Message-ID: <60727ac9d5da9330bb4bea0c691fec2ce37296ca.camel@j-davis.com>
Subject: Re: Improve WALRead() to suck data directly from WAL buffers when
 possible
From: Jeff Davis <pgsql@j-davis.com>
To: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, Dilip Kumar <dilipbalaut@gmail.com>,
  Kyotaro Horiguchi <horikyota.ntt@gmail.com>,
 pgsql-hackers@lists.postgresql.org, Nathan Bossart
 <nathandbossart@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>
Date: Fri, 19 Jan 2024 17:47:57 -0800
In-Reply-To: 
 <CALj2ACWPKuoUdA7r4VFKhsTZeNekyUr=ZwM6ckyvJ0qv2f6Whg@mail.gmail.com>
References: <0d84c025e38673cb575dcf4987d050fe7b1e1a1f.camel@j-davis.com>
	 <20231011224353.cl7c2s222dw3de4j@awork3.anarazel.de>
	 <CALj2ACU2DGH-BB_187N7gfVkLdxfJ+doVTcteS0ugLn_c8mLOw@mail.gmail.com>
	 <CALj2ACVgVgA5BSSrEYO2eTMEGB=QUbcYosYm3vZ3R2=GPB6tNw@mail.gmail.com>
	 <5c6e8e60c5c156a9f51ccf850f70829e45a985a1.camel@j-davis.com>
	 <CALj2ACVjzHgQvONnTLffyBJRACPwhsf-cYG4TQ2KHKrFfFop-w@mail.gmail.com>
	 <4132fe48f831ed6f73a9eb191af5fe475384969c.camel@j-davis.com>
	 <CALj2ACV123Ke6wn05QCnCgJhFpcarGCv7sKM1p39t+qpUNHUgQ@mail.gmail.com>
	 <20231104004348.zhxzk2p266i3r2z2@awork3.anarazel.de>
	 <CALj2ACUSydTHPcucftm4XdiJ4osH8zeNENyADd-zfDzEMf6akA@mail.gmail.com>
	 <20231109205836.zjoawdrn4q77yemv@awork3.anarazel.de>
	 <CALj2ACXo-_boM3h-PJuvfuvFzP1nv2wcZBoZN_YbRbQBGQYAUg@mail.gmail.com>
	 <CALj2ACVfFMfqD5oLzZSQQZWfXiJqd-NdX0_317veP6FuB31QWA@mail.gmail.com>
	 <3750ff9c2a5556808827e7fc5bcc0bd16e9facf4.camel@j-davis.com>
	 <CALj2ACXy5eA-Y4Qgm3MUYZTGr_opNm2SzGtN+Zj6dbcSzqHrJA@mail.gmail.com>
	 <73df9831747b01ced949102610dc44ca6026ee1c.camel@j-davis.com>
	 <CALj2ACWPKuoUdA7r4VFKhsTZeNekyUr=ZwM6ckyvJ0qv2f6Whg@mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
User-Agent: Evolution 3.44.4-0ubuntu2 
MIME-Version: 1.0
Archived-At: 
 <https://www.postgresql.org/message-id/60727ac9d5da9330bb4bea0c691fec2ce37296ca.camel%40j-davis.com>
Precedence: bulk

On Wed, 2024-01-10 at 19:59 +0530, Bharath Rupireddy wrote:
> I've addressed the above review comments and attached v19 patch-set.

Regarding:

-       if (!WALRead(state, cur_page, targetPagePtr, XLOG_BLCKSZ, tli,
-                                &errinfo))
+       if (!WALRead(state, cur_page, targetPagePtr, count, tli,
&errinfo))

I'd like to understand the reason it was using XLOG_BLCKSZ before. Was
it a performance optimization? Or was it to zero the remainder of the
caller's buffer (readBuf)? Or something else?

If it was to zero the remainder of the caller's buffer, then we should
explicitly make that the caller's responsibility.

Regards,
	Jeff Davis