I think that all things considered, SimplePersistence seems like a very easy place to start, and then I can "upgrade" when my super awesome idea (not), exceeds its bounds.
Sigh. Forget about the idea that it will be easy to switch your
persistence later. There are lots of little (and not so little)
things to consider for each approach, be it an ORM, an object
database or just a bunch of serialized objects. It starts with the
bookkeeping for references between objects. Is it enough to remove
an object from a Collection or will it somehow survive in your db
and come back as a surprise after you started a new transction?
Will a deleted object be deleted or just unreachable? Do I have to
care about all possible paths to this object if I really want it
to be deleted? Will my ORB possible re-insert it in the next
transaction because I don't understand how an ORM works?
Don't fool yourself into thinking there is something like a
transparent persistence layer. If anybody ever says so, walk away,
say thank you and forget about that person as fast as you can.
I am not commenting on SimplePersistence here, I don't even know what it does or doesn't. I am talking about experiences made with both OODBs and ORMs like Glorp.
I've been through tough times with an architecture that I thought
to be a good idea: keep persistence in a separate layer that just
spits out objects and swallows new or changed ones. Works well in
a prototype. But on top of Glorp and with a few more than a hand
full of objects, you end up wanting to write real database
queries. So you need to get a hold of something that represents
the database, say a Session object. You end up either trying to
wrapper the query building in your clever layer and end up with
friggin slow performance or give up on your nice layering to make
your application at least bearable. Sometimes you even give up
navigating between objects and replace a simple getter with a DB
query to get good performance (ever waited for 600 proxies in a
collection to each deserialize itself when accessing the #items of
your Stock object? - you better write a sql query fetching them
all at once...)
You need query by example? Good luck in an Object DB. You either use DB specific queries and hand-tuned indices, or you navigate your object net and have the user wait a little. Or you design your object model around the search paths (which is hard once your model has evolved a while).
In Mongo/Voyage, you need to make a decision of what objects will
always be tied closely together (referenced by a root) and can be
retrieved on their own. You think in object trees rather than
objects. We've thrown CouchDB out of our project. Not because it
is a bad NoSQL database, but because we couldn't make it work well
in our overall architecture in which the primary store is a
relational Database.
I guess this is not really helpful advice. I can't really tell you what is right. I am cursing at Glorp every few days, but I also love it for many great things it does for us. And I've had a few very "interesting" lessons along the way, and am still in the process of learning about its limits.
Joachim
I wonder if these answers should go somewhere in a tips section somewhere, and get updated yearly.
@jonathan I had forgotten about those server tools - I think the last time I did something it predated some earlier tips the Sven had given, so will check it out. Back then, I did have a GitLab build pipeline autodeploying for me, so I'm hoping I can re-incarnate all of that so I can get my little app running with no fuss... lets see.
While I have a love/hate with Docker - I did wonder if there was something for Pharo that just let me build my image into a container and then it would just work with little system knowledge needed (as I keep forgetting all the voodoo between times when I need it). Maybe there is, or maybe it might come one day soon...
Tim
On Tue, 6 Oct 2020, at 9:40 AM, Jonathan van Alteren wrote:
Hi Tim,
I've been running Seaside applications on Hetzner cloud servers for more than a year now, with great pleasure and success: https://www.hetzner.com/cloud
I guess their servers are similar to Digital Ocean, although I haven't followed the development of their products and solutions for quite a while. Setting up a new server at Hetzner is a breeze, and you can start already for as low as €2,49 per month!
We're using Voyage on MongoDB for persistence. After learning some hard lessons (and I'm sure there are more to come ;-)), I really enjoy the unobtrusiveness of it. Most of the time, it doesn't require much attention and allows me to add persistence to real OO designs quickly and easily. I find it a welcome change from the relational database work I used to (need to) do, back when I was still doing Java. The 'everything an object' principle of Pharo/Smalltalk really makes it shine.
I can't help you with a list of tradeoffs though. If you come across a set of arguments, I'd be happy to give feedback.
By the way, I forked Sven's pharo-server-tools project (here: https://github.com/objectguild/pharo-server-tools) and have a routine going that suits me well enough. Still lots of room for improvement, but it's OK for my current needs.
Future plans are to use the Hetzner API to provision a new server and use something like Chef or Ansible to install/configure it automatically to be ready to deploy a Seaside application. I'd like to integrate this into a full service CI/CD pipeline in the future, to be able to do automated production deployments without service interruption if possible. For this scenario, I would really also like to switch to using GemStone for persistence.
Hope this helps! Let me know what you decide and I might be able to help with some technical stuff.
Kind regards,
Jonathan van Alteren
Founding Member | Object Guild B.V.
Sustainable Software for Purpose-Driven Organizations
On 6 Oct 2020, 00:23 +0200, Tim Mackinnon [hidden email], wrote:
Hi everyone - I’m wondering what is the recommended way to save some simple user data for a Pharo application I would like to run on the cloud (probably initially digital ocean, but could be AWS if it came to it).
Initially I thought I might try and run my little app in Digital ocean (I followed someone’s steps a few years ago, and had a simple seaside app running quite well) - so I was thinking of starting there.
I know there is Sven’s P3 - but I’m not sure I’m ready to run and maintain a SQL database for a simple application, but could be persuaded it its simple to setup with little maintenance. Would mongo be a suggestion - is that easy to setup and run? (And is that Voyage?).
Possibly I could even use image persistence, and fuel out a Dictionary from time to time - but I think that might be a little bit too belt and braces for me.
Is there something that gives a little table of tradeoffs with some simple ways to get started?
Tim
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