Re: Patch: Write Amplification Reduction Method (WARM)

On Sat, 25 Mar 2017 at 11:03 PM, Peter Geoghegan <pg(at)bowt(dot)ie> wrote:

> On Sat, Mar 25, 2017 at 12:54 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
> wrote:
> > I am not sure how do you want to binary compare two datums, if you are
> > thinking datumIsEqual(), that won't work. I think you need to use
> > datatype specific compare function something like what we do in
> > _bt_compare().
>
> How will that interact with types like numeric, that have display
> scale or similar?
>
> I wonder why Amit thinks that datumIsEqual won't work once we convert the
heap values to index tuple and then fetch using index_get_attr. After all
that's how the current index tuple was constructed when it was inserted. In
fact, we must not rely on _bt_compare because that might return "false
positive" even for two different heap binary values (I think). To decide
whether to do WARM update or not in heap_update we only rely on binary
comparison. Could it happen that for two different binary heap values, we
still compute the same index attribute? Even when expression indexes are
not supported?

Thanks,
Pavan

> --
> Peter Geoghegan
>
--
Pavan Deolasee http://www.2ndQuadrant.com/
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