Re: [Postgres-xc-general] Our general use case

[Nikhil S. <ni...@st...>]

> Without HA, we might someday go out of business - without some claim to
> scalability, we can't get into business to begin with.
>
>
Rightly said.


> Can you (1) do a full dump, then (2) kill, drop and rebuild the
> cluster, and then (3) restore the entire cluster using pg_restore (or psql
> .. < dumpfile) through a coordinator?  This would be a last resort,
> obviously, since I'd lose all the data on every datanode since the last
> full dump, but if I know I can do that, at least I know I have that option.
>
>
Yeah, this is possible and it works. Once I tested this by modifying
pg_hba.conf to disallow all application connections. Then a did a dump of
global objects like users, roles etc. followed by dumps of each of the
databases that I had in my XC cluster. One can also use pg_dumpall if the
current cluster size is not too large. And all this was done by pointing to
a single coordinator, but everything was consistent at the cluster level.

And a subsequent pg_restore/psql to populate a new cluster worked pretty
well.


> as long as I'm going through a coordinator, the effects of the sql
> statements should replicate or distribute across the cluster depending on
> how the table was set up.. right?
>
>
Yes, the above is correct.


> I can probably create a temporary table on a single datanode, through a
> coordinator, just by telling it to distribute that table, and only list the
> one datanode I want it on, right?  Then I can do a data-only restore, of
> just that table, then from there I can use it through a coordinator, and
> affect whatever other tables I need to.
>
>
Yeah, the above is very much possible. See Michael's blog on this:

http://michael.otacoo.com/postgresql-2/pgxc-data-distribution-in-a-subset-of-nodes/


> Hmm, so I wonder what I actually would do if a datanode went down, or if
> the gtm server went down.
>

GTM server can be configured with a GTM-standby and you can failover to the
same in case of issues with the GTM.

A datanode can be configured with synchronous/asynchronous replicas and
again one can failover to the same in case of issues.

Using an HA framework and some PGXC tools that are being worked upon will
help automate this in the coming days.

HTH,
Nikhils


>
> On Fri, Oct 26, 2012 at 10:54 AM, David Hofstee <pg...@c0...> wrote:
>
>> **
>>
>>    1. No cluster without HA option; I agree.
>>    2. Integrate XC into PG; In the future I would like to think of a
>>    single PG instance as a 1-node cluster-able db.
>>
>> I think PGXC is the best thing that is happening. PGXC deserves to be the
>> most usable in the world too (instead of mysql). Gtx,
>>
>>
>> David
>>
>> Vladimir Stavrinov schreef op 2012-10-26 14:46:
>>
>> On Thu, Oct 25, 2012 at 4:13 AM, Michael Paquier
>> <mic...@gm...> wrote:
>>
>> 1) It is not our goal to oblige the users to user an HA solution or
>> another,
>>
>> Sounds fine. Where are those users? Who wants cluster without HA?
>> Everybody when hears word "cluster" implies "HA"
>>
>> Postgres code with XC. One of the reasons explaining that XC is able to
>> keep up with Postgres code pace easily is that we avoid to implement
>> solutions in core that might impact unnecessarily its interactions with
>> Postgres.
>>
>>  You are heroes.  How long You can continue "code pace" on this hard
>> way? This paradigm prevents You do not implement not only HA but lot
>> of other things that is necessary for cluster. I never saw this type
>> of fork. I believe at some point You will either become a part of
>> Postgres or  totally come off and go Your own way. The only question
>> is when? And best answer is "right now".
>>
>>
>>
>>
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