Re: Cluster solution for Postgresql 9.5

On Wed, Oct 5, 2016 at 7:56 AM, Poul Kristensen <bcc5226(at)gmail(dot)com> wrote:

> Hi !
>
> According to the documentation a shared disk failover is possible as shown
> below.
> According to discussions on the Internet it is a problem missing 1-2
> seconds
> in a failover situation.
> Does anyone know of the latest news in this case?
>

I would be very surprised if it were capable of causing that little
downtime. It's possible, but you'd have to fail at exactly the right
moment. Depending on your network, hardware and other factors, I would say
this would more likely take 15 seconds to 1 minute. This would *almost*
always be the case when using shared disk failover.

There are other strategies for low-downtime failover, but, most of them
will be in the same 15 - 60 seconds. The only real scenario would be to
use a multi-master solution (no promotion required), but, these have their
own issues and may have a performance impact.

--Scott

>
> Comparison of Different Solutions
> Shared Disk Failover
>
> Shared disk failover avoids synchronization overhead by having only one
> copy of the database. It uses a single disk array that is shared by
> multiple servers. If the main database server fails, the standby server is
> able to mount and start the database as though it were recovering from a
> database crash. This allows rapid failover with no data loss.
>
> Shared hardware functionality is common in network storage devices. Using
> a network file system is also possible, though care must be taken that the
> file system has fullPOSIX behavior (see Section 17.2.2
> <https://www.postgresql.org/docs/9.5/static/creating-cluster.html#CREATING-CLUSTER-NFS>).
> One significant limitation of this method is that if the shared disk array
> fails or becomes corrupt, the primary and standby servers are both
> nonfunctional. Another issue is that the standby server should never access
> the shared storage while the primary server is running.
> TIA !
>
> Poul
>
>

--
--
Scott Mead
Sr. Architect
*OpenSCG <http://openscg.com>*
http://openscg.com