[Pacemaker] PGSQL resource promotion issue

[Takatoshi MATSUO]

Hi Steven

2013/3/29 Steven Bambling <smbambling at arin.net>:
>
> On Mar 28, 2013, at 8:13 AM, Rainer Brestan <rainer.brestan at gmx.net> wrote:
>
> Hi Steve,
> i think, you have misunderstood how ip addresses are used with this setup,
> PGVIP should start after promotion.
> Take a look at Takatoshi´s Wiki.
> https://github.com/t-matsuo/resource-agents/wiki/Resource-Agent-for-PostgreSQL-9.1-streaming-replication
>
>
> I see that he has the master/replication VIPs with a resource order to force
> promotion before moving the VIPs to the new master.
>
>   I don't get how the postgres service is going to listen on those
> interfaces if they have not already migrated to the new master.  Even with
> setting the listen_addresses = "*"
>
>
> The promotion sequency is very simple.
> When no master is existing, all slaves write their current replay xlog into
> the node attribute PGSQL-xlog-loc during monitor call.
>
> Does this also hold true if a Master fails?
>
> From the looks of it, if there was a Master before the failure that the
> master score is set from the function that grabs the data_status from the
> master (STREAMING|SYNC, STREAMING|ASYNC, STREAMING|POTENTIAL, etc ).
>
> The reason I ask is if the master fails and the slaves don't then compare
> their xlog location, there is a potential for data loss if the incorrect
> slave is promoted.
>

If rep_mode is "async", the RA works as Rainer says
because the RA can't know which node should be promoted.

OTOH if rep_mode  is "sync",  the RA promote the node which has "SREAMING|SYNC"
if the master fails.
So the incorrenct slave can't be promoted.
Insted, Slaves whose xlog is newer than new Master's one
are failed forcedly on pre-promote.


>
> You can see all them with crm_mon -A1f.
> Each slave gets these attributes from all node configured in parameter
> node_list (hopefully your node names in Pacemaker are the same as in
> node_list) and compares them to get the highest.
> If the highest is this list is the own one, it sets the master-score to
> 1000, on other nodes to 100.
> Pacemaker then selects the node with the highest master score and promote
> this.
>
> Rainer
> Gesendet: Mittwoch, 27. März 2013 um 14:37 Uhr
> Von: "Steven Bambling" <smbambling at arin.net>
> An: "The Pacemaker cluster resource manager" <pacemaker at oss.clusterlabs.org>
> Betreff: Re: [Pacemaker] PGSQL resource promotion issue
> In talking with andreask from IRC, I  miss understood the need to include
> the op monitor.  I figured it was pulled from the resource script by
> default.
>
> I used pcs to add the new attributes and one was then promoted to master
>
> pcs resource add_operation PGSQL monitor interval=5s role=Master
> pcs resource add_operation PGSQL monitor interval=7s
>
> v/r
>
> STEVE
>

--
Takatoshi MATSUO