Why it matters

GC pauses hurt HBase p99. Off-heap avoids. Understanding shapes tuning at scale.

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The architecture

On-heap: Java-managed, GC-affected.

Off-heap: direct memory, GC-free but slower access.

HBase off-heapOn-heap cacheGC-affectedOff-heap (BucketCache)no GCOff-heap memstorenewerCombined mode: hot data on-heap, warm off-heap; balances speed + GC
Off-heap tiers.
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How it works end to end

BucketCache modes: heap, offheap, file (SSD).

Combined LRU + BucketCache: hot on-heap, warm off-heap.

Off-heap memstore (newer): reduces heap pressure further.