Eclipse and IntelliJ are the two competing IDEs in the industry. There are lot of passionate discussion going in the social media, forums to declare the winner in this race. We thought it would be a fun exercise to study which IDE utilizes memory efficiently?


To conduct this study, we used Eclipse Java EE Oxygen Release Milestone 2(4.7.0 M2) and IntelliJ IDEA 2018.2.4 (Ultimate Edition).  Both IDEs were running on Java 8.

To conduct this study effectively, we wanted to activate various features of the IDE. Thus, we ended up creating a simple Java project. In this project we created a JSP page, Manager class, DAO class which will write and read records from MySQL database. We were writing source code, compiling it, running unit tests to validate the behavior. It took us 1 hour and 45 minutes to do these activities. We conducted exact same exercise in both Eclipse and IntelliJ IDE.

How to study memory efficiency?

One of the best ways to study memory behavior of an application is to analyze garbage collection activity. Garbage collection activity would clearly show memory utilization pattern, object creation rate, object reclamation rate, Garbage collection pause time and other memory related details in nirvana.

How to study Garbage Collection activity?

Garbage collection activity can be studied by enabling Garbage Collection logs and using right tools to analyze Garbage collection logs. Garbage collection logs can be enabled by passing following JVM arguments:




For this exercise we used GCeasy tool to analyze garbage collection logs.

In the folder where Eclipse is installed there is eclipse.ini file. Its contents were looking like this:





















At the bottom of this file we added following arguments to enable garbage collection logs of the Eclipse IDE.




In folder where IntelliJ is installed you will notice idea64.exe.vmoptions file. Its contents were looking like this:










At the bottom of this file we added following arguments to enable garbage collection logs of the IntelliJ IDE.




NOTE: By default, IntelliJ initial heap size is kept as 128mb and max heap size is set to 750mb. Whereas Eclipse initial heap size was set to 256mb and max heap size set to 1024mb. Thus, to make apples to apples comparison we bumped up IntelliJ’s initial heap size to 256mb and max heap size to 1024mb.

Memory Behavior Comparison

Once our 1 hour and 45 minutes exercise was complete, we uploaded the garbage collection log file generated by both IDEs to GCeasy tool. Below are the detailed analysis reports generated by the tool. We encourage you to look at the report:

  1. Eclipse GC analysis report
  2. IntelliJ GC analysis report
eclipse-memory (3)
Fig: Eclipse IDE memory usage
intelliJ-memory (2)
Fig: IntelliJ IDE memory usage

Below key observations from the GC analysis report:

Object Creation RateEclipseIntelliJ
Object Creation Rate2.41 MB/sec69.65 MB/sec
Avg. GC Pause Time33 ms8 ms
Max. GC Pause Time340 ms270 ms
GC Throughput99.924%99.146%
GC AlgorithmG1 GCCMS GC
Is System.gc() invoke?YesNo

#1. Object Creation Rate

Apparently Eclipse created very small number of objects when compared to IntelliJ. Eclipse IDE was creating objects at the rate of 2.41 MB/sec, whereas IntelliJ was creating objects are the rate of 69.65 MB/sec (which is like 29x more than Eclipse). For the entire run Eclipse created only 15.19 GB, where IntelliJ created 430.2 GB of objects. Since more objects were created, CPU consumption was also higher when using the IntelliJ IDE.

#2. GC Pause Time

During certain phases of garbage collection entire application is paused. Apparently, Eclipse’s average GC pause time is 33 ms and max GC pause time is 340 ms. On the other hand, IntelliJ’s average GC pause time is only 8 ms and max GC pause time is 270 ms. Thus, in terms of GC Pause IntelliJ is comparatively better. Even though IntelliJ’s object creation rate is higher, however its average pause time is comparatively better than Eclipse because of better GC tuning done in IntelliJ.

#3. GC Throughput

GC Throughput is basically the amount of time your application spends in processing customer’s transactions vs amount of time your application spends in Garbage collection. In our study, Eclipse throughput is 99.924%, whereas IntelliJ’s through is 99.146%. Eclipse GC throughput is better than IntelliJ’s throughput.

#4. GC Algorithm

One of the primary reasons for GC pause time is influenced by the Garbage Collection algorithm and settings. Eclispe was configured to run with G1 GC algorithm, whereas IntelliJ was configured to run with CMS GC algorithm. Given that Eclipse is creating much less objects, with proper GC tuning, we believe Eclipse GC pause time can be reduced further.

#5. System.gc() calls

Apparently Eclispe IDE is issuing System.gc() calls explicitly. Unless there is a necessity, it’s not recommended to issue System.gc() from the application, as it muddles with JVM GC activity. It’s unclear why Eclipse IDE is explicitly issuing System.gc() calls.


Based on this limited study that we conducted, we can say that Eclipse IDE is memory efficient than IntelliJ, because to do same amount of work, IntelliJ is creating 29x more objects than Eclipse. On the other hand, IntelliJ’s pauses times are comparatively better than Eclipse. Of course, we believe that IDE selection shouldn’t be based on memory efficiency. It should be based on feature set, user preference and productivity criteria.

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