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How are NULLS stored on disk for PG 7.4?

P: n/a
Hi

How are column files in a table that have been assigned null stored on disk
in Postgresql 7.4?

Cheers
Arn
Nov 12 '05 #1
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5 Replies


P: n/a
Arnold Mavromatis wrote:
Hi

How are column files in a table that have been assigned null stored on disk
in Postgresql 7.4?


Each row has a bitmap showing all the NULL values on that row.

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Nov 12 '05 #2

P: n/a
Le mar 13/01/2004 à 00:43, Bruce Momjian a écrit :
Arnold Mavromatis wrote:
Hi

How are column files in a table that have been assigned null stored on disk
in Postgresql 7.4?


Each row has a bitmap showing all the NULL values on that row.


Is it the same for PG 7.3?

Yannick
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Nov 22 '05 #3

P: n/a
On Wed, 14 Jan 2004, Yannick Warnier wrote:
Le mar 13/01/2004 à 00:43, Bruce Momjian a écrit :
Arnold Mavromatis wrote:
Hi

How are column files in a table that have been assigned null stored on disk
in Postgresql 7.4?


Each row has a bitmap showing all the NULL values on that row.


Is it the same for PG 7.3?


Yes, Postgresql has done this for quite some time.
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Nov 22 '05 #4

P: n/a
> On Wed, 14 Jan 2004, Yannick Warnier wrote:
Le mar 13/01/2004 à 00:43, Bruce Momjian a écrit :
> Arnold Mavromatis wrote:
> > Hi
> >
> > How are column files in a table that have been assigned null stored

on disk
> > in Postgresql 7.4?
>
> Each row has a bitmap showing all the NULL values on that row.


Is it the same for PG 7.3?


Yes, Postgresql has done this for quite some time.

My understanding is that Oracle has a field showing the size of the column
prior to each column. A column size of of zero means that the column is
null.

I assume that this is why Oracle is unable to make a distinction between a
null and a zero length string but that PostgreSQL can?

Vincent

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Nov 22 '05 #5

P: n/a
Yannick Warnier wrote:
Le mar 13/01/2004 à 00:43, Bruce Momjian a écrit :
Arnold Mavromatis wrote:
> Hi
>
> How are column files in a table that have been assigned null stored on disk
> in Postgresql 7.4?


Each row has a bitmap showing all the NULL values on that row.


Is it the same for PG 7.3?


It has always been that way. But the bitmap is only there if there is at
least one NULL value. One bit in the tuple headers flags tells if there
is a bitmap or not.
Jan

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Nov 22 '05 #6

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