presto-main/src/main/java/io/prestosql/operator/aggregation/KeyValuePairs.java/KeyValuePairs/estimatedInMemorySize
class KeyValuePairs:    public long estimatedInMemorySize()
    {
        long size = INSTANCE_SIZE;
        size += keyBlockBuilder.getRetainedSizeInBytes();
        size += valueBlockBuilder.getRetainedSizeInBytes();
        size += sizeOf(keyPositionByHash);
        return size;
    }