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Re: Replication and coding good practices

From: Ivan Sergio Borgonovo <mail(at)webthatworks(dot)it>
To: <pgsql-general(at)postgresql(dot)org>
Subject: Re: Replication and coding good practices
Date: 2009-06-29 12:46:42
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-general
On Mon, 29 Jun 2009 19:11:43 +0800
Craig Ringer <craig(at)postnewspapers(dot)com(dot)au> wrote:

> On Sun, 2009-06-28 at 09:01 -0700, David Fetter wrote:
> > > Are there any rules of thumb to consider for making an
> > > application easier to work with a "general" replication
> > > solution?
> > > 
> > > The applications I mostly deal with are e-commerce sites.
> > 
> > It really depends on what replication solution you choose, along
> > with the environment you're deploying into.
> ... and why you need replication. Reliability/Availability? Data
> storage redundancy? Performance? And if performance, read-mostly
> performance or write-heavy performance?

1) performance, read-mostly
2) reliability
I'm making large use of plpgsql mainly for:
- encapsulation
- single point of truth
- implicit transaction

Most of the write operations don't have to be aware of a multi
user environment.
Still in some part of the code things have to be aware of
transactions, multi user environment (or better multiple connections
from the same user) etc...

Not only these parts are rare, they are seldom executed too.
So my main concern about the parts that may be problematic in a
replicated context is to keep maintenance low and development easy.

eg. I've started to use temp tables but I guess they may cause some
problems in conjunction with connection pooling systems.

> > That said, I've noticed that the things that are generally good
> > practice help you even more when you're doing replication.
> > 
> > Practices I've seen help directly:
> > 
> > * Separate read users and code from write users and code.
> > 
> > * Separate DDL from both of the above.
> > 
> > * Make DDL changes part of your deployment process and only
> > allow them in files which track in your SCM system.

> Version your schema, storing the schema version in a 1-row table
> or even as a stable function. This makes it much easier for
> deployment tools or staff to easily see what needs to be done to
> get the schema and app to the latest version - there's no "what
> the hell is the current state of this thing, anyway?" to worry
> about.

This is another area I'd like to learn more about available
techniques for managing development.
But currently I was more interested in coding techniques to avoid
maintenance/porting problems once I'll have to support a replication
At the moment schema changes are saved in a file together with the
web application code.
I was thinking to automate the application of schema changes with a
hook in svn, but right now it doesn't look as a good investment.

Still I'm very interested in techniques to version schema changes
and bring them together with code change and being able to diff them.


Ivan Sergio Borgonovo

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