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Re: reducing NUMERIC size for 9.1

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: reducing NUMERIC size for 9.1
Date: 2010-07-29 20:37:09
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Lists: pgsql-hackers
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Thu, Jul 29, 2010 at 1:20 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> On-disk is what I'm thinking about. Right now, a NaN's first word is
>> all dscale except the sign bits. You're proposing to change that
>> but I think it's unnecessary to do so.

> *Where* am I proposing this?

Um, your patch has the comment

!  * If the high bits of n_scale_dscale are NUMERIC_NAN, the two-byte header
!  * format is also used, but the low bits of n_scale_dscale are discarded in
!  * this case.

but now that I look a bit more closely, I don't think that's what the
code is doing.  You've got the NUMERIC_DSCALE and NUMERIC_WEIGHT access
macros testing specifically for NUMERIC_IS_SHORT, not for high-bit-set
which I think is what I was assuming they'd do.  So actually that code
is good as is: a NAN still has the old header format.  It's just the
comment that's wrong.

			regards, tom lane

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