Re: About "Our CLUSTER implementation is pessimal" patch

> Rule it out. Note you should be looking at pg_am.amcanorder, not
> hardwiring knowledge of particular index types.

Sorry, I replied "ok" too fast...

I can look at pg_am.amcanorder, but I would still need the ScanKey to be used

by tuplesort; and I can't find any other way of doing it than calling
_bt_mkscankey_nodata, which is btree-specific.

I guess either:

- add another function to the list of "Index Access Method Functions", something
that returns the ScanKey in case pg_am.amcanorder is true

or

- hardwiring the fact that the only way to seq scan + sort in CLUSTER is using
a btree... hence the call to _bt_mkscankey_nodata

But maybe there's another way of doing it, I don't know the code enough

Leonardo