Re: Hot Backup with rsync fails at pg_clog if under load

On Fri, Sep 23, 2011 at 4:41 AM, Heikki Linnakangas
<heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:

>> Unfortunately, it's impossible, because the error message "Could not read
>> from file "pg_clog/0001" at offset 32768: Success" is shown (and startup
>> aborted) before the turn for "redo starts at" message arrives.
>
> It looks to me that pg_clog/0001 exists, but it shorter than recovery
> expects. Which shouldn't happen, of course, because the start-backup
> checkpoint should flush all the clog that's needed by recovery to disk
> before the backup procedure begins to them.

I think the point here is that recover *never starts*. Something in
the standby startup is looking for a value in a clog block that
recovery hadn't had a chance to replay (produce) yet.

So the standby is looking into the data directory *before* recovery
has had a chance to run, and based on that,goes to look for something
in clog page that wasn't guarenteed to exists at the start of the
backup period, and bombing out before recovery has a chance to start
replaying WAL and write the new clog page.

a.

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