Date: Fri, 4 Dec 2020 14:01:45 -0500
From: Stephen Frost <sfrost@snowman.net>
To: Andres Freund <andres@anarazel.de>
Cc: Thomas Munro <thomas.munro@gmail.com>,
	Tomas Vondra <tomas.vondra@enterprisedb.com>,
	Tomas Vondra <tomas.vondra@2ndquadrant.com>,
	Dmitry Dolgov <9erthalion6@gmail.com>,
	David Steele <david@pgmasters.net>,
	Alvaro Herrera <alvherre@2ndquadrant.com>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: WIP: WAL prefetch (another approach)
Message-ID: <20201204190145.GW16415@tamriel.snowman.net>
References: 
 <CA+hUKGJyuSTC5sXTv-2FmtjfFPYFU8t8JPnhV4jdMKmuKJ4tHw@mail.gmail.com>
 <20201010112935.qrhm572v4djrjljo@development>
 <CA+hUKGJwuzYCLxCP7QpK54uHBxEDGNcnDF4CJuJnuvFDpn4h5A@mail.gmail.com>
 <5437ce5b-d305-bd85-23ec-ddb15735d93f@enterprisedb.com>
 <20201113151344.GU16415@tamriel.snowman.net>
 <CA+hUKGJ1=pOiNjSgXYJnjE3OyRtp8tjMRcON256e5EFpzPpgtA@mail.gmail.com>
 <20201118210039.GP16415@tamriel.snowman.net>
 <CA+hUKG+BEjLHiAxJEBw1QSckFJFL8Uq6EhAuqdK6KnavcHjefQ@mail.gmail.com>
 <20201204182738.GU16415@tamriel.snowman.net>
 <20201204185157.w3qtqyym6fixmnrg@alap3.anarazel.de>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha512;
	protocol="application/pgp-signature"; boundary="COhulpXxI8TEX8GP"
Content-Disposition: inline
In-Reply-To: <20201204185157.w3qtqyym6fixmnrg@alap3.anarazel.de>
User-Agent: Mutt/1.5.24 (2015-08-30)
Precedence: bulk


--COhulpXxI8TEX8GP
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

Greetings,

* Andres Freund (andres@anarazel.de) wrote:
> On 2020-12-04 13:27:38 -0500, Stephen Frost wrote:
> > If I follow correctly, this patch will scan ahead in the WAL and let
> > the kernel know that certain blocks will be needed soon.  Ideally,
> > though I don't think it does yet, we'd only do that for blocks that
> > aren't already in shared buffers, and only for non-FPIs (even better if
> > we can skip past pages for which we already, recently, passed an FPI).
>=20
> The patch uses PrefetchSharedBuffer(), which only initiates a prefetch
> if the page isn't already in s_b.

Great, glad that's already been addressed in this, that's certainly
good.  I think I knew that and forgot it while composing that response
over the past rather busy week. :)

> And once we have AIO, it can actually initiate IO into s_b at that
> point, rather than fetching it just into the kernel page cache.

Sure.

Thanks,

Stephen

--COhulpXxI8TEX8GP
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1
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=c3aB
-----END PGP SIGNATURE-----

--COhulpXxI8TEX8GP--