On Mon, Sep 11, 2006 at 01:15:43PM -0400, Tom Lane wrote:
> Gregory Stark <stark@enterprisedb.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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