CompositeSyntheticFieldLoader tweak

[martijnvg]

SourceLoader.SyntheticFieldLoader#write(...) is hot code, avoid using streams api and use loop and compute sum.

[elasticsearchmachine]

Pinging @elastic/es-storage-engine (Team:StorageEngine)

[martijnvg]

@elasticmachine update branch

[martijnvg]

Failed because:

[2025-05-26T19:10:08,074][WARN ][o.e.x.m.i.l.ModelLoadingService] [yamlRestTest-0] [a-classification-model] failed to load model definition
org.elasticsearch.ResourceNotFoundException: Could not find trained model definition [a-classification-model]
	at org.elasticsearch.xpack.ml.inference.persistence.TrainedModelProvider.lambda$getTrainedModelForInference$16(TrainedModelProvider.java:599) ~[?:?]
	at org.elasticsearch.xpack.ml.inference.persistence.ChunkedTrainedModelRestorer.doSearch(ChunkedTrainedModelRestorer.java:162) ~[?:?]
	at org.elasticsearch.xpack.ml.inference.persistence.ChunkedTrainedModelRestorer.lambda$restoreModelDefinition$0(ChunkedTrainedModelRestorer.java:134) ~[?:?]
	at org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingRunnable.run(ThreadContext.java:977) ~[elasticsearch-9.1.0-SNAPSHOT.jar:?]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1095) ~[?:?]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:619) ~[?:?]
	at java.lang.Thread.run(Thread.java:1447) ~[?:?]
[2025-05-26T19:10:08,093][ERROR][o.e.b.ElasticsearchUncaughtExceptionHandler] [yamlRestTest-0] fatal error in thread [elasticsearch[yamlRestTest-0][ml_utility][T#3]], exiting
java.lang.AssertionError: Used bytes: [-520] must be >= 0
	at org.elasticsearch.common.breaker.ChildMemoryCircuitBreaker.addWithoutBreaking(ChildMemoryCircuitBreaker.java:207) ~[elasticsearch-9.1.0-SNAPSHOT.jar:?]
	at org.elasticsearch.xpack.ml.inference.loadingservice.ModelLoadingService.lambda$loadModel$10(ModelLoadingService.java:489) ~[?:?]
	at org.elasticsearch.action.ActionListenerImplementations.safeAcceptException(ActionListenerImplementations.java:78) ~[elasticsearch-9.1.0-SNAPSHOT.jar:?]
	at org.elasticsearch.action.ActionListener$2.onFailure(ActionListener.java:266) ~[elasticsearch-9.1.0-SNAPSHOT.jar:?]
	at org.elasticsearch.xpack.ml.inference.persistence.TrainedModelProvider.lambda$getTrainedModelForInference$16(TrainedModelProvider.java:601) ~[?:?]
	at org.elasticsearch.xpack.ml.inference.persistence.ChunkedTrainedModelRestorer.doSearch(ChunkedTrainedModelRestorer.java:162) ~[?:?]
	at org.elasticsearch.xpack.ml.inference.persistence.ChunkedTrainedModelRestorer.lambda$restoreModelDefinition$0(ChunkedTrainedModelRestorer.java:134) ~[?:?]
	at org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingRunnable.run(ThreadContext.java:977) ~[elasticsearch-9.1.0-SNAPSHOT.jar:?]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1095) ~[?:?]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:619) ~[?:?]
	at java.lang.Thread.run(Thread.java:1447) ~[?:?]

This is unrelated to this change, so updating branch and see if that addresses that CI failure.

[elasticsearchmachine]

💚 Backport successful

Status	Branch	Result
✅	8.19