| From: | Fujii Masao <masao(dot)fujii(at)gmail(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Jeff Davis <pgsql(at)j-davis(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: tackling full page writes |
| Date: | 2011-05-26 04:38:15 |
| Message-ID: | BANLkTinEqvyoMKAxnLb4rL0MgyaPAhNkhg@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, May 26, 2011 at 1:18 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> The replay of the WAL record for A doesn't rely on the content of chunk 1
>> which B modified. So I don't think that "partial page writes" has such
>> a problem.
>> No?
>
> Sorry. WAL records today DO rely on the prior state of the page. If
> they didn't, we wouldn't need full page writes. They don't rely on
> them terribly heavily - things like where pd_upper is pointing, and
> what the page LSN is. But they do rely on them.
Yeah, I'm sure that normal WAL record (neither full page writes nor
"partial page writes") relies on the prior state of the page. But WAL
record for A is "partial page writes", which also relies on the prior
state?
Regards,
--
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center
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