On Thu, Dec 19, 2024 at 1:00 AM Masahiko Sawada <sawada.m...@gmail.com> wrote: > > On Tue, Dec 17, 2024 at 11:12 PM John Naylor <johncnaylo...@gmail.com> wrote: > > +1 in general, but I wonder if instead the iter_context should be > > created within RT_BEGIN_ITERATE -- I imagine that would have less > > duplication and would be as safe, but I haven't tried it. Is there > > some reason not to do that? > > I agree that it has less duplication. There is no strong reason I > didn't do that. I just didn't want to check 'if (!tree->iter_context)' > in RT_BEGIN_ITERATE for simplicity. I've changed the patch > accordingly.
I see what you mean. For v17, a bit of duplication is probably worth it for simplicity, so I'd say v1 is fine there. However, I think on master we should reconsider some aspects of memory management more broadly: 1. The creator allocates the root of the tree in a new child context, but an attaching process allocates it in its current context, and we pfree it when the caller wants to detach. It seems like we could always allocate this small struct in CurrentMemoryContext for consistency. 2. The iter_context is separate because the creator's new context could be a bump context which doesn't support pfree. But above we assume we can pfree in the caller's context. Also, IIUC we only allocate small iter objects, and it'd be unusual to need more than one at a time per backend, so it's a bit strange to have an entire context for that. Since we use a standard pattern of "begin; while(iter); end;", it seems unlikely that someone will cause a leak because of a coding mistake in iteration. If these tiny admin structs were always, not sometimes, in the callers current context, I think it would be easier to reason about because then the creator's passed context would be used only for local memory, specifically only for leaves and the inner node child contexts. Thoughts? Further, 3. I was never a fan of trying to second-guess the creator's new context and instead use slab for fixed-sized leaf allocations. If the creator passes a bump context, we say "no, no, no, use slab -- it's good for ya". Let's assume the caller knows what they're doing. 4. For local memory, an allocated "control object" serves no real purpose and wastes a few cycles on every access. I'm not sure it matters that much as a future micro-optimization, but I mention it here because if we did start allocating outer structs in the callers context, embedding would also remove the need to pfree it. -- John Naylor Amazon Web Services
