mysterious nbtree.c comment

In nbtree.c there's a path that calls btvacuumscan to gather statistics if
there aren't already statistics. I'm not exactly clear how this code path is
reached but that's not my question. There's a comment that "there's no need to
go through all the vacuum-cycle-ID pushups" in this case because no deletions
are being performed.

I don't see how the lack of deletions is relevant to needing vacuum-cycle-ID.
AFAICT there's still a risk that someone will come along and do a page split
underneath this scan and if the page is to the left of the scan it will be
missed.

Datum
btvacuumcleanup(PG_FUNCTION_ARGS)
{
IndexVacuumInfo *info = (IndexVacuumInfo *) PG_GETARG_POINTER(0);
IndexBulkDeleteResult *stats = (IndexBulkDeleteResult *) PG_GETARG_POINTER(1);

/*
* If btbulkdelete was called, we need not do anything, just return
* the stats from the latest btbulkdelete call. If it wasn't called,
* we must still do a pass over the index, to recycle any newly-recyclable
* pages and to obtain index statistics.
*
* Since we aren't going to actually delete any leaf items, there's no
* need to go through all the vacuum-cycle-ID pushups.
*/
if (stats == NULL)
{
stats = (IndexBulkDeleteResult *) palloc0(sizeof(IndexBulkDeleteResult));
btvacuumscan(info, stats, NULL, NULL, 0);
}

--
greg