Re: generic plans and "initial" pruning

On Wed, 19 Jan 2022 at 08:31, Amit Langote <amitlangote09@gmail.com> wrote:

> > Maybe force all DDL, or just DDL that would cause safety issues, to
> > update a hierarchy version number, so queries can tell whether they
> > need to replan. Don't know, just looking for an O(1) solution.
>
> Yeah, it would be great if it would suffice to take a single lock on
> the partitioned table mentioned in the query, rather than on all
> elements of the partition tree added to the plan.  AFAICS, ways to get
> that are 1) Prevent modifying non-root partition tree elements,

Can we reuse the concept of Strong/Weak locking here?

When a DDL request is in progress (for that partitioned table), take
all required locks for safety. When a DDL request is not in progress,
take minimal locks knowing it is safe.

We can take a single PartitionTreeModificationLock, nowait to prove
that we do not need all locks. DDL would request the lock in exclusive
mode. (Other mechanisms possible).

-- 
Simon Riggs                http://www.EnterpriseDB.com/