[Pgpool-general] The forgotten question

[Daniel.Crespo at l-3com.com]

What I understood about this is that you have to know what backend might
or will be part of the pool.

So, let's say you have only two backends, but you wish to add a 3rd.

Initially, you have:

backend_hostname0 = '172.16.10.10'
backend_port0 = 5432
backend_weight0 = 1
backend_data_directory0 = '/var/lib/postgresql/8.3/main'

backend_hostname1 = '172.16.10.11'
backend_port1 = 5432
backend_weight1 = 1
backend_data_directory1 = '/var/lib/postgresql/8.3/main'

But you would have to add:

backend_hostname2 = '172.16.10.12'
backend_port2 = 5432
backend_weight2 = 1
backend_data_directory2 = '/var/lib/postgresql/8.3/main'

Even if it is not still there.

When restarting pgpool, it will try to add the 3 nodes, but the last one
(let's say) is not ready yet.

After you start, you are going to be able to call the attach command
specifying to add the node 2 (zero-based node count)

Daniel

-----Original Message-----
From: pgpool-general-bounces at pgfoundry.org
[mailto:pgpool-general-bounces at pgfoundry.org] On Behalf Of Marcelo
Martins
Sent: Thursday, December 18, 2008 1:54 PM
To: Tatsuo Ishii
Cc: pgpool-general at pgfoundry.org
Subject: [Pgpool-general] The forgotten question

In the pgpool page there is section under online recovery that says "A  
recovery target node must have detached before doing online recovery.  
If you wish to add PostgreSQL server dynamically, add backend_*  
parameters and reload pgpool.conf. pgpool-II registers a new node as a  
detached node. ".

How should that "backend_*" be configured in the pgpool.conf file so  
that I could add nodes dynamically when needed. Say I already have 3  
backend_nodes that are already configured and I would like to have the  
option to attache new nodes dynamically without having to edit the  
pgpool.conf file and reload it.

I assume that such is what that comment above refers to be possible,  
am I interpreting that wrong ?

So should I have something like the below for that to work ?

backend_hostname0 = '172.16.10.10'
backend_port0 = 5432
backend_weight0 = 1
backend_data_directory0 = '/var/lib/postgresql/8.3/main'

backend_hostname1 = '172.16.10.11'
backend_port1 = 5432
backend_weight1 = 1
backend_data_directory1 = '/var/lib/postgresql/8.3/main'

backend_*



Marcelo
PostgreSQL DBA
Linux/Solaris System Administrator
http://www.zeroaccess.org

On Dec 18, 2008, at 12:21 PM, Marcelo Martins wrote:

> Hi Tatsuo,
>
> I understand that pgpool does pooling by saving the connections to PG
> and reusing them when the same user/database is used and indeed I see
> some pcp procs being reused 40+ times.  What I'm trying to figure out
> here is, does pgpool just passes the new query it receives through
> that same connection that has already been opened previously and such
> will be reused by this new request coming from the same user to the
> same database ?
>
> How does pgpool queues its incoming connections when it starts to
> receive more connections than num_init_children is available ? I'm
> pretty sure here that the "child_life_time" setting would be the one
> responsible for freeing up the pgpool a  child so that the new
> connection queued can obtain access to PG through pgpool and execute
> its query, correct ?
>
> In regards to the load balancing, that can indeed be very helpful
> specially since the master node is usually the one with a higher load.
> I'm pretty sure this may not be possible right now but it would be
> pretty cool if pgpool only opened a connection to the backend that it
> chooses to run the SELECT query against. I'm pretty sure this may be
> complicated to implement, if it all possible which may not be,  since
> this would affect how pgpool handles connections.
>
>
> Also you were right about the online recovery scripts. If I skip the
> second base backup it seems 30-50% faster in most cases. What takes
> the longest time is just the checkpoint that pg_start_backup has to do
> while there is a lot of writes are being done to the DB. But the new
> online recovery setting makes things perfect since the client just
> keeps on trying to send the data over and eventually when the 2nd
> stage is over the rest of all data resumes to be sent.
>
> can't remember the other questions right now, sorry :)
>
>
>
>
> Marcelo
> PostgreSQL DBA
> Linux/Solaris System Administrator
> http://www.zeroaccess.org
>
> _______________________________________________
> Pgpool-general mailing list
> Pgpool-general at pgfoundry.org
> http://pgfoundry.org/mailman/listinfo/pgpool-general

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