How Memory Settings Impact IntelliJ IDEA Performance: A Practical Test

Goal

The author plans to test different memory settings of IntelliJ IDEA in a realistic development scenario (loading a large monolith project, several micro‑service modules, and refreshing after a git pull) to find the configuration that offers the best balance of memory consumption and speed.

Test Machine and Projects

MacBook Pro Retina, 2.3 GHz Intel Core i7, 16 GB DDR3, SSD, macOS Yosemite

Monolith project: ~700 k lines of Java 8 and Groovy code, 303 Gradle modules

Two micro‑service projects: each ~10‑20 k lines of Java 8 and Groovy, one Gradle module each

Test Scenario

Close all projects in IDEA

Apply a specific idea.vmoptions file

Reboot the computer

Close unrelated projects after IDE launch

Measure IDEA startup time

Open the large monolith project and record time

Run jstat -gcutil Open the two micro‑service projects and record time

Run jstat -gcutil Return to the monolith project, click “Refresh Gradle” and record time

Run

jstat -gcutil

jstat -gcutil

-gcutil

provides a summary of garbage‑collection statistics, including survivor space, Eden, old generation, metaspace utilization, and counts/times of young and full GC events.

S0     S1    E     O     M    CCS  YGC YGCT FGC  FGCT   GCT
89.70 0.00 81.26 74.27 95.68 91.76 40 2.444 14  0.715  3.159

The most important metrics for this article are the number of GC events (YGC, FGC) and their collection times (YGCT, FGCT).

Test Settings

Four configurations were defined:

Default (gray)

-Xms128m
-Xmx750m
-XX:MaxPermSize=350m
-XX:ReservedCodeCacheSize=240m
-XX:+UseCompressedOops

Big (red)

-Xms1024m
-Xmx4096m
-XX:ReservedCodeCacheSize=1024m
-XX:+UseCompressedOops

Balanced (blue)

-Xms2g
-Xmx2g
-XX:ReservedCodeCacheSize=1024m
-XX:+UseCompressedOops

Sophisticated (orange)

-server
-Xms2g
-Xmx2g
-XX:NewRatio=3
-Xss16m
-XX:+UseConcMarkSweepGC
-XX:+CMSParallelRemarkEnabled
-XX:ConcGCThreads=4
-XX:ReservedCodeCacheSize=240m
-XX:+AlwaysPreTouch
-XX:+TieredCompilation
-XX:+UseCompressedOops
-XX:SoftRefLRUPolicyMSPerMB=50
-Dsun.io.useCanonCaches=false
-Djava.net.preferIPv4Stack=true
-Djsse.enableSNIExtension=false
-ea

The idea.vmoptions file was placed in ~/Library/Preferences/IntelliJIdea15/ (or the equivalent path on other OSes).

Results

IDEA Startup Time

Startup time was consistently around 10 seconds for all configurations, indicating that early‑stage IDE launch is not affected by memory settings.

Loading the Large Project

The default configuration took roughly three times longer than the custom settings. GC activity was much higher under the default setting, causing long Full GC pauses.

Full GC time was up to 50 times longer with the default memory, making the IDE sluggish.

Opening Two Micro‑service Projects

The sophisticated setting performed best, while the default lagged behind.

Reloading the Monolith After Refresh

The default (gray) bar was extremely high because IDEA crashed during the refresh, confirming insufficient memory.

Among the custom configurations, the “Big” setting yielded the shortest reload time, showing that larger heap improves responsiveness.

Conclusion

The experiment demonstrates that even modest adjustments to IntelliJ IDEA’s JVM memory options can dramatically improve performance, especially for large codebases. Allocating 2 GB–3 GB of heap generally offers the best trade‑off between speed and memory consumption, though the exact optimum may vary per project.

Discussion

Readers are invited to share their own idea.vmoptions configurations and any additional techniques for boosting IntelliJ IDEA performance.