[CI] DataStreamLifecycleDownsampleIT testUpdateDownsampleSamplingMode failing

[elasticsearchmachine]

Build Scans:

• elasticsearch-periodic-platform-support #11425 / windows-2025_checkpart2_platform-support-windows
• elasticsearch-pull-request #104364 / part-2
• elasticsearch-pull-request #104046 / part-2
• elasticsearch-pull-request #103939 / part-2
• elasticsearch-pull-request #103442 / part-2
• elasticsearch-pull-request #103314 / part-2
• elasticsearch-pull-request #103273 / part-2

Reproduction Line:

gradlew ":x-pack:plugin:downsample:internalClusterTest" --tests "org.elasticsearch.xpack.downsample.DataStreamLifecycleDownsampleIT.testUpdateDownsampleSamplingMode" -Dtests.seed=E624B31ED29AEFAE -Dtests.locale=sr-Latn -Dtests.timezone=Europe/Podgorica -Druntime.java=25

Applicable branches:
main

Reproduces locally?:
N/A

Failure History:
See dashboard

Failure Message:

java.lang.AssertionError: safeGet: listener was completed exceptionally

Issue Reasons:

• [main] 7 failures in test testUpdateDownsampleSamplingMode (0.8% fail rate in 881 executions)
• [main] 6 failures in step part-2 (1.0% fail rate in 575 executions)
• [main] 6 failures in pipeline elasticsearch-pull-request (1.1% fail rate in 563 executions)

Note:
This issue was created using new test triage automation. Please report issues or feedback to es-delivery.

[elasticsearchmachine]

This has been muted on branch main

Mute Reasons:

• [main] 7 failures in test testUpdateDownsampleSamplingMode (0.8% fail rate in 881 executions)
• [main] 6 failures in step part-2 (1.0% fail rate in 575 executions)
• [main] 6 failures in pipeline elasticsearch-pull-request (1.1% fail rate in 563 executions)

Build Scans:

• elasticsearch-periodic-platform-support #11425 / windows-2025_checkpart2_platform-support-windows
• elasticsearch-pull-request #104364 / part-2
• elasticsearch-pull-request #104046 / part-2
• elasticsearch-pull-request #103939 / part-2
• elasticsearch-pull-request #103442 / part-2
• elasticsearch-pull-request #103314 / part-2
• elasticsearch-pull-request #103273 / part-2

[elasticsearchmachine]

Pinging @elastic/es-data-management (Team:Data Management)

[elasticsearchmachine]

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

[nielsbauman]

@gmarouli I assigned you since this relates to your work in #137023. I just had a quick look at some failures, and they all time out here:

elasticsearch/x-pack/plugin/downsample/src/internalClusterTest/java/org/elasticsearch/xpack/downsample/DataStreamLifecycleDownsampleIT.java

Lines 354 to 365 in b2d3b9b

	String downsampledPrefix = "downsample-10m-";
	final var waitForUpdatedDownsamplingRound = ClusterServiceUtils.addMasterTemporaryStateListener(clusterState -> {
	ProjectMetadata projectMetadata = clusterState.metadata().getProject();
	final var dataStream = projectMetadata.dataStreams().get(dataStreamName);
	if (dataStream == null) {
	return false;
	}
	return dataStream.getIndices().size() > 2
	&& dataStream.getIndices().stream().filter(index -> index.getName().startsWith(downsampledPrefix)).count() == 2;
	});
	safeAwait(waitForUpdatedDownsamplingRound);

While in the logs I see:

[2025-11-16T15:00:46,182][INFO ][o.e.d.l.DataStreamLifecycleService][node_s1][transport_worker][T#1] Data stream lifecycle successfully downsampled index [.ds-metrics-baz-2025.11.16-000002] to index [downsample-10m-.ds-metrics-baz-2025.11.16-000002]	
[2025-11-16T15:00:46,452][INFO ][o.e.x.d.DataStreamLifecycleDownsampleIT][testUpdateDownsampleSamplingMode] [DataStreamLifecycleDownsampleIT#testUpdateDownsampleSamplingMode]: cleaning up after test

That looks to me like DLM was still progressing; it just took longer than 10 seconds to complete everything. I don't expect there's much we can do to speed up the test, so I don't think we have much choice other than increasing the timeout (which matches what we're doing with other tests in this class). I'll open a PR to do so, but let me know if you have other thoughts.