[teiid-designer-dev] [teiid-dev] VDB Versioning Feature

[Ramesh Reddy]

I carefully read through your reasoning, and I see only one main point
your are trying to  make. "Transparency in client connection thru
multiple versions"

It really depends on the environment client is being deployed in.
Usually we recommend users to use some kind of connection pool, and
externalize those properties that are specific to a URL connection. For
example, if client is in a container they are using a JNDI name to get
the connection, nobody makes JDBC connection directly. IMO, we are
shifting the problem from one location to another as there is a
deference already.

Ramesh..


On Mon, 2010-02-08 at 11:37 -0500, Ken Johnson wrote:
> I believe some of the characterizations below paint an overly negative 
> view of the current versioning capabilities.   These are generally 
> regarded by users as valuable and with the relatively new "default 
> version" property very flexible.  More inline.
> Ramesh Reddy wrote:
> > In Teiid a VDB is always represented by its name and version. Together
> > they both represented a unique name for VDB. Although a version
> > represents a particular schema version, 
> >
> > 1) It is considered as a entirely different schema then that of the
> > original VDB inside the Teiid runtime.
> >   
> True, from a runtime standpoint, Teiid doesn't distinguish a new vdb 
> from a new version of an existing vdb.  It's just another vdb.
> 
> > 2) Usually version numbers are presented in the repository systems with
> > implicit rollback behavior. Teiid gives no such rollback functionality.
> >   
> Repository is somewhat orthogonal here.  While users sometimes deploy 
> from a repository, the active VDB version is distinct from the 
> repository version if the repo is indeed being used at all.  Currently, 
> there is a roll-back capability in that a later version of a deployed 
> vdb can be deactivated and connections revert back to the previous 
> version (or the new default version if the default property is being used).
> 
> > 3) Confusion with automatic version upgrade. If a new VDB with same name
> > is deployed, then version on this VDB is upgraded to next numerical
> > number. The user does not even know what that version number is until
> > they use some tool to figure out which version number that VDB is
> > deployed under. This creates confusion.
> >   
> This is not confusing, it's beneficial.  For client apps that don't need 
> to know about a later version, they are not forced to change.  This is 
> particularly important for minor, non-breaking changes.  Client 
> applications should not be required to change simply because of a 
> version bump in the vdb.  Client app changes are highly disruptive in an 
> organization - even replacing a JDBC client JAR that does not require 
> app code changes often needs layers of approval and test cycles.
> 
> 
> > 4) If there are multiple VDB with different version numbers deployed in
> > runtime and client is connecting with no explicit version number, then
> > Teiid connects to "latest" or a VDB at "default" level. This again seems
> > magical than honoring the explicit behavior.
> >   
> This "magic" is good.  Clients *can* be explicit if desired but do not 
> *have to* be explicit.  Very powerful.
> 
> > 5) Schema version is generally not supported by any RDBMS vendors.
> >   
> True but IMHO this is not a reason to drop the feature.  Teiid, though 
> like a RDBMS in many ways is not a RDBMS. 
> 
> > 6) In MMx product line this meant to represent the metadata repository
> > version, but Teiid no longer has this concept. 
> >   
> This is not correct.  the version is disconnected from the repository 
> entirely.  It is simply a deployed version number.
> 
> > 7) It was a way to move production users from one version of the VDB to
> > another with out interruptions. In our opinion, this is more for the
> > development environments than prod.
> >   
> Agree this will be more common in pre-production, particularly staging 
> environments due to the level of dynamism.  However that does not mean 
> it's exclusive to pre-production. 
> > so, we would like to propose to remove this "version" feature from
> > Teiid. If users want they can manage the this through explicit VDB
> > names.
> >   
> I disagree with this proposal as it will tighten the coupling between 
> client applications and vdbs and take away a layer of indirection and 
> flexibility that's valuable at the data services layer. 
> > Please let us know if you think this feature is worth keeping and why?
> >   
> I do!
> 
> 
> > Thanks
> >
> > Ramesh..
> >
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> >   
> 
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