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Last active August 29, 2015 14:05
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GC Notes
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Three Variables for GC

  1. Throughput: The amount of work done by an application as a ratio of time spent in GC.
‑XX:GCTimeRatio=99

means 99% of time spent on application computation, 1% spent in GC

  1. Latency: The time taken by systems in responding to events which is impacted by pauses introduced by GC. Target latency with the flag
‑XX:MaxGCPauseMillis=<n>
  1. Memory: The amount of memory used to store state. Maximum heap size is set via the flag
–Xmx<n>

Generations

(Eden -> Survivor) -> Tenured -> Perm (deprecated)

TLAB: Thread Local Allocation Buffer (mechanism through which threads request memory). When a TLAB is filled, a thread requests a new one from Eden.

When Eden is filled, a minor collection commences. During minor collection, all live objects are copied over to a Survivor space or promoted to Tenured space.

Helpful Flags

‑XX:+PrintGCApplicationStoppedTime: Prints out the time needed to bring all threads to a safe point for Stop-The-World event

– XX:MaxTenuringThreshold: Threshold for collections survived before being promoted to Tenured

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