maria-developers team mailing list archive

[Ian Gilfillan <ian@xxxxxxxxxxx>]

I see the eq_range_index_dive_limit default has been set to 10 in 
10.4.3. I see some different EXPLAIN results in the commit, but I don't 
see any notes on why or how 10 was chosen over any other value. MySQL 
increased the default to 200 from MySQL 5.7.4, based it seems on some 
community feedback that 10 was too low, for example: 
https://www.facebook.com/notes/mysql-at-facebook/eq_range_index_dive_limit-system-variable-in-mysql-56/10151533648715933. 
What was the thinking behind choosing 10 as the new default?

On 2018/10/12 12:58, Sergey Petrunia wrote:
> Hello,
>
> So, MDEV-16934 introduced eq_range_index_dives_limit into 10.2.8 and 10.3.0.
>
> The default was set to 0 (which means no limit) in order to not introduce
> optimizer behavior change into stable versions.
>
> The question is: should 10.4 also have 0 by default or we can set it to some
> finite limit? MySQL's default value is 10.
>
> BR
>   Sergei