Raw pointers in C/C++ open up entire classes of error that are practically unimaginable in higher level languages. So why does anybody use them at all? Unfortunately, it’s impossible to write a profiler without getting close to some of the sharp edges of unsafe memory. The async-profiler code base contains a lot of low level tricks, and it’s worth studying how some of them work.
It can be hard to figure out why response times are high in Java applications. In my experience, people either apply a process of elimination to a set of recent commits, or might sometimes use profiles of the system to explain changes in metrics. Making guesses about recent commits can be frustrating for a number of reasons, but mostly because even if you pinpoint the causal change, you still…
When you open a profile in JMC, it normally takes a few seconds, but there are some profiles that JMC struggles to load. This happens when a profile contains events which violate an assumption made in JMC’s parser: events on the same thread are almost always disjoint in their durations. When JMC parses a JFR file, it splits the events of the same type emitted on the same thread into lanes so that…
I have just implemented support for (in)equality queries against a RangeBitmap, a succinct data structure in the RoaringBitmap library which supports range queries. RangeBitmap was designed to support range queries in Apache Pinot (more details here) but this enhancement would allow a range index to be used as a fallback for (in)equality queries in case nothing better is available. Supporting…
This post follows on from my last post about selecting objects satisfying a range predicate, and instead looks at how to count the objects. If you can select objects, you can count them too, but it’s a simpler problem so resources can be saved with a specialised solution.
Suppose you are doing some kind of data analysis in Java, perhaps you are analysing transactions (as in sales made). You have complex filters to evaluate before performing a calculation on Transaction objects.
Suppose you have an unsorted array of numeric values and need to find the set of indexes of all the values which are within a range. The range predicate will be evaluated many times, so any time spent preprocessing will be amortised, and non-zero spatial overhead is expected. If the data were sorted, this would be very easy, but the indexes of the values have meaning so the data cannot be sorted.…
My last post was about five very simple things you can do to avoid Java programs from being slower than they need to be. The reception to this post was mixed. Some readers agreed that the problems mentioned in the post were indeed very common, while others suggested more common inefficient patterns to avoid. For example, I could have suggested to precompile regular expressions, or not to program…
Most of the time it isn’t really necessary to optimise software, but this post contains 5 tips to avoid making software written in Java slower for the sake of it.
Loop fission is a process normally applied by a compiler to loops to make them faster. The idea is to split larger loop bodies which perform several distinct tasks into separate loops, in the hope that the individual loops can be optimised more effectively in isolation. As far as I’m aware, C2, Hotspot’s JIT compiler, doesn’t do this so you have to do it yourself. I came across a couple of cases…