This short guide explains how legacy HBase clusters were tuned with JVM options for CMS and ParallelGC and how MemStore-Local Allocation Buffers (MSLAB) help reduce GC pauses caused by old-generation fragmentation. Use this as a reference if you still run JDK7/8-based HBase 0.92-era installations or are migrating them, not as guidance for modern Java and HBase versions. Note (2025): The GC flags in this article apply to older Java 7/8 HBase deployments where CMS and ParallelGC were common choices. In newer JVMs, the Concurrent Mark-Sweep (CMS) collector is deprecated and removed in favour of collectors like G1GC. Treat the configuration below as legacy tuning for old HBase stacks, not as recommendations for new clusters. Why HBase GC tuning mattered so much HBase region servers keep a lot of data in memory (memstores and block cache). Without careful JVM tuning, garbage collection can easily cause long pauses, region server timeouts and client-visible outages. Adjusting HBA...
Fractional Chief Architect for Big Data Systems & Distributed Data Processing