Golang DB.Scan方法代碼示例

// getRangeKeys returns the end keys of all ranges.
func getRangeKeys(db *client.DB) ([]roachpb.Key, error) {
	rows, err := db.Scan(keys.Meta2Prefix, keys.MetaMax, 0)
	if err != nil {
		return nil, err
	}
	ret := make([]roachpb.Key, len(rows), len(rows))
	for i := 0; i < len(rows); i++ {
		ret[i] = bytes.TrimPrefix(rows[i].Key, keys.Meta2Prefix)
	}
	return ret, nil
}

// WaitForInitialSplits waits for the expected number of initial ranges to be
// populated in the meta2 table. If the expected range count is not reached
// within a configured timeout, an error is returned.
func WaitForInitialSplits(db *client.DB) error {
	expectedRanges := ExpectedInitialRangeCount()
	return util.RetryForDuration(initialSplitsTimeout, func() error {
		// Scan all keys in the Meta2Prefix; we only need a count.
		rows, err := db.Scan(keys.Meta2Prefix, keys.MetaMax, 0)
		if err != nil {
			return err
		}
		if a, e := len(rows), expectedRanges; a != e {
			return errors.Errorf("had %d ranges at startup, expected %d", a, e)
		}
		return nil
	})
}

// Run a particular schema change and run some OLTP operations in parallel, as
// soon as the schema change starts executing its backfill.
func runSchemaChangeWithOperations(
	t *testing.T,
	sqlDB *gosql.DB,
	kvDB *client.DB,
	schemaChange string,
	maxValue int,
	keyMultiple int,
	backfillNotification chan bool,
) {
	tableDesc := sqlbase.GetTableDescriptor(kvDB, "t", "test")

	// Run the schema change in a separate goroutine.
	var wg sync.WaitGroup
	wg.Add(1)
	go func() {
		start := timeutil.Now()
		// Start schema change that eventually runs a backfill.
		if _, err := sqlDB.Exec(schemaChange); err != nil {
			t.Error(err)
		}
		t.Logf("schema change %s took %v", schemaChange, timeutil.Since(start))
		wg.Done()
	}()

	// Wait until the schema change backfill starts.
	<-backfillNotification

	// Run a variety of operations during the backfill.

	// Grabbing a schema change lease on the table will fail, disallowing
	// another schema change from being simultaneously executed.
	sc := csql.NewSchemaChangerForTesting(tableDesc.ID, 0, 0, *kvDB, nil)
	if l, err := sc.AcquireLease(); err == nil {
		t.Fatalf("schema change lease acquisition on table %d succeeded: %v", tableDesc.ID, l)
	}

	// Update some rows.
	var updatedKeys []int
	for i := 0; i < 10; i++ {
		k := rand.Intn(maxValue)
		v := maxValue + i + 1
		if _, err := sqlDB.Exec(`UPDATE t.test SET v = $2 WHERE k = $1`, k, v); err != nil {
			t.Fatal(err)
		}
		updatedKeys = append(updatedKeys, k)
	}

	// Reupdate updated values back to what they were before.
	for _, k := range updatedKeys {
		if _, err := sqlDB.Exec(`UPDATE t.test SET v = $2 WHERE k = $1`, k, maxValue-k); err != nil {
			t.Fatal(err)
		}
	}

	// Delete some rows.
	deleteStartKey := rand.Intn(maxValue - 10)
	for i := 0; i < 10; i++ {
		if _, err := sqlDB.Exec(`DELETE FROM t.test WHERE k = $1`, deleteStartKey+i); err != nil {
			t.Fatal(err)
		}
	}
	// Reinsert deleted rows.
	for i := 0; i < 10; i++ {
		k := deleteStartKey + i
		if _, err := sqlDB.Exec(`INSERT INTO t.test VALUES($1, $2)`, k, maxValue-k); err != nil {
			t.Fatal(err)
		}
	}

	// Insert some new rows.
	numInserts := 10
	for i := 0; i < numInserts; i++ {
		if _, err := sqlDB.Exec(`INSERT INTO t.test VALUES($1, $2)`, maxValue+i+1, maxValue+i+1); err != nil {
			t.Fatal(err)
		}
	}

	wg.Wait() // for schema change to complete.

	// Verify the number of keys left behind in the table to validate schema
	// change operations.
	tablePrefix := roachpb.Key(keys.MakeTablePrefix(uint32(tableDesc.ID)))
	tableEnd := tablePrefix.PrefixEnd()
	if kvs, err := kvDB.Scan(tablePrefix, tableEnd, 0); err != nil {
		t.Fatal(err)
	} else if e := keyMultiple * (maxValue + numInserts + 1); len(kvs) != e {
		t.Fatalf("expected %d key value pairs, but got %d", e, len(kvs))
	}

	// Delete the rows inserted.
	for i := 0; i < numInserts; i++ {
		if _, err := sqlDB.Exec(`DELETE FROM t.test WHERE k = $1`, maxValue+i+1); err != nil {
			t.Fatal(err)
		}
	}
}