					default:
					}
				} else if !first && retries != nil {
					atomic.AddInt32(retries, 1)
				}
				first = false
				for j := 0; j <= int(src.Int31n(10)); j++ {
					key := randutil.RandBytes(src, 10)
					val := randutil.RandBytes(src, int(src.Int31n(valBytes)))
					if err := txn.Put(key, val); err != nil {
						log.Infof(context.Background(), "experienced an error in routine %d: %s", i, err)
						return err
					}
				}
				return nil
			})
			if err != nil {
				t.Error(err)
			} else {
				time.Sleep(1 * time.Millisecond)
			}
		}
	}
}

// purgeOldLeases refreshes the leases on a table. Unused leases older than
// minVersion will be released.
// If deleted is set, minVersion is ignored; no lease is acquired and all
// existing unused leases are released. The table is further marked for
// deletion, which will cause existing in-use leases to be eagerly released once
// they're not in use any more.
// If t has no active leases, nothing is done.
func (t *tableState) purgeOldLeases(
	db *client.DB, deleted bool, minVersion sqlbase.DescriptorVersion, store LeaseStore,
) error {
	t.mu.Lock()
	empty := len(t.active.data) == 0
	t.mu.Unlock()
	if empty {
		// We don't currently have a lease on this table, so no need to refresh
		// anything.
		return nil
	}

	// Acquire and release a lease on the table at a version >= minVersion.
	var lease *LeaseState
	err := db.Txn(context.TODO(), func(txn *client.Txn) error {
		var err error
		if !deleted {
			lease, err = t.acquire(txn, minVersion, store)
			if err == errTableDropped {
				deleted = true
			}
		}
		if err == nil || deleted {
			t.mu.Lock()
			defer t.mu.Unlock()
			var toRelease []*LeaseState
			if deleted {
				t.deleted = true
			}
			toRelease = append([]*LeaseState(nil), t.active.data...)

			t.releaseLeasesIfNotActive(toRelease, store)
			return nil
		}
		return err
	})
	if err != nil {
		return err
	}
	if lease == nil {
		return nil
	}
	return t.release(lease, store)
}

func (hv *historyVerifier) runCmds(
	cmds []*cmd, db *client.DB, t *testing.T,
) (string, map[string]int64, error) {
	var strs []string
	env := map[string]int64{}
	err := db.Txn(context.TODO(), func(txn *client.Txn) error {
		for _, c := range cmds {
			c.historyIdx = hv.idx
			c.env = env
			c.init(nil)
			fmtStr, err := c.execute(txn, t)
			if err != nil {
				return err
			}
			strs = append(strs, fmt.Sprintf(fmtStr, 0, 0))
		}
		return nil
	})
	return strings.Join(strs, " "), env, err
}

// restoreTable inserts the given DatabaseDescriptor. If the name conflicts with
// an existing table, the one being restored is rekeyed with a new ID and the
// old data is deleted.
func restoreTable(
	ctx context.Context,
	db client.DB,
	database sqlbase.DatabaseDescriptor,
	table *sqlbase.TableDescriptor,
	ranges []sqlbase.BackupRangeDescriptor,
) error {
	if log.V(1) {
		log.Infof(ctx, "Restoring Table %q", table.Name)
	}

	var newTableID sqlbase.ID
	if err := db.Txn(ctx, func(txn *client.Txn) error {
		// Make sure there's a database with a name that matches the original.
		if _, err := getDescriptorID(txn, tableKey{name: database.Name}); err != nil {
			return errors.Wrapf(err, "a database named %q needs to exist to restore table %q",
				database.Name, table.Name)
		}

		// Assign a new ID for the table. TODO(dan): For now, we're always
		// generating a new ID, but varints get longer as they get bigger and so
		// our keys will, too. We should someday figure out how to overwrite an
		// existing table and steal its ID.
		var err error
		newTableID, err = GenerateUniqueDescID(txn)
		return err
	}); err != nil {
		return err
	}

	// Create the iteration keys before we give the table its new ID.
	tableStartKeyOld := roachpb.Key(sqlbase.MakeIndexKeyPrefix(table, table.PrimaryIndex.ID))
	tableEndKeyOld := tableStartKeyOld.PrefixEnd()

	// This loop makes restoring multiple tables O(N*M), where N is the number
	// of tables and M is the number of ranges. We could reduce this using an
	// interval tree if necessary.
	var wg sync.WaitGroup
	result := struct {
		syncutil.Mutex
		firstErr error
		numErrs  int
	}{}
	for _, rangeDesc := range ranges {
		if len(rangeDesc.Path) == 0 {
			// Empty path means empty range.
			continue
		}

		intersectBegin, intersectEnd := IntersectHalfOpen(
			rangeDesc.StartKey, rangeDesc.EndKey, tableStartKeyOld, tableEndKeyOld)
		if intersectBegin != nil && intersectEnd != nil {
			// Write the data under the new ID.
			// TODO(dan): There's no SQL descriptors that point at this yet, so it
			// should be possible to remove it from the one txn this is all currently
			// run under. If we do that, make sure this data gets cleaned up on errors.
			wg.Add(1)
			go func(desc sqlbase.BackupRangeDescriptor) {
				for r := retry.StartWithCtx(ctx, base.DefaultRetryOptions()); r.Next(); {
					err := db.Txn(ctx, func(txn *client.Txn) error {
						return Ingest(ctx, txn, desc.Path, desc.CRC, intersectBegin, intersectEnd, newTableID)
					})
					if _, ok := err.(*client.AutoCommitError); ok {
						log.Errorf(ctx, "auto commit error during ingest: %s", err)
						// TODO(dan): Ingest currently does not rely on the
						// range being empty, but the plan is that it will. When
						// that change happens, this will have to delete any
						// partially ingested data or something.
						continue
					}

					if err != nil {
						log.Errorf(ctx, "%T %s", err, err)
						result.Lock()
						defer result.Unlock()
						if result.firstErr != nil {
							result.firstErr = err
						}
						result.numErrs++
					}
					break
				}
				wg.Done()
			}(rangeDesc)
		}
	}
	wg.Wait()
	// All concurrent accesses have finished, we don't need the lock anymore.
	if result.firstErr != nil {
		// This leaves the data that did get imported in case the user wants to
		// retry.
		// TODO(dan): Build tooling to allow a user to restart a failed restore.
		return errors.Wrapf(result.firstErr, "ingest encountered %d errors", result.numErrs)
	}

	table.ID = newTableID
	return db.Txn(ctx, func(txn *client.Txn) error {
//.........這裏部分代碼省略.........

// 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 err := db.Txn(context.TODO(), func(txn *client.Txn) error {
				txn.SetDebugName(fmt.Sprintf("test-%d", i), 0)

				// 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))
		gr, err := db.Get(context.TODO(), readKey)
		if err != nil {
			t.Fatal(err)
		}
		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)
	}
}