Improving iterator using prefetch

Signed-off-by: NadavGigi <[email protected]>

src/hashtable.c

@@ -934,6 +934,32 @@ static inline incrementalFind *incrementalFindFromOpaque(hashtableIncrementalFin
     return (incrementalFind *)(void *)state;
 }
 
+static void prefetchBucketEntries(bucket *b) {
+    if (b->chained) {
+        valkey_prefetch(bucketNext(b));
+    }
+    for (int pos = 0; pos < numBucketPositions(b); pos++) {
+        if (isPositionFilled(b, pos)) {
+            valkey_prefetch(b->entries[pos]);
+        }
+    }
+}
+
+static void prefetchNextFilledBucket(iter *iter, bucket *current_bucket) {
+    if (current_bucket->chained) {
+        prefetchBucketEntries(bucketNext(current_bucket));
+    } else {
+        size_t table_size = numBuckets(iter->hashtable->bucket_exp[iter->table]);
+        for (size_t bucket_index = (size_t)iter->index + 1; bucket_index < table_size; bucket_index++) {
+            bucket *b = &iter->hashtable->tables[iter->table][bucket_index];
+            if (b->presence) {
+                prefetchBucketEntries(b);
+                break;
+            }
+        }
+    }
+}
+
 /* --- API functions --- */
 
 /* Allocates and initializes a new hashtable specified by the given type. */
@@ -1890,6 +1916,9 @@ int hashtableNext(hashtableIterator *iterator, void **elemptr) {
             }
         }
         bucket *b = iter->bucket;
+        if (iter->pos_in_bucket == 0 && b->presence) {
+            prefetchNextFilledBucket(iter, b);
+        }
         if (!isPositionFilled(b, iter->pos_in_bucket)) {
             /* No entry here. */
             continue;