Re: I: About "Our CLUSTER implementation is pessimal" patch

> I reviewed
> your patch. It seems to be in good shape, and worked as
> expected. I
> suppressed a compiler warning in the patch and cleaned up
> whitespaces in it.
> Patch attached.

Thanks for the review!

I saw that you also changed the writing:

LogicalTapeWrite(state->tapeset, tapenum,
tuple, HEAPTUPLESIZE);
LogicalTapeWrite(state->tapeset, tapenum, tuple->t_data, tuple->t_len-HEAPTUPLESIZE);

and the reading:

tuple->t_len = tuplen - HEAPTUPLESIZE;
if (LogicalTapeRead(state->tapeset, tapenum, &tuple->t_self, tuplen-sizeof(tuplen)) != tuplen-sizeof(tuplen))
elog(ERROR, "unexpected end of data");

into (writing):

LogicalTapeWrite(state->tapeset, tapenum,
tuple, tuple->t_len);

(reading):

if (LogicalTapeRead(state->tapeset, tapenum, &tuple->t_self, tuplen-sizeof(tuplen)) != tuplen-sizeof(tuplen))

Are we sure it's 100% equivalent?

I remember I had issues with the fact that tuple->t_data wasn't
at HEAPTUPLESIZE distance from tuple:

http://osdir.com/ml/pgsql-hackers/2010-02/msg00744.html

> I think we need some documentation for the change. The
> only downside
> of the feature is that sorted cluster requires twice disk
> spaces of
> the target table (temp space for disk sort and the result
> table).
> Could I ask you to write documentation about the new
> behavior?
> Also, code comments can be improved; especially we need
> better
> description than "copy&paste from
> FormIndexDatum".

I'll try to improve the comments and add doc changes (but my English
will have to be double checked...)