Re: Resumable vacuum proposal and design overview

> > You haven't explained how saving the dead-tuple-list could be done
in
> > a safe mannner and it seems risky to me.
>
> The files are placed in a new directory $PGDATA/pg_vacuum
> with the name: spcNode.dbNode.relNode for each relations
> which have been interrupted during vacuum.
>
> It has the format likes:
>
> 1. VacStateFileHeader
> 2. VacStateData
> 3. Dead Tuple list
> 4. CRC32
>
> The files are removed
> - when original physical heap files are removed,
> - when vacuum full have been issued,
> - or after the content has been read in memory.
> - etc.
>
> Is there any potential big risk there? Correct me if I am wrong.

The main risc is not a corrupt file or broken list. The risc is, that a
ctid in the list points at a tuple that is not dead anymore. To avoid
that risc you would need to:
1. keep the vacuum lock open
2. leave the vacuum tx open

(or reevaluate visibility of list members upon resume)

Andreas