"Wrong number of children"

[ion-elgreco]

Describe the bug

A couple folks including me tried bumping Datafusion to v36 in Delta-RS but to no avail since we all are running in this Wrong number of children error. Which at that time I read is something in the optimizer?

Here are failing actions: https://github.com/delta-io/delta-rs/actions/runs/8339625658/job/22821968902#step:4:1 https://github.com/delta-io/delta-rs/actions/runs/8472960661/job/23243814572#step:4:1

I'm curious if you guys would know the issue, perhaps it's something that we missed

To Reproduce

Not sure, but our tests will failed in this branch: https://github.com/delta-io/delta-rs/pull/2214

Expected behavior

No response

Additional context

No response

[mustafasrepo]

If you can post a PhysicalPlan for one of the failing test cases. That might help to understand the problem better, then we can replicate it in this repo. As an educated guess, it might be related to the

• wrong fn children implementation for one of the custom ExecutionPlans in your repo (if you have those).

[ion-elgreco]

@mustafasrepo This is the childrends function, I'll get grab a plan in a bit

pub struct DeltaScan {
    /// The URL of the ObjectStore root
    pub table_uri: String,
    /// Column that contains an index that maps to the original metadata Add
    pub config: DeltaScanConfig,
    /// The parquet scan to wrap
    pub parquet_scan: Arc<dyn ExecutionPlan>,
    /// The schema of the table to be used when evaluating expressions
    pub logical_schema: Arc<ArrowSchema>,
}

    fn children(&self) -> Vec<Arc<dyn ExecutionPlan>> {
        vec![self.parquet_scan.clone()]
    }

    fn with_new_children(
        self: Arc<Self>,
        children: Vec<Arc<dyn ExecutionPlan>>,
    ) -> DataFusionResult<Arc<dyn ExecutionPlan>> {
        ExecutionPlan::with_new_children(self.parquet_scan.clone(), children)
    }

[abhiaagarwal]

@ion-elgreco try changing the children function to return an empty vec![] rather than the clone of the self.parquet_scan(). solved 29/32 test issues for me.

[mustafasrepo]

I think, changing implementation below

    fn with_new_children(
        self: Arc<Self>,
        children: Vec<Arc<dyn ExecutionPlan>>,
    ) -> DataFusionResult<Arc<dyn ExecutionPlan>> {
        ExecutionPlan::with_new_children(self.parquet_scan.clone(), children)
    }

to something like

    fn with_new_children(
        self: Arc<Self>,
        children: Vec<Arc<dyn ExecutionPlan>>,
    ) -> Result<Arc<dyn ExecutionPlan>> {
        // Make sure to received single child
        // It should be updated new parquet_scan.
        assert_eq!(children.len(), 1);
        Arc::new(DeltaScan {
            table_uri: self.table_uri.clone(),
            config: self.config.clone(),
            parquet_scan: children[0].clone(),
            logical_schema: self.logical_schema.clone(),
        })
        // ExecutionPlan::with_new_children(self.parquet_scan.clone(), children)
    }

might solve the problem (Just brainstorming, I didn't try it). I am not sure, what ExecutionPlan::with_new_children(self.parquet_scan.clone(), children) does. However, this line might be the root cause of the problem.

[ion-elgreco]

@mustafasrepo thanks for the tips! It's resolved now