make sure that only concat preallocates buffers (#382)

* MutableArrayData::with_capacities

* better pattern matching

* add binary capacities

* add list child data

* add struct capacities

* add panic for dictionary type

* change dictionary capacity enum variant

arrow/src/array/mod.rs

@@ -256,7 +256,7 @@ pub type DurationMillisecondBuilder = PrimitiveBuilder<DurationMillisecondType>;
 pub type DurationMicrosecondBuilder = PrimitiveBuilder<DurationMicrosecondType>;
 pub type DurationNanosecondBuilder = PrimitiveBuilder<DurationNanosecondType>;
 
-pub use self::transform::MutableArrayData;
+pub use self::transform::{Capacities, MutableArrayData};
 
 // --------------------- Array Iterator ---------------------
 

arrow/src/array/transform/mod.rs

@@ -326,9 +326,9 @@ fn build_extend_nulls(data_type: &DataType) -> ExtendNulls {
     })
 }
 
-fn preallocate_str_buffer<Offset: StringOffsetSizeTrait>(
+fn preallocate_offset_and_binary_buffer<Offset: StringOffsetSizeTrait>(
     capacity: usize,
-    arrays: &[&ArrayData],
+    binary_size: usize,
 ) -> [MutableBuffer; 2] {
     // offsets
     let mut buffer = MutableBuffer::new((1 + capacity) * mem::size_of::<Offset>());
@@ -338,33 +338,59 @@ fn preallocate_str_buffer<Offset: StringOffsetSizeTrait>(
     } else {
         buffer.push(0i32)
     }
-    let str_values_size = arrays
-        .iter()
-        .map(|data| {
-            // get the length of the value buffer
-            let buf_len = data.buffers()[1].len();
-            // find the offset of the buffer
-            // this returns a slice of offsets, starting from the offset of the array
-            // so we can take the first value
-            let offset = data.buffer::<Offset>(0)[0];
-            buf_len - offset.to_usize().unwrap()
-        })
-        .sum::<usize>();
 
     [
         buffer,
-        MutableBuffer::new(str_values_size * mem::size_of::<u8>()),
+        MutableBuffer::new(binary_size * mem::size_of::<u8>()),
     ]
 }
 
+/// Define capacities of child data or data buffers.
+#[derive(Debug, Clone)]
+pub enum Capacities {
+    /// Binary, Utf8 and LargeUtf8 data types
+    /// Define
+    /// * the capacity of the array offsets
+    /// * the capacity of the binary/ str buffer
+    Binary(usize, Option<usize>),
+    /// List and LargeList data types
+    /// Define
+    /// * the capacity of the array offsets
+    /// * the capacity of the child data
+    List(usize, Option<Box<Capacities>>),
+    /// Struct type
+    /// * the capacity of the array
+    /// * the capacities of the fields
+    Struct(usize, Option<Vec<Capacities>>),
+    /// Dictionary type
+    /// * the capacity of the array/keys
+    /// * the capacity of the values
+    Dictionary(usize, Option<Box<Capacities>>),
+    /// Don't preallocate inner buffers and rely on array growth strategy
+    Array(usize),
+}
 impl<'a> MutableArrayData<'a> {
     /// returns a new [MutableArrayData] with capacity to `capacity` slots and specialized to create an
     /// [ArrayData] from multiple `arrays`.
     ///
     /// `use_nulls` is a flag used to optimize insertions. It should be `false` if the only source of nulls
     /// are the arrays themselves and `true` if the user plans to call [MutableArrayData::extend_nulls].
     /// In other words, if `use_nulls` is `false`, calling [MutableArrayData::extend_nulls] should not be used.
-    pub fn new(arrays: Vec<&'a ArrayData>, mut use_nulls: bool, capacity: usize) -> Self {
+    pub fn new(arrays: Vec<&'a ArrayData>, use_nulls: bool, capacity: usize) -> Self {
+        Self::with_capacities(arrays, use_nulls, Capacities::Array(capacity))
+    }
+
+    /// Similar to [MutableArray::new], but lets users define the preallocated capacities of the array.
+    /// See also [MutableArray::new] for more information on the arguments.
+    ///
+    /// # Panic
+    /// This function panics if the given `capacities` don't match the data type of `arrays`. Or when
+    /// a [Capacities] variant is not yet supported.
+    pub fn with_capacities(
+        arrays: Vec<&'a ArrayData>,
+        mut use_nulls: bool,
+        capacities: Capacities,
+    ) -> Self {
         let data_type = arrays[0].data_type();
         use crate::datatypes::*;
 
@@ -374,12 +400,24 @@ impl<'a> MutableArrayData<'a> {
             use_nulls = true;
         };
 
-        // We can prevent reallocation by precomputing the needed size.
-        // This is faster and more memory efficient.
-        let [buffer1, buffer2] = match data_type {
-            DataType::LargeUtf8 => preallocate_str_buffer::<i64>(capacity, &arrays),
-            DataType::Utf8 => preallocate_str_buffer::<i32>(capacity, &arrays),
-            _ => new_buffers(data_type, capacity),
+        let mut array_capacity;
+
+        let [buffer1, buffer2] = match (data_type, &capacities) {
+            (DataType::LargeUtf8, Capacities::Binary(capacity, Some(value_cap)))
+            | (DataType::LargeBinary, Capacities::Binary(capacity, Some(value_cap))) => {
+                array_capacity = *capacity;
+                preallocate_offset_and_binary_buffer::<i64>(*capacity, *value_cap)
+            }
+            (DataType::Utf8, Capacities::Binary(capacity, Some(value_cap)))
+            | (DataType::Binary, Capacities::Binary(capacity, Some(value_cap))) => {
+                array_capacity = *capacity;
+                preallocate_offset_and_binary_buffer::<i32>(*capacity, *value_cap)
+            }
+            (_, Capacities::Array(capacity)) => {
+                array_capacity = *capacity;
+                new_buffers(data_type, *capacity)
+            }
+            _ => panic!("Capacities: {:?} not yet supported", capacities),
         };
 
         let child_data = match &data_type {
@@ -412,20 +450,66 @@ impl<'a> MutableArrayData<'a> {
                     .iter()
                     .map(|array| &array.child_data()[0])
                     .collect::<Vec<_>>();
-                vec![MutableArrayData::new(childs, use_nulls, capacity)]
+
+                let capacities = if let Capacities::List(capacity, ref child_capacities) =
+                    capacities
+                {
+                    array_capacity = capacity;
+                    child_capacities
+                        .clone()
+                        .map(|c| *c)
+                        .unwrap_or(Capacities::Array(array_capacity))
+                } else {
+                    Capacities::Array(array_capacity)
+                };
+
+                vec![MutableArrayData::with_capacities(
+                    childs, use_nulls, capacities,
+                )]
             }
             // the dictionary type just appends keys and clones the values.
             DataType::Dictionary(_, _) => vec![],
             DataType::Float16 => unreachable!(),
-            DataType::Struct(fields) => (0..fields.len())
-                .map(|i| {
-                    let child_arrays = arrays
-                        .iter()
-                        .map(|array| &array.child_data()[i])
-                        .collect::<Vec<_>>();
-                    MutableArrayData::new(child_arrays, use_nulls, capacity)
-                })
-                .collect::<Vec<_>>(),
+            DataType::Struct(fields) => match capacities {
+                Capacities::Struct(capacity, Some(ref child_capacities)) => {
+                    array_capacity = capacity;
+                    (0..fields.len())
+                        .zip(child_capacities)
+                        .map(|(i, child_cap)| {
+                            let child_arrays = arrays
+                                .iter()
+                                .map(|array| &array.child_data()[i])
+                                .collect::<Vec<_>>();
+                            MutableArrayData::with_capacities(
+                                child_arrays,
+                                use_nulls,
+                                child_cap.clone(),
+                            )
+                        })
+                        .collect::<Vec<_>>()
+                }
+                Capacities::Struct(capacity, None) => {
+                    array_capacity = capacity;
+                    (0..fields.len())
+                        .map(|i| {
+                            let child_arrays = arrays
+                                .iter()
+                                .map(|array| &array.child_data()[i])
+                                .collect::<Vec<_>>();
+                            MutableArrayData::new(child_arrays, use_nulls, capacity)
+                        })
+                        .collect::<Vec<_>>()
+                }
+                _ => (0..fields.len())
+                    .map(|i| {
+                        let child_arrays = arrays
+                            .iter()
+                            .map(|array| &array.child_data()[i])
+                            .collect::<Vec<_>>();
+                        MutableArrayData::new(child_arrays, use_nulls, array_capacity)
+                    })
+                    .collect::<Vec<_>>(),
+            },
             _ => {
                 todo!("Take and filter operations still not supported for this datatype")
             }
@@ -436,6 +520,9 @@ impl<'a> MutableArrayData<'a> {
                 0 => unreachable!(),
                 1 => Some(arrays[0].child_data()[0].clone()),
                 _ => {
+                    if let Capacities::Dictionary(_, _) = capacities {
+                        panic!("dictionary capacity not yet supported")
+                    }
                     // Concat dictionaries together
                     let dictionaries: Vec<_> =
                         arrays.iter().map(|array| &array.child_data()[0]).collect();
@@ -465,7 +552,7 @@ impl<'a> MutableArrayData<'a> {
             .map(|array| build_extend_null_bits(array, use_nulls))
             .collect();
 
-        let null_bytes = bit_util::ceil(capacity, 8);
+        let null_bytes = bit_util::ceil(array_capacity, 8);
         let null_buffer = MutableBuffer::from_len_zeroed(null_bytes);
 
         let extend_values = match &data_type {

arrow/src/compute/kernels/concat.rs

@@ -31,8 +31,26 @@
 //! ```
 
 use crate::array::*;
+use crate::datatypes::DataType;
 use crate::error::{ArrowError, Result};
 
+fn compute_str_values_length<Offset: StringOffsetSizeTrait>(
+    arrays: &[&ArrayData],
+) -> usize {
+    arrays
+        .iter()
+        .map(|&data| {
+            // get the length of the value buffer
+            let buf_len = data.buffers()[1].len();
+            // find the offset of the buffer
+            // this returns a slice of offsets, starting from the offset of the array
+            // so we can take the first value
+            let offset = data.buffer::<Offset>(0)[0];
+            buf_len - offset.to_usize().unwrap()
+        })
+        .sum()
+}
+
 /// Concatenate multiple [Array] of the same type into a single [ArrayRef].
 pub fn concat(arrays: &[&Array]) -> Result<ArrayRef> {
     if arrays.is_empty() {
@@ -56,7 +74,25 @@ pub fn concat(arrays: &[&Array]) -> Result<ArrayRef> {
 
     let arrays = arrays.iter().map(|a| a.data()).collect::<Vec<_>>();
 
-    let mut mutable = MutableArrayData::new(arrays, false, capacity);
+    let mut mutable = match arrays[0].data_type() {
+        DataType::Utf8 => {
+            let str_values_size = compute_str_values_length::<i32>(&arrays);
+            MutableArrayData::with_capacities(
+                arrays,
+                false,
+                Capacities::Binary(capacity, Some(str_values_size)),
+            )
+        }
+        DataType::LargeUtf8 => {
+            let str_values_size = compute_str_values_length::<i64>(&arrays);
+            MutableArrayData::with_capacities(
+                arrays,
+                false,
+                Capacities::Binary(capacity, Some(str_values_size)),
+            )
+        }
+        _ => MutableArrayData::new(arrays, false, capacity),
+    };
 
     for (i, len) in lengths.iter().enumerate() {
         mutable.extend(i, 0, *len)