[Pacemaker] PostgreSQL replicarion RA: PGSQL.lock

[Andrew]

12.02.2013 02:35, Takatoshi MATSUO пишет:
> Hi
>
> 2013/2/9 Andrew <nitr0 at seti.kr.ua>:
>> Hi all.
>> For what reason is implemented PGSQL.lock in RA, and what pbs may happen if
>> it'll be removed from RA code?
> It may cause data inconsistency.
> If the file exists in a node, you need to copy data from new master.
I noticed that during master migration lock still remains and postgresql 
isn't started on old master; demote also will fail with lock file. Also, 
if cluster fails (for ex., power failure occurs), old master will not 
start, and slave after startup will be promoted to master - it's OK when 
both nodes are crashed simultaneously, and it's really bad when old 
slave was crashed earlier. If postgres crashed/killed by OOM/etc - it 
also will not be restarted...

Maybe it'll be better to watch log files on slave that tries to sync 
with master/to check slave timeline, and if slave can't sync with error 
that timeline differs - to fail it with error (or even to sync with 
master with pg_basebackup - it supports connection to remote server and 
works quick: 
http://sharingtechknowledge.blogspot.com/2011/12/postgresql-pgbasebackup-forget-about.html 
- example)?

>
>> Also, 2nd question: how I can prevent pgsql RA from promoting master before
>> both nodes will brings up OR before timeout is reached (for ex., if 2nd node
>> is dead)?
> You can use xlog_check_count parameter set up with a large number.
> RA retries comparing data with specified number of times in Slave.
Thanks; I'll try this.
> Or you can use "target-role" such as below too.
> ----
> ms msPostgresql pgsql \
>      meta master-max="1" master-node-max="1" clone-max="2"
> clone-node-max="1" notify="true" target-role="Slave"
> ---
In that case, how can I choose on what node I should promote resource to 
master (which has fresher WAL position) - I should do this manually, or 
I can just run promote?
>> I think that clone of Delay RA for both nodes (to avoid switching
>> delay on node with Delay resource failure) will do this - but I can't find
>> how I should write such rule, it seems like rules in Pacemaker are too
>> simple (or too bad described). I expect something like this (in <> braces I
>> included rules that I don't know how to write):
>>
>> location pgsql_master_location ms_Postgresql \
>>      rule $role="master" -inf: <Delay RA is not running> and <ms_Postgresql
>> count eq 1>
>>
>> Is this possible?
>>
>> _______________________________________________
>> Pacemaker mailing list: Pacemaker at oss.clusterlabs.org
>> http://oss.clusterlabs.org/mailman/listinfo/pacemaker
>>
>> Project Home: http://www.clusterlabs.org
>> Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf
>> Bugs: http://bugs.clusterlabs.org
> _______________________________________________
> Pacemaker mailing list: Pacemaker at oss.clusterlabs.org
> http://oss.clusterlabs.org/mailman/listinfo/pacemaker
>
> Project Home: http://www.clusterlabs.org
> Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf
> Bugs: http://bugs.clusterlabs.org