> > You haven't explained how saving the dead-tuple-list could be done
> > 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)


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