The Jira says it's enabled by auto. Is there an official explaining this feature?
On Wednesday, April 9, 2014, Ted Yu <yuzhih...@gmail.com> wrote: > 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 <gor...@pragsis.com <javascript:;>> > 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. > > > > >
