| From: | "Bossart, Nathan" <bossartn(at)amazon(dot)com> |
|---|---|
| To: | Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> |
| Cc: | Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, "andres(at)anarazel(dot)de" <andres(at)anarazel(dot)de>, "masao(dot)fujii(at)oss(dot)nttdata(dot)com" <masao(dot)fujii(at)oss(dot)nttdata(dot)com>, "pgsql-hackers(at)lists(dot)postgresql(dot)org" <pgsql-hackers(at)lists(dot)postgresql(dot)org>, "mengjuan(dot)cmj(at)alibaba-inc(dot)com" <mengjuan(dot)cmj(at)alibaba-inc(dot)com>, "Jakub(dot)Wartak(at)tomtom(dot)com" <Jakub(dot)Wartak(at)tomtom(dot)com> |
| Subject: | Re: prevent immature WAL streaming |
| Date: | 2021-09-17 21:15:27 |
| Message-ID: | E063C45C-BD04-44B7-82A1-F7931D92D24C@amazon.com |
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| Lists: | pgsql-hackers |
On 9/17/21, 1:32 PM, "Alvaro Herrera" <alvherre(at)alvh(dot)no-ip(dot)org> wrote:
> 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.
I see. IMO feels a bit counterintuitive to validate a partial record
that you are ignoring anyway, but I suppose it's still valuable to
know when the WAL is badly broken. It's not expensive, and it doesn't
add a ton of complexity, either.
Nathan
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