Re: AW: AW: pg_index.indislossy

>
> > > > > > > > Can someone tell me what we use indislossy for?
> > > > >
> > > > > Ok, so the interpretation of this field is:
> > > > > A match in the index needs to be reevaluated in the heap tuple data,
> > > > > since a match in the index does not necessarily mean, that the heap tuple
> > > > > matches.
> > > > > If the heap tuple data matches, the index must always match.
> > >
> > > AFAIK, this is true for all indexes in PostgreSQL, because index rows
> > > don't store the transactions status. Of course those are two different
> > > underlying reasons why a heap lookup is always necessary, but there
> > > shouldn't be any functional difference in the current implementation.
> >
> > Seems it is something they added for the index abstraction and not for
> > practical use by PostgreSQL.
>
> Why, you do not need to call the comparison function on the heap data
> if the index is not lossy, saves some CPU cycles.

Because we don't know of the tuples expired status until we check the
heap.

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