Re: Optimize SnapBuildPurgeOlderTxn: use in-place compaction instead of temporary array

On Sat, Oct 18, 2025 at 01:59:40PM +0500, Kirill Reshke wrote:
> Indeed, these changes look correct.
> I wonder why b89e151054a0 did this place this way, hope we do not miss
> anything here.

Perhaps a lack of time back in 2014? It feels like an item where we
would need to research a bit some of the past threads, and see if this
has been discussed, or if there were other potential alternatives
discussed. This is not saying that what you are doing in this
proposal is actually bad, but it's a bit hard to say what an
"algorithm" should look like in this specific code path with XID
manipulations. Perhaps since 2014, we may have other places in the
tree that share similar characteristics as what's done here.

So it feels like this needs a bit more historical investigation first,
rather than saying that your proposal is the best choice on the table.
--
Michael