Sounds like we have reached a consensus, I guess.
Can we create a JIRA to allow users to create their own sub-class of
RelMetadataQuery?
- Haisheng
------------------------------------------------------------------
发件人：Julian Hyde<jh...@apache.org>
日 期：2019年10月22日 09:58:34
收件人：dev<dev@calcite.apache.org>
主 题：Re: [DISCUSSION] Extension of Metadata Query
Yes, the division of labor between MetadataFactory and RelMetadataQuery is a
good one, and we should keep them intact. One provides the raw metadata, and
the other provides a typed interface and transactions/caching.
It might be allowable for a user to create their own sub-class of
RelMetadataQuery that adds only handler fields and metadata methods, provided
that it follows the existing pattern. We could add a new thread-local in
RelMetadataQuery.instance() that is a factory to create the required sub-class
of RelMetadataQuery.
The process by which metadata factories re-generate themselves is delicate and
subtle:
public Double getMaxRowCount(RelNode rel) {
for (;;) {
try {
return maxRowCountHandler.getMaxRowCount(rel, this);
} catch (JaninoRelMetadataProvider.NoHandler e) {
maxRowCountHandler =
revise(e.relClass, BuiltInMetadata.MaxRowCount.DEF);
}
}
}
(Note that “revise” generates a new class, creating bytecode via janino, and
the generated code throws “NoHandler" when it needs to extend itself.) I don’t
trust the typical Calcite user to be able to write a sub-class that works
correctly and efficiently.
Julian
> On Oct 18, 2019, at 3:55 AM, XING JIN <jinxing.co...@gmail.com> wrote:
>
> +1 on Danny's comment.
> If we use MedataFactory to customize and use RelMetadataQuery for
> convenience, that will make user confused.
>
> Danny Chan <yuzhao....@gmail.com> 于2019年10月18日周五 下午12:33写道：
>
>> That is the point, we should supply a way to extend the RelMetadataQuery
>> conveniently for Calcite, because in most of the RelOptRules, user would
>> use the code like:
>>
>> RelOptRuleCall.getMetadataQuery
>>
>> To get a RMQ instead of using AbstractRelNode.metadata() to fetch a
>> MedataFactory.
>>
>> We should at lest unity the metadata query entrance/interfaces, or it
>> would confuse a lot.
>>
>> Best,
>> Danny Chan
>> 在 2019年10月18日 +0800 AM12:23，Seliverstov Igor <gvvinbl...@gmail.com>，写道：
>>> At least in our project (Apache Ignite) we use
>> AbstractRelNode.metadata().
>>>
>>> But it so because there is no way to put our metadata type into
>>> RelMetadataQuery without changes in Calcite.
>>>
>>> Regards,
>>> Igor
>>>
>>> чт, 17 окт. 2019 г., 19:16 Xiening Dai <xndai....@gmail.com>:
>>>
>>>> MetadataFactory is still useful. It provides a way to access Metadata
>>>> directly. If someone creates a new type of Metadata class, it can be
>>>> accessed through AbstractRelNode.metadata(). This way you don’t need to
>>>> update RelMetadataQuery interface to include the getter for this new
>> meta.
>>>> Although I don’t see this pattern being used often, but I do think it
>> is
>>>> still useful and shouldn’t be removed.
>>>>
>>>>
>>>> For your second point, I think you would still need a way to keep
>>>> RelMetadataQuery object during a rule call. If you choose to create new
>>>> instance, you will have to pass it around while applying the rule. That
>>>> actually complicates things a lot.
>>>>
>>>>
>>>>> On Oct 17, 2019, at 12:49 AM, XING JIN <jinxing.co...@gmail.com>
>> wrote:
>>>>>
>>>>> 1. RelMetadataQuery covers the functionality of MetadataFactory, why
>>>> should
>>>>> we keep/maintain both of them ? shall we just deprecate
>> MetadataFactory.
>>>> I
>>>>> see MetadataFactory is rarely used in current code. Also I
>>>>> think MetadataFactory is not good place to offering customized
>> metadata,
>>>>> which will make user confused for the difference between
>> RelMetadataQuery
>>>>> and MetadataFactory.
>>>>>
>>>>>> Customized RelMetadataQuery with code generated meta handler for
>>>>> customized metadata, also can provide convenient way to get metadata.
>>>>> It makes sense for me.
>>>>>
>>>>> 2. If the natural lifespan of a RelMetadataQuery is a RelOptCall,
>> shall
>>>> we
>>>>> deprecate RelOptCluster#getMetadataQuery ? If a user wants to get the
>>>>> metadata but without a RelOptCall, he/she will need to create a new
>>>>> instance of RelMetadataQuery.
>>>>>
>>>>> Xiening Dai <xndai....@gmail.com> 于2019年10月17日周四 上午2:27写道：
>>>>>
>>>>>> I have seen both patterns in current code base. In most places, for
>>>>>> example SubQueryRemoveRule, AggregateUnionTrasposeRule
>>>>>> SortJoinTransposeRule, etc., RelOptCluster.getMetadataQuery() is
>> used.
>>>> And
>>>>>> there are a few other places where new RelMetadataQuery instance is
>>>>>> created, which Haisheng attempts to fix.
>>>>>>
>>>>>> Currently RelOptCluster.invalidateMetadataQuery() is called at the
>> end
>>>> of
>>>>>> RelOptRuleCall.transformTo(). So the lifespan of RelMetadataQuery
>> is
>>>>>> guaranteed to be within a RelOptCall. I think Haisheng’s fix is
>> safe.
>>>>>>
>>>>>>
>>>>>>> On Oct 16, 2019, at 1:53 AM, Danny Chan <yuzhao....@gmail.com>
>> wrote:
>>>>>>>
>>>>>>> This is the reason I was struggling for the discussion.
>>>>>>>
>>>>>>> Best,
>>>>>>> Danny Chan
>>>>>>> 在 2019年10月16日 +0800 AM11:23，dev@calcite.apache.org，写道：
>>>>>>>>
>>>>>>>> RelMetadataQuery
>>>>>>
>>>>>>
>>>>
>>>>
>>
