[HBASE-15102] HeapMemoryTuner can "overtune" memstore size and suddenly drop it into blocking zone

• Type: Bug
• Status: Resolved
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 1.2.0, 1.3.0, 2.0.0
• Fix Version/s: 1.2.0, 1.3.0, 2.0.0
• Component/s: regionserver
• Hadoop Flags: Reviewed
• Assignee: Ashu Pachauri
• Reporter: Ashu Pachauri
• Created: 13/Jan/16 23:27
• Updated: 20/Jan/16 03:45
• Resolved: 19/Jan/16 20:54

Description

DefaultHeapMemoryTuner often resets the maximum step size for tuning to 8% of total heap size. Often, when the size of memstore is to be decreased while tuning, the 8% tuning can suddenly drop the memstore size below the low water mark of the previous memstore size (which could potentially be the used size of the memstore)
This is problematic because suddenly it blocks all the updates by suddenly causing a situation where memstore used size is above high water mark. This has a very bad performance impact on an otherwise fine HBase cluster.