use memory prefetch in hash map building

native-engine/datafusion-ext-plans/src/joins/join_hash_map.rs

@@ -107,7 +107,7 @@ impl Table {
  let mut num_valid_items = 0;
 
  // collect map items
- let mut map_items = vec![];
+ let mut map_items = unchecked!(vec![]);
  for (hash, chunk) in hashes
  .into_iter()
  .enumerate()
@@ -149,18 +149,32 @@ impl Table {
  let mut map = unchecked!(Vec::with_capacity((1usize << map_mod_bits) + 16));
  map.resize(1 << map_mod_bits, MapValueGroup::default());
 
- for (hash, item) in map_items {
- let mut i = (hash % (1 << map_mod_bits)) as usize;
+ macro_rules! entries {
+ [$i:expr] => (map_items[$i].0 % (1 << map_mod_bits))
+ }
+
+ const PREFETCH_AHEAD: usize = 4;
+ if map_items.len() >= PREFETCH_AHEAD {
+ for i in 1..PREFETCH_AHEAD - 1 {
+ prefetch_read_data!(&map[entries![i] as usize]);
+ }
+ }
+ for i in 0..map_items.len() {
+ if i + PREFETCH_AHEAD < map_items.len() {
+ prefetch_read_data!(&map[entries![i + PREFETCH_AHEAD] as usize]);
+ }
+
+ let mut e = entries![i] as usize;
  loop {
- let empty = map[i].hashes.simd_eq(Simd::splat(0));
+ let empty = map[e].hashes.simd_eq(Simd::splat(0));
  if let Some(j) = empty.first_set() {
- map[i].hashes.as_mut_array()[j] = hash;
- map[i].values[j] = item;
+ map[e].hashes.as_mut_array()[j] = map_items[i].0;
+ map[e].values[j] = map_items[i].1;
  break;
  }
 
- i += 1;
- if i == map.len() {
+ e += 1;
+ if e == map.len() {
  map.push(MapValueGroup::default());
  }
  }