[pgpool-general: 3236] Re: Postgres, Pgpool2 for Autoscaling in private cloud (OpenStack)

Job Cespedes jobcespedes at gmail.com
Sat Oct 18 09:56:11 JST 2014

Hi Sergey, glad you pointed out IO. I haven’t resolve how to deal with
scaling storage in the db layer. Shared file systems might scale well but I
am not sure about their IO performance.

However, what I would like to accomplish is a good grade of adaptability in
the application to scale in or out (elasticity) with zero downtime and not
much of it being able to grow bigger and bigger. I certainly should
consider it, though.


2014-10-17 18:03 GMT-06:00 Сергей Мелехин <cpro29a at gmail.com>:

> Hi, Job!
> Open transactions will fail on master failover.
> Vertical scaling is naturally limited, especially in cloud environment. IO
> is usually a bottleneck. After upgrading master to SSD storage, or even
> RAID10 SSD - you don't really have much cost-effective options in speeding
> it up, concidering you have enouch RAM.
> If you expect to scale big - you shoud concider sharding in some point.
> And it will almost invetibly envolve modifying application logic.
> With best regards, Sergey Melekhin
> С Уважением, Сергей Мелехин.
> 2014-10-18 10:41 GMT+11:00 Job Cespedes <jobcespedes at gmail.com>:
>> Hi,
>> I'm currently researching on HA, Failover, Autosacaling applications in
>> private clouds.  I consider Pgpool2 and Postgres a viable option for the
>> DB layer. But I have several question about whether to use horizontal or
>> vertical scaling. So far I think vertical scaling would be the way to go
>> for the DB layer. Adding more nodes in a master/slave configuration doesn’t
>> seem right performance-wise and it seems more complex also. Besides I think
>> could only add more slaves nodes. But maybe someone out there knows better.
>> Anyway my question is the following:
>> The promotion of a slave to master is transparent for the client
>> connected to pgpool or there’s a short connection loss (data loss)?
>> The scenario I have in mind is: for vertical scaling I could start by
>> shutting down a slave node, provisioning more resources, boot again, and
>> promote to master with the command pcp_promote_node, after that I could
>> do the same with the former master, now slave, and then do an online
>> recovery. However, I’m not sure this is completely transparent for clients
>> and whether or not it has zero downtime.
>> Thanks for any piece of advice,
>> --
>> Job Cespedes
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Job Cespedes
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