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Subject: Re: Sync Rep Design
From: Simon Riggs <simon@2ndQuadrant.com>
To: MARK CALLAGHAN <mdcallag@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, pgsql-hackers@postgresql.org
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Date: Mon, 03 Jan 2011 11:10:40 +0000
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On Sun, 2011-01-02 at 20:53 +0000, Simon Riggs wrote:
> On Sun, 2011-01-02 at 12:13 -0800, MARK CALLAGHAN wrote:
> > On Thu, Dec 30, 2010 at 9:02 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> > > <reads MySQL documentation>
> > >
> > > I see now that you've tried to design this feature in a way that is
> > > similar to MySQL's offering, which does have some value.  But it
> > > appears to me that the documentation you've written here is
> > > substantially similar to the MySQL 5.5 reference documentation.  That
> > > could get us into a world of legal trouble - that documentation is not
> > > even open source, let alone BSD.
> > >
> > > http://dev.mysql.com/doc/refman/5.5/en/replication-semisync.html
> 
> Sorry, only just read that bit. Are they that similar? My docs are about
> 3 times longer and cover all sorts of things. I didn't intentionally
> copy anything, but that doesn't really matter, what matters is that if
> you think they are similar, legal people might. I've only read the URL
> above, not the other links from it.
> 
> Robert, Can you identify which paragraphs need to be re-written? I won't
> argue, I will just rewrite them or delete them and start afresh. Thanks
> for being eagle-eyed.

Been through this to check. The first paragraph was pretty similar, so
I've reworded that a little. Trying to make a readable paragraph that
introduces the need for sync rep, based upon the deficiencies of async
rep is going to be very similar, whatever we do. I can't see any other
way to introduce a feature other than to explain the potential problem
and then explain how the new feature resolves that.

Parameters are set on both primary and standby. That design existed long
before I looked at the MySQL manual, and yes there is similarity, which
led to similar descriptions of how that works. Bear in mind that the two
designs are very different.

I can't see any other similarities. If anybody else can, please shout.

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