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use memory prefetch in hash map building #571

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Sep 14, 2024
Merged

use memory prefetch in hash map building #571

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30 changes: 22 additions & 8 deletions native-engine/datafusion-ext-plans/src/joins/join_hash_map.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -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()
Expand Down Expand Up @@ -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());
}
}
Expand Down
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