Re: Doubt in IndexScanDescData

take a look at that ...

http://www.postgresql.org/docs/8.3/static/indexam.html

this might clear up the problem.
here is an example making clear what happens:

select phone_number from phonebook where name = 'xy';

index is asked to find the right place in the heap to retrieve the data.
this is what happens during an index scan.
i suggest to step tnrough this process with a debugger to see what is
going on.

hans

On Feb 17, 2008, at 5:13 PM, Suresh wrote:

> Hans-Juergen Schoenig <postgres(at)cybertec(dot)at> wrote:
>
> On Feb 17, 2008, at 4:33 PM, Suresh wrote:
>
>> [ "include/access/relscan.h" ]
>>
>> In IndexScanDescData, whats the purpose of having two Relation
>> variables.
>>
>> typedef struct IndexScanDescData
>> {
>> Relation heapRelation; /* heap relation
>> descriptor, or NULL */
>> Relation indexRelation; /* index relation
>> descriptor */
>> ....
>> ...
>> }IndexScanDescData;
>
>
>
> The index does not contain the entire tuple. If you index column A
> the index will not contain values in column B of the same table.
> Thus, if you find a record in the index one of the things which
> have to be done is to get the record from disk to check visibility
> and other columns.
>
> Yes thats correct. But I still dont get it. To get record from the
> disk on match, we need Relation data. But whats the purpose having
> two seperate Relation variables ?
>
> Does it mean that heaprelation will contain only info about that
> particular column of the table and index relation will have info
> about the whole tuple of the relation ?
>
>
> best regards,
> hans-juergen schoenig
>
>
>
> --
> Cybertec Schönig & Schönig GmbH
> PostgreSQL Solutions and Support
> Gröhrmühlgasse 26, 2700 Wiener Neustadt
> Tel: +43/1/205 10 35 / 340
> www.postgresql.at, www.cybertec.at
>
>
>
>
> Never miss a thing. Make Yahoo your homepage.

--
Cybertec Schönig & Schönig GmbH
PostgreSQL Solutions and Support
Gröhrmühlgasse 26, 2700 Wiener Neustadt
Tel: +43/1/205 10 35 / 340
www.postgresql.at, www.cybertec.at