Hi Timo, Bowen, Unfortunately I did not have enough time to go through all the suggestions in details so I can not comment on the whole FLIP.
I just wanted to give my opinion on the "descriptor approach in
loadModule" part. I am not sure if we need it here. We might be
overthinking this a bit. It definitely makes sense for objects like
TableSource/TableSink etc. as they are logical definitions that nearly
always have to be persisted in a Catalog. I'm not sure if we really need
the same for a whole session. If we need a resume session feature, the
way to go would probably be to keep the session in memory on the server
side. I fear we will never be able to serialize the whole session
entirely (temporary objects, objects derived from DataStream etc.)
I think it is ok to use instances for objects like Catalogs or Modules
and have an overlay on top of that that can create instances from
properties.
Best,
Dawid
On 01/10/2019 11:28, Timo Walther wrote:
> Hi Bowen,
>
> thanks for your response.
>
> Re 2) I also don't have a better approach for this issue. It is
> similar to changing the general TableConfig between two statements. It
> would be good to add your explanation to the design document.
>
> Re 3) It would be interesting to know about which "core" functions we
> are actually talking about. Also for the overriding built-in functions
> that we discussed in the other FLIP. But I'm fine with leaving it to
> the user for now. How about we just introduce loadModule(),
> unloadModule() methods instead of useModules()? This would ensure that
> users don't forget to add the core module when adding an additional
> module and they need to explicitly call "unloadModule('core')".
>
> Re 4) Every table environment feature should also be designed with SQL
> statements in mind to verify the concept. SQL is also more popular
> that Java/Scala API or YAML file. I would like to add it to 1.10 for
> marking the feature as complete.
>
> SHOW MODULES -> sounds good to me, we should add a listModules():
> List<String> method to table environment
>
> LOAD MODULE 'hive' [WITH ('prop'='myProp', ...)] --> we should add a
> loadModule() method to table environment
>
> UNLOAD MODULE 'hive' --> we should add a unloadModule() method to
> table environment
>
> I would not introduce `USE MODULES 'x' 'y' 'z'` for simplicity and
> concise API. Users need to load the module anyway with properties.
> They can also load them "in order" immediately. CREATE TABLE can also
> not create multiple tables but only one at a time in that order.
>
> One thing that came to my mind, shall we use a descriptor approach for
> loadModule()? The past has shown that passing instances causes
> problems when persisting objects. That's why we also want to get rid
> of registerTableSource. I could image that users might want to persist
> a table environment's state for later use in the future. Even though
> this is future work, we should already keep such use cases in mind
> when adding new API methods. What do you think?
>
> Regards,
> Timo
>
>
> On 30.09.19 23:17, Bowen Li wrote:
>> Hi Timo,
>>
>> Re 1) I agree. I renamed the title to "Extend Core Table System with
>> Pluggable Modules" and all internal references
>>
>> Re 2) First, I'll rename the API to useModules(). The design doesn't
>> forbid
>> users to call useModules() multi times. Objects in modules are loaded on
>> demand instead of eagerly, so there won't be inconsistency. Users
>> have to
>> be fully aware of the consequences of resetting modules as that might
>> cause
>> that some objects can not be referenced anymore or resolution order
>> of some
>> objects changes.
>>
>> Re 3) Yes, we'd leave that to users.
>>
>> Another approach can be to have a non-optional "Core" module for all
>> objects that cannot be overrode like "CAST" and "AS" functions, and
>> have an
>> optional "ExtendedCore" module for other replaceable built-in objects.
>> "Core" should be positioned at the 1st in module list all the time.
>>
>> I'm fine with either solution.
>>
>> Re 4) It may sound like a nice-to-have advanced feature for 1.10, but we
>> can surely fully discuss it for the sake of feature completeness.
>>
>> Unlike other configs, the order of modules would matter in Flink, and it
>> implies the LOAD/UNLOAD commands would not be equal in operation
>> positions.
>> IIUYC, LOAD MODULE 'x' would be interpreted as appending x to the end of
>> module list, and UNLOAD MODULE 'x' would be interpreted as removing x
>> from
>> any position in the list?
>>
>> I'm thinking of the following list of commands:
>>
>> SHOW MODULES - list modules in order
>> LOAD MODULE 'hive' [WITH ('prop'='myProp', ...)] - load and append the
>> module to end of the module list
>> UNLOAD MODULE 'hive' - remove the module from module list, and other
>> modules remain the same relative positions
>> USE MODULES 'x' 'y' 'z' (wondering can parser take "'x' 'y' 'z'"?),
>> or USE
>> MODULES 'x,y,z' - to reorder module list completely
>>
>
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