Disclaimer: This post is based on HEAP/MyISAM’s sourcecode in Drizzle.
Here are my brief notes on investigating how index keys are generated in HEAP and MyISAM. I lurked through these because I’ve started preparing for decent index support in BlitzDB. I also wrote this to assist my biological memory for later grepping (I have terrible memory for names). I’m only going to cover key generation on write in this post. Otherwise this post is going to be massive.
The index structure of HEAP can be either BTREE or HASH (in MySQL doc terms). Like other engines HEAP has a structure for keeping Key definition (parts, type, logic and etc). This structure is called HP_KEYDEF and it contains function pointers for write, delete, and getting the length of the key. These function pointers are assigned to at table creation or when the table is opened. The assigned function depends on the data structure …[Read more]