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Incrementing large numbers
Nov. 29th, 2017 08:16 amAt work I program in Java 7 mostly. I was asked to add some statistics-gathering to some code that gets called a lot so performance is key. After some initial test runs, back-of-the-envelope calculations about for how long our servers may run, etc., I did not feel safe in assuming that even a eight-byte long counter would never wrap around. In practice, I do not think a production server facing a continuously heavy workload during many years' uptime would come close to overflowing my long but I am used to having so much margin to work with that I do not even have to think about the issue.
A surprising discovery for me is that Java 7 does not offer efficient incrementing of arbitrarily large integers. Coming from a functional programming background I appreciate immutable values but I also appreciate compilers that can optimize much of the heap allocation out of the native code they generate. I have far less faith in what Java does, or indeed may do, with BigInteger, and people on the Internet already seem to have done some performance testing.
Fortunately, not all surprising discoveries are bad. It also turns out to be easy to increment an arbitrarily large integer with few heap allocations by storing it as a byte array, here named count: ( Java code. ) To log the statistic readably it suffices to return new BigInteger(1, count).
A surprising discovery for me is that Java 7 does not offer efficient incrementing of arbitrarily large integers. Coming from a functional programming background I appreciate immutable values but I also appreciate compilers that can optimize much of the heap allocation out of the native code they generate. I have far less faith in what Java does, or indeed may do, with BigInteger, and people on the Internet already seem to have done some performance testing.
Fortunately, not all surprising discoveries are bad. It also turns out to be easy to increment an arbitrarily large integer with few heap allocations by storing it as a byte array, here named count: ( Java code. ) To log the statistic readably it suffices to return new BigInteger(1, count).
