Re: PGQ catalog representation and pg_dump support

Hi,

On 2026-09-02 17:33:38 -0400, Andres Freund wrote:
> - As mentioned in my last email, nothing protects the graph object against
> being altered while rewriteGraphTable() is running, due to AlterPropGraph()
> only holding an AccessShareLock. That's bad.

An particularly odd thing about that is that some things in
rewriteGraphTable.c actually use a more heavyweight lock level -
is_property_associated_with_label() and get_element_property_expr() use
RowShareLock. I don't really understand why? There's no comment about that
either?

There are also unexplained uses of RowShareLock in propgraphcmds.c - why is
e.g. pg_attribute opened with RowShareLock?

Separately (noticed when searching for RowShareLock uses): Isn't it somewhat
of a problem to do a seqscan of PropgraphLabelPropertyRelationId for
/* Remove any orphaned pg_propgraph_property entries */

I don't know why that code uses RowShareLock either. Not using AccessShareLock
makes sense, afaict the performDeletion() of PropgraphPropertyRelationId done
during the scan will recurse to PropgraphLabelPropertyRelationId - avoiding
deadlock hazards due to lock upgrades could make sense. But a deletion takes
RowExclusive, not RowShare? So what's the point of RowShare?

Greetings,

Andres Freund