Re: Is there anyway to create a TupleDesc with uint32 attribute easily?

Xiao Meng wrote:
> Hi, hackers.
> I'm working on my gsoc project - improving hash index.
> I need to create a TupldeDesc with uint32 attribute.
> Here is the reason why I need it -
> If we store hash code only in the tuple, then the TupleDesc's
> attribute should be uint32

Something along the lines of:

TupleDesc tupdesc = CreateTemplateTupleDesc(1, false);
TupleDescInitEntry(tupdesc, 1, "hashcode", INT4OID, -1, 0);

> In this way, we can use index_form_tuple() to create a tuple and
> needn't write a function for hash specially.

I would actually suggest ditching the normal page layout with line
pointers and IndexTuples altogether. All the entries are fixed size, so
you can get away with a much simpler structure, and store more entries
per page. Storing an IndexTuple with one int32 column takes

(sizeof(IndexTupleData) + sizeof(uint32) + sizeof(ItemIdData)) = 16 bytes,

but you only need a pointer to the heap tuple, and the hash code, which
is just 10 bytes in total. Or 12 if you have to align the hash code to 4
byte boundary.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com