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From: Alexander Korotkov <aekorotkov@gmail.com>
Date: Thu, 12 Mar 2026 00:22:02 +0200
Message-ID: 
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Subject: Re: Odd code around ginScanToDelete
To: Pavel Borisov <pashkin.elfe@gmail.com>
Cc: Xuneng Zhou <xunengzhou@gmail.com>, Andres Freund <andres@anarazel.de>,
	pgsql-hackers@postgresql.org
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On Tue, Mar 10, 2026 at 11:29=E2=80=AFAM Pavel Borisov <pashkin.elfe@gmail.=
com> wrote:
> Hi, Xuneng
>
> > > Is it worth/possible in recursive calls of ginScanToDelete() to free
> > > allocated myStackItem->child after processing all children of the
> > > current level, when they are not needed anymore?
> > > Previously to this patch, palloc-ed "me" variable also was't freed at
> > > recursion levels.
> >
> > Freeing/reallocating it per subtree would add churn and make the
> > lifetime rules harder to reason about without meaningful memory
> > savings (the number of nodes is bounded by tree depth, not number of
> > pages). We currently free the chain once after ginScanToDelete()
> > returns in ginVacuumPostingTree(), which matches the natural lifetime
> > boundary
> I proposed not freeing child when child iteration is complete. They
> indeed can be reused. I proposed cleaning children when "my" iteration
> is complete. At that time all the children iterations are completed
> and not needed when we return level up.

This is not clear for me.  We need stack items to keep track of left
pages until we scan the whole posting tree.  After scanning the whole
posting tree we can free stack items as we do now.

------
Regards,
Alexander Korotkov
Supabase