ZOOKEEPER-673. Fix observer documentation regarding leader election (flavio via mahadev)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/zookeeper/trunk@911674 13f79535-47bb-0310-9956-ffa450edef68

CHANGES.txt

@@ -218,6 +218,9 @@ BUGFIXES:
   ZOOKEEPER-589. When create a znode, a NULL ACL parameter cannot be accepted.
   (breed via mahadev)
 
+  ZOOKEEPER-673.  Fix observer documentation regarding leader election (flavio
+  via mahadev)
+
 IMPROVEMENTS:
   ZOOKEEPER-473. cleanup junit tests to eliminate false positives due to
   "socket reuse" and failure to close client (phunt via mahadev)

docs/zookeeperObservers.html

@@ -226,18 +226,6 @@ document.write("Last Published: " + document.lastModified);
 <h2 class="h3">Observers: Scaling ZooKeeper Without Hurting Write Performance
       </h2>
 <div class="section">
-<p>
-      
-<em>
-	Please note: the Observers feature currently only works with the basic
-	leader election protocol, not fast leader election or authenticated fast
-	leader election. This will be remedied when a bug in the leader election
-	protocol code is fixed in the near future. An exception will be thrown
-	if you try to start a cluster containing Observers without
-	electionAlg=0. See below for more details.
-      </em>
-    
-</p>
 <p>
       Although ZooKeeper performs very well by having clients connect directly
       to voting members of the ensemble, this architecture makes it hard to
@@ -272,32 +260,9 @@ document.write("Last Published: " + document.lastModified);
     </p>
 </div>
   
-<a name="N10022"></a><a name="sc_UsingObservers"></a>
+<a name="N1001C"></a><a name="sc_UsingObservers"></a>
 <h2 class="h3">How to use Observers</h2>
 <div class="section">
-<p>
-      
-<em>
-	Note that
-	until <a href="https://issues.apache.org/jira/browse/ZOOKEEPER-578">ZOOKEEPER-578</a>
-	is resolved, you must set electionAlg=0 in every server configuration
-	file. Otherwise an exception will be thrown when you try to start your
-	ensemble.
-      </em>
-    
-</p>
-<p>
-      
-<em>
-	The reason: because Observers do not participate in leader elections,
-	they rely on voting Followers to inform them of changes to the
-	Leader. Currently, only the basic leader election algorithm starts a
-	thread that responds to requests from Observers to identify the current
-	Leader. Work is in progress on other JIRAs to bring this functionality
-	to all leader election protocols.
-      </em>
-    
-</p>
 <p>Setting up a ZooKeeper ensemble that uses Observers is very simple,
     and requires just two changes to your config files. Firstly, in the config
     file of every node that is to be an Observer, you must place this line:
@@ -330,7 +295,7 @@ document.write("Last Published: " + document.lastModified);
 </div>
   
   
-<a name="N10051"></a><a name="ch_UseCases"></a>
+<a name="N1003B"></a><a name="ch_UseCases"></a>
 <h2 class="h3">Example use cases</h2>
 <div class="section">
 <p>

src/docs/src/documentation/content/xdocs/zookeeperObservers.xml

@@ -43,16 +43,6 @@
   <section id="ch_Introduction">
     <title>Observers: Scaling ZooKeeper Without Hurting Write Performance
       </title>
-    <para>
-      <emphasis>
-	Please note: the Observers feature currently only works with the basic
-	leader election protocol, not fast leader election or authenticated fast
-	leader election. This will be remedied when a bug in the leader election
-	protocol code is fixed in the near future. An exception will be thrown
-	if you try to start a cluster containing Observers without
-	electionAlg=0. See below for more details.
-      </emphasis>
-    </para>
     <para>
       Although ZooKeeper performs very well by having clients connect directly
       to voting members of the ensemble, this architecture makes it hard to
@@ -88,25 +78,6 @@
   </section>
   <section id="sc_UsingObservers">
     <title>How to use Observers</title>
-    <para>
-      <emphasis>
-	Note that
-	until <ulink url="https://issues.apache.org/jira/browse/ZOOKEEPER-578">ZOOKEEPER-578</ulink>
-	is resolved, you must set electionAlg=0 in every server configuration
-	file. Otherwise an exception will be thrown when you try to start your
-	ensemble.
-      </emphasis>
-    </para>
-    <para>
-      <emphasis>
-	The reason: because Observers do not participate in leader elections,
-	they rely on voting Followers to inform them of changes to the
-	Leader. Currently, only the basic leader election algorithm starts a
-	thread that responds to requests from Observers to identify the current
-	Leader. Work is in progress on other JIRAs to bring this functionality
-	to all leader election protocols.
-      </emphasis>
-    </para>
     <para>Setting up a ZooKeeper ensemble that uses Observers is very simple,
     and requires just two changes to your config files. Firstly, in the config
     file of every node that is to be an Observer, you must place this line: