MySQL has a number of global buffers, i.e. your SGA. There are also a number of per session/thread buffers that combined with other memory usage constitutes an unbounded PGA. One of the most common errors in mis-configured MySQL environments is the setting of the 4 primary per session buffers thinking they are global buffers.
Global buffers include:
- key_buffer_size – For MyISAM Indexes (note you can define multiple key_buffer’s …