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Revision 1302

Added by Jing Tao about 22 years ago

Change the documentation according our new feature in replication.

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replication.html
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    </tr>
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  </table>
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  <p>Metacat has built in replication to allow different Metacat servers to
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  share data between themselves.  The replication scheme that Metacat uses is
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  both push and pull.  There are several triggers that can start a replication
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  mechanism. </p>
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  share data between themselves. In this release, Metacat not only replicate
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  XML documents but also data files. </p>
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  <p> A new hub feature was added to Metacat too. Previous version of Metacat
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  only replicate XML documents whose home server is itself. But hub Metacat can
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  replicate both its documents and other's documents which replicated from
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  other server.</p>
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  <p>The replication scheme that Metacat uses is both push and pull.  There are
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  several triggers that can start a replication mechanism. </p>
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  <ul>
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    <li>Delta-T monitoring. At a set time interval a server checks each of the
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    other servers in its list for updated documents</li>
......
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    can give a lock for that file to be altered.</li>
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  </ul>
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  <p>Each server contains a list of servers to which it can replicate.  One-way
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  replication is enabled by the 'replicate' flag in the list.  The server list
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  may look like the following.</p>
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  replication is enabled by the 'replicate' and 'datareplicate' flags in the
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  list.  The server list may look like the following.</p>
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  <table border="1">
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    <tr>
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      <td><b>serverid</b></td>
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      <td><b>server</b></td>
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      <td><b>last_checked</b></td>
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      <td><b>replicate</b></td>
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      <td><b>datareplicate</b></td>
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      <td><b>hub</b></td>
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    </tr>
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    <tr>
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      <td>1</td>
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      <td>localhost</td>
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      <td>null</td>
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      <td>0</td>
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      <td>0</td>
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      <td>0</td>
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    </tr>
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    <tr>
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      <td>2</td>
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      <td>alpha.nceas.ucsb.edu:8080/berkley/servlet/replication</td>
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      <td>2001-01-22 14:52:12.1</td>
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      <td>1</td>
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      <td>0</td>
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      <td>0</td>
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      <td>0</td>
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    </tr>
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    <tr>
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      <td>3</td>
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      <td>dev.nceas.ucsb.edu/Metacat/servlet/replication</td>
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      <td>2001-01-23 9:10:02.5</td>
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      <td>1</td>
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      <td>1</td>
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      <td>0</td>
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    </tr>
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  </table>
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......
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  hence the servlet/replication on the end of both of the sample servers.  Note
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  that any port numbers (if your servlet engine is not running on port 80) must
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  also be included.  The replicate flag is set to 1 if you want this server to
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  copy data TO the remote host.  (Note that both servers (the local host and
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  the remote host) must have each other in their respective tables or replication
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  will not take place.)</p>
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  copy XML documents TO the remote host.  If replicate flag is set to 1 and
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  datareplicate is set to 1, this server can copy data file TO the remote host
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  too. If this server is a hub to the remote host, the hub flag should be set to
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  1. (Note that both servers (the local host and the remote host) must have each
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  other in their respective tables or replication will not take place.)</p>
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  <b>Example:</b>
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  <table border="1">
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    <tr>
......
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          <td><b>server</b></td>
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          <td><b>last_checked</b></td>
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          <td><b>replicate</b></td>
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          <td><b>datareplicate</b></td>
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          <td><b>hub</b></td>
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        </tr>
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        <tr>
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          <td>localhost</td>
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          <td>null</td>
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          <td>0</td>
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          <td>0</td>
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          <td>0</td>
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        </tr>
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        <tr>
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          <td>alpha.nceas.ucsb.edu:8080/berkley/servlet/replication&nbsp;&nbsp;&nbsp;</td>
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          <td>2001-01-22 14:52:12.1</td>
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          <td>1</td>
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          <td>0</td>
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          <td>0</td>
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          <td>0</td>
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        </tr>
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        <tr>
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          <td>dev.nceas.ucsb.edu/Metacat/servlet/replication</td>
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          <td>2001-01-23 9:10:02.5</td>
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          <td>1</td>
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          <td>1</td>
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          <td>0</td>
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        </tr>
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      </table>
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     </td>
......
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            <td><b>server</b></td>
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            <td><b>last_checked</b></td>
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            <td><b>replicate</b></td>
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            <td><b>datareplicate</b></td>
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            <td><b>hub</b></td>
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          </tr>
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          <tr>
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            <td>localhost</td>
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            <td>null</td>
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            <td>0</td>
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            <td>0</td>
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            <td>0</td>
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          </tr>
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          <tr>
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            <td>snoopy.nceas.ucsb.edu:8080/berkley/servlet/replication</td>
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            <td>2001-01-21 11:33:12.7</td>
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            <td>0</td>
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            <td>1</td>
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            <td>0</td>
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          </tr>
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          <tr>
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            <td>dev.nceas.ucsb.edu/Metacat/servlet/replication</td>
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            <td>2001-01-23 10:22:02.5</td>
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            <td>1</td>
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            <td>0</td>
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            <td>0</td>
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          </tr>
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        </table>
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      </td>
......
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            <td><b>server</b></td>
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            <td><b>last_checked</b></td>
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            <td><b>replicate</b></td>
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            <td><b>datareplicate</b></td>
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            <td><b>hub</b></td>
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          </tr>
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          <tr>
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            <td>localhost</td>
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            <td>null</td>
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            <td>0</td>
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            <td>0</td>
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            <td>0</td>
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          </tr>
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          <tr>
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            <td>snoopy.nceas.ucsb.edu:8080/berkley/servlet/replication</td>
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            <td>2001-01-21 11:33:12.7</td>
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            <td>0</td>
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            <td>0</td>
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            <td>0</td>
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          </tr>
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          <tr>
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            <td>alpha.nceas.ucsb.edu:8080/Metacat/servlet/replication</td>
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            <td>2001-01-22 12:15:32.5</td>
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            <td>1</td>
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            <td>1</td>
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            <td>1</td>
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          </tr>
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        </table>
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      </td>
......
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  </table>
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  <p>Our three servers, snoopy, alpha and dev are all set up to replicate
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  between themselves.  Snoopy is a one way replicator.  Meaning that it only
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  pushes data to alpha and dev but does not pull back from them.  This
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  pushes XML documents and data file to dev but does not pull back from it.  This
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  is achieved by dev and alpha setting snoopy's 'replicate' value to 0 indicating
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  that they do not want to send their files to snoopy.  Alpha and dev have a
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  two-way replication agreement since each of them have a 1 in their 'replicate'
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  value for the other.</p>
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  that they do not want to send their files to snoopy(Even in in Alpha,
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  'datareplicate' is set to 1 for snoopy but nothing will be sent to Snoopy from alpha).
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  Alpha and dev have a two-way replication agreement since each of them have a 1
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  in their 'replicate' value for the other.</p>
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  <p>Snoopy will replicate both XML documents and data file to dev because it
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  setting dev's 'replicata' and 'datareplicate' is 1. Alpha only replicate
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  XML documents to dev and this is caused by it setting dev's 'datareplicate' 0.
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  </p>
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  <p>Dev is a hub of alpha because it setting alpha's 'hub' value to be 1. Moreover,
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  dev set alpha's 'replicate' and 'datareplicate' value 1. So dev will replicate
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  XML documents and data file whose home server is dev or snoopy(replicated
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  from snoopy) to alpha</p>
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  <P>Note: if 'replicate' value is 0, the value for 'datareplicate' and 'hub'
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  has no sense.</P>
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  <p>There is an html control panel for controling replication.  After
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  <a href="./Metacatinstall.html">installing</a> Metacat, you can access
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  it by going through the Metacat servlet context you have setup and calling up

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