Re: POC: Cleaning up orphaned files using undo logs

On Mon, May 6, 2019 at 8:13 AM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> > In general, I find the code for updating transaction headers to be
> > really hard to understand. I'm not sure exactly what can be done
> > about that. Like, why is UndoRecordPrepareTransInfo unpacking undo?
>
> It's only unpacking header. But, yeah we can do better, instead of
> unpacking we can just read the main header and from uur_info we can
> calculate exact offset of the uur_next and in
> UndoRecordUpdateTransInfo we can directly update only uur_next by
> writing at that offset, instead of overwriting the complete header?

Hmm. I think it's reasonable to use the unpack infrastructure to
figure out where uur_next is. I don't know whether a bespoke method
of figuring that out would be any better. At least the comments
probably need some work.

> > Why does it take two undo record pointers as arguments and how are
> > they different?
> One is previous transaction's start header which we wants to update
> and other is current transaction's urec pointer what we want to set as
> uur_next in the previous transaction's start header.

So put some comments.

--
Robert Haas
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