Re: [HACKERS] logical decoding of two-phase transactions

On Mon, Nov 23, 2020 at 10:35 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> For the first two, as the xact is still not visible to others so we
> don't need to make it behave like a committed txn. To make the (DDL)
> changes visible to the current txn, the message
> REORDER_BUFFER_CHANGE_INTERNAL_COMMAND_ID copies the snapshot which
> fills the subxip array. This will be sufficient to make the changes
> visible to the current txn. For the third, I have checked the code
> that whenever we have any change message the base snapshot gets set
> via SnapBuildProcessChange. It is possible that I have missed
> something but I don't want to call SnapbuildCommittedTxn in
> DecodePrepare unless we have a clear reason for the same so leaving it
> for now. Can you or someone see any reason for the same?

I reviewed and tested this and like you said, SnapBuildProcessChange
sets the base snapshot for every change.
I did various tests using DDL updates and haven't seen any issues so
far. I agree with your analysis.

regards,
Ajin