Tuning buffer sizes

Overview

When the typical read/write size is small, using a buffer can make a significant improvement in performance. However when reading/writing large amounts of data, additional buffered doesn't help and can add a small amount of overhead.

Additionally, it can be tempting to assume; the larger the buffer the better. However is appears a more modest buffer size, around the size of your L1 cache could be better. e.g 8 KB to 32 KB.

The test

In the following test I compared using buffered and unbuffered reads and writes to a temporary file on a tmpfs filesystem (ram disk)

Size of read/write	Unbuffered Writes	Buffered Writes	Unbuffered Reads	Buffered Reads
1	2 MB/s	86 MB/s	3 MB/s	72 MB/s
2	4 MB/s	165 MB/s	6 MB/s	147 MB/s
4	8 MB/s	333 MB/s	11 MB/s	291 MB/s
8	17 MB/s	578 MB/s	24 MB/s	560 MB/s
16	34 MB/s	920 MB/s	49 MB/s	983 MB/s
32	67 MB/s	1,345 MB/s	99 MB/s	1,679 MB/s
64	133 MB/s	1,746 MB/s	198 MB/s	2,518 MB/s
128	254 MB/s	2,024 MB/s	391 MB/s	3,387 MB/s
256	463 MB/s	2,172 MB/s	742 MB/s	4,104 MB/s
512	798 MB/s	2,270 MB/s	1,334 MB/s	4,549 MB/s
1,024	1,270 MB/s	2,299 MB/s	2,355 MB/s	4,752 MB/s
2,048	1,789 MB/s	2,310 MB/s	3,704 MB/s	4,923 MB/s
4,096	2,287 MB/s	2,301 MB/s	5,324 MB/s	4,859 MB/s
8,192	2,589 MB/s	2,497 MB/s	6,346 MB/s	6,142 MB/s
16,384	2,534 MB/s	2,559 MB/s	5,764 MB/s	5,697 MB/s
32,768	2,591 MB/s	2,561 MB/s	5,793 MB/s	5,723 MB/s
65,536	2,613 MB/s	2,581 MB/s	5,861 MB/s	5,883 MB/s
131,072	2,580 MB/s	2,581 MB/s	5,401 MB/s	5,405 MB/s
262,144	1,918 MB/s	1,907 MB/s	3,269 MB/s	3,262 MB/s
524,288	1,749 MB/s	1,734 MB/s	2,845 MB/s	2,851 MB/s
1,048,576	1,471 MB/s	1,469 MB/s	2,501 MB/s	2,502 MB/s

The default size of a BufferedInputStream and BufferedOutputStream is 8KB. This is part of the reason why they don't help at this point and larger.

The code

BufferTest.java