Re: GROUP BY ROLLUP queries on views trigger full table scans (index usage not optimized)

Richard Guo <guofenglinux(at)gmail(dot)com> writes:
> I've been back and forth on whether to back-patch these two patches to
> v18, given that they can lead to plan changes.

Yeah, typically we lean to not back-patching planning changes,
for fear of de-optimizing queries that may have been tuned to the
old behavior.

However, in this case there is a mitigating factor: from the users'
point of view v18's behavior is a regression. Affected queries that
relied on indexes were fine in prior versions but now they fail to
use the indexes. v18 is new enough that it seems unlikely that any
applications have been tuned for its behavior; we should worry more
about de-optimizing applications that haven't yet been brought
forward.

So here, I think the don't-break-things rule points towards
back-patching.

regards, tom lane