Re: Fix premature xmin advancement during fast forward decoding

On Fri, Apr 25, 2025 at 10:46 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> What I'm concerned about is the back branches. With this approach all
> back branches will have such degradations and it doesn't make sense to
> me to optimize SnapBuildCommitTxn() codes in back branches.
>

One possibility could be that instead of maintaining an entire
snapshot in fast_forward mode, we can maintain snapshot's xmin in each
ReorderBufferTXN. But then also, how would we get the minimum
txns_by_base_snapshot_lsn as we are getting now in
ReorderBufferGetOldestXmin? I think we need to traverse the entire
list of txns to get it in fast_forward mode but that may not show up
because it will not be done for each transaction. We can try such a
thing, but it won't be clean to have fast_forward specific code and
also it would be better to add such things only for HEAD. Can you
think of any better ideas?

--
With Regards,
Amit Kapila.