Re: Cluster solution for Postgresql 9.5

Thanks a lot for a very fast responce. The reason for asking is this video
of march 2016
https://www.youtube.com/watch?v=iruaCgeG7qs /Josh Berkin is the speaker.

Josh Berkin talks about the possibility of datafile corruption on the
Postgres server connected by
a lot of Docker/Pod(Redhats Kubernetes with etcd to manage the failover)
images. In my understanding a Postgres cluster will act exactly the same
way nomatter which way the Postgres is connected.
So how come that Josh Berkin is worried about databasefile corruption?

TIA !

Poul

2016-10-05 14:22 GMT+02:00 Scott Mead <scottm(at)openscg(dot)com>:

>
>
> 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
>

--
Med venlig hilsen / Best regards
Poul Kristensen
Linux-OS/Virtualizationexpert and Oracle DBA