| From: | Thomas Munro <thomas(dot)munro(at)gmail(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, David Steele <david(at)pgmasters(dot)net>, Dmitry Dolgov <9erthalion6(at)gmail(dot)com>, Jakub Wartak <Jakub(dot)Wartak(at)tomtom(dot)com>, Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: WIP: WAL prefetch (another approach) |
| Date: | 2021-04-29 04:27:36 |
| Message-ID: | CA+hUKGJ5egYKng4U5PQzv6zcX_7=NvJb_WXiB2gU8NBcohD1kg@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, Apr 29, 2021 at 3:14 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
> To me it looks like a smaller version of the problem is present in < 14,
> albeit only when the page header is at a record boundary. In that case
> we don't validate the page header immediately, only once it's completely
> read. But we do believe the total size, and try to allocate
> that.
>
> There's a really crufty escape hatch (from 70b4f82a4b) to that:
Right, I made that problem worse, and that could probably be changed
to be no worse than 13 by reordering those operations.
PS Sorry for my intermittent/slow responses on this thread this week,
as I'm mostly away from the keyboard due to personal commitments.
I'll be back in the saddle next week to tidy this up, most likely by
reverting. The main thought I've been having about this whole area is
that, aside from the lack of general testing of recovery, which we
should definitely address[1], what it really needs is a decent test
harness to drive it through all interesting scenarios and states at a
lower level, independently.
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