Re: eliminate xl_heap_visible to reduce WAL (and eventually set VM on-access)

On Wed, 3 Sept 2025 at 04:11, Melanie Plageman
<melanieplageman(at)gmail(dot)com> wrote:
>
> On Tue, Sep 2, 2025 at 5:52 PM Melanie Plageman
> <melanieplageman(at)gmail(dot)com> wrote:
> >
> > On Thu, Aug 28, 2025 at 5:12 AM Kirill Reshke <reshkekirill(at)gmail(dot)com> wrote:
> > >
> > > I did micro git-blame research here. I spotted only one related change
> > > [0]. Looks like before this change pin was indeed needed.
> > > But not after this change, so this visibilitymap_pin is just an oversight?
> > > Related thread is [1]. I quickly checked the discussion in this
> > > thread, and it looks like no one was bothered about these lines or VM
> > > logging changes (in this exact pin buffer aspect). The discussion was
> > > of other aspects of this commit.
> >
> > Wow, thanks so much for doing that research. Looking at it myself, it
> > does indeed seem like just an oversight. It isn't harmful since it
> > won't take another pin, but it is confusing, so I think we should at
> > least remove it in master. I'm not as sure about back branches.
>
> I've updated the commit message in the patch set to reflect the
> research you did in attached v8.
>
> - Melanie

Hi!

small comments regarding new series

0001, 0002, 0017 LGTM

In 0015:

```
reshke(at)yezzey-cbdb-bench:~/postgres$ git diff
src/backend/access/heap/pruneheap.c
diff --git a/src/backend/access/heap/pruneheap.c
b/src/backend/access/heap/pruneheap.c
index 05b51bd8d25..0794af9ae89 100644
--- a/src/backend/access/heap/pruneheap.c
+++ b/src/backend/access/heap/pruneheap.c
@@ -1398,7 +1398,7 @@ heap_prune_record_unchanged_lp_normal(Page page,
PruneState *prstate, OffsetNumb
/*
* For now always use prstate->cutoffs
for this test, because
* we only update 'all_visible' when
freezing is requested. We
- * could use
GlobalVisTestIsRemovableXid instead, if a
+ * could use GlobalVisXidVisibleToAll
instead, if a
* non-freezing caller wanted to set the VM bit.
*/
Assert(prstate->cutoffs);
```

Also, maybe GlobalVisXidTestAllVisible is a slightly better name? (The
term 'all-visible' is one that we occasionally utilize)

--
Best regards,
Kirill Reshke