[GitHub] [arrow] alamb commented on a change in pull request #10078: ARROW-12432: [Rust] [DataFusion] Add metrics to SortExec

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alamb commented on a change in pull request #10078:
URL: https://github.com/apache/arrow/pull/10078#discussion_r615377229



##########
File path: rust/arrow/Cargo.toml
##########
@@ -47,7 +47,7 @@ regex = "1.3"
 lazy_static = "1.4"
 packed_simd = { version = "0.3.4", optional = true, package = "packed_simd_2" }
 chrono = "0.4"
-flatbuffers = "^0.8"
+flatbuffers = "=0.8.3" # 0.8.4 introduces const generics

Review comment:
       this may be accidentally included from  https://github.com/apache/arrow/pull/10081

##########
File path: rust/datafusion/src/physical_plan/sort.rs
##########
@@ -379,7 +430,8 @@ mod tests {
         assert_eq!(DataType::Float32, *sort_exec.schema().field(0).data_type());
         assert_eq!(DataType::Float64, *sort_exec.schema().field(1).data_type());
 
-        let result: Vec<RecordBatch> = collect(sort_exec).await?;
+        let result: Vec<RecordBatch> = collect(sort_exec.clone()).await?;
+        assert_eq!(sort_exec.metrics().get("outputRows").unwrap().value, 8);
         assert_eq!(result.len(), 1);

Review comment:
       Maybe also assert that the time counter was greater than zero?

##########
File path: rust/datafusion/src/physical_plan/sort.rs
##########
@@ -56,7 +63,12 @@ impl SortExec {
         expr: Vec<PhysicalSortExpr>,
         input: Arc<dyn ExecutionPlan>,
     ) -> Result<Self> {
-        Ok(Self { expr, input })
+        Ok(Self {
+            expr,
+            input,
+            output_rows: SQLMetric::counter("outputRows"),
+            sort_time_nanos: SQLMetric::time_nanos("sortTime"),

Review comment:
       Given Rust's focus on compile time type checking, what would you think about using typed counters rather than `String` keys? 
   
   So make the code look something like:
   
   ```suggestion
               output_rows: SQLMetric<OutputRows>::new(),
               sort_time_nanos: SQLMetric<SortTime>::new(),
   ```

##########
File path: rust/datafusion/src/physical_plan/mod.rs
##########
@@ -52,6 +52,8 @@ pub type SendableRecordBatchStream = Pin<Box<dyn RecordBatchStream + Send + Sync
 pub enum MetricType {
     /// Simple counter
     Counter,
+    /// Time in nanoseconds

Review comment:
       It would probably help to explicitly mention if this was wall clock time, or cpu time . It looks like this PR saves wallclock time for sort
   
   Both are probably interesting counters / metrics to eventually have




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