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 <[EMAIL PROTECTED]> 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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