docs/gsg_db_rep/C/electiontimes.html

   1 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
   2 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
   3 <html xmlns="http://www.w3.org/1999/xhtml">
   4   <head>
   5     <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
   6     <title>Managing Election Times</title>
   7     <link rel="stylesheet" href="gettingStarted.css" type="text/css" />
   8     <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
   9     <link rel="start" href="index.html" title="Getting Started with Replicated Berkeley DB Applications" />
  10     <link rel="up" href="repapp.html" title="Chapter 3. The DB Replication Manager" />
  11     <link rel="prev" href="fwrkpermmessage.html" title="Permanent Message Handling" />
  12     <link rel="next" href="fmwrkconnectretry.html" title="Managing Connection Retries" />
  13   </head>
  14   <body>
  15     <div xmlns="" class="navheader">
  16       <div class="libver">
  17         <p>Library Version 11.2.5.3</p>
  18       </div>
  19       <table width="100%" summary="Navigation header">
  20         <tr>
  21           <th colspan="3" align="center">Managing Election Times</th>
  22         </tr>
  23         <tr>
  24           <td width="20%" align="left"><a accesskey="p" href="fwrkpermmessage.html">Prev</a> </td>
  25           <th width="60%" align="center">Chapter 3. The DB Replication Manager</th>
  26           <td width="20%" align="right"> <a accesskey="n" href="fmwrkconnectretry.html">Next</a></td>
  27         </tr>
  28       </table>
  29       <hr />
  30     </div>
  31     <div class="sect1" lang="en" xml:lang="en">
  32       <div class="titlepage">
  33         <div>
  34           <div>
  35             <h2 class="title" style="clear: both"><a id="electiontimes"></a>Managing Election Times</h2>
  36           </div>
  37         </div>
  38       </div>
  39       <div class="toc">
  40         <dl>
  41           <dt>
  42             <span class="sect2">
  43               <a href="electiontimes.html#electiontimeout">Managing Election Timeouts</a>
  44             </span>
  45           </dt>
  46           <dt>
  47             <span class="sect2">
  48               <a href="electiontimes.html#electretrytime">Managing Election Retry Times</a>
  49             </span>
  50           </dt>
  51         </dl>
  52       </div>
  53       <p>
  54                     Where it comes to elections, there are two timeout
  55                     values with which you should be concerned: election
  56                     timeouts and election retries.
  57             </p>
  58       <div class="sect2" lang="en" xml:lang="en">
  59         <div class="titlepage">
  60           <div>
  61             <div>
  62               <h3 class="title"><a id="electiontimeout"></a>Managing Election Timeouts</h3>
  63             </div>
  64           </div>
  65         </div>
  66         <p>
  67                         When an environment calls for an election, it will wait
  68                         some amount of time for the other replicas in the
  69                         replication group to respond. The amount of time
  70                         that the environment will wait before declaring the
  71                         election completed is the <span class="emphasis"><em>election timeout</em></span>.
  72                     </p>
  73         <p>
  74                             If the environment hears from all other known replicas before
  75                             the election timeout occurs, the election is considered
  76                             a success and a master is elected.
  77                     </p>
  78         <p>
  79                             If only a subset of replicas respond, then the success
  80                             or failure of the election is determined by
  81                             how many replicas have participated in the
  82                             election. It only takes a simple
  83                             majority of replicas to elect a master. If
  84                             there are enough votes for a given environment to
  85                             meet that standard, then the master has been
  86                             elected and the election is considered a
  87                             success.
  88                     </p>
  89         <p>
  90                             However, if not enough replicas have participated in
  91                             the election when the election timeout value is
  92                             reached, the election is considered a failure
  93                             and a master is not elected. At this point,
  94                             your replication group is operating without a
  95                             master, which means that, essentially,
  96                             your replicated application has been placed in
  97                             read-only mode.
  98                     </p>
  99         <p>
 100                             Note, however, that the Replication Manager will attempt a
 101                             new election after a given amount of time has
 102                             passed. See the next section for details.
 103                     </p>
 104         <p>
 105                             You set the election timeout value using
 106                             <span><code class="methodname">DB_ENV-&gt;rep_set_timeout()</code>.</span>
 107
 108                             To do so, specify the
 109                             <code class="literal">DB_REP_ELECTION_TIMEOUT</code>
 110                             value to the <code class="literal">which</code> parameter and then a
 111                             timeout value in microseconds to the
 112                             <code class="literal">timeout</code> parameter.
 113                     </p>
 114       </div>
 115       <div class="sect2" lang="en" xml:lang="en">
 116         <div class="titlepage">
 117           <div>
 118             <div>
 119               <h3 class="title"><a id="electretrytime"></a>Managing Election Retry Times</h3>
 120             </div>
 121           </div>
 122         </div>
 123         <p>
 124                             In the event that a election fails (see the
 125                             previous section), an election will not be
 126                             attempted again until the election retry
 127                             timeout value has expired.
 128                     </p>
 129         <p>
 130                             You set the retry timeout value using
 131                             <span><code class="methodname">DB_ENV-&gt;rep_set_timeout()</code>.</span>
 132
 133                             To do so, specify the
 134                             <code class="literal">DB_REP_ELECTION_RETRY</code>
 135                             value to the <code class="literal">which</code> parameter and then a
 136                             retry value in microseconds to the
 137                             <code class="literal">timeout</code> parameter.
 138                     </p>
 139         <p>
 140                         Note that this <span>flag</span>
 141                          is only
 142                         valid when you are using the Replication Manager. If you are
 143                         using the Base APIs, then this
 144                         <span>flag</span>
 145                          is
 146                         ignored.
 147                     </p>
 148       </div>
 149     </div>
 150     <div class="navfooter">
 151       <hr />
 152       <table width="100%" summary="Navigation footer">
 153         <tr>
 154           <td width="40%" align="left"><a accesskey="p" href="fwrkpermmessage.html">Prev</a> </td>
 155           <td width="20%" align="center">
 156             <a accesskey="u" href="repapp.html">Up</a>
 157           </td>
 158           <td width="40%" align="right"> <a accesskey="n" href="fmwrkconnectretry.html">Next</a></td>
 159         </tr>
 160         <tr>
 161           <td width="40%" align="left" valign="top">Permanent Message Handling </td>
 162           <td width="20%" align="center">
 163             <a accesskey="h" href="index.html">Home</a>
 164           </td>
 165           <td width="40%" align="right" valign="top"> Managing Connection Retries</td>
 166         </tr>
 167       </table>
 168     </div>
 169   </body>
 170 </html>