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.
Ifit wasn't called, * we must still do a pass over the index, to recycle any newly-recyclable * pages and to obtain
indexstatistics. * * Since we aren't going to actually delete any leaf items, there's no * need to go through all the
vacuum-cycle-IDpushups. */if (stats == NULL){    stats = (IndexBulkDeleteResult *)
palloc0(sizeof(IndexBulkDeleteResult));   btvacuumscan(info, stats, NULL, NULL, 0);}
 


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greg