How to Check What Garbage Collection Algorithm is Used by a Running JVM

• For Java version 8 and earlier:

Execute the following command: 

jmap -heap $(pidof java)

Example:

$ jmap -heap 10458
Attaching to process ID 2679, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.265-b01

using thread-local object allocation.
Mark Sweep Compact GC

From the above output, the GC algorithm used is: Mark Sweep Compact GC

• For Java version 9 and later:

jcmd <pid> VM.info | grep gc

Example:

jcmd 10459 VM.info | grep gc
# Java VM: OpenJDK 64-Bit Server VM Temurin-17.0.15+6 (17.0.15+6, mixed mode, tiered, compressed oops, compressed class ptrs, g1 gc, bsd-amd64)

From the above output, the GC algorithm used is: G1GC