That's nice - I'd encourage you to play around with attaching e.g. JMC [1] to the process to better understand why things are as they are.
I tried recreating your DataInputStream + BufferedInputStream (wrote the 1brc data to separate output files, read using your code - I had to guess at ResultObserver implementation though). On my machine it roughly in the same time frame as yours - ~1min.
According to Flight Recorder:
- ~49% of the time is spent in reading the strings (city names). Almost all of it in the DataInputStream.readUTF/readFully methods.
- ~5% of the time is spent reading temperature (readShort)
- ~41% of the time is spent doing hashmap look-ups for computeIfAbsent()
- About 50GB of memory is allocated - %99.9 of it for Strings (and the wrapped byte[] array in them). This likely causes quite a bit of GC pressure.
Hash-map lookups are not de-serialization, yet the lookup likely affected the benchmarks quite a bit. The rest of the time is mostly spent in reading and allocating strings. I would guess that that is true for some of the other implementations in the original post as well.
I tried recreating your DataInputStream + BufferedInputStream (wrote the 1brc data to separate output files, read using your code - I had to guess at ResultObserver implementation though). On my machine it roughly in the same time frame as yours - ~1min.
According to Flight Recorder:
Hash-map lookups are not de-serialization, yet the lookup likely affected the benchmarks quite a bit. The rest of the time is mostly spent in reading and allocating strings. I would guess that that is true for some of the other implementations in the original post as well.[1] https://github.com/openjdk/jmc
edit: better link to JMC