For increment workloads, retain memstores in memory after flushing them
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Key: HBASE-3327
URL: https://issues.apache.org/jira/browse/HBASE-3327
Project: HBase
Issue Type: Improvement
Components: regionserver
Reporter: Karthik Ranganathan
This is an improvement based on our observation of what happens in an increment
workload. The working set is typically small and is contained in the memstores.
1. The reason the memstores get flushed is because the number of wal logs limit
gets hit.
2. This in turn triggers compactions, which evicts the block cache.
3. Flushing of memstore and eviction of the block cache causes disk reads for
increments coming in after this because the data is no longer in memory.
We could solve this elegantly by retaining the memstores AFTER they are flushed
into files. This would mean we can quickly populate the new memstore with the
working set of data from memory itself without having to hit disk. We can
throttle the number of such memstores we retain, or the memory allocated to it.
In fact, allocating a percentage of the block cache to this would give us a
huge boost.
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