Thanks Jane for the summary and starting the discussion in the mailing
list.
Here are my thoughts:
1) syntax to reorder modules
I agree with Rui Li it would be quite useful if we can have some syntax to
reorder modules.
I slightly prefer `USE MODULES x, y, z` than `RELOAD MODULES x, y, z`,
because USE has a more sense of effective and specifying ordering, than
RELOAD.
>From my feeling, RELOAD just means we unregister and register x,y,z modules
again,
it sounds like other registered modules are still in use and in the order.
3) mapping modules purely by name
This can definitely improve the usability of loading modules, because
the 'type=' property
looks really redundant. We can think of this as a syntax sugar that the
default type value is the module name.
And we can support to specify 'type=' property in the future to allow
multiple modules for one module type.
Besides, I would like to mention one more change, that the module name
proposed in FLIP-68 is a string literal.
But I think we are all on the same page to change it into a simple
(non-compound) identifier.
LOAD/UNLOAD MODULE 'core'
==>
LOAD/UNLOAD MODULE core
Best,
Jark
On Sat, 30 Jan 2021 at 04:00, Jane Chan <qingyue....@gmail.com> wrote:
> Hi everyone,
>
> I would like to start a discussion on FLINK-21045 [1] about supporting
> `LOAD MODULE` and `UNLOAD MODULE` SQL syntax. It's first proposed by
> FLIP-68 [2] as following.
>
> -- load a module with the given name and append it to the end of the module
> list
> LOAD MODULE 'name' [WITH ('type'='xxx', 'prop'='myProp', ...)]
>
> --unload a module by name from the module list and other modules remain in
> the same relative positions
> UNLOAD MODULE 'name'
>
> After a round of discussion on the Jira ticket, it seems some unanswered
> questions need more opinions and suggestions.
>
> 1. The way to redefine resolution order easily
>
> Rui Li suggested introducing `USE MODULES` and adding similar
> functionality to the API because
>
> > 1) It's very tedious to unload old modules just to reorder them.
>
> 2) Users may not even know how to "re-load" an old module if it was not
> > initially loaded by the user, e.g. don't know which type to use.
>
>
> Jane Chan wondered that module is not like the catalog which has a
> concept of namespace could specify, and `USE` sounds like a
> mutual-exclusive concept.
> Maybe `RELOAD MODULES` can express upgrading the priority of the loaded
> module(s).
>
>
> 2. `LOAD/UNLOAD MODULE` v.s. `CREATE/DROP MODULE` syntax
> Jark Wu and Nicholas Jiang proposed to use `CREATE/DROP MODULE` instead
> of `LOAD/UNLOAD MODULE` because
>
> > 1) From a pure SQL user's perspective, maybe `CREATE MODULE + USE
> MODULE`
> > is easier to use rather than `LOAD/UNLOAD`.
> > 2) This will be very similar to what the catalog used now.
>
>
> Timo Walther would rather stick to the agreed design because
> loading/unloading modules is a concept known from kernels etc.
>
> 3. Simplify the module design by mapping modules purely by name
>
> LOAD MODULE geo_utils
> LOAD MODULE hive WITH ('version'='2.1') -- no dedicated 'type='/'module='
> but allow only 1 module to be loaded parameterized
> UNLOAD hive
> USE MODULES hive, core
>
>
> Please find more details in the reference link. Looking forward to your
> feedback.
>
> [1] https://issues.apache.org/jira/browse/FLINK-21045#
> <
> https://cwiki.apache.org/confluence/display/FLINK/FLIP-68%3A+Extend+Core+Table+System+with+Pluggable+Modules
> >
> [2]
>
> https://cwiki.apache.org/confluence/display/FLINK/FLIP-68%3A+Extend+Core+Table+System+with+Pluggable+Modules
>
> Best,
> Jane
>
