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Showing posts from March, 2013

HBase: MSLAB and CMS vs. ParallelGC

Tuning Java opts for HBase, for example, are necessary steps to get the best performance and stability in large installations. The optimal recommendation looks like: HBASE_OPTS="-XX:+UseParNewGC -XX:+UseConcMarkSweepGC -XX:CMSInitiatingOccupancyFraction=70 -XX:+CMSParallelRemarkEnabled" But you can also achieve great success with: HBASE_OPTS="-server -XX:+UseParallelGC XX:+UseParallelOldGC -XX:ParallelGCThreads=8" What are the differences between ParallelGC and CMS?   CMS uses more CPU, but runs concurrently. If a thread is failing, CMS falls back to a non-parallel mode and stops the VM for the entire time it's collecting. But this risk can be minimized by using MSLAB in your HBase configuration. ParallelGC have a better throughput and longer pause times, and stop the VM on every collection. Means for HBase, you'll have a pause (around 1 sec per GB), which can lead on high loaded clusters to outages in a non acceptable time range. MSLAB