SPI cursors pinned buffer and moving to the first tuple.

Hi,
I need to verify something.
I use spi cursors in a C function (which return a SETOF).
I am using the spi cursors to run the following query:
"SELECT DISTINCT * FROM mytable".
Each time the system gets back to the function
spi cursor can give me the next tuple which I can return.
Q1:My question is, does an SPI cursor pin its last buffer,
I.e. if I will take 1 tuple from SPI each time and
a page can contain 10 tuples, would there be 10 I/Os
or just 1 (since the last page is always pinned in memory).

I tried to reason the answer from the code but its not as clear as
the heap_fetch,etc... functions.

Q2:If I move to the first tuple in the cursor, does it reads everything
in its way back? I don't want the database to start another SELECT
DISTINCT
and use what is already ready.

Thanks.

Regards,
tzahi.

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