Re: [HACKERS] Allow GiST opcalsses without compress\decompres functions

Andrew Borodin <borodin@octonica.com> writes:
> 2017-05-28 22:22 GMT+05:00 Tom Lane <tgl@sss.pgh.pa.us>:

>> 2. If compress/decompress are omitted, then we could support index-only
>> scans all the time, that is a no-op fetch function would work.  The
>> patch should cover that interaction too.

> I do not think so. Decompress have to get att to the state where
> consistency function can understand it. In theory. I've checked like a
> dozen of types and have not found places where fetch should differ
> from decompress.

But if compress is omitted, then we know the in-index representation
is the same as the original.  Therefore the fetch function would always
be a no-op and we can implement IOS whether or not the opclass designer
bothered to supply one.

                        regards, tom lane