Re: record identical operator

* Kevin Grittner (kgrittn(at)ymail(dot)com) wrote:
> ... like
> just refreshing a view so that the new contents are the same as
> what you would see if you re-ran the query defining the matview.

I've heard this notion a few times of wanting to make sure that what you
get from running the query matches the matview. While that makes sense
when the equality operator and what-you-see actually match, it doesn't
when they don't because the what-you-see ends up being non-deterministic
and can change based on the order the datums are seen in during the
query processing which can change with different data ordering on disk
and even due to simply different plans for the same data, I believe.

Consider a GROUP BY with a citext column as one of the key fields.
You're going to get whatever value the aggregate happened to come across
first when building the HashAgg. Having the binary equality operator
doesn't help that and seems like it could even result in change storms
happening due to a different plan when the actual data didn't change.

Thanks,

Stephen