The Ultimate Guide to High Availability with MariaDB

Maximum columns per index

I have a question about the maximum columns per index.

In the MariaDB documention I have noticed that the maximum columns per index is 16: https://mariadb.com/kb/en/mariadb/myisam-overview/

This is aligned with the comment it has on the code: https://github.com/MariaDB/server/blob/5.5/sql/item_subselect.cc#L4354

In contradict to the above, the code shows a different value for this 'define' (#define MAX_REF_PARTS 32): https://github.com/MariaDB/server/blob/5.5/sql/sql_const.h#L33

MariaDB was forked from mysql 5.5 (to my knowledge), in which, this 'define' was indeed 16: https://github.com/twitter/mysql/blob/master/sql/sql_const.h#L33

To me it seems like the code has changed, but documentation & comment are outdated. Is this correct or am I missing something regarding this value?

Best regards, Maya

Answer Answered by Ian Gilfillan in this comment.

Thanks, you are correct, this limit was changed (in 2010!). The docs have been updated, and the comment in the code will be shortly.

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