Re: Recommended changes to my.cnf

[Rick James]

I suggest leaving max_allowed_packet at the default of 1M unless you get the error discussed here:
http://dev.mysql.com/doc/refman/5.1/en/packet-too-large.html
(Very few systems hit that problem.)

Before 5.1.24 setting read_buffer_size > max_allowed_packet could cause LOAD DATA INFILE to fail.

Here's an attempt at picking a good size for read_buffer_size:
http://www.mysqlperformanceblog.com/2007/09/17/mysql-what-read_buffer_size-value-is-optimal/
My summary: It does not matter much. However, since it is allocated for every connection that needs it, a large value can chew up RAM.
I like somewhere between 64K and 256K. (Note: that's K, not M.)