From: Itai Zukerman <zukerman@math-hat.com>
To: pgsql-sql@postgresql.org
Subject: OffsetNumber, picksplit, and GiST
Date: Tue, 25 Feb 2003 22:29:11 -0500
Message-ID: <87bs0z1zzs.fsf@matt.w80.math-hat.com> (raw)
Is the GiST examples I've looked through, in the picksplit functions,
I see code that looks roughly like this:
bytea *entryvec = (bytea *) PG_GETARG_POINTER(0);
OffsetNumber i, maxoff;
maxoff = ((VARSIZE(entryvec) - VARHDRSZ) / sizeof(GISTENTRY)) - 1;
for (i = FirstOffsetNumber; i <= maxoff; i = OffsetNumberNext(i))
{
... DatumGetPointer((((GISTENTRY *) (VARDATA(entryvec)))[i].key)) ...
}
I'm wondering, since FirstOffsetNumber is 1, what about the 0'th index
in entryvec? Is it just not set?
Also, is there some rationalle for using OffsetNumber in
GIST_SPLITVEC? I see in off.h:
/*
* OffsetNumber:
*
* this is a 1-based index into the linp (ItemIdData) array in the
* header of each disk page.
*/
and I don't get the connection with what picksplit is doing (keeping
in mind that I don't know what "linp", "ItemIdData" or "disk page"
mean).
I have a very tenuous understanding of all this, so please bear with me.
--
Itai Zukerman <http://www.math-hat.com/~zukerman/;
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To: pgsql-sql@postgresql.org
Cc: zukerman@math-hat.com
Subject: Re: OffsetNumber, picksplit, and GiST
In-Reply-To: <87bs0z1zzs.fsf@matt.w80.math-hat.com>
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