jlangevin at loomlearning.com
Mon Jul 4 10:33:38 EDT 2011
Thanks Justin for the helpful response :-)
Can you define what you would consider "huge" regarding # keys?
Wilmington, NC: (910) 241-0433 - jlangevin at loomlearning.com -
www.loomlearning.com - Skype: intel352
On Mon, Jul 4, 2011 at 10:14 AM, Justin Sheehy <justin at basho.com> wrote:
> Hi, Jonathan.
> On Mon, Jul 4, 2011 at 9:42 AM, Jonathan Langevin
> <jlangevin at loomlearning.com> wrote:
> > I've seen users show concern of Bitcask's space usage overhead. How does
> > compare against LevelDB?
> Bitcask doesn't have much in the way of disk space "overhead" unless
> you mean that the space used by deleted or overwritten values is not
> reclaimed until after a merge. In that way LevelDB is similar since
> space used by deleted and overwritten items is reclaimed as they are
> moved into older "levels" of the DB. The behavior here is not
> identical, but similar in concept.
> By way of comparison, InnoDB imposes about a 2x space overhead cost on
> many common datasets but the overhead is usually fairly static.
> > If using a Level backend, what advantages do we lose of Bitcask? ls
> replication &
> > availability an issue at all?
> The functionality provided by Riak above the storage engines (such as
> replication and system-wide availability) are generally not impacted
> by your choice of storage engine.
> There are two main things you would lose today:
> 1 - latency
> 2 - stability
> The first of these is fundamental: for many usage patterns Bitcask
> will have a latency advantage over LevelDB due to being able to
> guarantee that it will never perform more than a single disk seek per
> The second is just about the relative immaturity of LevelDB: we have
> not yet seen LevelDB in production environments for an extended amount
> of time as we have with Bitcask. Anyone using it now as a Bitcask
> replacement should realize that they are on the leading edge and
> taking the usual risks that come with adopting new software. That
> said, we expect LevelDB to do well over time as one of the alternative
> Riak storage engines.
> The main reason to use LevelDB under Riak would be if your number of
> keys is huge and thus the RAM consumption of Bitcask would make it
> unsuitable. That is, we expect people to use LevelDB in the same
> situations that they might previously have chosen Innostore as their
> storage engine.
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