From: | mark(at)mark(dot)mielke(dot)cc |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Gregory Stark <stark(at)enterprisedb(dot)com>, Gregory Stark <gsstark(at)mit(dot)edu>, Bruce Momjian <bruce(at)momjian(dot)us>, Peter Eisentraut <peter_e(at)gmx(dot)net>, pgsql-hackers(at)postgresql(dot)org, Martijn van Oosterhout <kleptog(at)svana(dot)org> |
Subject: | Re: Fixed length data types issue |
Date: | 2006-09-11 19:00:16 |
Message-ID: | 20060911190016.GA18102@mark.mielke.cc |
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Lists: | pgsql-hackers |
On Mon, Sep 11, 2006 at 01:15:43PM -0400, Tom Lane wrote:
> Gregory Stark <stark(at)enterprisedb(dot)com> writes:
> > In any case it seems a bit backwards to me. Wouldn't it be better to
> > preserve bits in the case of short length words where they're precious
> > rather than long ones? If we make 0xxxxxxx the 1-byte case it means ...
> Well, I don't find that real persuasive: you're saying that it's
> important to have a 1-byte not 2-byte header for datums between 64 and
> 127 bytes long. Which is by definition less than a 2% savings for those
> values. I think its's more important to pick bitpatterns that reduce
> the number of cases heap_deform_tuple has to think about while decoding
> the length of a field --- every "if" in that inner loop is expensive.
I like your thought process on this, Tom. I read your suggestions and
didn't respond because I was in full agreement with them.
The 1-byte header would be valuable even if it only worked for
32-bytes. It is important to keep CPU overhead down by making it
easy to switch off the bit patterns.
Cheers,
mark
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