maria-developers team mailing list archive

[Sergei Golubchik <serg@xxxxxxxxxxx>]

Hi, Nikita!

On Dec 05, Nikita Malyavin wrote:
> Heh, unfortunately comparing refs will not work in conjunction with KEYREAD:
> 
> for innodb ref can be a primary key, if it has it, so index is not
> clustered. The index we're evaluating can be different from a primary key.
> 
> In that case some values can be left unfetched with KEYREAD.
> 
> All that is because if innodb has primary key, it just does key_copy

In InnoDB every secondary key automatically has primary key at the
end, because after finding the key value in a secondary index,
InnoDB needs to fetch the corresponding row, so it has to know the PK
value for that secondary key.

Generalizing, every secondary key has to have the "ref" for the
corresponding row. In InnoDB it's PK, in MyISAM it's the row offset, in
MEMORY it's pointer. But either way, in any engine, any secondary key
knows the ref for the corresponding row.

Regards,
Sergei
VP of MariaDB Server Engineering
and security@xxxxxxxxxxx