Merge pull request #169 from alamb/alamb/hash_reuse

Reuse hashes buffer when emitting partial join results

Author: korowa

datafusion/physical-plan/src/joins/hash_join.rs

@@ -669,6 +669,7 @@ impl ExecutionPlan for HashJoinExec {
             state: HashJoinStreamState::WaitBuildSide,
             build_side: BuildSide::Initial(BuildSideInitialState { left_fut }),
             batch_size,
+            hashes_buffer: vec![],
         }))
     }
 
@@ -979,6 +980,8 @@ struct HashJoinStream {
     build_side: BuildSide,
     /// Maximum output batch size
     batch_size: usize,
+    /// Scratch space for computing hashes
+    hashes_buffer: Vec<u64>,
 }
 
 impl RecordBatchStream for HashJoinStream {
@@ -1044,6 +1047,7 @@ fn lookup_join_hashmap<T: JoinHashMapType>(
     probe_on: &[Column],
     random_state: &RandomState,
     null_equals_null: bool,
+    hashes_buffer: &mut Vec<u64>,
     limit: usize,
     offset: JoinHashMapOffset,
 ) -> Result<(UInt64Array, UInt32Array, Option<JoinHashMapOffset>)> {
@@ -1059,8 +1063,9 @@ fn lookup_join_hashmap<T: JoinHashMapType>(
         })
         .collect::<Result<Vec<_>>>()?;
 
-    let mut hashes_buffer = vec![0; probe_batch.num_rows()];
-    let hash_values = create_hashes(&keys_values, random_state, &mut hashes_buffer)?;
+    hashes_buffer.clear();
+    hashes_buffer.resize(probe_batch.num_rows(), 0);
+    let hash_values = create_hashes(&keys_values, random_state, hashes_buffer)?;
 
     let (mut probe_builder, mut build_builder, next_offset) = build_hashmap
         .get_matched_indices_with_limit_offset(
@@ -1263,6 +1268,7 @@ impl HashJoinStream {
             &self.on_right,
             &self.random_state,
             self.null_equals_null,
+            &mut self.hashes_buffer,
             self.batch_size,
             state.offset,
         )?;
@@ -2930,6 +2936,7 @@ mod tests {
         );
 
         let join_hash_map = JoinHashMap::new(hashmap_left, next);
+        let mut hashes_buffer = vec![0];
 
         let (l, r, _) = lookup_join_hashmap(
             &join_hash_map,
@@ -2939,6 +2946,7 @@ mod tests {
             &[Column::new("a", 0)],
             &random_state,
             false,
+            &mut hashes_buffer,
             8192,
             (0, None),
         )?;