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Simplify map initial sizing #126767

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7729714
Simplify map initial sizing
idegtiarenko Apr 14, 2025
f1c5b6e
fix test projects ordering
idegtiarenko Apr 14, 2025
7dd4636
Merge branch 'main' into map_sizing
idegtiarenko Apr 14, 2025
1bcd3dd
Merge branch 'main' into map_sizing
idegtiarenko Apr 15, 2025
5736036
Merge branch 'main' into map_sizing
idegtiarenko Apr 22, 2025
01114fb
Merge branch 'main' into map_sizing
idegtiarenko Apr 24, 2025
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11 changes: 3 additions & 8 deletions server/src/main/java/org/elasticsearch/common/util/Maps.java
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Original file line number Diff line number Diff line change
Expand Up @@ -280,7 +280,7 @@ public static <K, V> Map<K, V> newMapWithExpectedSize(int expectedSize) {
* @return a new pre-sized {@link HashMap}
*/
public static <K, V> Map<K, V> newHashMapWithExpectedSize(int expectedSize) {
return new HashMap<>(capacity(expectedSize));
return HashMap.newHashMap(expectedSize);
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@idegtiarenko idegtiarenko Apr 14, 2025

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Since 19 both HashMap and LinkedHashMap could be presized using standard lib factories.

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@rjernst rjernst Apr 17, 2025

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nit: perhaps then (doesn't have to be here) we should convert all the uses of this helper to use HashMap.newHashMap directly?

}

/**
Expand All @@ -292,7 +292,7 @@ public static <K, V> Map<K, V> newHashMapWithExpectedSize(int expectedSize) {
* @return a new pre-sized {@link HashMap}
*/
public static <K, V> Map<K, V> newConcurrentHashMapWithExpectedSize(int expectedSize) {
return new ConcurrentHashMap<>(capacity(expectedSize));
return new ConcurrentHashMap<>(expectedSize);
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@idegtiarenko idegtiarenko Apr 14, 2025 •
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ConcurrentHashMap does this sizing computation internally:

according to the javadoc: Params: initialCapacity – The implementation performs internal sizing to accommodate this many elements.

and constructor code:

        long size = (long)(1.0 + (long)initialCapacity / loadFactor);
        int cap = (size >= (long)MAXIMUM_CAPACITY) ?
            MAXIMUM_CAPACITY : tableSizeFor((int)size);

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@rjernst rjernst Apr 17, 2025

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Similar to the above note, this utility method doesn't seem to be doing anything anymore, so perhaps it should be removed.

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@idegtiarenko idegtiarenko Apr 22, 2025

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(here and above comment) Yeap, newMapWithExpectedSize, newHashMapWithExpectedSize, newConcurrentHashMapWithExpectedSize, newLinkedHashMapWithExpectedSize can all be inlined.

}

/**
Expand All @@ -304,12 +304,7 @@ public static <K, V> Map<K, V> newConcurrentHashMapWithExpectedSize(int expected
* @return a new pre-sized {@link LinkedHashMap}
*/
public static <K, V> LinkedHashMap<K, V> newLinkedHashMapWithExpectedSize(int expectedSize) {
return new LinkedHashMap<>(capacity(expectedSize));
}

static int capacity(int expectedSize) {
assert expectedSize >= 0;
return expectedSize < 2 ? expectedSize + 1 : (int) (expectedSize / 0.75 + 1.0);
return LinkedHashMap.newLinkedHashMap(expectedSize);
}

/**
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17 changes: 0 additions & 17 deletions server/src/test/java/org/elasticsearch/common/util/MapsTests.java
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Expand Up @@ -32,7 +32,6 @@
import static org.hamcrest.Matchers.equalTo;
import static org.hamcrest.Matchers.greaterThan;
import static org.hamcrest.Matchers.hasItem;
import static org.hamcrest.Matchers.lessThanOrEqualTo;

public class MapsTests extends ESTestCase {

Expand Down Expand Up @@ -270,22 +269,6 @@ public void testFlatten() {
}
}

public void testCapacityIsEnoughForMapToNotBeResized() {
for (int i = 0; i < 1000; i++) {
int size = randomIntBetween(0, 1_000_000);
int capacity = Maps.capacity(size);
assertThat(size, lessThanOrEqualTo((int) (capacity * 0.75f)));
}
}

public void testCapacityForMaxSize() {
assertEquals(Integer.MAX_VALUE, Maps.capacity(Integer.MAX_VALUE));
}

public void testCapacityForZeroSize() {
assertEquals(1, Maps.capacity(0));
}

@SuppressWarnings("unchecked")
private static Object deepGet(String path, Object obj) {
Object cur = obj;
Expand Down