Serial GC is very similar to Parallel GC except that it does all its work in a single thread. The single-threaded approach allows for a less complex GC implementation and requires very few external runtime data structures. The memory footprint is the lowest of all HotSpot collectors. The challenges with Serial GC are similar to those for Parallel GC. Pause times can be long, and they grow more or less linearly with the heap size and amount of live data. In addition, with Serial GC the long pauses are more pronounced, since the GC work is done in a single thread.
Because of the low memory footprint, Serial GC is the default on the Java HotSpot Client VM. It also addresses the requirements for many embedded use cases. Serial GC can be explicitly specified as the GC to use with the -XX:+UseSerialGC HotSpot command-line option.
Figure 1.2 illustrates how Java application threads (gray arrows) are stopped and a single GC thread (black arrow) takes over to do the garbage collection work on a machine running eight Java application threads. Because it is single-threaded, Serial GC in most cases will take longer to execute a GC event than Parallel GC since Parallel GC can spread out the GC work to multiple threads.
Figure 1.2 How Java application threads are interrupted by a single GC thread when Serial GC is used