Lag, Drag and Post-Mortem Heap Profiling

The context for this paper is functional computation by graph reduction. Our overall aim is more efficient use of memory. The specific topic is the detection of dormant cells in the live graph --- those retained in heap memory though not actually playing a useful role in computation. We describe a profiler that can identify heap consumption by such `useless' cells. Unlike heap profilers based on traversals of the live heap, this profiler works by examining cells post-mortem. Early experience with applications confirms our suspicions about space-efficiency: as usual, it is even worse than expected! 1 Introduction A typical computation by graph reduction involves a large and changing population of heap-memory cells. Taking a census of this population at regular intervals can be very instructive, both for functional programmers and for functionallanguage implementors. A heap profiler [RW93] records population counts for different classes of cells (eg. representing different values, creat..