Re: Idea for nested transactions / savepoints

> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > My idea is that we not put UNDO information into WAL but keep a List of
> > rel ids / tuple ids in the memory of each backend and do the undo inside
> > the backend.
> 
> The complaints about WAL size amount to "we don't have the disk space
> to keep track of this, for long-running transactions".  If it doesn't
> fit on disk, how likely is it that it will fit in memory?

Sure, we can put on the disk if that is better.  I thought the problem
with WAL undo is that you have to keep UNDO info around for all
transactions that are older than the earliest transaction.  So, if I
start a nested transaction, and then sit at a prompt for 8 hours, all
WAL logs are kept for 8 hours.

We can create a WAL file for every backend, and record just the nested
transaction information.  In fact, once a nested transaction finishes,
we don't need the info anymore.  Certainly we don't need to flush these
to disk.

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