On Tue, Aug 3, 2021 at 8:44 PM Peter Geoghegan <p...@bowt.ie> wrote: > This time it's quite different: we're truncating the line pointer > array during pruning. Pruning often occurs opportunistically, during > regular query processing. In fact I'd say that it's far more common > than pruning by VACUUM. So the chances of line pointer array > truncation hurting rather than helping seems higher.
How would it hurt? It's easy to see the harm caused by not shortening the line pointer array when it is possible to do so: we're using up space in the page that could have been made free. It's not so obvious to me what the downside of shortening it might be. I suppose there is a risk that we shorten it and get no benefit, or even shorten it and have to lengthen it again almost immediately. But neither of those things really matters unless shortening is expensive. If we can piggy-back it on an existing WAL record, I don't really see what the problem is. -- Robert Haas EDB: http://www.enterprisedb.com
