[HBASE-16650] Wrong usage of BlockCache eviction stat for heap memory tuning

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.0.0
• Fix Version/s: 2.0.0
• Hadoop Flags: Incompatible change, Reviewed
• Release Note: Changed tracking of evictedBlocks count NOT to include evictions of blocks for a removed HFile. HFiles gets removed after compaction
• Assignee: Anoop Sam John
• Reporter: Anoop Sam John
• Created: 18/Sep/16 17:10
• Updated: 22/Sep/16 19:19
• Resolved: 22/Sep/16 16:02

Description

1. We use the stat evictedBlocksCount - A block can get evicted because of eviction thread due to lack of space or because of removal of an HFile itself (After a compaction). We should not consider the latter in the tune decision at all. These are actually invalidation of blocks. Should the stat counter itself not use this count of evicted blocks? I think yes. This will give wrong message to users that there are lot of real eviction happening.
2. In case L1+ L2 combined block cache, what we use is the sum of evictions from both. But we will be tuning L1 size alone. Eviction count from L2 should not affect the tuning of L1