Re: POC: Cleaning up orphaned files using undo logs

Hi,

On 2019-08-22 10:19:04 +0530, Dilip Kumar wrote:
> On Thu, Aug 22, 2019 at 9:58 AM Andres Freund <andres@anarazel.de> wrote:
> >
> > Hi,
> >
> > On 2019-08-22 09:51:22 +0530, Dilip Kumar wrote:
> > > We can not know the complete size of the record even by reading the
> > > header because we have a payload that is variable part and payload
> > > length are stored in the payload header which again can be at random
> > > offset.
> >
> > Wait, but that's just purely self inflicted damage, no? The initial
> > length just needs to include the payload. And all this is not an issue
> > anymore?
> >
> Actually, we store the undo length only at the end of the record and
> that is for traversing the transaction's undo record chain during bulk
> fetch.  Ac such in the beginning of the record we don't have the undo
> length.  We do have uur_info but that just tell us which all optional
> header are included in the record.

But why? It makes a *lot* more sense to have it in the beginning. I
don't think bulk-fetch really requires it to be in the end - we can
still process records forward on a page-by-page basis.

Greetings,

Andres Freund