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

Leonardo F <m_lists(at)yahoo(dot)it> wrote:

> I saw that you also changed the writing:
(snip)
> Are we sure it's 100% equivalent?

I think writetup_rawheap() and readtup_rawheap() are a little complex,
but should work as long as there are no padding between t_len and t_self
in HeapTupleData struct.

- It might be cleaner if you write the total item length
and tuple data separately.
- "(char *) tuple + sizeof(tuplen)" might be more robust
than "&tuple->t_self".

Here is a sample code. writetup() and readtup() will be alike.

BTW, we could have LogicalTapeReadExact() as an alias of
LogicalTapeRead() and checking the result because we have
many duplicated codes for "unexpected end of data" errors.

static void
writetup_rawheap(Tuplesortstate *state, int tapenum, SortTuple *stup)
{
HeapTuple tuple = (HeapTuple) stup->tuple;
int tuplen = tuple->t_len + HEAPTUPLESIZE;

LogicalTapeWrite(state->tapeset, tapenum,
&tuplen, sizeof(tuplen));
LogicalTapeWrite(state->tapeset, tapenum,
(char *) tuple + sizeof(tuplen),
HEAPTUPLESIZE - sizeof(tuplen);
LogicalTapeWrite(state->tapeset, tapenum, tuple->t_data, tuple->t_len);
if (state->randomAccess) /* need trailing length word? */
LogicalTapeWrite(state->tapeset, tapenum, &tuplen, sizeof(tuplen));

FREEMEM(state, GetMemoryChunkSpace(tuple));
heap_freetuple(tuple);
}

static void
readtup_rawheap(Tuplesortstate *state, SortTuple *stup,
int tapenum, unsigned int tuplen)
{
HeapTuple tuple = (HeapTuple) palloc(tuplen);

USEMEM(state, GetMemoryChunkSpace(tuple));

tuple->t_len = tuplen - HEAPTUPLESIZE;
if (LogicalTapeRead(state->tapeset, tapenum,
(char *) tuple + sizeof(tuplen),
HEAPTUPLESIZE - sizeof(tuplen)) != HEAPTUPLESIZE - sizeof(tuplen))
elog(ERROR, "unexpected end of data");
tuple->t_data = (HeapTupleHeader) ((char *) tuple + HEAPTUPLESIZE);
if (LogicalTapeRead(state->tapeset, tapenum,
tuple->t_data, tuple->t_len) != tuple->t_len)
elog(ERROR, "unexpected end of data");
if (state->randomAccess) /* need trailing length word? */
if (LogicalTapeRead(state->tapeset, tapenum, &tuplen,
sizeof(tuplen)) != sizeof(tuplen))
elog(ERROR, "unexpected end of data");

Regards,
---
Takahiro Itagaki
NTT Open Source Software Center