Please take a look at http://www.n10k.com/blog/blockcache-101/
For D, hbase.regionserver.global.memstore.size is specified in terms of percentage of heap. Unless you enable HBASE-5349 'Automagically tweak global memstore and block cache sizes based on workload' On Wed, Apr 9, 2014 at 12:24 AM, gortiz <[email protected]> wrote: > I've been reading the book definitive guide and hbase in action a little. > I found this question from Cloudera that I'm not sure after looking some > benchmarks and documentations from HBase. Could someone explain me a little > about? . I think that when you do a large scan you should disable the > blockcache becuase the blocks are going to swat a lot, so you didn't get > anything from cache, I guess you should be penalized since you're spending > memory, calling GC and CPU with this task. > > *You want to do a full table scan on your data. You decide to disable > block caching to see if this** > **improves scan performance. Will disabling block caching improve scan > performance?* > > A. > No. Disabling block caching does not improve scan performance. > > B. > Yes. When you disable block caching, you free up that memory for other > operations. With a full > table scan, you cannot take advantage of block caching anyway because your > entire table won't fit > into cache. > > C. > No. If you disable block caching, HBase must read each block index from > disk for each scan, > thereby decreasing scan performance. > > D. > Yes. When you disable block caching, you free up memory for MemStore, > which improves, > scan performance. > >
