presto-memory-context/src/main/java/io/prestosql/memory/context/AbstractAggregatedMemoryContext.java/AbstractAggregatedMemoryContext/toString
class AbstractAggregatedMemoryContext:    @Override
    public synchronized String toString()
    {
        return toStringHelper(this)
                .add("usedBytes", usedBytes)
                .add("closed", closed)
                .toString();
    }