Impossible compression ratio on ZFS

Šimun Mikecin numisemis at gmail.com
Mon Jun 13 09:29:08 UTC 2011


2011/6/13 Steven Hartland <killing at multiplay.co.uk>

> I've just done an optimisation of a mysql table which is located
> on a compressed zfs partition and spotted that the size reported
> by du is impossibly small for the file:-
>
> du -h detail*
> 1.5K    detail.frm
> 7.5K    detail.ibd
>
> ls -l detail*
> -rw-rw----  1 mysql  mysql       8660 Jun 13 10:00 detail.frm
> -rw-rw----  1 mysql  mysql  650117120 Jun 13 10:04 detail.ibd
>
> The table format for those interested is 3 int's, 3 indexes and
> contains 8million rows.
>
> I highly doubt that my 620MB table is taking up just 7.5K on disk
> any ideas?
>

It is possible if the file detail.ibd is mostly filled with zeros (that
would be the case unless you have 620MB of real data).


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