| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>, Melanie Plageman <melanieplageman(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Georgios <gkokolatos(at)protonmail(dot)com>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Konstantin Knizhnik <knizhnik(at)garret(dot)ru>, Dilip Kumar <dilipbalaut(at)gmail(dot)com> |
| Subject: | Re: index prefetching |
| Date: | 2024-02-15 05:05:13 |
| Message-ID: | CA+TgmoYmZ+5mO1YaNfwcC2Kh3WDssksQQthoZ=xdDQyfdvoBuw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, Feb 15, 2024 at 10:33 AM Andres Freund <andres(at)anarazel(dot)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
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