Hi everyone,
first, I was also questioning my proposal. But Bowen's proposal of
`tEnv.offloadToYaml(<file_path>)` would not work with the current design
because we don't know how to serialize a catalog or module into
properties. Currently, there is no converter from instance to
properties. It is a one way conversion. We can add a `toProperties`
method to both Catalog and Module class in the future to solve this.
Solving the table environment serializability can be future work.
However, I find the current proposal for the TableEnvironment methods is
contradicting:
tableEnv.loadModule(new Yyy());
tableEnv.unloadModule(“Xxx”);
The loading is specified programmatically whereas the unloading requires
a string that is not specified in the module itself. But is defined in
the factory according to the current design.
SQL does it more consistently. There, the name `xxx` is used when
loading and unloading the module:
LOAD MODULE 'xxx' [WITH ('prop'='myProp', ...)]
UNLOAD MODULE 'xxx’
How about:
tableEnv.loadModule("xxx", new Yyy());
tableEnv.unloadModule(“xxx”);
This would be similar to the catalog interfaces. The name is not part of
the instance itself.
What do you think?
Thanks,
Timo
On 01.10.19 21:17, Bowen Li wrote:
If something like the yaml file is the way to go and achieve such
motivation, we would cover that with current design.
On Tue, Oct 1, 2019 at 12:05 Bowen Li <bowenl...@gmail.com> wrote:
Hi Timo, Dawid,
I've added the suggested SQL and related changes to TableEnvironment API
and other classes to the google doc. Also removed "USE MODULE" and its
APIs. Will update FLIP wiki once we have a consensus.
W.r.t. descriptor approach, my gut feeling is similar to Dawid's. Besides,
I feel yaml file would be a better solution to persist serializable state
of an environment as the file itself is in serializable format already.
Though yaml file only serves SQL CLI at this moment, we may be able to
extend its reach to Table API and allow users to load/offload a
TableEnvironment from/to yaml files, as something like "TableEnvironment
tEnv = TableEnvironment.loadFromYaml(<file_path>)" and
"tEnv.offloadToYaml(<file_path>)" to restore and persist state, and try to
make yaml file more expressive.
On Tue, Oct 1, 2019 at 6:47 AM Dawid Wysakowicz <dwysakow...@apache.org>
wrote:
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
