Re: Doubt in IndexScanDescData

Hans-Juergen Schoenig <postgres@cybertec.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

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