Re: POC: Cleaning up orphaned files using undo logs

On Thu, Aug 22, 2019 at 1:34 AM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> Yeah, we can handle the bulk fetch as you suggested and it will make
> it a lot easier. But, currently while registering the undo request
> (especially during the first pass) we need to compute the from_urecptr
> and the to_urecptr. And, for computing the from_urecptr, we have the
> end location of the transaction because we have the uur_next in the
> transaction header and that will tell us the end of our transaction
> but we still don't know the undo record pointer of the last record of
> the transaction. As of know, we read previous 2 bytes from the end of
> the transaction to know the length of the last record and from there
> we can compute the undo record pointer of the last record and that is
> our from_urecptr.=

I don't understand this. If we're registering an undo request at "do"
time, we don't need to compute the starting location; we can just
remember the UndoRecPtr of the first record we inserted. If we're
reregistering an undo request after a restart, we can (and, I think,
should) work forward from the discard location rather than backward
from the insert location.

--
Robert Haas
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