Thread

Re: [HACKERS] database size

Bruce Momjian <maillist@candle.pha.pa.us> — 1998-01-07T01:18:26Z

> 
> > I created a table with two columns of type int, and loaded about 300 K records
> > in it. So, the total size of the table is approx. that of 600 K integers,
> > roughly 2.4 MB.
> > But, the file corresponding to the table in pgsql/data/base directory
> > has a size of 19 MB. I was wondering if I have done something wrong in
> > the installation or usage, or is it the normal behavior ?
> 
> 48 bytes + each row header (on my aix box..._your_ mileage may vary)
>  8 bytes + two int fields @ 4 bytes each
>  4 bytes + pointer on page to tuple
> -------- =
> 60 bytes per tuple
> 
> 8192 / 60 give 136 tuples per page.
> 
> 300000 / 136 ... round up ... need 2206 pages which gives us ...
> 
> 2206 * 8192 = 18,071,532
> 
> So 19 MB is about right.  And this is the best to be done, unless
> you can make do with int2s which would optimally shrink the table
> size to 16,834,560 bytes.  Any nulls in there might add a few bytes
> per offending row too, but other than that, this should be considered
> normal postgresql behavior.


Nice math exercise.

Does anyone want to tell me the row overhead on commercial databases?

-- 
Bruce Momjian
maillist@candle.pha.pa.us