Re: Enabling Checksums

On Mon, Mar 18, 2013 at 06:24:37PM +0000, Simon Riggs wrote:
> On 18 March 2013 17:52, Bruce Momjian <bruce@momjian.us> wrote:
> > On Sun, Mar 17, 2013 at 05:50:11PM -0700, Greg Smith wrote:
> >> As long as the feature is off by default, so that people have to
> >> turn it on to hit the biggest changed code paths, the exposure to
> >> potential bugs doesn't seem too bad.  New WAL data is no fun, but
> >> it's not like this hasn't happened before.
> >
> > With a potential 10-20% overhead,
> 
> ... for some workloads.
> 
> 
> > I am unclear who would enable this at initdb time.
> 
> Anybody that cares a lot about their data.
> 
> > I assume a user would wait until they suspected corruption to turn it
> > on, and because it is only initdb-enabled, they would have to
> > dump/reload their cluster.  The open question is whether this is a
> > usable feature as written, or whether we should wait until 9.4.
> 
> When two experienced technical users tell us this is important and
> that they will use it, we should listen.
> 
> 
> > In fact, this feature is going to need
> > pg_upgrade changes to detect from pg_controldata that the old/new
> > clusters have the same checksum setting.
> 
> I don't see any way they can differ.
> 
> pg_upgrade and checksums don't mix, in this patch, at least.

Jeff has already addressed the issue in the patch, e.g. if someone
initdb's the new cluster with checksums.

I am now fine with the patch based on the feedback I received.  I needed
to hear that the initdb limitation and the new performance numbers still
produced a useful feature.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +