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Re: NULL saves disk space?

From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Phoenix Kiula <phoenix(dot)kiula(at)gmail(dot)com>
Cc: PG-General Mailing List <pgsql-general(at)postgresql(dot)org>
Subject: Re: NULL saves disk space?
Date: 2011-04-28 14:59:39
Message-ID: BANLkTimCGA9qDsAorBOr=FqibRVxhjhkHw@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-general
On Wed, Apr 27, 2011 at 5:24 PM, Phoenix Kiula <phoenix(dot)kiula(at)gmail(dot)com> wrote:
> Possibly a dumb question but there isn't much about this.
> http://www.google.com/search?sourceid=chrome&ie=UTF-8&q=postgresql+null+value+disk+space
> I have some BOOLEAN columns. 90% of the cases of the columns is FALSE. Do I
> save disk space by having them as NULL instead of FALSE? So my application
> would have conditional code for NULL and TRUE, instead of FALSE and TRUE.
> Thanks...

Yes, NULL values take no additional space, but the row needs a null
bitmap so it is possible that if this was the only NULL then it could
occupy more space.

If you have multiple columns, then you should use NULLs.

-- 
 Simon Riggs                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

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