feat: Add support for high resolution fractional by chrfwow · Pull Request #1740 · open-feature/java-sdk-contrib

chrfwow · 2026-03-12T14:20:26Z

This PR

Adds high resolution fractional support

Related Issues

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

gemini-code-assist · 2026-03-12T14:20:57Z

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the fractional targeting mechanism by extending its compatibility to include Number and Boolean types as bucketing keys, in addition to the existing String support. The core change involves a refactored hashing and bucketing algorithm that utilizes a high-resolution approach, aiming to provide more precise and consistent fractional evaluations across diverse input types.

Highlights

Expanded Input Types for Fractional Targeting: The fractional targeting mechanism now supports Number and Boolean types as bucketing keys, in addition to the existing String support. This allows for more flexible and diverse input values when determining fractional distributions.
High-Resolution Fractional Bucketing: Implemented a new high-resolution fractional bucketing algorithm. This enhancement utilizes MurmurHash3 and bit shifting operations to provide more precise and consistent fractional evaluations, especially for large numbers.
Robust Number to Byte Array Conversion: Introduced a utility method, numberToByteArray, to consistently convert various numeric types (including Integer, Double, Long, BigInteger, Byte, Short, Float, and BigDecimal) into byte arrays. This ensures uniform input for the hashing function, improving reliability across different number representations.

Changelog

tools/flagd-core/src/main/java/dev/openfeature/contrib/tools/flagd/core/targeting/Fractional.java
- Updated the bucketBy variable type from String to byte[] to accommodate various input types.
- Added logic to convert Number and Boolean arguments into byte arrays for consistent hashing.
- Introduced a numberToByteArray helper method to handle conversions for different numeric types.
- Modified the distributeValue method to use a new high-resolution bucketing algorithm based on MurmurHash3 and bitwise operations.
- Adjusted the FractionProperty constructor's error message formatting.
tools/flagd-core/src/test/resources/fractional/boolean.json
- Added a new test case for boolean input in fractional targeting.
tools/flagd-core/src/test/resources/fractional/largeDouble.json
- Added a new test case for large double input in fractional targeting.
tools/flagd-core/src/test/resources/fractional/largeInt.json
- Added a new test case for large integer input in fractional targeting.
tools/flagd-core/src/test/resources/fractional/selfContainedFractionalB.json
- Modified the expected result in a fractional targeting test case.
tools/flagd-core/src/test/resources/fractional/string.json
- Added a new test case for string input in fractional targeting.

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chrfwow · 2026-03-12T14:20:59Z

tools/flagd-core/src/test/resources/fractional/selfContainedFractionalB.json

    ]
  ],
-  "result": "blue"
+  "result": "red"


In some cases, we will compute a different bucket now

chrfwow · 2026-03-12T14:21:24Z

Do we want more tests for this? I stuck to the current test suite

gemini-code-assist

Code Review

The pull request refactors the fractional targeting logic to support various input types (numbers, booleans) for bucketing by converting them to byte arrays and introduces a new numberToByteArray helper. The core bucketing algorithm was also revised to use an integer-based bit shift operation. Review comments highlight two key areas for improvement: the numberToByteArray method has a potential precision loss issue for BigDecimal and could be made more concise using ByteBuffer, and the bucketing logic has a subtle bug related to handling signed vs. unsigned integers from the MurmurHash3 function, which requires a bitmask for correct range mapping.

.../flagd-core/src/main/java/dev/openfeature/contrib/tools/flagd/core/targeting/Fractional.java

gemini-code-assist · 2026-03-12T14:26:20Z

.../flagd-core/src/main/java/dev/openfeature/contrib/tools/flagd/core/targeting/Fractional.java

+        long mmrHash = MurmurHash3.hash32x86(hashKey, 0, hashKey.length, 0);
+        int bucket = (int) (((mmrHash * totalWeight) >> 32) & 0xFFFFFFFFL);


The bucketing logic has a subtle issue with signed vs. unsigned integers. MurmurHash3.hash32x86 returns a signed int. To correctly use it for range mapping as an unsigned 32-bit value, it should be converted to a long using a bitmask to avoid sign extension. This ensures the bucketing is fair and consistent across different hash values.

long mmrHash = MurmurHash3.hash32x86(hashKey, 0, hashKey.length, 0) & 0xFFFFFFFFL; int bucket = (int) ((mmrHash * totalWeight) >> 32);

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

chrfwow · 2026-03-12T16:48:50Z

Idk why there are PMD errors, but I think they are unrelated and false positives

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

chrfwow · 2026-03-13T11:26:41Z

...gd-core/src/test/java/dev/openfeature/contrib/tools/flagd/core/targeting/FractionalTest.java

+            Integer.MIN_VALUE,
+            Integer.MIN_VALUE + 1
+    })
+    void edgeCasesDoNotThrow(int hash) throws JsonLogicException {


This only tests that we will find a bucket for edge case inputs, but it will not validate the correctness

removed, validated through the gherkin suite

chrfwow · 2026-03-13T11:27:36Z

...gd-core/src/test/java/dev/openfeature/contrib/tools/flagd/core/targeting/FractionalTest.java

+    }
+
+    @Test
+    void statistics() throws JsonLogicException {


This tests the statistical distribution. The test takes 340ms on my machine, I think we can live with it, but I can also delete or disable it if we want to

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

# Conflicts: # providers/flagd/src/test/java/dev/openfeature/contrib/providers/flagd/e2e/RunInProcessTest.java

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

chrfwow · 2026-03-16T16:13:22Z

tools/flagd-core/src/main/resources/flagd/schemas/flags.json

-  "type": "object",
-  "properties": {
-    "flags": {
+  "$ref": "#/definitions/providerConfig",


I don't understand why there are changes in this file. They seem to be auto-generated when running the flagd-core test target

could be that those are copied from the flagd-schema repo

Ya I think that's what it is - I believe it's coming from there.

I think maybe we should gitignore it?

it already is gitignored 🤔

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

chrfwow · 2026-03-17T07:02:42Z

Waiting for open-feature/flagd-testbed#340

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

.../flagd-core/src/main/java/dev/openfeature/contrib/tools/flagd/core/targeting/Fractional.java

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

Signed-off-by: Todd Baert <todd.baert@dynatrace.com>

toddbaert · 2026-03-18T16:18:43Z

@chrfwow there was some e2e test failures but I fixed them by updating to the latest git submodule in the testkit module, and adding the v1 exclusion to the file mode suite, and excluding v2 in the RPC suite (since flagd doesn't support this yet).

I will coordinate the release of flagd, then update the RPC suite here and release everything simultaneously.

Signed-off-by: Todd Baert <todd.baert@dynatrace.com>

high resolution fractional

ce6fab9

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

chrfwow requested a review from a team as a code owner March 12, 2026 14:20

chrfwow commented Mar 12, 2026

View reviewed changes

gemini-code-assist bot reviewed Mar 12, 2026

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chrfwow added 4 commits March 12, 2026 15:30

high resolution fractional

d42a51d

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

high resolution fractional

411d642

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

high resolution fractional

9586f8c

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

high resolution fractional

1ae9e2f

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

chrfwow marked this pull request as draft March 12, 2026 16:34

fix negative numbers

a14ed15

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

chrfwow marked this pull request as ready for review March 12, 2026 16:48

chrfwow marked this pull request as draft March 13, 2026 07:28

chrfwow added 2 commits March 13, 2026 12:24

fix bucketing algo

c5f4e15

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

fix bucketing algo

195a836

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

chrfwow commented Mar 13, 2026

View reviewed changes

fix bucketing algo

40c6ee7

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

chrfwow changed the title ~~feat: Add support for high resolution fractional~~ feat: Add support for high resolution fractional and arbitrary targeting key types Mar 13, 2026

chrfwow marked this pull request as ready for review March 13, 2026 11:52

aepfli mentioned this pull request Mar 16, 2026

test(fractional): add statistical distribution test mirroring Java PR #1740 open-feature/flagd-evaluator#29

Open

fix bucketing algo

f1a2ad1

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

aepfli mentioned this pull request Mar 16, 2026

feat(fractional): support nested JSON Logic expressions as bucket variant names open-feature/flagd-evaluator#31

Merged

chrfwow added 2 commits March 16, 2026 10:58

fix bucketing algo

4fda79b

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

fix bucketing algo

d1f4bdc

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

github-actions bot assigned beeme1mr, Kavindu-Dodan and thisthat Mar 16, 2026

github-actions bot assigned toddbaert Mar 16, 2026

github-actions bot requested review from Kavindu-Dodan, beeme1mr, thisthat and toddbaert March 16, 2026 10:39

chrfwow added 4 commits March 16, 2026 11:45

fix bucketing algo

a78a6c6

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

Merge branch 'main' into high-resolution-fractional

7295961

# Conflicts: # providers/flagd/src/test/java/dev/openfeature/contrib/providers/flagd/e2e/RunInProcessTest.java

fix stuff

602238c

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

fix stuff

3eee949

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

chrfwow commented Mar 16, 2026

View reviewed changes

use byte buffer

6738b17

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

chrfwow added 3 commits March 18, 2026 11:20

Merge branch 'main' into high-resolution-fractional

c8d7388

use fixed test bed

de038b2

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

use fixed test bed

16cb01c

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

toddbaert reviewed Mar 18, 2026

View reviewed changes

.../flagd-core/src/main/java/dev/openfeature/contrib/tools/flagd/core/targeting/Fractional.java Outdated Show resolved Hide resolved

remove arbitrary bucketing values

5413b01

Signed-off-by: christian.lutnik <christian.lutnik@dynatrace.com>

chrfwow changed the title ~~feat: Add support for high resolution fractional and arbitrary targeting key types~~ feat: Add support for high resolution fractional Mar 18, 2026

toddbaert added 2 commits March 18, 2026 11:52

fixup: update submodule

a282617

Signed-off-by: Todd Baert <todd.baert@dynatrace.com>

fixup: update exclusions

ec3aec4

Signed-off-by: Todd Baert <todd.baert@dynatrace.com>

fixup: spotless

b038afb

Signed-off-by: Todd Baert <todd.baert@dynatrace.com>

toddbaert self-requested a review March 18, 2026 17:43

		long mmrHash = MurmurHash3.hash32x86(hashKey, 0, hashKey.length, 0);
		int bucket = (int) (((mmrHash * totalWeight) >> 32) & 0xFFFFFFFFL);

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