Re: diskspace

Thanks for all the responses....

On 5 February 2013 19:36, Rosser Schwarz <rosser(dot)schwarz(at)gmail(dot)com> wrote:
>
> On Tue, Feb 5, 2013 at 11:00 AM, Scott Mead <scottm(at)openscg(dot)com> wrote:
>>
>> Agreed, don't forget, you have indexes, free space, vacuum-able stuff,
>> etc... all laying in your datafiles. Your measurements are telling you
>> what you have purely in a raw form.
>>
>
Indexes are stored separately. There should be no free space (why would
there be? FILLFACTOR is 100!) and I've vacuumed already.

Additionally, postgres has a number of "metadata" columns (e.g., xmin,
> xmax, cmin, cmax, &c). Those can add up, particularly when their net size
> is greater than the user data size of a row.
>

That's a fair point.

611MB (actual disk size) - 138MB (summed data size) = 483MB
11M rows (ish).

That's nearly 48 bytes extra per row.

http://www.postgresql.org/docs/9.2/static/storage-page-layout.html gives
detail...

Let's say around 249MB (23 bytes per row, according to that page) for the
columns you mention, so that leaves 234MB unexplained.

I can see 44 bytes per page header (given 5 columns, so 20 bytes
ItemIdData, with 24 bytes PageHeaderData). Given page size of 8kb that
would imply page headers of about 3.3MB over a 611MB table.

Even with some bytes for alignment I'm Still not seeing where 230MB (more
than the space taken by the data itself) of my disk is gone.

Thanks!

Geoff