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From Igor Sapego <isap...@apache.org>
Subject Re: Binary clients: fallback to the previous versions of the protocol
Date Wed, 13 Feb 2019 10:45:20 GMT
The approach you suggest looks to me pretty much the same as installing
a new version of client software in C++ or Java. The issue here that we
break
existing installed software and require for user to update software in order
to have ability to connect to a server. Just imagine that application which
made
with thin client is not used by a developer that knows how to use pip and
all the
stuff, but someone with another background. Imagine, you have thousands of
such users. And now imagine, you want to update your servers.

Best Regards,
Igor


On Tue, Feb 12, 2019 at 8:51 PM Dmitry Melnichuk <
dmitry.melnichuk@nobitlost.com> wrote:

> Igor,
>
> Thank you for your explanation. I think the matter begins to clear up
> for me now.
>
> The backward compatibility issue you described can not be applied to
> Python, because Python applications, unlike Java ones, do not have to
> be built. They rely on package manager (pip, conda, et c.) to run
> anywhere, including production.
>
> At the stage of deployment, the package manager collects dependencies
> using a specially crafted response file, often called
> `requirements.txt`.
>
> For example, to ensure that their application will work with the
> current _and_ future minor versions of pyignite, the user may include a
> line in their `requirements.txt` file:
>
> pyignite < x
>
> where x is a next major version number. In compliance with semantic
> versioning, the line is basically says: “Use the latest available
> version, that is earlier than x”.
>
> When upgrading Ignite server, system administrator or devops engineer
> must also update or recreate the app's environment, or update OS-level
> packages, or redeploy the app using Docker − the exact procedure may
> vary, but in any case it should be completely standard − to deliver the
> latest suitable dependencies.
>
> And then the same app connects to a latest Ignite server.
>
> Here is more about how pip understands versions:
>
> https://pip.pypa.io/en/stable/reference/pip_install/#requirement-specifiers
>
> What we really need to do for this to work seamlessly, is to establish
> the clear relation between products' versions. Regretfully, I have not
> done this before; just did not expect for this issue to come up. I
> think it would be best for pyignite major and minor to be set according
> to the Ignite binary protocol versions, i.e. pyignite 1.2.z handles
> Ignite binary protocol v1.2, and so on. But that is another matter.
>
> On Tue, 2019-02-12 at 13:39 +0300, Igor Sapego wrote:
> > Hi,
> >
> > Well, this approach was used for quite some time in ODBC and JDBC,
> > so thin client has just inherited it, as we have the same port and
> > the
> > same handshake message header. Maybe that's why you could not find
> > any mention of versioning in thin client context.
> >
> > 3. Let's start from this point as this is the root of the issue.
> > Preconditions
> > are simple - the backward compatibility. We should guarantee that
> > user
> > can use any version of thin client with any version of server while
> > they
> > share the same major version. This can be important, if someone have
> > user applications built with thin client and they don't want to break
> > their
> > user applications, when they just want to update servers. What is
> > appropriate here is to give user some kind of warning that they use
> > outdated client or server.
> >
> > Can you explain how your approach is going to work in the example
> > above? I'm not quite sure I understand you correctly.
> >
> > 1. The API for this can be as simple as a set of allowed version in
> > a configuration for both server and client. Maybe we should discuss
> > such
> > kind of API as it can be useful for example in terms of security.
> >
> > 2. Complexity is the price developers have to pay for better user
> > experience.
> > Nothing new here. Software is not designed for developers, it's
> > designed
> > for a user.
> >
> > Best Regards,
> > Igor
> >
> >
> > On Tue, Feb 12, 2019 at 11:56 AM Dmitry Melnichuk <
> > dmitry.melnichuk@nobitlost.com> wrote:
> >
> > > Hello fellow igniters!
> > >
> > > I recently started reconnaissance before the
> > > implementation of IEP-23 [1] in Python thin client. I think it is
> > > an
> > > interesting and much promising feature. As I understand, the
> > > changes
> > > associated with this feature will result in a new version of the
> > > binary
> > > protocol.
> > >
> > > What bothers me is not the changes required by the
> > > implementation itself, but the upcoming changes in the way that the
> > > fallback to the previous versions of the protocol is going to be
> > > handled.
> > >
> > > I have not found a open discussion on this topic neither on
> > > this mailing list, nor in Jira. If such a discussion took place,
> > > please
> > > inform me with a link. Based on what I have heard so far, I made
> > > the
> > > following conclusions:
> > >
> > > 1) the client is now expected to handle multiple
> > > binary protocol versions;
> > > 2) since the protocol is implemented the way
> > > the client first reports its version to the server on handshake,
> > > and
> > > not the other way, the client now must try to connect to the server
> > > using its preferred version of the protocol, and in case of an
> > > error,
> > > reconnect with another version.
> > >
> > > These changes are raised some concerns
> > > for me, for example:
> > >
> > > 1) the version negotiation mechanism implemented on
> > > client can not be made transparent to the end user. We must give
> > > the
> > > user an option, so that they could choose from the entire set of
> > > versions supported by the client, a subset of the versions their
> > > application is designed to work with. That will complicate the user
> > > API;
> > >
> > > 2) the complexity of the client will also be increased, especially
> > > considering unit testing. Certain tests will require a certain
> > > version
> > > of Ignite server, so they can no longer be implemented environment-
> > > agnostically, leading to a weird mix on unit and integration
> > > levels;
> > >
> > > 3)
> > > I do not see, or not aware of, the preconditions to such changes. I
> > > think the number of potential applications that can benefit from
> > > multi-
> > > protocol client is quite low. Usually all the hassle of version
> > > matching lie on the deployment level, above the app level. Please
> > > prove
> > > me wrong on this subject.
> > >
> > > Instead of supporting multiple binary
> > > protocols inside one client package, I would strongly prefer to
> > > support
> > > each version of the protocol separately, in the corresponding
> > > branch of
> > > the package repository. It would still be possible for the end user
> > > to
> > > use multiple protocols in one app, but with certain code-level and
> > > deployment-level efforts combined.
> > >
> > > Again, I most probably lack awareness
> > > on the subject, and therefore my conclusions may be premature, but
> > > anyway, let us discuss. I will appreciate any bit of knowledge from
> > > the
> > > community.
> > >
> > > [1] https://cwiki.apache.org/confluence/display/IGNITE/IEP-
> > > 23:+Best+Effort+Affinity+for+thin+clients
> > >
> > >
>
>

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