Re: Determining size of a database before dumping

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On 10/02/06 16:19, Tom Lane wrote:
> Alexander Staubo <alex(at)purefiction(dot)net> writes:
>> You could count the disk space usage of the actual stored tuples,
>> though this will necessarily be inexact:
>> http://www.postgresql.org/docs/8.1/static/diskusage.html
>> Or you could count the size of the physical database files (/var/lib/
>> postgresql or wherever). While these would be estimates, you could at
>> least guarantee that the dump would not *exceed* the esimtate.
>
> You could guarantee no such thing; consider compression of TOAST values.
> Even for uncompressed data, datatypes such as int and float can easily
> print as more bytes than they occupy on-disk.
>
> Given all the non-data overhead involved (eg for indexes), it's probably
> unlikely that a text dump would exceed the "du" size of the database,
> but it's far from "guaranteed".

It's my experience that when there are lots of numeric fields,
fixed-width text records are approx 2.5x larger than the original
binary records.

- --
Ron Johnson, Jr.
Jefferson LA USA

Is "common sense" really valid?
For example, it is "common sense" to white-power racists that
whites are superior to blacks, and that those with brown skins
are mud people.
However, that "common sense" is obviously wrong.
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