The failing test test_storage_keeps_constant_memory_on_one_active_reader is asserting that memory usage should increase by less than 2000 bytes during 10,000 iterations, but it's actually increasing by 65,536 bytes.

Root Cause: The DeltaStorage class is not properly cleaning up or releasing memory for inactive readers. When only reader 0 is active (calling collect(0)), the storage should not accumulate data for reader 1 (which is never collected).

The Issue at Line 127:

PHP
$this->assertLessThan(2000, memory_get_usage() - $memory);
The test expects constant memory with only one active reader, but memory is growing by 65,536 bytes (approximately 64KB), suggesting that metrics data is being retained for the inactive reader instead of being released after collection.

Fix for DeltaStorage:

The DeltaStorage class needs to implement logic that removes metrics from readers that have collected them. When a reader collects a delta, if that reader is the only one who hasn't collected yet, the metric should be purged from storage.

Key changes needed in the DeltaStorage implementation:

Track which readers have collected each metric version
Remove metrics once all active readers have collected them
Ensure proper cleanup to prevent memory accumulation
The test validates that with only one active reader consistently collecting, the memory footprint remains stable. The current implementation is likely keeping historical metric data that should be discarded once a reader has accessed it.

Verification: After fixing the storage cleanup logic, the memory growth during 10,000 iterations with only one active reader should remain under 2000 bytes, confirming that old data is properly released.