> > > > > > > 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.
Andreas