presto-main/src/main/java/io/prestosql/operator/project/MergingPageOutput.java/MergingPageOutput/getRetainedSizeInBytes
class MergingPageOutput:    public long getRetainedSizeInBytes()
    {
        long retainedSizeInBytes = INSTANCE_SIZE;
        retainedSizeInBytes += pageBuilder.getRetainedSizeInBytes();
        for (Page page : outputQueue) {
            retainedSizeInBytes += page.getRetainedSizeInBytes();
        }
        return retainedSizeInBytes;
    }