Two instances of Postgres with single data directory

On Thu, Nov 13, 2014 at 9:17 PM, dineshkaarthick
<dineshkaarthick@yahoo.co.uk> wrote:

All,

I need to know is it possible to execute two instances of Postgres with
single data directory shared between the two instances.

No, a server instance cannot run on a data folder being used by an
existing instance.
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Michael

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Michael,

Appreciate your quick response. Thank you.

I would like to know how is the "Shared Disk Failover" replication achieved
if it is not possible to share the data directory ? I am referring to the
1st solution in the mentioned link,
http://www.postgresql.org/docs/9.3/static/different-replication-solutions.html

Regards
Dina

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Hi,

On Fri, 2014-11-14 at 02:57 -0700, dineshkaarthick wrote:

I would like to know how is the "Shared Disk Failover" replication
achieved if it is not possible to share the data directory ? I am
referring to the 1st solution in the mentioned link,
http://www.postgresql.org/docs/9.3/static/different-replication-solutions.html

It is not a replication -- it is HA solution. That particular one can be
used along with Red Hat Cluster Suite (now called Red Hat High
Availability Addon). A presentation is here:

http://www.gunduz.org/download.php?dlid=208

Regards,
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Devrim GÜNDÜZ
Principal Systems Engineer @ EnterpriseDB: http://www.enterprisedb.com
PostgreSQL Danışmanı/Consultant, Red Hat Certified Engineer
Twitter: @DevrimGunduz , @DevrimGunduzTR

dineshkaarthick wrote:

I would like to know how is the "Shared Disk Failover" replication achieved
if it is not possible to share the data directory ? I am referring to the
1st solution in the mentioned link,
http://www.postgresql.org/docs/9.3/static/different-replication-solutions.html

You have some cluster software that makes dead sure that one node is *not*
running the database server before starting it on the other.

Yours,
Laurenz Albe

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On 11/14/2014 2:24 AM, Albe Laurenz wrote:

dineshkaarthick wrote:

I would like to know how is the "Shared Disk Failover" replication achieved
if it is not possible to share the data directory ? I am referring to the
1st solution in the mentioned link,
http://www.postgresql.org/docs/9.3/static/different-replication-solutions.html

You have some cluster software that makes dead sure that one node is*not*
running the database server before starting it on the other.

more specifically, that the data volume isn't even MOUNTED by the other
server. typically this is enforced with hardware 'fencing' such that
the standby server is blocked from even trying to mount the shared
volume, until it decides to take over, then it fences the original
'master', unfences itself, and mounts the volume, then starts its copy
of postgresql. this fencing is often done in a storage switch
(fiberchannel most commonly).

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somewhere on the middle of the left coast