// maxBufferSize is the maximum buffer size.
	// Buffers larger than this is not reused.
	maxBufferSize = 96 << 10

	// This is the assumed size of bigger buffers and allocation size.
	biggerBufMin = 32 << 10

	// This is the maximum size of bigger buffers.
	biggerBufMax = maxBufferSize

	// If there is a queue, merge up to this many messages.
	maxMergeMessages = 30

	// Fill buffers
	b := globalBytePoolCap.Load().Get()
	shardSize := int(e.ShardSize())
	if cap(b) < len(readers)*shardSize {
		// We should always have enough capacity, but older objects may be bigger.
		globalBytePoolCap.Load().Put(b)
		b = nil
	} else {
		// Seed the buffers.
		for i := range bufs {
			bufs[i] = b[i*shardSize : (i+1)*shardSize]
		}
	}

	return &parallelReader{