The problem with the article is Amdahl's law: he is speeding up the part of the code that takes a small fraction of the time and handwaving the bottleneck that

The problem with the article is Amdahl's law: he is speeding up the part of the code that takes a small fraction of the time and handwaving the bottleneck that takes most of the time. "Currently the bottleneck is writing to the file system..." (and then the rest of the paragraph makes no sense at all). "We cannot do writing to disk from several threads for the following reasons..." - so his threading speeds up everything except the bottleneck that takes all the time.