Re: pg_database_size differs from df -s

On Wed, Jun 6, 2012 at 6:28 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Frank Lanitz <frank(at)frank(dot)uvena(dot)de> writes:
> > Am 06.06.2012 17:49, schrieb Tom Lane:
> >> For me, pg_database_size gives numbers that match up fairly well with
> >> what "du" says. I would not expect an exact match, since du probably
> >> knows about filesystem overhead (such as metadata) whereas
> >> pg_database_size does not. Something's fishy if it's off by any large
> >> factor, though. Perhaps you have some tables in a nondefault
> >> tablespace, where du isn't seeing them?
>
> > Nope. Its a pretty much clean database without any fancy stuff.
>
> Peculiar. If you want to put some time into it, you could try comparing
> sizes table-by-table to see if you can isolate where the discrepancy is.
>
>
Perhaps with the contrib adminpack you may easily find where it comes from
comparing size from pg_table_size and pg_stat_file ?

> The only reason I can think of for du to report a size smaller than the
> nominal file length (which is which the pg_xxx_size functions look at)
> is if the file contains unallocated "holes". That really shouldn't ever
> happen with PG tables though.
>
> regards, tom lane
>
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