Author: buildbot
Date: Sun Apr 12 01:05:23 2015
New Revision: 947258
Log:
Staging update by buildbot for mahout
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websites/staging/mahout/trunk/content/ (props changed)
websites/staging/mahout/trunk/content/users/environment/h2o-internals.html
Propchange: websites/staging/mahout/trunk/content/
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<h1 id="introduction">Introduction</h1>
-<p>This document provides an overview of how the Mahout Scala DSL (distributed
algebraic operators) is implemented over the H2O backend engine. The document
is aimed at Mahout developers, to give a high level description of the design
so that one can explore the code inside <code>h2o/</code> with some context.</p>
+<p>This document provides an overview of how the Mahout Samsara environment is
implemented over the H2O backend engine. The document is aimed at Mahout
developers, to give a high level description of the design so that one can
explore the code inside <code>h2o/</code> with some context.</p>
<h2 id="h2o-overview">H2O Overview</h2>
<p>H2O is a distributed scalable machine learning system. Internal
architecture of H2O has a distributed math engine (h2o-core) and a separate
layer on top for algorithms and UI. The Mahout integration requires only the
math engine (h2o-core).</p>
<h2 id="h2o-data-model">H2O Data Model</h2>
<p>The data model of the H2O math engine is a distributed columnar store (of
primarily numbers, but also strings). A column of numbers is called a Vector,
which is broken into Chunks (of a few thousand elements). Chunks are
distributed across the cluster based on a deterministic hash. Therefore, any
member of the cluster knows where a particular Chunk of a Vector is homed. Each
Chunk is separately compressed in memory and elements are individually
decompressed on the fly upon access with purely register operations (thereby
achieving high memory throughput). An ordered set of similarly partitioned Vecs
are composed into a Frame. A Frame is therefore a large two dimensional table
of numbers. All elements of a logical row in the Frame are guaranteed to be
homed in the same server of the cluster. Generally speaking, H2O works well on
"tall skinny" data, i.e, lots of rows (100s of millions) and modest number of
columns (10s of thousands).</p>
<h2 id="mahout-drm">Mahout DRM</h2>
-<p>The Mahout DRM, or Distributed Row Matrix, is an abstraction for storing a
large matrix of numbers in-memory in a cluster by distributing logical rows
among servers. The DSL provides an abstract API on DRMs for backend engines to
provide implementations of this API. Examples are the Spark and H2O backend
engines. Each engine has it's own design of mapping the abstract API onto its
data model and provides implementations for algebraic operators over that
mapping.</p>
-<h2 id="h2o-dsl-engine">H2O DSL Engine</h2>
+<p>The Mahout DRM, or Distributed Row Matrix, is an abstraction for storing a
large matrix of numbers in-memory in a cluster by distributing logical rows
among servers. Mahout's scala DSL provides an abstract API on DRMs for backend
engines to provide implementations of this API. Examples are the Spark and H2O
backend engines. Each engine has it's own design of mapping the abstract API
onto its data model and provides implementations for algebraic operators over
that mapping.</p>
+<h2 id="h2o-environment-engine">H2O Environment Engine</h2>
<p>The H2O backend implements the abstract DRM as an H2O Frame. Each logical
column in the DRM is an H2O Vector. All elements of a logical DRM row are
guaranteed to be homed on the same server. A set of rows stored on a server are
presented as a read-only virtual in-core Matrix (i.e BlockMatrix) for the
closure method in the <code>mapBlock(...)</code> API.</p>
<p>H2O provides a flexible execution framework called <code>MRTask</code>. The
<code>MRTask</code> framework typically executes over a Frame (or even a
Vector), supports various types of map() methods, can optionally modify the
Frame or Vector (though this never happens in the Mahout integration), and
optionally create a new Vector or set of Vectors (to combine them into a new
Frame, and consequently a new DRM).</p>
<h2 id="source-layout">Source Layout</h2>
