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Re: page corruption on 8.3+ that makes it to standby

From: Jeff Davis <pgsql(at)j-davis(dot)com>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: page corruption on 8.3+ that makes it to standby
Date: 2010-07-27 21:08:47
Message-ID: 1280264927.8505.57.camel@jdavis-ux.asterdata.local (view raw or flat)
Thread:
Lists: pgsql-hackers
On Tue, 2010-07-27 at 15:50 -0400, Robert Haas wrote:
> > 1. Have log_newpage() and heap_xlog_newpage() only call PageSetLSN() and
> > PageSetTLI() if the page is not new. This seems slightly awkward because
> > most WAL replay stuff doesn't have to worry about zero pages, but in
> > this case I think it does.
> >
> > 2. Have copy_relation_data() initialize new pages. I don't like this
> > because (a) it's not really the job of SET TABLESPACE to clean up zero
> > pages; and (b) it could be an index with different special size, etc.,
> > and it doesn't seem like a good place to figure that out.
> 
> It appears to me that all of the callers of log_newpage() other than
> copy_relation_data() do so with pages that they've just constructed,
> and which therefore can't be new.  So maybe we could just modify
> copy_relation_data to check PageIsNew(buf), or something like that,
> and only call log_newpage() if that returns true.

My first concern with that idea was that it may create an inconsistency
between the primary and the standby. The primary could have a bunch of
zero pages that never make it to the standby.

However, it looks like all WAL recovery stuff passes true for "init"
when calling XLogReadBuffer(), so I think it's safe.

I'll test it and submit a patch.

Regards,
	Jeff Davis


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Next:From: Robert HaasDate: 2010-07-27 21:18:18
Subject: Re: page corruption on 8.3+ that makes it to standby
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Subject: Re: do we need to postpone beta4?

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