How does MySQL's read_buffer_size parameter affect write buffering and write performance?

An article from a foreign blog describes how MySQL's read_buffer_size parameters affect write buffering and write performance.

It is said that the Read_buffer_size parameter only affects the performance of write data in the following two scenarios:

• SELECT into ... OUTFILE 'fileName'
  • When writing to the OUTFILE, the writes is buffered before writing to OUTFILE
• When Filesort was used, during merge buffers and when merged results was written to a temporary file, then writes was Buffe Red

The following table is some of the data that this article tests:

Read_buffer_size	Physical writes	EXE time in secs
=0 (defaults to 8200)	23495	28.39
=131072 (default)	2937	27.44
=16777216	23	26.71
=33554432	12	26.00
=536870912	1	26.72

For details, please read the original text:

http://venublog.com/2010/06/23/how-read_buffer_size-impacts-write-buffering-and-write-performance/

How does MySQL's read_buffer_size parameter affect write buffering and write performance?