Magma use with low bandwidth and weird situation

[Chris Muller]

On Feb 12, 2008 6:25 AM, Hilaire Fernandes <hilaire at ofset.org> wrote:
> In iStoa, the client (kids with Morphic application) connect to a Magma
> database through an ADSL connection. When a kids has finished with an
> exercice, several instances relative to kid achievements are recorded in
> the remote Magma database. Later the teacher can review (and replay) the
> kid actions and results.

Wow, what a neat app!

> 1. My first constraint is the 128 kbits/s up limit used to upload in the
> database the instances. Indeed the client is blocked for 1 miniute
> waiting for the data persistence.
> A first idea is to compress all the serialised data sent to the Magma
> server. Is it possible?

Yes it should be, and the byteArrays magma sends back and forth should
compress well.  There's a layer called "Ma client server" just between
"Magma client" and "Ma object serialization", like this:

  Magma client
     uses Ma client server
        uses Ma object serialization

The enhancement could be made in MaClientSocket and MaServerSocket
could be changed to "compress at the last second", at the entrace to
the network, so it is transparent.  That would probably be a nice
option that may help.  Do you know how to compress/uncompress a
ByteArray rapidly?

> Other option is to embed the Magma commit in a separate thread.  I did
> some tests, but it randomly leads to crash on the server. Is it
> something some of you look at?

Look for the a discussion Bert and I had on this list when he was
doing his Magma back-end for squeaksource.  In a nutshell, if the
server detects a change to the object-model occurred during
serialization, it will signal an error back to you, so you have to use
one of the significant (high-priority) blocking methods, which of
course dilutes the background benefit..  :(

> 2. Next the teacher reviews the kids activities through a web
> application (seaside based) + Squeak web plugin. The Squeak web plugin
> is used to connect to the Magma database and to replay cinematically the
> kids activities. From there, at each use of the plugin, a connection to
> the Magma database is opened, and it is slow, too slow. Any thought
> about how to optimise that?

Interesting, are you saying you have a Squeak image running inside a
web-browser?  Which image?  Also, did you have to adjust the plug-in
VM to allow Network?

Is the image saved with the connection open?  That way it will connect
as soon as the image launches.  But is it also too slow when this
image is started on its own straight in the OS?