After a day or two, our Jenkins master becomes very unresponsive, taking 100% CPU of all available cores. The response time drops to tens of seconds, or sometimes even minutes to load a single page.

Investigation with VisualVM shows much garbage collection taking place, with the heap nearly maxed out (at 1GB use of 1.25GB max). Looking at a heap snapshot, I discovered that the majority of memory is taken up by String[] objects, containing 5-tuples of Strings (referencing char[] arrays in turn). There are over a million of these small string arrays, each having contents similar to ["35300", "Size", "709", "1526866800302", ""].

Tracing the references of the objects reveals that they are held by the rawPlotData of MatrixPlotPublisher objects. rawPlotData is itself an array; a single sample object in our snapshot contains 106710 string arrays like the one above.

The most likely plot that's causing this is a CSVSeries plot tracking the size of ~7000 generated files (per matrix build). That's still several orders of magnitude less than the number of objects being built internally.