Re: POC: Cleaning up orphaned files using undo logs

On Thu, Jul 18, 2019 at 4:41 PM Thomas Munro <thomas(dot)munro(at)gmail(dot)com> wrote:
>
> On Tue, Jul 16, 2019 at 8:39 AM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> > Thomas has already objected to another proposal to add functions that
> > turn 32-bit XIDs into 64-bit XIDs. Therefore, I feel confident in
> > predicting that he will likewise object to GetEpochForXid. I think
> > this needs to be changed somehow, maybe by doing what the XXX comment
> > you added suggests.
>
> Perhaps we should figure out how to write GetOldestFullXmin() and friends.
>
> For FinishPreparedTransaction(), the XXX comment sounds about right
> (TwoPhaseFileHeader should hold an fxid).
>

I think we can do that, but what about subxids in TwoPhaseFileHeader?
Shall we store them as fxids as well? If we don't do that then it
will appear inconsistent and if we want to store subxids as fxids,
then we need to track them as fxids in TransactionStateData. It might
not be a very big change, but certainly, more work as compared to if
we just store top-level fxid or use GetEpochForXid as we are currently
using in the patch. Another thing is changing subxids to fxids can
increase the size of two-phase file for a xact having many
sub-transactions which again might be okay, but not completely sure.

Thoughts?

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com