hbase-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Ted Yu <yuzhih...@gmail.com>
Subject Re: BlockCache for large scans.
Date Wed, 09 Apr 2014 14:07:00 GMT
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 <gortiz@pragsis.com> 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.

  • Unnamed multipart/alternative (inline, None, 0 bytes)
View raw message