Hi Charles,
You can join the squeak-dev list here: http://lists.squeakfoundation.org/mailman/listinfo/squeak-dev
Chris Muller, the developer of Magma, is very active on that list and I am sure he will be happy to answer any questions.
For commercial applications you should also we aware of Gemstone, which is a well regarded Smalltalk object-oriented database that can be used in conjunction with Squeak or Pharo. It's marketed as a database but it is really more like a multi-user Smalltalk with unlimited persistence.
If your background is with the typical sort of Java (or whatever) backed by relational database, you may be surprised at how much you can do with a few hundred megabytes of Smalltalk, using simple image persistence and no database at all. A little bit of good design goes a long way, and that's a lot easier to do with Smalltalk (and Magma or Gemstone).
Hi Charles,
I don't know enough about Magma to answer your questions. I'm really a VA Smalltalk guy and only play a little with Squeak. I knew just enough about Magma to point you to it. I'm sure there are a lot of Squeakers that know about Magma and can probably answer your questions but they are probably not reading this list. Try re-posting on: gmane.comp.lang.smalltalk.squeak.general. There may also be a Magma specific list but I'm not sure about that.
Before you decide you need a database for sure maybe you could experiment with creating a lot of data in your image and see how long it takes to load/save. If it isn't too long then the OS paging out pieces and then back when needed might not be too bad?
Also, if you are going to use a database maybe you could use a hash (big) for the id's?
Lou
On Thu, 31 Oct 2013 14:53:03 -0700, Charles Hixson charleshixsn@earthlink.net wrote:
On 10/31/2013 01:28 PM, Louis LaBrunda wrote:
Hi Charles,
If I'm going to need to use a database, and handle my own rolling in and out anyway, then Smalltalk isn't a good choice. And while multiple processing is only a speed-up thing, that's a pretty important thing in and of itself.
I think you may need an OODB, you should take a look at Magma http://wiki.squeak.org/squeak/2665. You may not need to do as much rolling in and out on your own as you think.
Lou
Louis LaBrunda Keystone Software Corp. SkypeMe callto://PhotonDemon mailto:Lou@Keystone-Software.com http://www.Keystone-Software.com
Short answer: Probably not sufficient.
Long answer (excuse the rambling, I was thinking it through as I wrote it): If I'm understanding http://wiki.squeak.org/squeak/2639 correctly, which I may not be, I'd still need to recode the entire graph structure to be designed in terms of id#s (keys) rather than direct references. I.e., I'd need to code it in terms of two collections one of which would contain keys that, when interpreted, referenced itself. This does appear to move the plan into the area of the possible, but at the cost of the advantage that I'd hoped Smalltalk would provide of a large persistent image. I thought at first when it was talking about transparency that this wouldn't be necessary, but:
Magma *can* maintain and quickly "search" large, flat structures, but the normal Smalltalk collections such as Bag or OrderedCollection are not suitable for this. The contiguous ByteArray records Magma uses to store and transport Smalltalk objects would be impractical for a large Smalltalk Collection
Seems to mean that the Graph couldn't be stored as something that Magma would recognize as a graph. So does "Objects are persisted by reachability", though that has other possible interpretations. But since the graph would contain a very large number of cycles in multiple "dimensions"... OTOH http://wiki.squeak.org/squeak/2638 on Read Strategies appears to mean that it wouldn't automatically (or rather could be set to not automatically) pull in items that are references within the object being read.
Again, http://wiki.squeak.org/squeak/5722 , may mean that a class with named variables holding 4 arrays of arrays of length 3 (reference float float) and a few other variables containing things like bools and strings and ints, would be handled without problem. But note that each of those references is to an item of the same type, and it could include cycles. So I can't decide WHAT it means. Do I need to recode the references as id#s? Does that even suffice? (If it does, then it's still a good deal. But if I must name each entry separately, it's not a good deal at all, as the number of entries in each of the 4 outer level arrays is highly variable, and though I intend to apply an upper limit, only experiment can determine what a reasonable upper limit is.)
And yet again (if I'm understanding correctly) I'm going to need to violate just about every one of the hints on performance in http://wiki.squeak.org/squeak/2985 . I'm not sure how much MagmaArray keeps in RAM of things that aren't currently in use. At one point it sounded like 6 bytes. This is actually a lot of overhead in this kind of a system.
Additionally, it appears that Magma doesn't have anyway to detect that a reference is "stale" (i.e., hasn't been referenced in a long time), an use that to decide to roll it out. It looks as if this needs to be done by the program...but that time-stamp (and a few other items mustn't (well, needn't...but I sure would need to overwrite it when I read it in) itself be included in the items rolled out. So I need to solve THAT problem.
Magma seems to be a good object database, but I can't see that it makes Smalltalk a desirable choice for this project (It may, this could be a documentation problem...either my not understanding it or the information not being clear.) If I'm going to recode the references into id#s, then either Ruby or Python make it trivial to turn the object into a string (and to reconstitute it later), and they also make it trivial to leave out any volatile variables. Perhaps Magma does the latter, but this wasn't clear.
Definitely a part of my problem is that I don't have a clear image of how I would proceed. The only examples given were small fragments, extremely useful in clarifying points, but insufficient to yield a larger idea of how to use things. (E.g., I have no idea how to do Ma Object Serialization, but I may need to implement it anyway.)
Perhaps this is all because I don't really know Smalltalk well...which I assuredly don't. I was hoping to use Smalltalk to avoid the database problem, trading RAM (including virtual RAM) consumption for capacity, but it looks as if I end up at a database anyway. And in that case I should use a language that I'm already familiar with. (I'd really been hoping that the persistent image would be the answer.) If I do a decomposition I could even get away with using a key-value store. The only problem is that the id# requires lookup via an indirect reference. (Is it in the Directory? If not, get it from the database, if not, it's a new value.) Once I do the recoding of references to id#s, the database portion is "trivial, but annoying". But now I've added thousands of additional indirections/second. However, IIUC, Magma would be doing that under the hood anyway (as opposed to the image, which would be handled in hardware memory translation), and If I code it, I can put in things like automatically rolling out when it's stale. (By the way, does "stub" mean remove from memory, or remove from the database? From context I decided it probably meant remove from memory, but I couldn't decide whether dirty data would be written before being removed from memory, and I couldn't be really sure it wasn't just being deleted. That needs rephrasing by someone who knows what it's supposed to mean.)
To me this appears to be, again, not the project that justifies implementation in Smalltalk. Perhaps if I were already experienced in Smalltalk I wouldn't see things that way, as Magma clearly means that Smalltalk *can* handle doing the project.
Thank you for your suggestion.
Louis LaBrunda Keystone Software Corp. SkypeMe callto://PhotonDemon mailto:Lou@Keystone-Software.com http://www.Keystone-Software.com
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