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Re: Online base backup from the hot-standby

From: Simon Riggs <simon(at)2ndquadrant(dot)com>
To: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Cc: Steve Singer <ssinger_pg(at)sympatico(dot)ca>, Jun Ishiduka <ishizuka(dot)jun(at)po(dot)ntts(dot)co(dot)jp>, magnus(at)hagander(dot)net, heikki(dot)linnakangas(at)enterprisedb(dot)com, pgsql-hackers(at)postgresql(dot)org, robertmhaas(at)gmail(dot)com, cedric(dot)villemain(dot)debian(at)gmail(dot)com
Subject: Re: Online base backup from the hot-standby
Date: 2012-01-20 11:15:55
Message-ID: CA+U5nMJFBKTJttaL6r-aHZPfWSBA+Byhz7FK+EF8R86TzPPHnQ@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Tue, Jan 17, 2012 at 10:38 AM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
> On Fri, Jan 13, 2012 at 5:02 PM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
>> The amount of code changes to allow pg_basebackup to make a backup from
>> the standby seems to be small. So I ended up merging that changes and the
>> infrastructure patch. WIP patch attached. But I'd happy to split the patch again
>> if you want.
>
> Attached is the updated version of the patch. I wrote the limitations of
> standby-only backup in the document and changed the error messages.


I'm looking at this patch and wondering why we're doing so many
press-ups to ensure full_page_writes parameter is on. This will still
fail if you use a utility that removes the full page writes, but fail
silently.

I think it would be beneficial to explicitly check that all WAL
records have full page writes actually attached to them until we
achieve consistency.

Surprised to see XLOG_FPW_CHANGE is there again after I objected to it
and it was removed. Not sure why? We already track other parameters
when they change, so I don't want to introduce a whole new WAL record
for each new parameter whose change needs tracking.

Please make a note for committer that wal version needs bumping.

I think its probably time to start a README.recovery to explain why
this works the way it does. Other changes can then start to do that as
well, so we can keep this to sane levels of complexity.

-- 
 Simon Riggs                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

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