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From omal...@apache.org
Subject svn commit: r1079233 - /hadoop/mapreduce/branches/yahoo-merge/src/docs/src/documentation/content/xdocs/gridmix.xml
Date Tue, 08 Mar 2011 05:58:41 GMT
Author: omalley
Date: Tue Mar  8 05:58:40 2011
New Revision: 1079233

URL: http://svn.apache.org/viewvc?rev=1079233&view=rev
Log:
commit dd3c532c7ff128b6de9ec0983c513a4a377a6e14
Author: Ranjit Mathew <ranjit@yahoo-inc.com>
Date:   Wed Dec 22 10:47:15 2010 +0530

    MAPREDUCE-1931: Update GridMix3 documentation.

Modified:
    hadoop/mapreduce/branches/yahoo-merge/src/docs/src/documentation/content/xdocs/gridmix.xml

Modified: hadoop/mapreduce/branches/yahoo-merge/src/docs/src/documentation/content/xdocs/gridmix.xml
URL: http://svn.apache.org/viewvc/hadoop/mapreduce/branches/yahoo-merge/src/docs/src/documentation/content/xdocs/gridmix.xml?rev=1079233&r1=1079232&r2=1079233&view=diff
==============================================================================
--- hadoop/mapreduce/branches/yahoo-merge/src/docs/src/documentation/content/xdocs/gridmix.xml
(original)
+++ hadoop/mapreduce/branches/yahoo-merge/src/docs/src/documentation/content/xdocs/gridmix.xml
Tue Mar  8 05:58:40 2011
@@ -15,150 +15,542 @@
   See the License for the specific language governing permissions and
   limitations under the License.
 -->
-
 <!DOCTYPE document PUBLIC "-//APACHE//DTD Documentation V2.0//EN" "http://forrest.apache.org/dtd/document-v20.dtd">
-
 <document>
-
-<header>
-  <title>Gridmix</title>
-</header>
-
-<body>
-
-  <section>
-  <title>Overview</title>
-
-  <p>Gridmix is a benchmark for live clusters. It submits a mix of synthetic
-  jobs, modeling a profile mined from production loads.</p>
-
-  <p>There exist three versions of the Gridmix tool. This document discusses
-  the third (checked into contrib), distinct from the two checked into the
-  benchmarks subdirectory. While the first two versions of the tool included
-  stripped-down versions of common jobs, both were principally saturation
-  tools for stressing the framework at scale. In support of a broader range of
-  deployments and finer-tuned job mixes, this version of the tool will attempt
-  to model the resource profiles of production jobs to identify bottlenecks,
-  guide development, and serve as a replacement for the existing gridmix
-  benchmarks.</p>
-
-  </section>
-
-  <section id="usage">
-
-  <title>Usage</title>
-
-  <p>To run Gridmix, one requires a job trace describing the job mix for a
-  given cluster. Such traces are typically genenerated by Rumen (see related
-  documentation). Gridmix also requires input data from which the synthetic
-  jobs will draw bytes. The input data need not be in any particular format,
-  as the synthetic jobs are currently binary readers. If one is running on a
-  new cluster, an optional step generating input data may precede the run.</p>
-
-  <p>Basic command line usage:</p>
-<source>
-
-bin/mapred org.apache.hadoop.mapred.gridmix.Gridmix [-generate &lt;MiB&gt;] &lt;iopath&gt;
&lt;trace&gt;
-</source>
-
-  <p>The <code>-generate</code> parameter accepts standard units, e.g.
-  <code>100g</code> will generate 100 * 2<sup>30</sup> bytes. The
-  &lt;iopath&gt; parameter is the destination directory for generated and/or
-  the directory from which input data will be read. The &lt;trace&gt;
-  parameter is a path to a job trace. The following configuration parameters
-  are also accepted in the standard idiom, before other Gridmix
-  parameters.</p>
-
-  <section>
-  <title>Configuration parameters</title>
-  <p></p>
-  <table>
-    <tr><th> Parameter </th><th> Description </th><th>
Notes </th></tr>
-    <tr><td><code>gridmix.output.directory</code></td>
-        <td>The directory into which output will be written. If specified, the
-        <code>iopath</code> will be relative to this parameter.</td>
-        <td>The submitting user must have read/write access to this
-        directory. The user should also be mindful of any quota issues that
-        may arise during a run.</td></tr>
-    <tr><td><code>gridmix.client.submit.threads</code></td>
-        <td>The number of threads submitting jobs to the cluster. This also
-        controls how many splits will be loaded into memory at a given time,
-        pending the submit time in the trace.</td>
-        <td>Splits are pregenerated to hit submission deadlines, so
-        particularly dense traces may want more submitting threads. However,
-        storing splits in memory is reasonably expensive, so one should raise
-        this cautiously.</td></tr>
-    <tr><td><code>gridmix.client.pending.queue.depth</code></td>
-        <td>The depth of the queue of job descriptions awaiting split
-        generation.</td>
-        <td>The jobs read from the trace occupy a queue of this depth before
-        being processed by the submission threads. It is unusual to configure
-        this.</td></tr>
-    <tr><td><code>gridmix.min.key.length</code></td>
-        <td>The key size for jobs submitted to the cluster.</td>
-        <td>While this is clearly a job-specific, even task-specific property,
-        no data on key length is currently available. Since the intermediate
-        data are random, memcomparable data, not even the sort is likely
-        affected. It exists as a tunable as no default value is appropriate,
-        but future versions will likely replace it with trace data.</td></tr>
-  </table>
-
-  </section>
-</section>
-
-<section id="assumptions">
-
-  <title>Simplifying Assumptions</title>
-
-  <p>Gridmix will be developed in stages, incorporating feedback and patches
-  from the community. Currently, its intent is to evaluate Map/Reduce and HDFS
-  performance and not the layers on top of them (i.e. the extensive lib and
-  subproject space). Given these two limitations, the following
-  characteristics of job load are not currently captured in job traces and
-  cannot be accurately reproduced in Gridmix.</p>
-
-  <table>
-  <tr><th>Property</th><th>Notes</th></tr>
-  <tr><td>CPU usage</td><td>We have no data for per-task CPU usage,
so we
-  cannot attempt even an approximation. Gridmix tasks are never CPU bound
-  independent of I/O, though this surely happens in practice.</td></tr>
-  <tr><td>Filesystem properties</td><td>No attempt is made to match
block
-  sizes, namespace hierarchies, or any property of input, intermediate, or
-  output data other than the bytes/records consumed and emitted from a given
-  task. This implies that some of the most heavily used parts of the system-
-  the compression libraries, text processing, streaming, etc.- cannot be
-  meaningfully tested with the current implementation.</td></tr>
-  <tr><td>I/O rates</td><td>The rate at which records are consumed/emitted
is
-  assumed to be limited only by the speed of the reader/writer and constant
-  throughout the task.</td></tr>
-  <tr><td>Memory profile</td><td>No data on tasks' memory usage over
time is
-  available, though the max heap size is retained.</td></tr>
-  <tr><td>Skew</td><td>The records consumed and emitted to/from a
given task
-  are assumed to follow observed averages, i.e. records will be more regular
-  than may be seen in the wild. Each map also generates a proportional
-  percentage of data for each reduce, so a job with unbalanced input will be
-  flattened.</td></tr>
-  <tr><td>Job failure</td><td>User code is assumed to be correct.</td></tr>
-  <tr><td>Job independence</td><td>The output or outcome of one job
does not
-  affect when or whether a subsequent job will run.</td></tr>
-  </table>
-
-</section>
-
-<section>
-
-  <title>Appendix</title>
-
-  <p>Issues tracking the implementations of <a
-  href="https://issues.apache.org/jira/browse/HADOOP-2369">gridmix1</a>, <a
-  href="https://issues.apache.org/jira/browse/HADOOP-3770">gridmix2</a>, and
-  <a href="https://issues.apache.org/jira/browse/MAPREDUCE-776">gridmix3</a>.
-  Other issues tracking the development of Gridmix can be found by searching
-  the Map/Reduce <a
-  href="https://issues.apache.org/jira/browse/MAPREDUCE">JIRA</a></p>
-
-</section>
-
-</body>
-
+  <header>
+    <title>GridMix</title>
+  </header>
+  <body>
+    <section id="overview">
+      <title>Overview</title>
+      <p>GridMix is a benchmark for Hadoop clusters. It submits a mix of
+      synthetic jobs, modeling a profile mined from production loads.</p>
+      <p>There exist three versions of the GridMix tool. This document
+      discusses the third (checked into <code>src/contrib</code>), distinct
+      from the two checked into the <code>src/benchmarks</code> sub-directory.
+      While the first two versions of the tool included stripped-down versions
+      of common jobs, both were principally saturation tools for stressing the
+      framework at scale. In support of a broader range of deployments and
+      finer-tuned job mixes, this version of the tool will attempt to model
+      the resource profiles of production jobs to identify bottlenecks, guide
+      development, and serve as a replacement for the existing GridMix
+      benchmarks.</p>
+      <p>To run GridMix, you need a MapReduce job trace describing the job mix
+      for a given cluster. Such traces are typically generated by Rumen (see
+      Rumen documentation). GridMix also requires input data from which the
+      synthetic jobs will be reading bytes. The input data need not be in any
+      particular format, as the synthetic jobs are currently binary readers.
+      If you are running on a new cluster, an optional step generating input
+      data may precede the run.</p>
+      <p>In order to emulate the load of production jobs from a given cluster
+      on the same or another cluster, follow these steps:</p>
+      <ol>
+	<li>Locate the job history files on the production cluster. This
+	location is specified by the
+	<code>mapreduce.jobtracker.jobhistory.completed.location</code>
+	configuration property of the cluster.</li>
+	<li>Run Rumen to build a job trace in JSON format for all or select
+	jobs.</li>
+	<li><em>(Optional)</em> Use Rumen to fold this job trace to scale
+	the load.</li>
+	<li>Use GridMix with the job trace on the benchmark cluster.</li>
+      </ol>
+      <p>Jobs submitted by GridMix have names of the form
+      &quot;<code>GRIDMIXnnnnn</code>&quot;, where
+      &quot;<code>nnnnn</code>&quot; is a sequence number padded with
leading
+      zeroes.</p>
+    </section>
+    <section id="usage">
+      <title>Usage</title>
+      <p>Basic command-line usage without configuration parameters:</p>
+      <source>
+org.apache.hadoop.mapred.gridmix.Gridmix [-generate &lt;size&gt;] [-users &lt;users-list&gt;]
&lt;iopath&gt; &lt;trace&gt;
+      </source>
+      <p>Basic command-line usage with configuration parameters:</p>
+      <source>
+org.apache.hadoop.mapred.gridmix.Gridmix \
+  -Dgridmix.client.submit.threads=10 -Dgridmix.output.directory=foo \
+  [-generate &lt;size&gt;] [-users &lt;users-list&gt;] &lt;iopath&gt;
&lt;trace&gt;
+      </source>
+      <note>
+	Configuration parameters like
+	<code>-Dgridmix.client.submit.threads=10</code> and
+	<code>-Dgridmix.output.directory=foo</code> as given above should
+	be used <em>before</em> other GridMix parameters.
+      </note>
+      <p>The <code>-generate</code> option is used to generate input data
+      for the synthetic jobs. It accepts size suffixes, e.g.
+      <code>100g</code> will generate 100 * 2<sup>30</sup> bytes.</p>
+      <p>The <code>-users</code> option is used to point to a users-list
+      file (see <a href="#usersqueues">Emulating Users and Queues</a>).</p>
+      <p>The <code>&lt;iopath&gt;</code> parameter is the destination
+      directory for generated output and/or the directory from which input
+      data will be read. Note that this can either be on the local file-system
+      or on HDFS, but it is highly recommended that it be the same as that for
+      the original job mix so that GridMix puts the same load on the local
+      file-system and HDFS respectively.</p>
+      <p>The <code>&lt;trace&gt;</code> parameter is a path to
a job trace
+      generated by Rumen. This trace can be compressed (it must be readable
+      using one of the compression codecs supported by the cluster) or
+      uncompressed. Use &quot;-&quot; as the value of this parameter if you
+      want to pass an <em>uncompressed</em> trace via the standard
+      input-stream of GridMix.</p>
+      <p>The class <code>org.apache.hadoop.mapred.gridmix.Gridmix</code>
can
+      be found in the JAR
+      <code>contrib/gridmix/hadoop-$VERSION-gridmix.jar</code> inside your
+      Hadoop installation, where <code>$VERSION</code> corresponds to the
+      version of Hadoop installed. A simple way of ensuring that this class
+      and all its dependencies are loaded correctly is to use the
+      <code>hadoop</code> wrapper script in Hadoop:</p>
+      <source>
+hadoop jar &lt;gridmix-jar&gt; org.apache.hadoop.mapred.gridmix.Gridmix \
+  [-generate &lt;size&gt;] [-users &lt;users-list&gt;] &lt;iopath&gt;
&lt;trace&gt;
+      </source>
+      <p>The supported configuration parameters are explained in the
+      following sections.</p>
+    </section>
+    <section id="cfgparams">
+      <title>General Configuration Parameters</title>
+      <p/>
+      <table>
+        <tr>
+          <th>Parameter</th>
+          <th>Description</th>
+        </tr>
+        <tr>
+          <td>
+            <code>gridmix.output.directory</code>
+          </td>
+          <td>The directory into which output will be written. If specified,
+	  <code>iopath</code> will be relative to this parameter. The
+	  submitting user must have read/write access to this directory. The
+	  user should also be mindful of any quota issues that may arise
+	  during a run. The default is &quot;<code>gridmix</code>&quot;.</td>
+        </tr>
+        <tr>
+          <td>
+            <code>gridmix.client.submit.threads</code>
+          </td>
+          <td>The number of threads submitting jobs to the cluster. This
+	  also controls how many splits will be loaded into memory at a given
+	  time, pending the submit time in the trace. Splits are pre-generated
+	  to hit submission deadlines, so particularly dense traces may want
+	  more submitting threads. However, storing splits in memory is
+	  reasonably expensive, so you should raise this cautiously. The
+	  default is 1 for the SERIAL job-submission policy (see
+	  <a href="#policies">Job Submission Policies</a>) and one more than
+	  the number of processors on the client machine for the other
+	  policies.</td>
+        </tr>
+	<tr>
+	  <td>
+	    <code>gridmix.submit.multiplier</code>
+	  </td>
+	  <td>The multiplier to accelerate or decelerate the submission of
+	  jobs. The time separating two jobs is multiplied by this factor.
+	  The default value is 1.0. This is a crude mechanism to size
+	  a job trace to a cluster.</td>
+	</tr>
+        <tr>
+          <td>
+            <code>gridmix.client.pending.queue.depth</code>
+          </td>
+          <td>The depth of the queue of job descriptions awaiting split
+	  generation. The jobs read from the trace occupy a queue of this
+	  depth before being processed by the submission threads. It is
+	  unusual to configure this. The default is 5.</td>
+        </tr>
+	<tr>
+	  <td>
+	    <code>gridmix.gen.blocksize</code>
+	  </td>
+	  <td>The block-size of generated data. The default value is 256
+	  MiB.</td>
+	</tr>
+	<tr>
+	  <td>
+	    <code>gridmix.gen.bytes.per.file</code>
+	  </td>
+	  <td>The maximum bytes written per file. The default value is 1
+	  GiB.</td>
+	</tr>
+        <tr>
+          <td>
+            <code>gridmix.min.file.size</code>
+          </td>
+          <td>The minimum size of the input files. The default limit is 128
+	  MiB. Tweak this parameter if you see an error-message like
+	  &quot;Found no satisfactory file&quot; while testing GridMix with
+	  a relatively-small input data-set.</td>
+        </tr>
+        <tr>
+          <td>
+            <code>gridmix.max.total.scan</code>
+          </td>
+          <td>The maximum size of the input files. The default limit is 100
+	  TiB.</td>
+        </tr>
+      </table>
+    </section>
+    <section id="jobtypes">
+      <title>Job Types</title>
+      <p>GridMix takes as input a job trace, essentially a stream of
+      JSON-encoded job descriptions. For each job description, the submission
+      client obtains the original job submission time and for each task in
+      that job, the byte and record counts read and written. Given this data,
+      it constructs a synthetic job with the same byte and record patterns as
+      recorded in the trace. It constructs jobs of two types:</p>
+      <table>
+        <tr>
+          <th>Job Type</th>
+          <th>Description</th>
+        </tr>
+        <tr>
+          <td>
+            <code>LOADJOB</code>
+          </td>
+          <td>A synthetic job that emulates the workload mentioned in Rumen
+	  trace. In the current version we are supporting I/O. It reproduces
+	  the I/O workload on the benchmark cluster. It does so by embedding
+	  the detailed I/O information for every map and reduce task, such as
+	  the number of bytes and records read and written, into each
+	  job's input splits. The map tasks further relay the I/O patterns of
+	  reduce tasks through the intermediate map output data.</td>
+        </tr>
+        <tr>
+          <td>
+            <code>SLEEPJOB</code>
+          </td>
+	  <td>A synthetic job where each task does <em>nothing</em> but sleep
+	  for a certain duration as observed in the production trace. The
+	  scalability of the Job Tracker is often limited by how many
+	  heartbeats it can handle every second. (Heartbeats are periodic
+	  messages sent from Task Trackers to update their status and grab new
+	  tasks from the Job Tracker.) Since a benchmark cluster is typically
+	  a fraction in size of a production cluster, the heartbeat traffic
+	  generated by the slave nodes is well below the level of the
+	  production cluster. One possible solution is to run multiple Task
+	  Trackers on each slave node. This leads to the obvious problem that
+	  the I/O workload generated by the synthetic jobs would thrash the
+	  slave nodes. Hence the need for such a job.</td>
+        </tr>
+      </table>
+      <p>The following configuration parameters affect the job type:</p>
+      <table>
+        <tr>
+          <th>Parameter</th>
+          <th>Description</th>
+        </tr>
+        <tr>
+          <td>
+            <code>gridmix.job.type</code>
+          </td>
+          <td>The value for this key can be one of LOADJOB or SLEEPJOB. The
+	  default value is LOADJOB.</td>
+        </tr>
+        <tr>
+          <td>
+            <code>gridmix.key.fraction</code>
+          </td>
+          <td>For a LOADJOB type of job, the fraction of a record used for
+	  the data for the key. The default value is 0.1.</td>
+        </tr>
+        <tr>
+          <td>
+            <code>gridmix.sleep.maptask-only</code>
+          </td>
+          <td>For a SLEEPJOB type of job, whether to ignore the reduce
+	  tasks for the job. The default is <code>false</code>.</td>
+        </tr>
+        <tr>
+          <td>
+            <code>gridmix.sleep.fake-locations</code>
+          </td>
+          <td>For a SLEEPJOB type of job, the number of fake locations
+	  for map tasks for the job. The default is 0.</td>
+        </tr>
+        <tr>
+          <td>
+            <code>gridmix.sleep.max-map-time</code>
+          </td>
+          <td>For a SLEEPJOB type of job, the maximum runtime for map
+	  tasks for the job in milliseconds. The default is unlimited.</td>
+        </tr>
+        <tr>
+          <td>
+            <code>gridmix.sleep.max-reduce-time</code>
+          </td>
+          <td>For a SLEEPJOB type of job, the maximum runtime for reduce
+	  tasks for the job in milliseconds. The default is unlimited.</td>
+        </tr>
+      </table>
+    </section>
+    <section id="policies">
+      <title>Job Submission Policies</title>
+      <p>GridMix controls the rate of job submission. This control can be
+      based on the trace information or can be based on statistics it gathers
+      from the Job Tracker. Based on the submission policies users define,
+      GridMix uses the respective algorithm to control the job submission.
+      There are currently three types of policies:</p>
+      <table>
+        <tr>
+          <th>Job Submission Policy</th>
+          <th>Description</th>
+        </tr>
+        <tr>
+          <td>
+            <code>STRESS</code>
+          </td>
+          <td>Keep submitting jobs so that the cluster remains under stress.
+	  In this mode we control the rate of job submission by monitoring
+	  the real-time load of the cluster so that we can maintain a stable
+	  stress level of workload on the cluster. Based on the statistics we
+	  gather we define if a cluster is <em>underloaded</em> or
+	  <em>overloaded</em>. We consider a cluster <em>underloaded</em>
if
+	  and only if the following three conditions are true:
+	  <ol>
+	    <li>the number of pending and running jobs are under a threshold
+	    TJ</li>
+	    <li>the number of pending and running maps are under threshold
+	    TM</li>
+	    <li>the number of pending and running reduces are under threshold
+	    TR</li>
+	  </ol>
+          The thresholds TJ, TM and TR are proportional to the size of the
+	  cluster and map, reduce slots capacities respectively. In case of a
+	  cluster being <em>overloaded</em>, we throttle the job submission.
+	  In the actual calculation we also weigh each running task with its
+	  remaining work - namely, a 90% complete task is only counted as 0.1
+	  in calculation. Finally, to avoid a very large job blocking other
+	  jobs, we limit the number of pending/waiting tasks each job can
+	  contribute.</td>
+        </tr>
+        <tr>
+          <td>
+            <code>REPLAY</code>
+          </td>
+          <td>In this mode we replay the job traces faithfully. This mode
+	  exactly follows the time-intervals given in the actual job
+	  trace.</td>
+        </tr>
+        <tr>
+          <td>
+            <code>SERIAL</code>
+          </td>
+          <td>In this mode we submit the next job only once the job submitted
+	  earlier is completed.</td>
+        </tr>
+      </table>
+      <p>The following configuration parameters affect the job submission
+      policy:</p>
+      <table>
+        <tr>
+          <th>Parameter</th>
+          <th>Description</th>
+        </tr>
+        <tr>
+          <td>
+            <code>gridmix.job-submission.policy</code>
+          </td>
+          <td>The value for this key would one of the three: STRESS, REPLAY or
+	  SERIAL. In most of the cases the value of key would be STRESS or
+	  REPLAY. The default value is STRESS.</td>
+        </tr>
+        <tr>
+          <td>
+            <code>gridmix.throttle.jobs-to-tracker-ratio</code>
+          </td>
+          <td>In STRESS mode, the minimum ratio of running jobs to Task
+	  Trackers in a cluster for the cluster to be considered
+	  <em>overloaded</em>. This is the threshold TJ referred to earlier.
+	  The default is 1.0.</td>
+        </tr>
+        <tr>
+          <td>
+            <code>gridmix.throttle.maps.task-to-slot-ratio</code>
+          </td>
+          <td>In STRESS mode, the minimum ratio of pending and running map
+	  tasks (i.e. incomplete map tasks) to the number of map slots for
+	  a cluster for the cluster to be considered <em>overloaded</em>.
+	  This is the threshold TM referred to earlier. Running map tasks are
+	  counted partially. For example, a 40% complete map task is counted
+	  as 0.6 map tasks. The default is 2.0.</td>
+        </tr>
+        <tr>
+          <td>
+            <code>gridmix.throttle.reduces.task-to-slot-ratio</code>
+          </td>
+          <td>In STRESS mode, the minimum ratio of pending and running reduce
+	  tasks (i.e. incomplete reduce tasks) to the number of reduce slots
+	  for a cluster for the cluster to be considered <em>overloaded</em>.
+	  This is the threshold TR referred to earlier. Running reduce tasks
+	  are counted partially. For example, a 30% complete reduce task is
+	  counted as 0.7 reduce tasks. The default is 2.5.</td>
+        </tr>
+        <tr>
+          <td>
+            <code>gridmix.throttle.maps.max-slot-share-per-job</code>
+          </td>
+          <td>In STRESS mode, the maximum share of a cluster's map-slots
+	  capacity that can be counted toward a job's incomplete map tasks in
+	  overload calculation. The default is 0.1.</td>
+        </tr>
+        <tr>
+          <td>
+            <code>gridmix.throttle.reducess.max-slot-share-per-job</code>
+          </td>
+          <td>In STRESS mode, the maximum share of a cluster's reduce-slots
+	  capacity that can be counted toward a job's incomplete reduce tasks
+	  in overload calculation. The default is 0.1.</td>
+        </tr>
+      </table>
+    </section>
+    <section id="usersqueues">
+      <title>Emulating Users and Queues</title>
+      <p>Typical production clusters are often shared with different users and
+      the cluster capacity is divided among different departments through job
+      queues. Ensuring fairness among jobs from all users, honoring queue
+      capacity allocation policies and avoiding an ill-behaving job from
+      taking over the cluster adds significant complexity in Hadoop software.
+      To be able to sufficiently test and discover bugs in these areas,
+      GridMix must emulate the contentions of jobs from different users and/or
+      submitted to different queues.</p>
+      <p>Emulating multiple queues is easy - we simply set up the benchmark
+      cluster with the same queue configuration as the production cluster and
+      we configure synthetic jobs so that they get submitted to the same queue
+      as recorded in the trace. However, not all users shown in the trace have
+      accounts on the benchmark cluster. Instead, we set up a number of testing
+      user accounts and associate each unique user in the trace to testing
+      users in a round-robin fashion.</p>
+      <p>The following configuration parameters affect the emulation of users
+      and queues:</p>
+      <table>
+        <tr>
+          <th>Parameter</th>
+          <th>Description</th>
+        </tr>
+        <tr>
+          <td>
+            <code>gridmix.job-submission.use-queue-in-trace</code>
+          </td>
+          <td>When set to <code>true</code> it uses exactly the same set
of
+	  queues as those mentioned in the trace. The default value is
+	  <code>false</code>.</td>
+        </tr>
+        <tr>
+          <td>
+            <code>gridmix.job-submission.default-queue</code>
+          </td>
+          <td>Specifies the default queue to which all the jobs would be
+	  submitted. If this parameter is not specified, GridMix uses the
+	  default queue defined for the submitting user on the cluster.</td>
+        </tr>
+        <tr>
+          <td>
+            <code>gridmix.user.resolve.class</code>
+          </td>
+          <td>Specifies which <code>UserResolver</code> implementation
to use.
+	  We currently have three implementations:
+	  <ol>
+	    <li><code>org.apache.hadoop.mapred.gridmix.EchoUserResolver</code>
+	    - submits a job as the user who submitted the original job. All
+	    the users of the production cluster identified in the job trace
+	    must also have accounts on the benchmark cluster in this case.</li>
+	    <li><code>org.apache.hadoop.mapred.gridmix.SubmitterUserResolver</code>
+	    - submits all the jobs as current GridMix user. In this case we
+	    simply map all the users in the trace to the current GridMix user
+	    and submit the job.</li>
+	    <li><code>org.apache.hadoop.mapred.gridmix.RoundRobinUserResolver</code>
+	    - maps trace users to test users in a round-robin fashion. In
+	    this case we set up a number of testing user accounts and
+	    associate each unique user in the trace to testing users in a
+	    round-robin fashion.</li>
+	  </ol>
+	  The default is
+	  <code>org.apache.hadoop.mapred.gridmix.SubmitterUserResolver</code>.</td>
+        </tr>
+      </table>
+      <p>If the parameter <code>gridmix.user.resolve.class</code> is set
to
+      <code>org.apache.hadoop.mapred.gridmix.RoundRobinUserResolver</code>,
+      we need to define a users-list file with a list of test users and groups.
+      This is specified using the <code>-users</code> option to GridMix.</p>
+      <note>
+      Specifying a users-list file using the <code>-users</code> option is
+      mandatory when using the round-robin user-resolver. Other user-resolvers
+      ignore this option.
+      </note>
+      <p>A users-list file has one user-group-information (UGI) per line, each
+      UGI of the format:</p>
+      <source>
+      &lt;username&gt;,&lt;group&gt;[,group]*
+      </source>
+      <p>For example:</p>
+      <source>
+      user1,group1
+      user2,group2,group3
+      user3,group3,group4
+      </source>
+      <p>In the above example we have defined three users <code>user1</code>,
+      <code>user2</code> and <code>user3</code> with their respective
groups.
+      Now we would associate each unique user in the trace to the above users
+      defined in round-robin fashion. For example, if traces users are
+      <code>tuser1</code>, <code>tuser2</code>, <code>tuser3</code>,
+      <code>tuser4</code> and <code>tuser5</code>, then the mappings
would
+      be:</p>
+      <source>
+      tuser1 -&gt; user1
+      tuser2 -&gt; user2
+      tuser3 -&gt; user3
+      tuser4 -&gt; user1
+      tuser5 -&gt; user2
+      </source>
+    </section>
+    <section id="assumptions">
+      <title>Simplifying Assumptions</title>
+      <p>GridMix will be developed in stages, incorporating feedback and
+      patches from the community. Currently its intent is to evaluate
+      MapReduce and HDFS performance and not the layers on top of them (i.e.
+      the extensive lib and sub-project space). Given these two limitations,
+      the following characteristics of job load are not currently captured in
+      job traces and cannot be accurately reproduced in GridMix:</p>
+      <ul>
+	<li><em>CPU Usage</em> - We have no data for per-task CPU usage, so we
+	cannot even attempt an approximation. GridMix tasks are never
+	CPU-bound independent of I/O, though this surely happens in
+	practice.</li>
+	<li><em>Filesystem Properties</em> - No attempt is made to match block
+	sizes, namespace hierarchies, or any property of input, intermediate
+	or output data other than the bytes/records consumed and emitted from
+	a given task. This implies that some of the most heavily-used parts of
+	the system - the compression libraries, text processing, streaming,
+	etc. - cannot be meaningfully tested with the current
+	implementation.</li>
+	<li><em>I/O Rates</em> - The rate at which records are
+	consumed/emitted is assumed to be limited only by the speed of the
+	reader/writer and constant throughout the task.</li>
+	<li><em>Memory Profile</em> - No data on tasks' memory usage over time
+	is available, though the max heap-size is retained.</li>
+	<li><em>Skew</em> - The records consumed and emitted to/from a given
+	task are assumed to follow observed averages, i.e. records will be
+	more regular than may be seen in the wild. Each map also generates
+	a proportional percentage of data for each reduce, so a job with
+	unbalanced input will be flattened.</li>
+	<li><em>Job Failure</em> - User code is assumed to be correct.</li>
+	<li><em>Job Independence</em> - The output or outcome of one job does
+	not affect when or whether a subsequent job will run.</li>
+      </ul>
+    </section>
+    <section id="appendix">
+      <title>Appendix</title>
+      <p>Issues tracking the original implementations of <a
+      href="https://issues.apache.org/jira/browse/HADOOP-2369">GridMix1</a>,
+      <a href="https://issues.apache.org/jira/browse/HADOOP-3770">GridMix2</a>,
+      and <a
+      href="https://issues.apache.org/jira/browse/MAPREDUCE-776">GridMix3</a>
+      can be found on the Apache Hadoop MapReduce JIRA. Other issues tracking
+      the current development of GridMix can be found by searching <a
+      href="https://issues.apache.org/jira/browse/MAPREDUCE/component/12313086">the
+      Apache Hadoop MapReduce JIRA</a></p>
+    </section>
+  </body>
 </document>



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