Re: [Postgres-xc-developers] proxy setup on standby server

[Karthik S. <kse...@ad...>]

+Alex and Sasi

On 3/21/13 7:58 AM, "Bei Xu" <be...@ad...> wrote:

>Hi, Koichi:
>Base on your reply,
>
>Since slave is a copy of master, the slave has the same GTM_proxy listed
>in postgresql.conf as the master, it will connect to server3's proxy AFTER
>SLAVE IS STARTED,
>And we will only change the slave's proxy to server 4 AFTER promotion,
>correct?
>
>Thus, looks like SLAVE needs to connect to A PROXY at ALL TIME: before
>promotion is server3's proxy, after promotion is server 4's proxy.
>
>Please take a look at following 2 senarios:
>Senario1: If slave was configured with server4's proxy AFTER SLAVE IS
>STARTED, upon server 3 failure, we will do :
>1) promote on slave
>Since slave is already connect server 4's proxy, we don't have to do
>anything here.
>
>senario2: If slave was configured with server3's proxy AFTER SLAVE IS
>STARTED, upon server 3 failure, we will do:
>1) restart slave to change proxy from server3's proxy value to server4's
>proxy value
>2) promote on slave
>
>Obviously, senario1 has less steps and simpler, senario2 is suggested by
>you. Is there any reason you suggested senario2?
>
>My concern is, If a slave is connect to any active proxy (the proxy is
>started and pointing to the GTM), will the transaction be applied TWICE?
>One from proxy, one from the master?
>
>
>
>
> 
>
>On 3/21/13 12:40 AM, "Koichi Suzuki" <koi...@gm...> wrote:
>
>>Only after promotion.   Before promotion, they will not be connected
>>to gtm_proxy.
>>
>>Regards;
>>----------
>>Koichi Suzuki
>>
>>
>>2013/3/21 Bei Xu <be...@ad...>:
>>> Hi Koichi:
>>>      Thanks for the reply. I still have doubts for item 1.  If we setup
>>> proxy on server 4, do we reconfigure server 4's coordinator/datanodes
>>>to
>>> point to server 4's proxy at ALL TIME(after replication is setup, I can
>>> change gtm_host to point to server4's proxy before I bring up slaves)
>>>or
>>> only AFTER promotion?
>>>
>>>
>>> On 3/20/13 11:08 PM, "Koichi Suzuki" <koi...@gm...> wrote:
>>>
>>>>1. It's better to have gtm proxy at server 4 when you failover to this
>>>>server.   We need gtm proxy now to failover GTM while
>>>>coordinators/datanodes are running.   When you simply make a copy of
>>>>coordinator/datanode with pg_basebackup and promote them, they will
>>>>try to connect to gtm_proxy at server3.   You need to reconfigure them
>>>>to connect to gtm_proxy at server4.
>>>>
>>>>2. Only one risk is the recovery point could be different from
>>>>component to component, I mean, some transaction may be committed at
>>>>some node but aborted at another because there could be some
>>>>difference in available WAL records.   It may possible to improve the
>>>>core to handle this to some extent but please understand there will be
>>>>some corner case, especially if DDL is involved in such a case.  This
>>>>chance could be small and you may be able to correct this manually or
>>>>this can be allowed in some applications.
>>>>
>>>>Regards;
>>>>----------
>>>>Koichi Suzuki
>>>>
>>>>
>>>>2013/3/21 Bei Xu <be...@ad...>:
>>>>> Hi, I want to set up HA for pgxc, please see below for my current
>>>>>setup.
>>>>>
>>>>> server1: 1 GTM
>>>>> server2: 1 GTM_Standby
>>>>> server3 (master):  1 proxy
>>>>>                                   1 coordinator
>>>>>                                   2 datanode
>>>>>
>>>>> Server4: (stream replication slave) :  1 standalone proxy ??
>>>>>                                   1 replicated coordinator (slave of
>>>>> server3's coordinator)
>>>>>                                    2 replicated datanode  (slave of
>>>>> server3's datanodes)
>>>>>
>>>>>
>>>>> server3's coordinator and datanodes are the master of the server4's
>>>>> coordinator/datanodes by stream replication.
>>>>>
>>>>> Question.
>>>>> 1. Should there be a proxy on server 4?   If not, which proxy  should
>>>>>the
>>>>> server4's coordinator and datanodes pointing to? (I have to specify
>>>>>the
>>>>> gtm_host in postgresql.conf)/
>>>>> 2. Do I have to use synchronous replication vs Asynchrous
>>>>>replication?
>>>>>I am
>>>>> currently using Asynchrnous replication because I think if I use
>>>>> synchronous, slave failour will affect master.
>>>>>
>>>>>
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>>>>>
>>>>
>>>
>>>
>>
>