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From Tom Bentley <t.j.bent...@gmail.com>
Subject Re: [DISCUSS] KIP-201: Rationalising Policy interfaces
Date Mon, 02 Oct 2017 14:15:27 GMT
Hi All,

I've updated KIP-201 again so there is now a single policy interface (and
thus a single key by which to configure it) for topic creation,
modification, deletion and record deletion, which each have their own
validation method.

There are still a few loose ends:

1. I currently propose validateAlterTopic(), but it would be possible to be
more fine grained about this: validateAlterConfig(), validAddPartitions()
and validateReassignPartitions(), for example. Obviously this results in a
policy method per operation, and makes it more clear what is being changed.
I guess the down side is its more work for implementer, and potentially
makes it harder to change the interface in the future.

2. A couple of TODOs about what the TopicState interface should return when
a topic's partitions are being reassigned.

Your thoughts on these or any other points are welcome.

Thanks,

Tom

On 27 September 2017 at 11:45, Paolo Patierno <ppatierno@live.com> wrote:

> Hi Ismael,
>
>
>   1.  I don't have a real requirement now but "deleting" is an operation
> that could be really dangerous so it's always better having a way for
> having more control on that. I know that we have the authorizer used for
> that (delete on topic) but fine grained control could be better (even
> already happens for topic deletion).
>   2.  I know about the problem of restarting broker due to changes on
> policies but what do you mean by doing that on the clients ?
>
>
> Paolo Patierno
> Senior Software Engineer (IoT) @ Red Hat
> Microsoft MVP on Azure & IoT
> Microsoft Azure Advisor
>
> Twitter : @ppatierno<http://twitter.com/ppatierno>
> Linkedin : paolopatierno<http://it.linkedin.com/in/paolopatierno>
> Blog : DevExperience<http://paolopatierno.wordpress.com/>
>
>
> ________________________________
> From: ismaelj@gmail.com <ismaelj@gmail.com> on behalf of Ismael Juma <
> ismael@juma.me.uk>
> Sent: Wednesday, September 27, 2017 10:30 AM
> To: dev@kafka.apache.org
> Subject: Re: [DISCUSS] KIP-201: Rationalising Policy interfaces
>
> A couple of questions:
>
> 1. Is this a concrete requirement from a user or is it hypothetical?
> 2. You sure you would want to do this in the broker instead of the clients?
> It's worth remembering that updating broker policies involves a rolling
> restart of the cluster, so it's not the right place for things that change
> frequently.
>
> Ismael
>
> On Wed, Sep 27, 2017 at 11:26 AM, Paolo Patierno <ppatierno@live.com>
> wrote:
>
> > Hi Ismael,
> >
> > regarding motivations for delete records, as I said during the discussion
> > on KIP-204, it gives the possibility to avoid deleting messages for
> > specific partitions (inside the topic) and starting from a specific
> offset.
> > I could think on some users solutions where they know exactly what the
> > partitions means in a specific topic (because they are using a custom
> > partitioner on the producer side) so they know what kind of messages are
> > inside a partition allowing to delete them but not the others.  In such a
> > policy a user could also check the timestamp related to the offset for
> > allowing or not deletion on time base.
> >
> >
> > Paolo Patierno
> > Senior Software Engineer (IoT) @ Red Hat
> > Microsoft MVP on Azure & IoT
> > Microsoft Azure Advisor
> >
> > Twitter : @ppatierno<http://twitter.com/ppatierno>
> > Linkedin : paolopatierno<http://it.linkedin.com/in/paolopatierno>
> > Blog : DevExperience<http://paolopatierno.wordpress.com/>
> >
> >
> > ________________________________
> > From: ismaelj@gmail.com <ismaelj@gmail.com> on behalf of Ismael Juma <
> > ismael@juma.me.uk>
> > Sent: Wednesday, September 27, 2017 10:18 AM
> > To: dev@kafka.apache.org
> > Subject: Re: [DISCUSS] KIP-201: Rationalising Policy interfaces
> >
> > A couple more comments:
> >
> > 1. "If this KIP is accepted for Kafka 1.1.0 this removal could happen in
> > Kafka 1.2.0 or a later release." -> we only remove code in major
> releases.
> > So, if it's deprecated in 1.1.0, it would be removed in 2.0.0.
> >
> > 2. Deleting all messages in a topic is not really the same as deleting a
> > topic. The latter will cause consumers and producers to error out while
> the
> > former will not. It would be good to motivate the need for the delete
> > records policy more.
> >
> > Ismael
> >
> > On Wed, Sep 27, 2017 at 11:12 AM, Ismael Juma <ismael@juma.me.uk> wrote:
> >
> > > Another quick comment: the KIP states that having multiple interfaces
> > > imply that the logic must be in 2 places. That is not true because the
> > same
> > > class can implement multiple interfaces (this aspect was considered
> when
> > we
> > > decided to introduce policies incrementally).
> > >
> > > The main reason why I think the original approach doesn't work well is
> > > that there is no direct mapping between an operation and the policy.
> That
> > > is, we initially thought we would have create/alter/delete topics, but
> > that
> > > didn't work out as the alter case is better served by multiple request
> > > types. Given that, it's a bit awkward to maintain the original approach
> > and
> > > a policy for topic management seemed easier to understand. On that
> note,
> > > would `TopicManagementPolicy` be a better name?
> > >
> > > Looking at the updated KIP, I notice that we actually have a
> > > TopicDeletionPolicy with a separate config. That seems to be a halfway
> > > house. Not sure about that.
> > >
> > > Ismael
> > >
> > > On Wed, Sep 27, 2017 at 10:47 AM, Tom Bentley <t.j.bentley@gmail.com>
> > > wrote:
> > >
> > >> I have updated the KIP to add a common policy interface for topic and
> > >> message deletion. This included pulling ClusterState and TopicState
> > >> interfaces up to the top level so that they can be shared between the
> > two
> > >> policies.
> > >>
> > >> Cheers,
> > >>
> > >> Tom
> > >>
> > >> On 26 September 2017 at 18:09, Edoardo Comar <ECOMAR@uk.ibm.com>
> wrote:
> > >>
> > >> > Thanks Tom,
> > >> > In my original KIP-170 I mentioned that the method
> > >> >
> > >> > public Map<String, Integer> topicsPartitionCount();
> > >> >
> > >> > was just a starting point for a general purpose ClusterState
> > >> > as it happened to be exactly the info we needed for our policy
> > >> > implementation :-)
> > >> > it definitely doesn't feel general purpose enough.
> > >> >
> > >> > what about
> > >> >
> > >> >     interface ClusterState {
> > >> >         public TopicState topicState(String topicName);
> > >> >         public Set<String> topics();
> > >> >     }
> > >> >
> > >> > I think that the implementation of ClusterState that the server will
> > >> pass
> > >> > to the policy.validate method
> > >> > would just lazily tap into MetadataCache. No need for big upfront
> > >> > allocations.
> > >> >
> > >> > ciao,
> > >> > Edo
> > >> > --------------------------------------------------
> > >> >
> > >> > Edoardo Comar
> > >> >
> > >> > IBM Message Hub
> > >> >
> > >> > IBM UK Ltd, Hursley Park, SO21 2JN
> > >> >
> > >> >
> > >> >
> > >> > From:   Tom Bentley <t.j.bentley@gmail.com>
> > >> > To:     dev@kafka.apache.org
> > >> > Date:   26/09/2017 17:39
> > >> > Subject:        Re: [DISCUSS] KIP-201: Rationalising Policy
> interfaces
> > >> >
> > >> >
> > >> >
> > >> > Hi Edoardo,
> > >> >
> > >> >
> > >> > what about a single method in ClusterState
> > >> > >
> > >> > >     interface ClusterState {
> > >> > >         public Map<String,TopicState> topicsState();
> > >> > >
> > >> > >     }
> > >> > >
> > >> > > which could return a read-only snapshot of the cluster metadata
?
> > >> > >
> > >> >
> > >> > Sure that would work too. A concern with that is that we end up
> > >> allocating
> > >> > a potentially rather large amount for the Map and the collections
> > >> present
> > >> > in the TopicStates in order to provide the snapshot. The caller
> might
> > >> only
> > >> > be interested in one item from the TopicState for one topic in the
> > map.
> > >> > Accessing this information via methods means the caller only pays
> for
> > >> what
> > >> > they use.
> > >> >
> > >> > Cheers,
> > >> >
> > >> > Tom
> > >> >
> > >> >
> > >> >
> > >> > Unless stated otherwise above:
> > >> > IBM United Kingdom Limited - Registered in England and Wales with
> > number
> > >> > 741598.
> > >> > Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire
> PO6
> > >> 3AU
> > >> >
> > >>
> > >
> > >
> >
>

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