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About our C4 Garbage Collector

Azul’s C4, our Continuously Concurrent Compacting Collector is an updated generational form of the Pauseless Garbage Collector Algorithm described in 2005 at the First International Conference on Virtual Execution Environments and is one of the key technologies behind the Zing JVM.

C4 uses a read barrier to support:

  • Concurrent Compaction
  • Concurrent Remapping
  • Concurrent Incremental Update Tracing

Azul Systems Zing runtime has been shipping a production implementation of the C4 collector mechanism since 2010.

How C4 differentiates itself from other Garbage Collectors?

Support simultaneous-generational concurrency while others use concurrent mechanisms that can be simultaneously and independently active.

GC collectors that are concurrent but not generational remain experimental

Perform concurrent young generation collections, even during long periods of concurrent full heap collection.

GC collectors that are concurrent but not generational remain experimental

Sustain high allocation rates and maintain the efficiency typical to generational collectors, without sacrificing response times or reverting to stop-the-world operation.

One of the primary advantages of the C4 collector is the ability to adapt to a wide variety of use cases without the need for tuning. It is equally useful in web-facing/human-response-sensitive applications, in throughput-sensitive batch analytics, and in latency-sensitive applications like real-time risk analytics. C4 is also appropriate for memory configurations ranging anywhere from 512 MB to (as of this writing) 8 TB, although most production instances using Zing run in configurations supporting between 4GB and 256GB of memory.

Understanding Java GC

Understanding Java Garbage collection

Azul Pauseless Garbage Collection

Azul Pauseless Garbage Collection

The Continuously Concurrent Compacting Collector

C4: The Continuously Concurrent Compacting Collector

Java Runs Better with Zing®

Zing®  is the only JVM with pauseless garbage collection technology, ensuring fast startup and consistent high performance without GC pauses, jitter, or application timeouts.

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