[CX] Error when running flush-bucket test case: HYR0088: Cannot modify index

I got test failure when running IntegrationTest/flush-bucket:

org.apache.hyracks.api.exceptions.HyracksDataException: HYR0088: Cannot modify index (Disk is full)

        at org.apache.hyracks.api.exceptions.HyracksDataException.create(HyracksDataException.java:49)

        at org.apache.hyracks.storage.am.lsm.common.impls.LSMHarness.ensureIndexModifiable(LSMHarness.java:690)

        at org.apache.hyracks.storage.am.lsm.common.impls.LSMHarness.getAndEnterComponents(LSMHarness.java:137)

        at org.apache.hyracks.storage.am.lsm.common.impls.LSMHarness.enter(LSMHarness.java:635)

        at org.apache.hyracks.storage.am.lsm.common.impls.LSMHarness.batchOperate(LSMHarness.java:656)

        at org.apache.hyracks.storage.am.lsm.common.impls.LSMTreeIndexAccessor.batchOperate(LSMTreeIndexAccessor.java:214)

        at org.apache.asterix.runtime.operators.LSMPrimaryUpsertOperatorNodePushable.nextFrame(LSMPrimaryUpsertOperatorNodePushable.java:280)

        at org.apache.asterix.external.feed.dataflow.SyncFeedRuntimeInputHandler.nextFrame(SyncFeedRuntimeInputHandler.java:46)

        at org.apache.asterix.external.operators.FeedMetaStoreNodePushable.nextFrame(FeedMetaStoreNodePushable.java:141)

        at org.apache.hyracks.control.nc.Task.pushFrames(Task.java:393)

        at org.apache.hyracks.control.nc.Task.run(Task.java:318)

        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)

        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)

        at java.lang.Thread.run(Thread.java:745)

There's enough disk space on my machine, so the message is misleading.

This is with spock build 5.0.0-4506