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From Ryan Blue <rb...@netflix.com.INVALID>
Subject Re: [DISCUSS] Out of order optimizer rules?
Date Wed, 02 Oct 2019 16:18:49 GMT
Where can I find a design doc for dynamic partition pruning that explains
how it works?

The JIRA issue, SPARK-11150, doesn't seem to describe dynamic partition
pruning (as pointed out by Henry R.) and doesn't have any comments about
the implementation's approach. And the PR description also doesn't have
much information. It lists 3 cases for how a filter is built, but
nothing about the overall approach or design that helps when trying to find
out where it should be placed in the optimizer rules. It also isn't clear
why this couldn't be part of spark-catalyst.

On Wed, Oct 2, 2019 at 1:48 AM Wenchen Fan <cloud0fan@gmail.com> wrote:

> dynamic partition pruning rule generates "hidden" filters that will be
> converted to real predicates at runtime, so it doesn't matter where we run
> the rule.
>
> For PruneFileSourcePartitions, I'm not quite sure. Seems to me it's better
> to run it before join reorder.
>
> On Sun, Sep 29, 2019 at 5:51 AM Ryan Blue <rblue@netflix.com.invalid>
> wrote:
>
>> Hi everyone,
>>
>> I have been working on a PR that moves filter and projection pushdown
>> into the optimizer for DSv2, instead of when converting to physical plan.
>> This will make DSv2 work with optimizer rules that depend on stats, like
>> join reordering.
>>
>> While adding the optimizer rule, I found that some rules appear to be out
>> of order. For example, PruneFileSourcePartitions that handles filter
>> pushdown for v1 scans is in SparkOptimizer (spark-sql) in a batch that
>> will run after all of the batches in Optimizer (spark-catalyst)
>> including CostBasedJoinReorder.
>>
>> SparkOptimizer also adds the new “dynamic partition pruning” rules
>> *after* both the cost-based join reordering and the v1 partition pruning
>> rule. I’m not sure why this should run after join reordering and partition
>> pruning, since it seems to me like additional filters would be good to have
>> before those rules run.
>>
>> It looks like this might just be that the rules were written in the
>> spark-sql module instead of in catalyst. That makes some sense for the v1
>> pushdown, which is altering physical plan details (FileIndex) that have
>> leaked into the logical plan. I’m not sure why the dynamic partition
>> pruning rules aren’t in catalyst or why they run after the v1 predicate
>> pushdown.
>>
>> Can someone more familiar with these rules clarify why they appear to be
>> out of order?
>>
>> Assuming that this is an accident, I think it’s something that should be
>> fixed before 3.0. My PR fixes early pushdown, but the “dynamic” pruning may
>> still need to be addressed.
>>
>> rb
>> --
>> Ryan Blue
>> Software Engineer
>> Netflix
>>
>

-- 
Ryan Blue
Software Engineer
Netflix

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