Re: POC: Cleaning up orphaned files using undo logs

[Dilip Kumar]

On Fri, Jul 19, 2019 at 6:37 PM Robert Haas <robertmh...@gmail.com> wrote:
>
> On Fri, Jul 19, 2019 at 7:54 AM Amit Khandekar <amitdkhan...@gmail.com> wrote:
> > + * We just want to mask the cid in the undo record header.  So
> > + * only if the partial record in the current page include the undo
> > + * record header then we need to mask the cid bytes in this page.
> > + * Otherwise, directly jump to the next record.
> > Here, I think you mean : "So only if the partial record in the current
> > page includes the *cid* bytes", rather than "includes the undo record
> > header"
> > May be we can say :
> > We just want to mask the cid. So do the partial record masking only if
> > the current page includes the cid bytes from the partial record
> > header.
>
> Hmm, but why is it correct to mask the CID at all?  Shouldn't that match?
>
We don't write CID in the WAL. Because In hot-standby or after
recovery we don't need actual CID for the visibility.   So during REDO
while generating the undo record we set CID as 'FirstCommandId' which
is different from the DO time.  That's the reason we mask it.
-- 
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com