Re: [Postgres-xc-general] postgres xc cluster query

[Ying He <yin...@ya...>]

Thank you for your response. I have a few questions:

1. when I use pgxc_ctl monitor command to check status, is the tool connect to the target db and execute a query to see it is working fine or what does it do?

2. I did run into cases when I bring down gtm and not able to stop gtm_proxy, coordinator, so what should be the correct order of stopping each component if I need maintenance of a host. I will give a sample layout here and if you could advise what should be the right order of stopping components and restart them:
host1 has gtm master 
host2 has gtm slave 
host3 has gtm_proxy1, coordinator1, datanode1
host4 has gtm_proxy2, coordinator2, datanode2

all tables are replicated not sharded so datanode1 and datanode2 should hold the same copy. Let's say if I need bring down:
* host1. promote host2 as gtm master, reconnect gtm_proxy to new master. commands like ssh gtm_slave_host gtm_ctl promote -Z gtm -D gtm_slave_dir in the presentation, can I do it in pgxc_ctl?
* host2. should be ok, it is a slave gtm
* host3/host4. what is the correct order of stopping and restarting things, assuming my app can detect down of a coordinator and connect to another available one.

3. for the sample layout, if host3 has power outages and down for a day and 10G new data is in host4. what is the steps to bring it up?

4. for the sample layout, if I want to add host5 which has a set of gtm_proxy3, coordinator3, datanode3, I should be able to use pgxc_ctl to add it but if the existing datanode1 and datanode2 each holds 1Teribyte data, will it take a really long time for it to be in synch with the rest and start serving app, does the wait depend on how much data is already in the existing datanodes?

I understand these are long and detailed questions to answer but it will help me evaluate this tool better for serious adoption. Thank you for your help.

For those also wondering about any real company adoption, I find this thread on linkedin http://www.linkedin.com/groups/Postgres-XC-77585.S.202900648, that is the only one i find so far.

best,
Ying





On Monday, January 13, 2014 8:51 PM, Koichi Suzuki <koi...@gm...> wrote:
 
Monitoring a node status is another thing.   pgxc_ctl provides a means
to check the status of each component.   You should be careful to
check if GTM is alive.   If it's dead, then all the query will be
blocked.   I mean, before you try to check if a coordinator or a
datanode is alive, you should check if the GTM is alive.

Regards;
---
Koichi Suzuki



2014/1/14 Michael Paquier <mic...@gm...>:
> On Tue, Jan 14, 2014 at 12:15 AM, Ying He <yin...@ya...> wrote:
>> hi,
>>
>> I am new to postgres xc. Is there a psql command that can be issued to
>> coordinator to query the current cluster's coordinators and datanodes? I
>> followed the setup steps and did CREATE NODE for coordinator and data nodes
>> and they are up and running, just wonder whether a command exists that can
>> query the current NODE and its status.
> You can have a look at the list of nodes registered with that:
> SELECT * FROM pgxc_node;
> Regards,
> --
> Michael
>
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