Presizing and pretransitioning are run-time optimizations that avoid reallocations of resizable arrays. These optimizations were previously presented for VMs where the runtime optimizer can interact with the garbage collection system.

Dynamic language runtimes written for the GraalVM do not have access to the GC. These implementations cannot directly apply the prior work to optimize resizable arrays and alternative implementation strategies pose different challenges.

In this paper we explore and analyze one approach on how GraalVM languages could incorporate these optimizations, using the Python implementation for GraalVM as an example. We substantiate these thoughts with rough performance numbers taken from a prototype on which we tested different implementation approaches.