maria-discuss team mailing list archive

[Jan Lindström <jplindst@xxxxxxxxxxx>]

Hi,
> Jan,
>
> I think "InnoDB file space defragmentation" could use significantly 
> more explanation.
>
> By my understanding, delete-marked rows are in fact "physically 
> deleted" (re-linked to the garbage record list) during purge. However, 
> the garbage records in the list are not reclaimed unless: a. the first 
> record in the list has enough usable space for a newly inserted 
> records (potentially leaving some of the record's space unused); or b. 
> the page becomes full and gets re-organized, freeing all garbage space 
> implicitly. Of course then even in the best case the page is still 
> "used" and not free.

This all is true.
> Freeing unused file space is an entirely different problem, involving 
> potentially relocating used pages to be more contiguous, and then 
> reducing the free limit and then the page count for the space.
This is what I was proposing with defragmentation, either physically 
freeing unused pages or relocating used pages to be more contiguous, 
reducing the free limit and page count.
> They seem to be entirely different problems and without much overlap 
> at all. They are both potentially useful, and interesting. (Although I 
> am not sure why to make it an external tool as opposed to internal 
> functionality, that seems unnecessary.)
Both are useful, but you need to start from somewhere. I could use 
internal functionality if there is suitable syntax that can be used to 
do this already, I would not like to extend SQL-again.


R: Jan

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Jan Lindström, Principal Engineer
SkySQL - The MariaDB Company