Re: question about checksum in 9.3

Thanks for the responses, that clarifies the checksum feature for me.

FWIW, my pgbench tests between a 9.2 server and a 9.3 server with checksum
showed very similar performance characteristics and system resource
utilization. Im going to set up another load test with our actual
application to see if that reveals any noticeable performance difference.

Thanks again
Mike

On Mon, Jan 13, 2014 at 7:11 PM, Michael Paquier
<michael(dot)paquier(at)gmail(dot)com>wrote:

> On Tue, Jan 14, 2014 at 1:50 AM, Mike Broers <mbroers(at)gmail(dot)com> wrote:
> > Hello, I am in the process of planning a 9.3 migration of postgres and I
> am
> > curious about the checksum features available. In my test 9.3 instance
> it
> > seemed like this feature provides a log entry of the exact database/oid
> of
> > the corrupt object when it is accessed, but not much else. I can't find
> > much documentation on anything else this feature provides.
> Few things:
> - The only way to know if a server is using data checksums is to use
> pg_controldata.
> - Be aware as well of the potential performance impact on your CPU,
> checksums are checked each time a page is read, and recalculated each
> time a page is updated.
> - ignore_checksum_failure can be used to ignore failures. Don't use
> that on a production system.
>
> > Is there a built-in method of scanning the server to check for
> corruption or
> > will I have to wait for a corrupt object to be accessed to see the log
> > entry?
> You can as well access manually tables with some for example
> sequential scan to check if blocks are broken or not.
>
> > Is there a relation that stores last checksum status or anyway of
> > reporting on what objects are identified by postgres as corrupt or not
> > corrupt?
> No, you could build one though with a background worker that scans
> relation pages and registers that failing blocks.
>
> > Are there any other features of the checksum I am missing besides the log
> > entry?
> 9.4 has a new GUC parameter called data_checksums that allow you to
> check with a psql client if checksums are used on a server.
>
> Regards,
> --
> Michael
>