Method getMultiBatched

cache/memcached_client.go:676–753

(ctx context.Context, keys []string, opts ...memcache.Option)

}

func (c *MemcachedClient) getMultiBatched(ctx context.Context, keys []string, opts ...memcache.Option) ([]map[string]*memcache.Item, error) {
	// Do not batch if the input keys are less than the max batch size.
	if (c.config.MaxGetMultiBatchSize <= 0) || (len(keys) <= c.config.MaxGetMultiBatchSize) {
		// Even if we're not splitting the input into batches, make sure that our single request
		// still counts against the concurrency limit.
		if c.config.MaxGetMultiConcurrency > 0 {
			if err := c.getMultiGate.Start(ctx); err != nil {
				return nil, errors.Wrapf(err, "failed to wait for turn. Instance: %s", c.name)
			}

			defer c.getMultiGate.Done()
		}

		items, err := c.getMultiSingle(ctx, keys, opts...)
		if err != nil {
			return nil, err
		}

		return []map[string]*memcache.Item{items}, nil
	}

	// Calculate the number of expected results.
	batchSize := c.config.MaxGetMultiBatchSize
	numResults := len(keys) / batchSize
	if len(keys)%batchSize != 0 {
		numResults++
	}

	// If max concurrency is disabled, use a nil gate for the doWithBatch method which will
	// not apply any limit to the number goroutines started to make batch requests in that case.
	var getMultiGate gate.Gate
	if c.config.MaxGetMultiConcurrency > 0 {
		getMultiGate = c.getMultiGate
	}

	// Sort keys based on which memcached server they will be sharded to. Sorting keys that
	// are on the same server together before splitting into batches reduces the number of
	// connections required and increases the number of "gets" per connection.
	sortedKeys := c.sortKeysByServer(keys)

	// Allocate a channel to store results for each batch request. The max concurrency will be
	// enforced by doWithBatch.
	results := make(chan *memcachedGetMultiResult, numResults)
	defer close(results)

	// Ignore the error here since it can only be returned by our provided function which
	// always returns nil. NOTE also we are using a background context here for the doWithBatch
	// method. This is to ensure that it runs the expected number of batches _even if_ our
	// context (`ctx`) is canceled since we expect a certain number of batches to be read
	// from `results` below. The wrapped `getMultiSingle` method will still check our context
	// and short-circuit if it has been canceled.
	_ = doWithBatch(context.Background(), len(keys), c.config.MaxGetMultiBatchSize, getMultiGate, func(startIndex, endIndex int) error {
		batchKeys := sortedKeys[startIndex:endIndex]

		res := &memcachedGetMultiResult{}
		res.items, res.err = c.getMultiSingle(ctx, batchKeys, opts...)

		results <- res