Horton

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

Simon Riggs <simon@2ndquadrant.com>

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From: Simon Riggs <simon@2ndQuadrant.com>
To: Florian Pflug <fgp@phlo.org>
Cc: Aidan Van Dyk <aidan@highrise.ca>, Daniel Farina <daniel@heroku.com>, Chris Redekop <chris@replicon.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2011-10-27T14:30:06Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Derive oldestActiveXid at correct time for Hot Standby.

  2. Start Hot Standby faster when initial snapshot is incomplete.

  3. Fix timing of Startup CLOG and MultiXact during Hot Standby

On Thu, Oct 27, 2011 at 3:03 PM, Florian Pflug <fgp@phlo.org> wrote:

>> I think you make a good case for doing this.
>>
>> However, I'm concerned that moving LogStandbySnapshot() in a backpatch
>> seems more risky than it's worth. We could easily introduce a new bug
>> into what we would all agree is a complex piece of code. Minimal
>> change seems best in this case.
>
> OTOH, we currently compute oldestActiveXid within LogStandbySnapshot().
> Your proposed patch changes that, which also carries a risk since something
> could depend on these values being in sync. Especially since both the logged
> snapshot and oldestActiveXid influence the snapshot tracking on the slave.
>
> But since you wrote most of that code, your judgement about the relative
> risks of these two approaches obviously out-weights mine.

We must move oldestActiveXid since that is the source of a bug. There
is no need to move LogStandbySnapshot(), so I am suggesting we don't
do that for the backpatch. I was going to implement it the way you
suggest in HEAD, since I agree that is a cleaner way.

-- 
 Simon Riggs                   http://www.2ndQuadrant.com/
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