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Re: How many fields in a table are too many

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Jan Wieck <JanWieck(at)Yahoo(dot)com>, btober(at)seaworthysys(dot)com,scrawford(at)pinpointresearch(dot)com, kleptog(at)svana(dot)org,m_tessier(at)sympatico(dot)ca, pgsql-general(at)postgresql(dot)org
Subject: Re: How many fields in a table are too many
Date: 2003-06-28 19:17:40
Message-ID: 200306281917.h5SJHeX14044@candle.pha.pa.us (view raw or flat)
Thread:
Lists: pgsql-general
Tom Lane wrote:
> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > However, I am not sure how useful NOT NULL is in practice because there
> > are lots of columns that don't specify NOT NULL but have mostly nulls or
> > mostly non-nulls, which kills our caching --- what I was hoping to do
> > some day was to cache the null bitmask and offsets of the previous tuple
> > and use those if the new tuple has the same null bitmask as the previous
> > tuple.
> 
> We already cache fairly effectively in cases where there are no nulls.
> I'm not sure it's worth trying to do something with the idea that two
> adjacent tuples might have nulls in the same places.

I was thinking of trying it and seeing how often it would be a win,
because right now, when we hit a null, our cache is dead.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman(at)candle(dot)pha(dot)pa(dot)us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

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