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@@ -530,13 +530,27 @@ document.write("Last Published: " + document.lastModified);
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atomically. Reads get all the data bytes associated with a znode and a
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write replaces all the data. Each node has an Access Control List
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(ACL) that restricts who can do what.</p>
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-<a name="N100E2"></a><a name="Ephemeral+Nodes"></a>
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+<p>ZooKeeper was not designed to be a general database or large
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+ object store. Instead, it manages coordination data. This data can
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+ come in the form of configuration, status information, rendezvous, etc.
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+ A common property of the various forms of coordination data is that
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+ they are relatively small: measured in kilobytes.
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+ The ZooKeeper client and the server implementations have sanity checks
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+ to ensure that znodes have less than 1M of data, but the data should
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+ be much less than that on average. Operating on relatively large data
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+ sizes will cause some operations to take much more time than others and
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+ will affect the latencies of some operations because of the extra time
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+ needed to move more data over the network and onto storage media. If
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+ large data storage is needed, the usually pattern of dealing with such
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+ data is to store it on a bulk storage system, such as NFS or HDFS, and
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+ store pointers to the storage locations in ZooKeeper.</p>
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+<a name="N100E5"></a><a name="Ephemeral+Nodes"></a>
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<h4>Ephemeral Nodes</h4>
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<p>ZooKeeper also has the notion of ephemeral nodes. These znodes
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exists as long as the session that created the znode is active. When
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the session ends the znode is deleted. Because of this behavior
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ephemeral znodes are not allowed to have children.</p>
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-<a name="N100EC"></a><a name="Sequence+Nodes+--+Unique+Naming"></a>
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+<a name="N100EF"></a><a name="Sequence+Nodes+--+Unique+Naming"></a>
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<h4>Sequence Nodes -- Unique Naming</h4>
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<p>When creating a znode you can also request that
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ZooKeeper append a monotonicly increasing counter to the end
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@@ -550,7 +564,7 @@ document.write("Last Published: " + document.lastModified);
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(4bytes) maintained by the parent node, the counter will
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overflow when incremented beyond 2147483647 (resulting in a
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name "<path>-2147483647").</p>
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-<a name="N100FB"></a><a name="sc_timeInZk"></a>
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+<a name="N100FE"></a><a name="sc_timeInZk"></a>
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<h3 class="h4">Time in ZooKeeper</h3>
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<p>ZooKeeper tracks time multiple ways:</p>
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<ul>
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@@ -619,7 +633,7 @@ document.write("Last Published: " + document.lastModified);
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</li>
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</ul>
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-<a name="N10133"></a><a name="sc_zkStatStructure"></a>
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+<a name="N10136"></a><a name="sc_zkStatStructure"></a>
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<h3 class="h4">ZooKeeper Stat Structure</h3>
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<p>The Stat structure for each znode in ZooKeeper is made up of the
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following fields:</p>
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@@ -754,7 +768,7 @@ document.write("Last Published: " + document.lastModified);
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</div>
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-<a name="N101A5"></a><a name="ch_zkSessions"></a>
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+<a name="N101A8"></a><a name="ch_zkSessions"></a>
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<h2 class="h3">ZooKeeper Sessions</h2>
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<div class="section">
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<p>To create a client session the application code must provide
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@@ -842,7 +856,7 @@ document.write("Last Published: " + document.lastModified);
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</div>
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-<a name="N101CF"></a><a name="ch_zkWatches"></a>
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+<a name="N101D2"></a><a name="ch_zkWatches"></a>
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<h2 class="h3">ZooKeeper Watches</h2>
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<div class="section">
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<p>All of the read operations in ZooKeeper - <strong>getData()</strong>, <strong>getChildren()</strong>, and <strong>exists()</strong> - have the option of setting a watch as a
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@@ -925,7 +939,7 @@ document.write("Last Published: " + document.lastModified);
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general this all occurs transparently. There is one case where a watch
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may be missed: a watch for the existance of a znode not yet created will
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be missed if the znode is created and deleted while disconnected.</p>
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-<a name="N10205"></a><a name="sc_WatchGuarantees"></a>
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+<a name="N10208"></a><a name="sc_WatchGuarantees"></a>
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<h3 class="h4">What ZooKeeper Guarantees about Watches</h3>
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<p>With regard to watches, ZooKeeper maintains these
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guarantees:</p>
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@@ -960,7 +974,7 @@ document.write("Last Published: " + document.lastModified);
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</li>
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</ul>
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-<a name="N1022A"></a><a name="sc_WatchRememberThese"></a>
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+<a name="N1022D"></a><a name="sc_WatchRememberThese"></a>
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<h3 class="h4">Things to Remember about Watches</h3>
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<ul>
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@@ -1019,7 +1033,7 @@ document.write("Last Published: " + document.lastModified);
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</div>
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-<a name="N10256"></a><a name="sc_ZooKeeperAccessControl"></a>
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+<a name="N10259"></a><a name="sc_ZooKeeperAccessControl"></a>
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<h2 class="h3">ZooKeeper access control using ACLs</h2>
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<div class="section">
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<p>ZooKeeper uses ACLs to control access to its znodes (the
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@@ -1054,7 +1068,7 @@ document.write("Last Published: " + document.lastModified);
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example, the pair <em>(ip:19.22.0.0/16, READ)</em>
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gives the <em>READ</em> permission to any clients with
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an IP address that starts with 19.22.</p>
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-<a name="N10289"></a><a name="sc_ACLPermissions"></a>
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+<a name="N1028C"></a><a name="sc_ACLPermissions"></a>
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<h3 class="h4">ACL Permissions</h3>
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<p>ZooKeeper supports the following permissions:</p>
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<ul>
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@@ -1110,7 +1124,7 @@ document.write("Last Published: " + document.lastModified);
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node, but nothing more. (The problem is, if you want to call
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zoo_exists() on a node that doesn't exist, there is no
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permission to check.)</p>
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-<a name="N102DF"></a><a name="sc_BuiltinACLSchemes"></a>
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+<a name="N102E2"></a><a name="sc_BuiltinACLSchemes"></a>
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<h4>Builtin ACL Schemes</h4>
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<p>ZooKeeeper has the following built in schemes:</p>
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<ul>
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@@ -1159,7 +1173,7 @@ document.write("Last Published: " + document.lastModified);
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</ul>
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-<a name="N10323"></a><a name="ZooKeeper+C+client+API"></a>
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+<a name="N10326"></a><a name="ZooKeeper+C+client+API"></a>
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<h4>ZooKeeper C client API</h4>
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<p>The following constants are provided by the ZooKeeper C
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library:</p>
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@@ -1381,7 +1395,7 @@ int main(int argc, char argv) {
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</div>
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-<a name="N1043A"></a><a name="sc_ZooKeeperPluggableAuthentication"></a>
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+<a name="N1043D"></a><a name="sc_ZooKeeperPluggableAuthentication"></a>
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<h2 class="h3">Pluggable ZooKeeper authentication</h2>
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<div class="section">
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<p>ZooKeeper runs in a variety of different environments with
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@@ -1467,7 +1481,7 @@ authProvider.2=com.f.MyAuth2
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</div>
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-<a name="N104A6"></a><a name="ch_zkGuarantees"></a>
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+<a name="N104A9"></a><a name="ch_zkGuarantees"></a>
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<h2 class="h3">Consistency Guarantees</h2>
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<div class="section">
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<p>ZooKeeper is a high performance, scalable service. Both reads and
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@@ -1593,12 +1607,12 @@ authProvider.2=com.f.MyAuth2
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</div>
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-<a name="N1050D"></a><a name="ch_bindings"></a>
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+<a name="N10510"></a><a name="ch_bindings"></a>
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<h2 class="h3">Bindings</h2>
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<div class="section">
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<p>The ZooKeeper client libraries come in two languages: Java and C.
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The following sections describe these.</p>
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-<a name="N10516"></a><a name="Java+Binding"></a>
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+<a name="N10519"></a><a name="Java+Binding"></a>
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<h3 class="h4">Java Binding</h3>
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<p>There are two packages that make up the ZooKeeper Java binding:
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<strong>org.apache.zookeeper</strong> and <strong>org.apache.zookeeper.data</strong>. The rest of the
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@@ -1665,7 +1679,7 @@ authProvider.2=com.f.MyAuth2
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(SESSION_EXPIRED and AUTH_FAILED), the ZooKeeper object becomes invalid.
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On a close, the two threads shut down and any further access on zookeeper
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handle is undefined behavior and should be avoided. </p>
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-<a name="N1055F"></a><a name="C+Binding"></a>
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+<a name="N10562"></a><a name="C+Binding"></a>
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<h3 class="h4">C Binding</h3>
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<p>The C binding has a single-threaded and multi-threaded library.
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The multi-threaded library is easiest to use and is most similar to the
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@@ -1682,7 +1696,7 @@ authProvider.2=com.f.MyAuth2
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(i.e. FreeBSD 4.x). In all other cases, application developers should
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link with zookeeper_mt, as it includes support for both Sync and Async
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API.</p>
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-<a name="N1056E"></a><a name="Installation"></a>
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+<a name="N10571"></a><a name="Installation"></a>
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<h4>Installation</h4>
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<p>If you're building the client from a check-out from the Apache
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repository, follow the steps outlined below. If you're building from a
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@@ -1813,7 +1827,7 @@ authProvider.2=com.f.MyAuth2
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</li>
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</ol>
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-<a name="N10617"></a><a name="Using+the+C+Client"></a>
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+<a name="N1061A"></a><a name="Using+the+C+Client"></a>
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<h4>Using the C Client</h4>
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<p>You can test your client by running a ZooKeeper server (see
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instructions on the project wiki page on how to run it) and connecting
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@@ -1871,7 +1885,7 @@ authProvider.2=com.f.MyAuth2
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</div>
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-<a name="N1065D"></a><a name="ch_guideToZkOperations"></a>
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+<a name="N10660"></a><a name="ch_guideToZkOperations"></a>
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<h2 class="h3">Building Blocks: A Guide to ZooKeeper Operations</h2>
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<div class="section">
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<p>This section surveys all the operations a developer can perform
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@@ -1889,28 +1903,28 @@ authProvider.2=com.f.MyAuth2
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</li>
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</ul>
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-<a name="N10671"></a><a name="sc_errorsZk"></a>
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+<a name="N10674"></a><a name="sc_errorsZk"></a>
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<h3 class="h4">Handling Errors</h3>
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<p>Both the Java and C client bindings may report errors. The Java client binding does so by throwing KeeperException, calling code() on the exception will return the specific error code. The C client binding returns an error code as defined in the enum ZOO_ERRORS. API callbacks indicate result code for both language bindings. See the API documentation (javadoc for Java, doxygen for C) for full details on the possible errors and their meaning.</p>
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-<a name="N1067B"></a><a name="sc_connectingToZk"></a>
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+<a name="N1067E"></a><a name="sc_connectingToZk"></a>
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<h3 class="h4">Connecting to ZooKeeper</h3>
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<p></p>
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-<a name="N10684"></a><a name="sc_readOps"></a>
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+<a name="N10687"></a><a name="sc_readOps"></a>
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<h3 class="h4">Read Operations</h3>
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<p></p>
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-<a name="N1068D"></a><a name="sc_writeOps"></a>
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+<a name="N10690"></a><a name="sc_writeOps"></a>
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<h3 class="h4">Write Operations</h3>
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<p></p>
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-<a name="N10696"></a><a name="sc_handlingWatches"></a>
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+<a name="N10699"></a><a name="sc_handlingWatches"></a>
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<h3 class="h4">Handling Watches</h3>
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<p></p>
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-<a name="N1069F"></a><a name="sc_miscOps"></a>
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+<a name="N106A2"></a><a name="sc_miscOps"></a>
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<h3 class="h4">Miscelleaneous ZooKeeper Operations</h3>
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<p></p>
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</div>
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-<a name="N106A9"></a><a name="ch_programStructureWithExample"></a>
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+<a name="N106AC"></a><a name="ch_programStructureWithExample"></a>
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<h2 class="h3">Program Structure, with Simple Example</h2>
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<div class="section">
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<p>
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@@ -1919,7 +1933,7 @@ authProvider.2=com.f.MyAuth2
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</div>
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-<a name="N106B4"></a><a name="ch_gotchas"></a>
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+<a name="N106B7"></a><a name="ch_gotchas"></a>
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<h2 class="h3">Gotchas: Common Problems and Troubleshooting</h2>
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<div class="section">
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<p>So now you know ZooKeeper. It's fast, simple, your application
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Mahadev Konar