Re: index prefetching

On Thu, Feb 15, 2024 at 10:33 AM Andres Freund <andres@anarazel.de> wrote:
> The issue here is that we need to read index leaf pages (synchronously for
> now!) to get the tids to do readahead of table data. What you describe is done
> for the table data (IMO not a good idea medium term [1]), but the problem at
> hand is that once we've done readahead for all the tids on one index page, we
> can't do more readahead without looking at the next index leaf page.

Oh, right.

> However, if we want to issue table readahead for tids on the neighboring index
> leaf page, we'll - as the patch stands - not hold a pin on the "current" index
> leaf page. Which makes index prefetching as currently implemented incompatible
> with kill_prior_tuple, as that requires the index leaf page pin being held.

But I think it probably also breaks MVCC, as Peter was saying.

--
Robert Haas
EDB: http://www.enterprisedb.com