[Newbies] Re: Is Squeak/Pharo an appropriate language choice?
charleshixsn at earthlink.net
Thu Oct 31 21:53:03 UTC 2013
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.
> Louis LaBrunda
> Keystone Software Corp.
> SkypeMe callto://PhotonDemon
> mailto:Lou at Keystone-Software.com http://www.Keystone-Software.com
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
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 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.
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