private static BufferAllocator createBufferAllocatorFromSystemConfig(final EmbulkSystemProperties embulkSystemProperties) {
        final String byteSizeRepresentation = embulkSystemProperties.getProperty("page_size");
        if (byteSizeRepresentation == null) {
            return PooledBufferAllocator.create();
        } else {
            final int byteSize = parseByteSizeRepresentation(byteSizeRepresentation);
            return PooledBufferAllocator.create(byteSize);
        }
    }
Sets an alternative {@code BulkLoader} instance mainly for testing-purpose.
embulk-core/src/main/java/org/embulk/EmbulkEmbed.java