[GemStone-Smalltalk] [GBS] How often does this error affect you?

Richard Sargent richard.sargent at gemtalksystems.com
Wed May 14 08:44:01 PDT 2014

If you have a class in your client image mapped to the latest (or only)
version of a server class, creating a new version of the server class will
result in replication errors until you reconnect the client class to the new
server class version.

GBS is designed to automatically migrate instances of older versions of a
server class to the version that the client is connected to when you
replicate such an instance. This is the "skew" case.

The problem case is the anti-skew, in which the automatic migration - if it
were to happen - would have migrated instances of newer versions of the
class to older versions. GBS throws an error. This error can arise as soon
as you change the class definition and agree to "commit and migrate", if you
already have an instance of the class replicated into the client image. It
can also occur at any point following this event, if any subsequent
replication tries to bring back an object graph referencing an instances of
the new class version.

The error is a GbsClassGenerationError. It will occur more frequently
starting with server version 3.2, since we corrected the problem of #become:
not notifying the GCI client (GBS in this case) of the change. Migration of
instances to the new class version uses #become:.

There are two workarounds to the error. One is to log out and back in again.
The second is to use the Connector Browser and reconnect the class to the
server. (The browser would show the class as disconnected, since the class
is mapped to an older version, rather than the latest version of the named

We would appreciate your feedback on how much of a problem this has been for
you in the past, and if you have started to upgrade to 3.2, how much it
impacts you now. Additionally, feedback on how you would like GBS to handle
this case (other than "don't throw an error") would help us determine what
we need to do.

Thank you,
Richard Sargent

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