ijuma commented on a change in pull request #10334:
URL: https://github.com/apache/kafka/pull/10334#discussion_r595558838
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File path: metadata/src/main/java/org/apache/kafka/timeline/BaseHashTable.java
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@@ -56,12 +58,30 @@
this.elements = new Object[expectedSizeToCapacity(expectedSize)];
}
+ /**
+ * Calculate the capacity we should provision, given the expected size.
+ *
+ * Our capacity must always be a power of 2, and never less than 2.
+ */
static int expectedSizeToCapacity(int expectedSize) {
- if (expectedSize <= 1) {
- return 2;
+ if (expectedSize >= MAX_CAPACITY / 2) {
+ return MAX_CAPACITY;
+ }
+ return Math.max(MIN_CAPACITY, roundUpToPowerOfTwo(expectedSize * 2));
+ }
+
+ private static int roundUpToPowerOfTwo(int i) {
+ if (i < 0) {
+ return 0;
}
- double sizeToFit = expectedSize / MAX_LOAD_FACTOR;
- return (int) Math.min(MAX_CAPACITY, Math.ceil(Math.log(sizeToFit) /
LN_2));
+ i = i - 1;
+ i |= i >> 1;
+ i |= i >> 2;
+ i |= i >> 4;
+ i |= i >> 8;
+ i |= i >> 16;
+ i = i + 1;
+ return i < 0 ? MAX_CAPACITY : i;
Review comment:
Can you do something like:
```java
static final int tableSizeFor(int cap) {
int n = -1 >>> Integer.numberOfLeadingZeros(cap - 1);
return (n < 0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : n + 1;
}
```
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