Op 28 mrt 2010, om 11:07 heeft Tadipathri Raghu het volgende geschreven:
Hi All,
I want to give some more light on this by analysing more like this
1. In my example I have created a table with one column as
INT( which occupies 4 bytes)
2. Initially it occupies one page of space on the file that is (8kb).
So, here is it assuming these many rows may fit in this page.
Clarify me on this Please.
See these chapters in the manual:
http://www.postgresql.org/docs/8.4/interactive/storage.html
The minimum size of a file depends on the block size, by default 8kb:
http://www.postgresql.org/docs/8.4/interactive/install-procedure.html
Regards,
Frank
Regards
Raghavendra
On Sun, Mar 28, 2010 at 2:06 PM, Gary Doades <g...@gpdnet.co.uk> wrote:
On 28/03/2010 8:33 AM, Tadipathri Raghu wrote:
Hi Guz,
It is assuming that there are 2400 rows in this table. Probably
you've deleted some rows from the table leaving just one.
Frankly speaking its a newly created table without any operation on
it as you have seen the example. Then how come it showing those
many rows where we have only one in it.
Thanks if we have proper explination on this..
It's not *showing* any rows at all, it's *guessing* 2400 rows
because you've never analyzed the table. Without any statistics at
all, postgres will use some form of in-built guess for a table that
produces reasonable plans under average conditions. As you've
already seen, once you analyze the table, the guess get's much
better and therefore would give you a more appropriate plan.
Regards,
Gary.
