Date: Fri, 17 Sep 2021 17:31:34 -0300
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: "Bossart, Nathan" <bossartn@amazon.com>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>,
	"andres@anarazel.de" <andres@anarazel.de>,
	"masao.fujii@oss.nttdata.com" <masao.fujii@oss.nttdata.com>,
	"pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>,
	"mengjuan.cmj@alibaba-inc.com" <mengjuan.cmj@alibaba-inc.com>,
	"Jakub.Wartak@tomtom.com" <Jakub.Wartak@tomtom.com>
Subject: Re: prevent immature WAL streaming
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On 2021-Sep-17, Bossart, Nathan wrote:

> I gave the patch a read-through.  I'm wondering if the
> XLOG_OVERWRITE_CONTRECORD records are actually necessary.  IIUC we
> will set XLP_FIRST_IS_ABORTED_PARTIAL on the next page, and
> xlp_pageaddr on that page will already be validated in
> XLogReaderValidatePageHeader().  Does adding this new record also help
> ensure the page header is filled in and flushed to disk?

That was the first implementation, a few versions of the patch ago.  An
added benefit of a separate WAL record is that you can carry additional
data for validation, such as -- as suggested by Andres -- the CRC of the
partial data contained in the message that we're skipping.  I didn't
implement that, but it should be trivial to add it.

-- 
Álvaro Herrera           39°49'30"S 73°17'W  —  https://www.EnterpriseDB.com/
"How strange it is to find the words "Perl" and "saner" in such close
proximity, with no apparent sense of irony. I doubt that Larry himself
could have managed it."         (ncm, http://lwn.net/Articles/174769/)