IBM User Guide for Java V7 on Windows > IBM SDK for Java > The collector and the allocator > Global garbage collection > Sweep phase

Parallel bitwise sweep

Parallel bitwise sweep improves the sweep time by using available processors. In parallel bitwise sweep, the Garbage Collector uses the same helper threads that are used in parallel mark, so the default number of helper threads is also the same and can be changed with the -Xgcthreads option.

The heap is divided into sections of 256 KB and each thread (helper or master) takes a section at a time and scans it, performing a modified bitwise sweep. The results of this scan are stored for each section. When all sections have been scanned, the freelist is built.

With the Balanced Garbage Collection policy, -Xgcpolicy:balanced, the Java™ heap is divided into approximately 1000 sections, providing a granular base for the parallel bitwise sweep.

Parent: Sweep phase

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