<entry align="center"></entry>
     <entry align="center"></entry>
    </row>

    <row>
     <entry>No waiting for multiple servers</entry>
     <entry align="center">&bull;</entry>
     <entry align="center"></entry>
     <entry align="center">with sync off</entry>
     <entry align="center">with sync off</entry>
     <entry align="center">&bull;</entry>
     <entry align="center"></entry>
     <entry align="center">&bull;</entry>
     <entry align="center"></entry>
    </row>

    <row>
     <entry>Primary failure will never lose data</entry>
     <entry align="center">&bull;</entry>
     <entry align="center">&bull;</entry>
     <entry align="center">with sync on</entry>
     <entry align="center">with sync on</entry>
     <entry align="center"></entry>
     <entry align="center">&bull;</entry>
     <entry align="center"></entry>
     <entry align="center">&bull;</entry>
    </row>

    <row>
     <entry>Replicas accept read-only queries</entry>
     <entry align="center"></entry>
     <entry align="center"></entry>
     <entry align="center">with hot standby</entry>
     <entry align="center">&bull;</entry>
     <entry align="center">&bull;</entry>
     <entry align="center">&bull;</entry>
     <entry align="center">&bull;</entry>
     <entry align="center">&bull;</entry>
    </row>

    <row>
     <entry>Per-table granularity</entry>
     <entry align="center"></entry>
     <entry align="center"></entry>
     <entry align="center"></entry>
     <entry align="center">&bull;</entry>
     <entry align="center">&bull;</entry>
     <entry align="center"></entry>
     <entry align="center">&bull;</entry>
     <entry align="center">&bull;</entry>
    </row>

    <row>
     <entry>No conflict resolution necessary</entry>
     <entry align="center">&bull;</entry>
     <entry align="center">&bull;</entry>
     <entry align="center">&bull;</entry>
     <entry align="center"></entry>
     <entry align="center">&bull;</entry>
     <entry align="center">&bull;</entry>
     <entry align="center"></entry>
     <entry align="center">&bull;</entry>
    </row>

   </tbody>
  </tgroup>
 </table>

 <para>
  There are a few solutions that do not fit into the above categories:
 </para>

 <variablelist>

  <varlistentry>
   <term>Data Partitioning</term>
   <listitem>

    <para>
     Data partitioning splits tables into data sets.  Each set can
     be modified by only one server.  For example, data can be
     partitioned by offices, e.g., London and Paris, with a server
     in each office.  If queries combining London and Paris data
     are necessary, an application can query both servers, or
     primary/standby replication can be used to keep a read-only copy
     of the other office's data on each server.
    </para>
   </listitem>
  </varlistentry>

  <varlistentry>
   <term>Multiple-Server Parallel Query Execution</term>
   <listitem>

    <para>
     Many of the above solutions allow multiple servers to handle multiple
     queries, but none allow a single query to use multiple servers to
     complete faster.  This solution allows multiple servers to work
     concurrently on a single query.  It is usually accomplished by
     splitting the data among servers and having each server execute its
     part of the query and return results to a central server where they
     are combined and returned to the user. This can be implemented using the
     <productname>PL/Proxy</productname> tool set.
    </para>

   </listitem>
  </varlistentry>

 </variablelist>

  <para>
   It should also be noted that because <productname>PostgreSQL</productname>
   is open source and easily extended, a number of companies have
   taken <productname>PostgreSQL</productname> and created commercial
   closed-source solutions with unique failover, replication, and load
   balancing capabilities.  These are not discussed here.
  </para>

 </sect1>


 <sect1 id="warm-standby">
 <title>Log-Shipping Standby Servers</title>


  <para>
   Continuous archiving can