The 13.4 release notes document the following:
> Fix mis-planning of repeated application of a projection step (Tom Lane)
>
> The planner could create an incorrect plan in cases where two
> ProjectionPaths were stacked on top of each other. The only known
> way to trigger that situation involves parallel sort operations,
> but there may be other instances. The result would be crashes or
> incorrect query results. Disclosure of server memory contents is also
> possible. (CVE-2021-3677)
>
Is there a way to detect if this is happening and could this problem cause very bad, but successful, plans to be
created? We are seeing 13.3 create horrible plans for some queries, where 13.4 creates great plans for the same
queries.
PJ