Skip site navigation (1) Skip section navigation (2)

Re: [SQL] OffsetNumber, picksplit, and GiST

From: Teodor Sigaev <teodor(at)stack(dot)net>
To: Itai Zukerman <zukerman(at)math-hat(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: [SQL] OffsetNumber, picksplit, and GiST
Date: 2003-03-03 09:46:00
Message-ID: 3E632458.7000100@stack.net (view raw or flat)
Thread:
Lists: pgsql-hackers
Just historical reasons...

Itai Zukerman wrote:
> I didn't get any responses on pgsql-sql, so I'm re-posting here...
> 
> 
>>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?
> 
> 
> In backend/access/gist/gist.c I see how entryvec is built:
> 
>    storage = palloc(MAXALIGN(VARHDRSZ) + (*len + 1) * sizeof(GISTENTRY));
>    entryvec = (bytea *) (storage + MAXALIGN(VARHDRSZ) - VARHDRSZ);
>    decompvec = (bool *) palloc((*len + 1) * sizeof(bool));
>    VARATT_SIZEP(entryvec) = (*len + 1) * sizeof(GISTENTRY) + VARHDRSZ;
>    for (i = 1; i <= *len; i++)
>    {
>      [...] gistdentryinit(giststate, 0, &((GISTENTRY *) VARDATA(entryvec))[i], [...]
>    }
> 
> So it looks like the 0'th entry indeed is empty.  Why?
> 
> Also, in gist.c the index "i" has type "int".  No mention of
> OffsetNumber anywhere.  Any reason for that?
> 
> 
> 
> ------------------------------------------------------------------------
> 
> 
> 
> ------------------------------------------------------------------------
> 
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 6: Have you searched our list archives?
> 
> http://archives.postgresql.org

-- 
Teodor Sigaev
teodor(at)stack(dot)net



In response to

pgsql-hackers by date

Next:From: Teodor SigaevDate: 2003-03-03 09:51:12
Subject: Re: GIST_LEAF vs. leaf_key; gist?entryinit
Previous:From: Teodor SigaevDate: 2003-03-03 09:43:03
Subject: Re: btree_gist, gint4_union

Privacy Policy | About PostgreSQL
Copyright © 1996-2014 The PostgreSQL Global Development Group