Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp> writes:
> At Tue, 25 Sep 2018 16:45:09 -0700, Andres Freund <andres@anarazel.de> wrote in
<20180925234509.3hrrf6tmvy5tfith@alap3.anarazel.de>
>> On 2018-09-04 18:35:34 +0530, Amit Khandekar wrote:
>>> Pack the boolean members in TupleTableSlot into a 16 bit tts_flags.
>>> This reduces the size of TupleTableSlot since each bool member takes
>>> at least a byte on the platforms where bool is defined as a char.
> About bitfields, an advantage of it is debugger awareness. We
> don't need to look aside to the definitions of bitwise macros
> while using debugger. And the current code is preserved in
> appearance by using it.
FWIW, I would expect a change like this to be a net loss performance-wise
on most platforms. Testing the contents of a byte-wide variable is pretty
cheap on any architecture invented later than ~ 1970. Testing a bit,
though, requires a masking operation that is not free. I am not seeing
how making TupleTableSlot a little smaller buys that back ... we don't
normally have that many active slots in a plan.
regards, tom lane