Classic vs New UI Framework Heap Allocation Variance in Long-Running IntelliJ Sessions

Integration Boundary: UI Framework and JVM Memory Subsystem

IntelliJ IDEA 2024.1+ ships with two supported UI frameworks: the Classic UI based on Swing and the New UI built on a modernized rendering pipeline. Both frameworks share the same JVM heap managed by the JetBrains Runtime (JBR 17/21), yet exhibit divergent memory consumption profiles during extended indexing and editing sessions.

The precise goal is to characterize the allocation-rate difference between frameworks when processing large multi-module projects (>50k files) over sessions exceeding 8 hours. Constraints include the JBR vendor (JBR 17 vs JBR 21), GC algorithm (G1 vs ZGC), and whether the memory indicator reflects framework-specific overhead or shared indexing structures.

Uncertainty remains whether the variance stems from retained UI component references, differences in editor component pooling, or asynchronous indexing thread interactions unique to each framework.

• What allocation-rate delta (MB/hr) separates Classic and New UI under identical project load and JBR version?
• Does the variance persist when forcing identical GC settings (-XX:+UseG1GC) across both frameworks?
• Which heap regions (eden, survivor, old) show the strongest framework-specific growth pattern?