Skip to content

Use hashingutils for MetricsKey's hash #10677

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
gh-worker-dd-mergequeue-cf854d merged 1 commit into from
Feb 25, 2026
+14 −36
Merged

Use hashingutils for MetricsKey's hash #10677

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
50 changes: 14 additions & 36 deletions dd-trace-core/src/main/java/datadog/trace/common/metrics/MetricKey.java
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@
import static datadog.trace.bootstrap.instrumentation.api.UTF8BytesString.EMPTY;

import datadog.trace.bootstrap.instrumentation.api.UTF8BytesString;
import datadog.trace.util.HashingUtils;
import java.util.Collections;
import java.util.List;
import java.util.Objects;
Expand Down Expand Up @@ -49,42 +50,19 @@ public MetricKey(
this.httpMethod = httpMethod == null ? null : UTF8BytesString.create(httpMethod);
this.httpEndpoint = httpEndpoint == null ? null : UTF8BytesString.create(httpEndpoint);

// Unrolled polynomial hashcode to avoid varargs allocation
// and eliminate data dependency between iterations as in Arrays.hashCode.
// Coefficient constants are powers of 31, with integer overflow (hence negative numbers).
// See
// https://richardstartin.github.io/posts/collecting-rocks-and-benchmarks
// https://richardstartin.github.io/posts/still-true-in-java-9-handwritten-hash-codes-are-faster

// Only include httpMethod and httpEndpoint in hash if they are not null
// This ensures backward compatibility when the feature is disabled

// Note: all the multiplication got constant folded at compile time (see javap -verbose ...)
int tmpHash =
(int) (31L * 31 * 31 * 31 * 31 * 31 * 31 * 31) * Boolean.hashCode(this.isTraceRoot) // 8
Copy link
Copy Markdown
Contributor

@bric3 bric3 Feb 25, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Thanks I was looking into doing something similar. But I had one question for @dougqh: This code had multiplications being constant-folded at compile time. Do you think the change to addToHash will be on par ? I believe the overhead to be acceptable in this case, but since it happens on every span stats publication I'd like to challenge this thought.

+ (int) (31L * 31 * 31 * 31 * 31 * 31 * 31) * this.spanKind.hashCode() // 7
+ 31 * 31 * 31 * 31 * 31 * 31 * this.peerTags.hashCode() // 6
+ 31 * 31 * 31 * 31 * 31 * this.resource.hashCode() // 5
+ 31 * 31 * 31 * 31 * this.service.hashCode() // 4
+ 31 * 31 * 31 * this.operationName.hashCode() // 3
+ 31 * 31 * this.type.hashCode() // 2
+ 31 * this.httpStatusCode // 1
+ (this.synthetics ? 1 : 0); // 0
// optional fields
if (this.serviceSource != null) {
tmpHash +=
(int) (31L * 31 * 31 * 31 * 31 * 31 * 31 * 31 * 31) * this.serviceSource.hashCode(); // 9
}
if (this.httpEndpoint != null) {
tmpHash +=
(int) (31L * 31 * 31 * 31 * 31 * 31 * 31 * 31 * 31 * 31)
* this.httpEndpoint.hashCode(); // 10
}
if (this.httpMethod != null) {
tmpHash +=
(int) (31L * 31 * 31 * 31 * 31 * 31 * 31 * 31 * 31 * 31 * 31)
* this.httpMethod.hashCode(); // 11
}
int tmpHash = 0;
tmpHash = HashingUtils.addToHash(tmpHash, this.isTraceRoot);
tmpHash = HashingUtils.addToHash(tmpHash, this.spanKind);
tmpHash = HashingUtils.addToHash(tmpHash, this.peerTags);
tmpHash = HashingUtils.addToHash(tmpHash, this.resource);
tmpHash = HashingUtils.addToHash(tmpHash, this.service);
tmpHash = HashingUtils.addToHash(tmpHash, this.operationName);
tmpHash = HashingUtils.addToHash(tmpHash, this.type);
tmpHash = HashingUtils.addToHash(tmpHash, this.httpStatusCode);
tmpHash = HashingUtils.addToHash(tmpHash, this.synthetics);
tmpHash = HashingUtils.addToHash(tmpHash, this.serviceSource);
tmpHash = HashingUtils.addToHash(tmpHash, this.httpEndpoint);
tmpHash = HashingUtils.addToHash(tmpHash, this.httpMethod);
this.hash = tmpHash;
}

Expand Down
Loading