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<h4 class="panel-title"> - <a role="button" data-toggle="collapse" data-parent="#accordion" href="#collapsetroubleshooting" aria-expanded="false" aria-controls="collapsetroubleshooting"> - Troubleshooting - </a> - </h4> - </div> - <div id="collapsetroubleshooting" class="panel-collapse collapse" role="tabpanel" aria-labelledby="headingOne"> - <div class="panel-body"> - - - <div class="row doc-sidebar-link"><a href="/docs/unreleased/troubleshooting/overview">Overview</a></div> - - </div> - </div> - - - - </div> - </div> - </div> - <div class="col-md-9"> - - <p><a href="/docs/unreleased/">Accumulo unreleased docs</a> >> Administration >> Overview</p> - - - <h1>Overview</h1> - - <h2 id="hardware">Hardware</h2> - -<p>Because we are running essentially two or three systems simultaneously layered -across the cluster: HDFS, Accumulo and MapReduce, it is typical for hardware to -consist of 4 to 8 cores, and 8 to 32 GB RAM. This is so each running process can have -at least one core and 2 - 4 GB each.</p> - -<p>One core running HDFS can typically keep 2 to 4 disks busy, so each machine may -typically have as little as 2 x 300GB disks and as much as 4 x 1TB or 2TB disks.</p> - -<p>It is possible to do with less than this, such as with 1u servers with 2 cores and 4GB -each, but in this case it is recommended to only run up to two processes per -machine â i.e. DataNode and TabletServer or DataNode and MapReduce worker but -not all three. The constraint here is having enough available heap space for all the -processes on a machine.</p> - -<h2 id="network">Network</h2> - -<p>Accumulo communicates via remote procedure calls over TCP/IP for both passing -data and control messages. In addition, Accumulo uses HDFS clients to -communicate with HDFS. To achieve good ingest and query performance, sufficient -network bandwidth must be available between any two machines.</p> - -<p>In addition to needing access to ports associated with HDFS and ZooKeeper, Accumulo will -use the following default ports. Please make sure that they are open, or change -their value in accumulo-site.xml.</p> - -<table> - <thead> - <tr> - <th>Port</th> - <th>Description</th> - <th>Property Name</th> - </tr> - </thead> - <tbody> - <tr> - <td>4445</td> - <td>Shutdown Port (Accumulo MiniCluster)</td> - <td>n/a</td> - </tr> - <tr> - <td>4560</td> - <td>Accumulo monitor (for centralized log display)</td> - <td>monitor.port.log4j</td> - </tr> - <tr> - <td>9995</td> - <td>Accumulo HTTP monitor</td> - <td>monitor.port.client</td> - </tr> - <tr> - <td>9997</td> - <td>Tablet Server</td> - <td>tserver.port.client</td> - </tr> - <tr> - <td>9998</td> - <td>Accumulo GC</td> - <td>gc.port.client</td> - </tr> - <tr> - <td>9999</td> - <td>Master Server</td> - <td>master.port.client</td> - </tr> - <tr> - <td>12234</td> - <td>Accumulo Tracer</td> - <td>trace.port.client</td> - </tr> - <tr> - <td>42424</td> - <td>Accumulo Proxy Server</td> - <td>n/a</td> - </tr> - <tr> - <td>10001</td> - <td>Master Replication service</td> - <td>master.replication.coordinator.port</td> - </tr> - <tr> - <td>10002</td> - <td>TabletServer Replication service</td> - <td>replication.receipt.service.port</td> - </tr> - </tbody> -</table> - -<p>In addition, the user can provide <code class="highlighter-rouge">0</code> and an ephemeral port will be chosen instead. This -ephemeral port is likely to be unique and not already bound. Thus, configuring ports to -use <code class="highlighter-rouge">0</code> instead of an explicit value, should, in most cases, work around any issues of -running multiple distinct Accumulo instances (or any other process which tries to use the -same default ports) on the same hardware. Finally, the *.port.client properties will work -with the port range syntax (M-N) allowing the user to specify a range of ports for the -service to attempt to bind. The ports in the range will be tried in a 1-up manner starting -at the low end of the range to, and including, the high end of the range.</p> - -<h2 id="installation">Installation</h2> - -<p>Download a binary distribution of Accumulo and install it to a directory on a disk with -sufficient space:</p> - -<div class="highlighter-rouge"><pre class="highlight"><code>cd <install directory> -tar xzf accumulo-X.Y.Z-bin.tar.gz # Replace 'X.Y.Z' with your Accumulo version -cd accumulo-X.Y.Z -</code></pre> -</div> - -<p>Repeat this step on each machine in your cluster. Typically, the same <code class="highlighter-rouge"><install directory></code> -is chosen for all machines in the cluster.</p> - -<p>There are four scripts in the <code class="highlighter-rouge">bin/</code> directory that are used to manage Accumulo:</p> - -<ol> - <li><code class="highlighter-rouge">accumulo</code> - Runs Accumulo command-line tools and starts Accumulo processes</li> - <li><code class="highlighter-rouge">accumulo-service</code> - Runs Accumulo processes as services</li> - <li><code class="highlighter-rouge">accumulo-cluster</code> - Manages Accumulo cluster on a single node or several nodes</li> - <li><code class="highlighter-rouge">accumulo-util</code> - Accumulo utilities for creating configuration, native libraries, etc.</li> -</ol> - -<p>These scripts will be used in the remaining instructions to configure and run Accumulo.</p> - -<h2 id="dependencies">Dependencies</h2> - -<p>Accumulo requires HDFS and ZooKeeper to be configured and running -before starting. Password-less SSH should be configured between at least the -Accumulo master and TabletServer machines. It is also a good idea to run Network -Time Protocol (NTP) within the cluster to ensure nodesâ clocks donât get too out of -sync, which can cause problems with automatically timestamped data.</p> - -<h2 id="configuration">Configuration</h2> - -<p>The Accumulo tarball contains a <code class="highlighter-rouge">conf/</code> directory where Accumulo looks for configuration. If you -installed Accumulo using downstream packaging, the <code class="highlighter-rouge">conf/</code> could be something else like -<code class="highlighter-rouge">/etc/accumulo/</code>.</p> - -<p>Before starting Accumulo, the configuration files <code class="highlighter-rouge">accumulo-env.sh</code> and <code class="highlighter-rouge">accumulo-site.xml</code> must -exist in <code class="highlighter-rouge">conf/</code> and be properly configured. If you are using <code class="highlighter-rouge">accumulo-cluster</code> to launch -a cluster, the <code class="highlighter-rouge">conf/</code> directory must also contain hosts file for Accumulo services (i.e <code class="highlighter-rouge">gc</code>, -<code class="highlighter-rouge">masters</code>, <code class="highlighter-rouge">monitor</code>, <code class="highlighter-rouge">tservers</code>, <code class="highlighter-rouge">tracers</code>). You can either create these files manually or run -<code class="highlighter-rouge">accumulo-cluster create-config</code>.</p> - -<p>Logging is configured in <code class="highlighter-rouge">accumulo-env.sh</code> to use three log4j configuration files in <code class="highlighter-rouge">conf/</code>. The -file used depends on the Accumulo command or service being run. Logging for most Accumulo services -(i.e Master, TabletServer, Garbage Collector) is configured by <code class="highlighter-rouge">log4j-service.properties</code> except for -the Monitor which is configured by <code class="highlighter-rouge">log4j-monitor.properties</code>. All Accumulo commands (i.e <code class="highlighter-rouge">init</code>, -<code class="highlighter-rouge">shell</code>, etc) are configured by <code class="highlighter-rouge">log4j.properties</code>.</p> - -<h3 id="configure-accumulo-envsh">Configure accumulo-env.sh</h3> - -<p>Accumulo needs to know where to find the software it depends on. Edit accumulo-env.sh -and specify the following:</p> - -<ol> - <li>Enter the location of Hadoop for <code class="highlighter-rouge">$HADOOP_PREFIX</code></li> - <li>Enter the location of ZooKeeper for <code class="highlighter-rouge">$ZOOKEEPER_HOME</code></li> - <li>Optionally, choose a different location for Accumulo logs using <code class="highlighter-rouge">$ACCUMULO_LOG_DIR</code></li> -</ol> - -<p>Accumulo uses <code class="highlighter-rouge">HADOOP_PREFIX</code> and <code class="highlighter-rouge">ZOOKEEPER_HOME</code> to locate Hadoop and Zookeeper jars -and add them the <code class="highlighter-rouge">CLASSPATH</code> variable. If you are running a vendor-specific release of Hadoop -or Zookeeper, you may need to change how your <code class="highlighter-rouge">CLASSPATH</code> is built in <code class="highlighter-rouge">accumulo-env.sh</code>. If -Accumulo has problems later on finding jars, run <code class="highlighter-rouge">accumulo classpath -d</code> to debug and print -Accumuloâs classpath.</p> - -<p>You may want to change the default memory settings for Accumuloâs TabletServer which are -by set in the <code class="highlighter-rouge">JAVA_OPTS</code> settings for âtserversâ in <code class="highlighter-rouge">accumulo-env.sh</code>. Note the -syntax is that of the Java JVM command line options. This value should be less than the -physical memory of the machines running TabletServers.</p> - -<p>There are similar options for the masterâs memory usage and the garbage collector -process. Reduce these if they exceed the physical RAM of your hardware and -increase them, within the bounds of the physical RAM, if a process fails because of -insufficient memory.</p> - -<p>Note that you will be specifying the Java heap space in accumulo-env.sh. You should -make sure that the total heap space used for the Accumulo tserver and the Hadoop -DataNode and TaskTracker is less than the available memory on each worker node in -the cluster. On large clusters, it is recommended that the Accumulo master, Hadoop -NameNode, secondary NameNode, and Hadoop JobTracker all be run on separate -machines to allow them to use more heap space. If you are running these on the -same machine on a small cluster, likewise make sure their heap space settings fit -within the available memory.</p> - -<h3 id="native-map">Native Map</h3> - -<p>The tablet server uses a data structure called a MemTable to store sorted key/value -pairs in memory when they are first received from the client. When a minor compaction -occurs, this data structure is written to HDFS. The MemTable will default to using -memory in the JVM but a JNI version, called the native map, can be used to significantly -speed up performance by utilizing the memory space of the native operating system. The -native map also avoids the performance implications brought on by garbage collection -in the JVM by causing it to pause much less frequently.</p> - -<h4 id="building">Building</h4> - -<p>32-bit and 64-bit Linux and Mac OS X versions of the native map can be built by executing -<code class="highlighter-rouge">accumulo-util build-native</code>. If your systemâs default compiler options are insufficient, -you can add additional compiler options to the command line, such as options for the -architecture. These will be passed to the Makefile in the environment variable <code class="highlighter-rouge">USERFLAGS</code>.</p> - -<p>Examples:</p> - -<div class="highlighter-rouge"><pre class="highlight"><code>accumulo-util build-native -accumulo-util build-native -m32 -</code></pre> -</div> - -<p>After building the native map from the source, you will find the artifact in -<code class="highlighter-rouge">lib/native</code>. Upon starting up, the tablet server will look -in this directory for the map library. If the file is renamed or moved from its -target directory, the tablet server may not be able to find it. The system can -also locate the native maps shared library by setting <code class="highlighter-rouge">LD_LIBRARY_PATH</code> -(or <code class="highlighter-rouge">DYLD_LIBRARY_PATH</code> on Mac OS X) in <code class="highlighter-rouge">accumulo-env.sh</code>.</p> - -<h4 id="native-maps-configuration">Native Maps Configuration</h4> - -<p>As mentioned, Accumulo will use the native libraries if they are found in the expected -location and <code class="highlighter-rouge">tserver.memory.maps.native.enabled</code> is set to <code class="highlighter-rouge">true</code> (which is the default). -Using the native maps over JVM Maps nets a noticeable improvement in ingest rates; however, -certain configuration variables are important to modify when increasing the size of the -native map.</p> - -<p>To adjust the size of the native map, increase the value of <code class="highlighter-rouge">tserver.memory.maps.max</code>. -By default, the maximum size of the native map is 1GB. When increasing this value, it is -also important to adjust the values of <code class="highlighter-rouge">table.compaction.minor.logs.threshold</code> and -<code class="highlighter-rouge">tserver.walog.max.size</code>. <code class="highlighter-rouge">table.compaction.minor.logs.threshold</code> is the maximum -number of write-ahead log files that a tablet can reference before they will be automatically -minor compacted. <code class="highlighter-rouge">tserver.walog.max.size</code> is the maximum size of a write-ahead log.</p> - -<p>The maximum size of the native maps for a server should be less than the product -of the write-ahead log maximum size and minor compaction threshold for log files:</p> - -<p><code class="highlighter-rouge">$table.compaction.minor.logs.threshold * $tserver.walog.max.size >= $tserver.memory.maps.max</code></p> - -<p>This formula ensures that minor compactions wonât be automatically triggered before the native -maps can be completely saturated.</p> - -<p>Subsequently, when increasing the size of the write-ahead logs, it can also be important -to increase the HDFS block size that Accumulo uses when creating the files for the write-ahead log. -This is controlled via <code class="highlighter-rouge">tserver.wal.blocksize</code>. A basic recommendation is that when -<code class="highlighter-rouge">tserver.walog.max.size</code> is larger than 2GB in size, set <code class="highlighter-rouge">tserver.wal.blocksize</code> to 2GB. -Increasing the block size to a value larger than 2GB can result in decreased write -performance to the write-ahead log file which will slow ingest.</p> - -<h3 id="cluster-specification">Cluster Specification</h3> - -<p>If you are using <code class="highlighter-rouge">accumulo-cluster</code> to start a cluster, configure the following on the -machine that will serve as the Accumulo master:</p> - -<ol> - <li>Write the IP address or domain name of the Accumulo Master to the <code class="highlighter-rouge">conf/masters</code> file.</li> - <li>Write the IP addresses or domain name of the machines that will be TabletServers in <code class="highlighter-rouge">conf/tservers</code>, one per line.</li> -</ol> - -<p>Note that if using domain names rather than IP addresses, DNS must be configured -properly for all machines participating in the cluster. DNS can be a confusing source -of errors.</p> - -<h3 id="configure-accumulo-sitexml">Configure accumulo-site.xml</h3> - -<p>Specify appropriate values for the following settings in <code class="highlighter-rouge">accumulo-site.xml</code>:</p> - -<div class="language-xml highlighter-rouge"><pre class="highlight"><code><span class="nt"><property></span> - <span class="nt"><name></span>instance.zookeeper.host<span class="nt"></name></span> - <span class="nt"><value></span>zooserver-one:2181,zooserver-two:2181<span class="nt"></value></span> - <span class="nt"><description></span>list of zookeeper servers<span class="nt"></description></span> -<span class="nt"></property></span> -</code></pre> -</div> - -<p>This enables Accumulo to find ZooKeeper. Accumulo uses ZooKeeper to coordinate -settings between processes and helps finalize TabletServer failure.</p> - -<div class="language-xml highlighter-rouge"><pre class="highlight"><code><span class="nt"><property></span> - <span class="nt"><name></span>instance.secret<span class="nt"></name></span> - <span class="nt"><value></span>DEFAULT<span class="nt"></value></span> -<span class="nt"></property></span> -</code></pre> -</div> - -<p>The instance needs a secret to enable secure communication between servers. Configure your -secret and make sure that the <code class="highlighter-rouge">accumulo-site.xml</code> file is not readable to other users. -For alternatives to storing the <code class="highlighter-rouge">instance.secret</code> in plaintext, please read the -<code class="highlighter-rouge">Sensitive Configuration Values</code> section.</p> - -<p>Some settings can be modified via the Accumulo shell and take effect immediately, but -some settings require a process restart to take effect. See the <a href="/docs/unreleased/administration/configuration-management">configuration management</a> -documentation for details.</p> - -<h3 id="hostnames-in-configuration-files">Hostnames in configuration files</h3> - -<p>Accumulo has a number of configuration files which can contain references to other hosts in your -network. All of the âhostâ configuration files for Accumulo (<code class="highlighter-rouge">gc</code>, <code class="highlighter-rouge">masters</code>, <code class="highlighter-rouge">tservers</code>, <code class="highlighter-rouge">monitor</code>, -<code class="highlighter-rouge">tracers</code>) as well as <code class="highlighter-rouge">instance.volumes</code> in accumulo-site.xml must contain some host reference.</p> - -<p>While IP address, short hostnames, or fully qualified domain names (FQDN) are all technically valid, it -is good practice to always use FQDNs for both Accumulo and other processes in your Hadoop cluster. -Failing to consistently use FQDNs can have unexpected consequences in how Accumulo uses the FileSystem.</p> - -<p>A common way for this problem can be observed is via applications that use Bulk Ingest. The Accumulo -Master coordinates moving the input files to Bulk Ingest to an Accumulo-managed directory. However, -Accumulo cannot safely move files across different Hadoop FileSystems. This is problematic because -Accumulo also cannot make reliable assertions across what is the same FileSystem which is specified -with different names. Naively, while 127.0.0.1:8020 might be a valid identifier for an HDFS instance, -Accumulo identifies <code class="highlighter-rouge">localhost:8020</code> as a different HDFS instance than <code class="highlighter-rouge">127.0.0.1:8020</code>.</p> - -<h3 id="deploy-configuration">Deploy Configuration</h3> - -<p>Copy accumulo-env.sh and accumulo-site.xml from the <code class="highlighter-rouge">conf/</code> directory on the master to all Accumulo -tablet servers. The âhostâ configuration files files <code class="highlighter-rouge">accumulo-cluster</code> only need to be on servers -where that command is run.</p> - -<h3 id="sensitive-configuration-values">Sensitive Configuration Values</h3> - -<p>Accumulo has a number of properties that can be specified via the accumulo-site.xml -file which are sensitive in nature, instance.secret and trace.token.property.password -are two common examples. Both of these properties, if compromised, have the ability -to result in data being leaked to users who should not have access to that data.</p> - -<p>In Hadoop-2.6.0, a new CredentialProvider class was introduced which serves as a common -implementation to abstract away the storage and retrieval of passwords from plaintext -storage in configuration files. Any Property marked with the <code class="highlighter-rouge">Sensitive</code> annotation -is a candidate for use with these CredentialProviders. For version of Hadoop which lack -these classes, the feature will just be unavailable for use.</p> - -<p>A comma separated list of CredentialProviders can be configured using the Accumulo Property -<code class="highlighter-rouge">general.security.credential.provider.paths</code>. Each configured URL will be consulted -when the Configuration object for accumulo-site.xml is accessed.</p> - -<h3 id="using-a-javakeystorecredentialprovider-for-storage">Using a JavaKeyStoreCredentialProvider for storage</h3> - -<p>One of the implementations provided in Hadoop-2.6.0 is a Java KeyStore CredentialProvider. -Each entry in the KeyStore is the Accumulo Property key name. For example, to store the -<code class="highlighter-rouge">instance.secret</code>, the following command can be used:</p> - -<div class="highlighter-rouge"><pre class="highlight"><code>hadoop credential create instance.secret --provider jceks://file/etc/accumulo/conf/accumulo.jceks -</code></pre> -</div> - -<p>The command will then prompt you to enter the secret to use and create a keystore in:</p> - -<div class="highlighter-rouge"><pre class="highlight"><code>/path/to/accumulo/conf/accumulo.jceks -</code></pre> -</div> - -<p>Then, accumulo-site.xml must be configured to use this KeyStore as a CredentialProvider:</p> - -<div class="language-xml highlighter-rouge"><pre class="highlight"><code><span class="nt"><property></span> - <span class="nt"><name></span>general.security.credential.provider.paths<span class="nt"></name></span> - <span class="nt"><value></span>jceks://file/path/to/accumulo/conf/accumulo.jceks<span class="nt"></value></span> -<span class="nt"></property></span> -</code></pre> -</div> - -<p>This configuration will then transparently extract the <code class="highlighter-rouge">instance.secret</code> from -the configured KeyStore and alleviates a human readable storage of the sensitive -property.</p> - -<p>A KeyStore can also be stored in HDFS, which will make the KeyStore readily available to -all Accumulo servers. If the local filesystem is used, be aware that each Accumulo server -will expect the KeyStore in the same location.</p> - -<h3 id="client-configuration">Client Configuration</h3> - -<p>In version 1.6.0, Accumulo included a new type of configuration file known as a client -configuration file. One problem with the traditional âsite.xmlâ file that is prevalent -through Hadoop is that it is a single file used by both clients and servers. This makes -it very difficult to protect secrets that are only meant for the server processes while -allowing the clients to connect to the servers.</p> - -<p>The client configuration file is a subset of the information stored in accumulo-site.xml -meant only for consumption by clients of Accumulo. By default, Accumulo checks a number -of locations for a client configuration by default:</p> - -<ul> - <li><code class="highlighter-rouge">/path/to/accumulo/conf/client.conf</code></li> - <li><code class="highlighter-rouge">/etc/accumulo/client.conf</code></li> - <li><code class="highlighter-rouge">/etc/accumulo/conf/client.conf</code></li> - <li><code class="highlighter-rouge">~/.accumulo/config</code></li> -</ul> - -<p>These files are <a href="https://en.wikipedia.org/wiki/.properties";>Java Properties files</a>. These files -can currently contain information about ZooKeeper servers, RPC properties (such as SSL or SASL -connectors), distributed tracing properties. Valid properties are defined by the <a href="https://github.com/apache/accumulo/blob/f1d0ec93d9f13ff84844b5ac81e4a7b383ced467/core/src/main/java/org/apache/accumulo/core/client/ClientConfiguration.java#L54";>ClientProperty</a> -enum contained in the client API.</p> - -<h4 id="custom-table-tags">Custom Table Tags</h4> - -<p>Accumulo has the ability for users to add custom tags to tables. This allows -applications to set application-level metadata about a table. These tags can be -anything from a table description, administrator notes, date created, etc. -This is done by naming and setting a property with a prefix <code class="highlighter-rouge">table.custom.*</code>.</p> - -<p>Currently, table properties are stored in ZooKeeper. This means that the number -and size of custom properties should be restricted on the order of 10âs of properties -at most without any properties exceeding 1MB in size. ZooKeeperâs performance can be -very sensitive to an excessive number of nodes and the sizes of the nodes. Applications -which leverage the user of custom properties should take these warnings into -consideration. There is no enforcement of these warnings via the API.</p> - -<h4 id="configuring-the-classloader">Configuring the ClassLoader</h4> - -<p>Accumulo builds its Java classpath in <code class="highlighter-rouge">accumulo-env.sh</code>. After an Accumulo application has started, it will load classes from the locations -specified in the deprecated <code class="highlighter-rouge">general.classpaths</code> property. Additionally, Accumulo will load classes from the locations specified in the -<code class="highlighter-rouge">general.dynamic.classpaths</code> property and will monitor and reload them if they change. The reloading feature is useful during the development -and testing of iterators as new or modified iterator classes can be deployed to Accumulo without having to restart the database. -/ -Accumulo also has an alternate configuration for the classloader which will allow it to load classes from remote locations. This mechanism -uses Apache Commons VFS which enables locations such as http and hdfs to be used. This alternate configuration also uses the -<code class="highlighter-rouge">general.classpaths</code> property in the same manner described above. It differs in that you need to configure the -<code class="highlighter-rouge">general.vfs.classpaths</code> property instead of the <code class="highlighter-rouge">general.dynamic.classpath</code> property. As in the default configuration, this alternate -configuration will also monitor the vfs locations for changes and reload if necessary.</p> - -<p>The Accumulo classpath can be viewed in human readable format by running <code class="highlighter-rouge">accumulo classpath -d</code>.</p> - -<h5 id="classloader-contexts">ClassLoader Contexts</h5> - -<p>With the addition of the VFS based classloader, we introduced the notion of classloader contexts. A context is identified -by a name and references a set of locations from which to load classes and can be specified in the accumulo-site.xml file or added -using the <code class="highlighter-rouge">config</code> command in the shell. Below is an example for specify the app1 context in the accumulo-site.xml file:</p> - -<div class="language-xml highlighter-rouge"><pre class="highlight"><code><span class="nt"><property></span> - <span class="nt"><name></span>general.vfs.context.classpath.app1<span class="nt"></name></span> - <span class="nt"><value></span>hdfs://localhost:8020/applicationA/classpath/.*.jar,file:///opt/applicationA/lib/.*.jar<span class="nt"></value></span> - <span class="nt"><description></span>Application A classpath, loads jars from HDFS and local file system<span class="nt"></description></span> -<span class="nt"></property></span> -</code></pre> -</div> - -<p>The default behavior follows the Java ClassLoader contract in that classes, if they exists, are loaded from the parent classloader first. -You can override this behavior by delegating to the parent classloader after looking in this classloader first. An example of this -configuration is:</p> - -<div class="language-xml highlighter-rouge"><pre class="highlight"><code><span class="nt"><property></span> - <span class="nt"><name></span>general.vfs.context.classpath.app1.delegation=post<span class="nt"></name></span> - <span class="nt"><value></span>hdfs://localhost:8020/applicationA/classpath/.*.jar,file:///opt/applicationA/lib/.*.jar<span class="nt"></value></span> - <span class="nt"><description></span>Application A classpath, loads jars from HDFS and local file system<span class="nt"></description></span> -<span class="nt"></property></span> -</code></pre> -</div> - -<p>To use contexts in your application you can set the <code class="highlighter-rouge">table.classpath.context</code> on your tables or use the <code class="highlighter-rouge">setClassLoaderContext()</code> method on Scanner -and BatchScanner passing in the name of the context, app1 in the example above. Setting the property on the table allows your minc, majc, and scan -iterators to load classes from the locations defined by the context. Passing the context name to the scanners allows you to override the table setting -to load only scan time iterators from a different location.</p> - -<h2 id="initialization">Initialization</h2> - -<p>Accumulo must be initialized to create the structures it uses internally to locate -data across the cluster. HDFS is required to be configured and running before -Accumulo can be initialized.</p> - -<p>Once HDFS is started, initialization can be performed by executing -<code class="highlighter-rouge">accumulo init</code> . This script will prompt for a name -for this instance of Accumulo. The instance name is used to identify a set of tables -and instance-specific settings. The script will then write some information into -HDFS so Accumulo can start properly.</p> - -<p>The initialization script will prompt you to set a root password. Once Accumulo is -initialized it can be started.</p> - -<h2 id="running">Running</h2> - -<h3 id="starting-accumulo">Starting Accumulo</h3> - -<p>Make sure Hadoop is configured on all of the machines in the cluster, including -access to a shared HDFS instance. Make sure HDFS and ZooKeeper are running. -Make sure ZooKeeper is configured and running on at least one machine in the -cluster. -Start Accumulo using <code class="highlighter-rouge">accumulo-cluster start</code>.</p> - -<p>To verify that Accumulo is running, check the <a href="/docs/unreleased/administration/overview#monitoring">Accumulo monitor</a>. -In addition, the Shell can provide some information about the status of tables via reading the metadata tables.</p> - -<h3 id="stopping-accumulo">Stopping Accumulo</h3> - -<p>To shutdown cleanly, run <code class="highlighter-rouge">accumulo-cluster stop</code> and the master will orchestrate the -shutdown of all the tablet servers. Shutdown waits for all minor compactions to finish, so it may -take some time for particular configurations.</p> - -<h3 id="adding-a-tablet-server">Adding a Tablet Server</h3> - -<p>Update your <code class="highlighter-rouge">conf/tservers</code> file to account for the addition.</p> - -<p>Next, ssh to each of the hosts you want to add and run:</p> - -<div class="highlighter-rouge"><pre class="highlight"><code>accumulo-service tserver start -</code></pre> -</div> - -<p>Make sure the host in question has the new configuration, or else the tablet -server wonât start; at a minimum this needs to be on the host(s) being added, -but in practice itâs good to ensure consistent configuration across all nodes.</p> - -<h3 id="decomissioning-a-tablet-server">Decomissioning a Tablet Server</h3> - -<p>If you need to take a node out of operation, you can trigger a graceful shutdown of a tablet -server. Accumulo will automatically rebalance the tablets across the available tablet servers.</p> - -<div class="highlighter-rouge"><pre class="highlight"><code>accumulo admin stop <host(s)> {<host> ...} -</code></pre> -</div> - -<p>Alternatively, you can ssh to each of the hosts you want to remove and run:</p> - -<div class="highlighter-rouge"><pre class="highlight"><code>accumulo-service tserver stop -</code></pre> -</div> - -<p>Be sure to update your <code class="highlighter-rouge">conf/tservers</code> file to -account for the removal of these hosts. Bear in mind that the monitor will not re-read the -tservers file automatically, so it will report the decommissioned servers as down; itâs -recommended that you restart the monitor so that the node list is up to date.</p> - -<p>The steps described to decommission a node can also be used (without removal of the host -from the <code class="highlighter-rouge">conf/tservers</code> file) to gracefully stop a node. This will -ensure that the tabletserver is cleanly stopped and recovery will not need to be performed -when the tablets are re-hosted.</p> - -<h3 id="restarting-process-on-a-node">Restarting process on a node</h3> - -<p>Occasionally, it might be necessary to restart the processes on a specific node. In addition -to the <code class="highlighter-rouge">accumulo-cluster</code> script, Accumulo has a <code class="highlighter-rouge">accumulo-service</code> script that -can be use to start/stop processes on a node.</p> - -<h4 id="a-note-on-rolling-restarts">A note on rolling restarts</h4> - -<p>For sufficiently large Accumulo clusters, restarting multiple TabletServers within a short window can place significant -load on the Master server. If slightly lower availability is acceptable, this load can be reduced by globally setting -<code class="highlighter-rouge">table.suspend.duration</code> to a positive value.</p> - -<p>With <code class="highlighter-rouge">table.suspend.duration</code> set to, say, <code class="highlighter-rouge">5m</code>, Accumulo will wait -for 5 minutes for any dead TabletServer to return before reassigning that TabletServerâs responsibilities to other TabletServers. -If the TabletServer returns to the cluster before the specified timeout has elapsed, Accumulo will assign the TabletServer -its original responsibilities.</p> - -<p>It is important not to choose too large a value for <code class="highlighter-rouge">table.suspend.duration</code>, as during this time, all scans against the -data that TabletServer had hosted will block (or time out).</p> - -<h3 id="running-multiple-tabletservers-on-a-single-node">Running multiple TabletServers on a single node</h3> - -<p>With very powerful nodes, it may be beneficial to run more than one TabletServer on a given -node. This decision should be made carefully and with much deliberation as Accumulo is designed -to be able to scale to using 10âs of GB of RAM and 10âs of CPU cores.</p> - -<p>Accumulo TabletServers bind certain ports on the host to accommodate remote procedure calls to/from -other nodes. Running more than one TabletServer on a host requires that you set the environment variable -<code class="highlighter-rouge">ACCUMULO_SERVICE_INSTANCE</code> to an instance number (i.e 1, 2) for each instance that is started. Also, set -these properties in <code class="highlighter-rouge">accumulo-site.xml</code>:</p> - -<div class="language-xml highlighter-rouge"><pre class="highlight"><code> <span class="nt"><property></span> - <span class="nt"><name></span>tserver.port.search<span class="nt"></name></span> - <span class="nt"><value></span>true<span class="nt"></value></span> - <span class="nt"></property></span> - <span class="nt"><property></span> - <span class="nt"><name></span>replication.receipt.service.port<span class="nt"></name></span> - <span class="nt"><value></span>0<span class="nt"></value></span> - <span class="nt"></property></span> -</code></pre> -</div> - -<h2 id="monitoring">Monitoring</h2> - -<h3 id="accumulo-monitor">Accumulo Monitor</h3> - -<p>The Accumulo Monitor provides an interface for monitoring the status and health of -Accumulo components. The Accumulo Monitor provides a web UI for accessing this information at -<code class="highlighter-rouge">http://_monitorhost_:9995/</code>.</p> - -<p>Things highlighted in yellow may be in need of attention. -If anything is highlighted in red on the monitor page, it is something that definitely needs attention.</p> - -<p>The Overview page contains some summary information about the Accumulo instance, including the version, instance name, and instance ID. -There is a table labeled Accumulo Master with current status, a table listing the active Zookeeper servers, and graphs displaying various metrics over time. -These include ingest and scan performance and other useful measurements.</p> - -<p>The Master Server, Tablet Servers, and Tables pages display metrics grouped in different ways (e.g. by tablet server or by table). -Metrics typically include number of entries (key/value pairs), ingest and query rates. -The number of running scans, major and minor compactions are in the form <em>number_running</em> (<em>number_queued</em>). -Another important metric is hold time, which is the amount of time a tablet has been waiting but unable to flush its memory in a minor compaction.</p> - -<p>The Server Activity page graphically displays tablet server status, with each server represented as a circle or square. -Different metrics may be assigned to the nodesâ color and speed of oscillation. -The Overall Avg metric is only used on the Server Activity page, and represents the average of all the other metrics (after normalization). -Similarly, the Overall Max metric picks the metric with the maximum normalized value.</p> - -<p>The Garbage Collector page displays a list of garbage collection cycles, the number of files found of each type (including deletion candidates in use and files actually deleted), and the length of the deletion cycle. -The Traces page displays data for recent traces performed (see the following section for information on <a href="/docs/unreleased/administration/overview#tracing">tracing</a>). -The Recent Logs page displays warning and error logs forwarded to the monitor from all Accumulo processes. -Also, the XML and JSON links provide metrics in XML and JSON formats, respectively.</p> - -<h3 id="ssl">SSL</h3> - -<p>SSL may be enabled for the monitor page by setting the following properties in the <code class="highlighter-rouge">accumulo-site.xml</code> file:</p> - -<div class="highlighter-rouge"><pre class="highlight"><code>monitor.ssl.keyStore -monitor.ssl.keyStorePassword -monitor.ssl.trustStore -monitor.ssl.trustStorePassword -</code></pre> -</div> - -<p>If the Accumulo conf directory has been configured (in particular the <code class="highlighter-rouge">accumulo-env.sh</code> file must be set up), the -<code class="highlighter-rouge">accumulo-util gen-monitor-cert</code> command can be used to create the keystore and truststore files with random passwords. The command -will print out the properties that need to be added to the <code class="highlighter-rouge">accumulo-site.xml</code> file. The stores can also be generated manually with the -Java <code class="highlighter-rouge">keytool</code> command, whose usage can be seen in the <code class="highlighter-rouge">accumulo-util</code> script.</p> - -<p>If desired, the SSL ciphers allowed for connections can be controlled via the following properties in <code class="highlighter-rouge">accumulo-site.xml</code>:</p> - -<div class="highlighter-rouge"><pre class="highlight"><code>monitor.ssl.include.ciphers -monitor.ssl.exclude.ciphers -</code></pre> -</div> - -<p>If SSL is enabled, the monitor URL can only be accessed via https. -This also allows you to access the Accumulo shell through the monitor page. -The left navigation bar will have a new link to Shell. -An Accumulo user name and password must be entered for access to the shell.</p> - -<h2 id="metrics">Metrics</h2> - -<p>Accumulo can expose metrics through a legacy metrics library and using the Hadoop Metrics2 library.</p> - -<h3 id="legacy-metrics">Legacy Metrics</h3> - -<p>Accumulo has a legacy metrics library that can be exposes metrics using JMX endpoints or file-based logging. These metrics can -be enabled by setting <code class="highlighter-rouge">general.legacy.metrics</code> to <code class="highlighter-rouge">true</code> in <code class="highlighter-rouge">accumulo-site.xml</code> and placing the <code class="highlighter-rouge">accumulo-metrics.xml</code> -configuration file on the classpath (which is typically done by placing the file in the <code class="highlighter-rouge">conf/</code> directory). A template for -<code class="highlighter-rouge">accumulo-metrics.xml</code> can be found in <code class="highlighter-rouge">conf/templates</code> of the Accumulo tarball.</p> - -<h3 id="hadoop-metrics2">Hadoop Metrics2</h3> - -<p>Hadoop Metrics2 is a library which allows for routing of metrics generated by registered MetricsSources to -configured MetricsSinks. Examples of sinks that are implemented by Hadoop include file-based logging, Graphite and Ganglia. -All metric sources are exposed via JMX when using Metrics2.</p> - -<p>Metrics2 is configured by examining the classpath for a file that matches <code class="highlighter-rouge">hadoop-metrics2*.properties</code>. The Accumulo tarball -contains an example <code class="highlighter-rouge">hadoop-metrics2-accumulo.properties</code> file in <code class="highlighter-rouge">conf/templates</code> which can be copied to <code class="highlighter-rouge">conf/</code> to place -on classpath. This file is used to enable file, Graphite or Ganglia sinks (some minimal configuration required for Graphite -and Ganglia). Because the Hadoop configuration is also on the Accumulo classpath, be sure that you do not have multiple -Metrics2 configuration files. It is recommended to consolidate metrics in a single properties file in a central location to -remove ambiguity. The contents of <code class="highlighter-rouge">hadoop-metrics2-accumulo.properties</code> can be added to a central <code class="highlighter-rouge">hadoop-metrics2.properties</code> -in <code class="highlighter-rouge">$HADOOP_CONF_DIR</code>.</p> - -<p>As a note for configuring the file sink, the provided path should be absolute. A relative path or file name will be created relative -to the directory in which the Accumulo process was started. External tools, such as logrotate, can be used to prevent these files -from growing without bound.</p> - -<p>Each server process should have log messages from the Metrics2 library about the sinks that were created. Be sure to check -the Accumulo processes log files when debugging missing metrics output.</p> - -<p>For additional information on configuring Metrics2, visit the <a href="https://hadoop.apache.org/docs/current/api/org/apache/hadoop/metrics2/package-summary.html";>Javadoc page for Metrics2</a>.</p> - -<h2 id="tracing">Tracing</h2> - -<p>It can be difficult to determine why some operations are taking longer -than expected. For example, you may be looking up items with very low -latency, but sometimes the lookups take much longer. Determining the -cause of the delay is difficult because the system is distributed, and -the typical lookup is fast.</p> - -<p>Accumulo has been instrumented to record the time that various -operations take when tracing is turned on. The fact that tracing is -enabled follows all the requests made on behalf of the user throughout -the distributed infrastructure of accumulo, and across all threads of -execution.</p> - -<p>These time spans will be inserted into the <code class="highlighter-rouge">trace</code> table in -Accumulo. You can browse recent traces from the Accumulo monitor -page. You can also read the <code class="highlighter-rouge">trace</code> table directly like any -other table.</p> - -<p>The design of Accumuloâs distributed tracing follows that of <a href="http://research.google.com/pubs/pub36356.html";>Googleâs Dapper</a>.</p> - -<h3 id="tracers">Tracers</h3> - -<p>To collect traces, Accumulo needs at least one tracer server running. If you are using <code class="highlighter-rouge">accumulo-cluster</code> to start your cluster, -configure your server in <code class="highlighter-rouge">conf/tracers</code>. The server collects traces from clients and writes them to the <code class="highlighter-rouge">trace</code> table. The Accumulo -user that the tracer connects to Accumulo with can be configured with the following properties (see the <a href="/docs/unreleased/administration/configuration-management">configuration management</a> -page for setting Accumulo server properties)</p> - -<div class="highlighter-rouge"><pre class="highlight"><code>trace.user -trace.token.property.password -</code></pre> -</div> - -<p>Other tracer configuration properties include</p> - -<div class="highlighter-rouge"><pre class="highlight"><code>trace.port.client - port tracer listens on -trace.table - table tracer writes to -trace.zookeeper.path - zookeeper path where tracers register -</code></pre> -</div> - -<p>The zookeeper path is configured to /tracers by default. If -multiple Accumulo instances are sharing the same ZooKeeper -quorum, take care to configure Accumulo with unique values for -this property.</p> - -<h3 id="configuring-tracing">Configuring Tracing</h3> - -<p>Traces are collected via SpanReceivers. The default SpanReceiver -configured is org.apache.accumulo.core.trace.ZooTraceClient, which -sends spans to an Accumulo Tracer process, as discussed in the -previous section. This default can be changed to a different span -receiver, or additional span receivers can be added in a -comma-separated list, by modifying the property</p> - -<div class="highlighter-rouge"><pre class="highlight"><code>trace.span.receivers -</code></pre> -</div> - -<p>Individual span receivers may require their own configuration -parameters, which are grouped under the trace.span.receiver.* -prefix. ZooTraceClient uses the following properties. The first -three properties are populated from other Accumulo properties, -while the remaining ones should be prefixed with -trace.span.receiver. when set in the Accumulo configuration.</p> - -<div class="highlighter-rouge"><pre class="highlight"><code>tracer.zookeeper.host - populated from instance.zookeepers -tracer.zookeeper.timeout - populated from instance.zookeeper.timeout -tracer.zookeeper.path - populated from trace.zookeeper.path -tracer.send.timer.millis - timer for flushing send queue (in ms, default 1000) -tracer.queue.size - max queue size (default 5000) -tracer.span.min.ms - minimum span length to store (in ms, default 1) -</code></pre> -</div> - -<p>Note that to configure an Accumulo client for tracing, including -the Accumulo shell, the client configuration must be given the same -trace.span.receivers, trace.span.receiver.*, and trace.zookeeper.path -properties as the servers have.</p> - -<p>Hadoop can also be configured to send traces to Accumulo, as of -Hadoop 2.6.0, by setting properties in Hadoopâs core-site.xml -file. Instead of using the trace.span.receiver.* prefix, Hadoop -uses hadoop.htrace.*. The Hadoop configuration does not have -access to Accumuloâs properties, so the -hadoop.htrace.tracer.zookeeper.host property must be specified. -The zookeeper timeout defaults to 30000 (30 seconds), and the -zookeeper path defaults to /tracers. An example of configuring -Hadoop to send traces to ZooTraceClient is</p> - -<div class="language-xml highlighter-rouge"><pre class="highlight"><code> <span class="nt"><property></span> - <span class="nt"><name></span>hadoop.htrace.spanreceiver.classes<span class="nt"></name></span> - <span class="nt"><value></span>org.apache.accumulo.core.trace.ZooTraceClient<span class="nt"></value></span> - <span class="nt"></property></span> - <span class="nt"><property></span> - <span class="nt"><name></span>hadoop.htrace.tracer.zookeeper.host<span class="nt"></name></span> - <span class="nt"><value></span>zookeeperHost:2181<span class="nt"></value></span> - <span class="nt"></property></span> - <span class="nt"><property></span> - <span class="nt"><name></span>hadoop.htrace.tracer.zookeeper.path<span class="nt"></name></span> - <span class="nt"><value></span>/tracers<span class="nt"></value></span> - <span class="nt"></property></span> - <span class="nt"><property></span> - <span class="nt"><name></span>hadoop.htrace.tracer.span.min.ms<span class="nt"></name></span> - <span class="nt"><value></span>1<span class="nt"></value></span> - <span class="nt"></property></span> -</code></pre> -</div> - -<p>The accumulo-core, accumulo-tracer, accumulo-fate and libthrift -jars must also be placed on Hadoopâs classpath.</p> - -<h5 id="adding-additional-spanreceivers">Adding additional SpanReceivers</h5> - -<p><a href="https://github.com/openzipkin/zipkin";>Zipkin</a> has a SpanReceiver supported by HTrace and popularized by Twitter -that users looking for a more graphical trace display may opt to use. -The following steps configure Accumulo to use <code class="highlighter-rouge">org.apache.htrace.impl.ZipkinSpanReceiver</code> -in addition to the Accumuloâs default ZooTraceClient, and they serve as a template -for adding any SpanReceiver to Accumulo:</p> - -<ol> - <li> - <p>Add the Jar containing the ZipkinSpanReceiver class file to the -<code class="highlighter-rouge">lib/</code> directory. It is critical that the Jar is placed in -<code class="highlighter-rouge">lib/</code> and NOT in <code class="highlighter-rouge">lib/ext/</code> so that the new SpanReceiver class -is visible to the same class loader of htrace-core.</p> - </li> - <li> - <p>Add the following to <code class="highlighter-rouge">accumulo-site.xml</code>:</p> - - <div class="highlighter-rouge"><pre class="highlight"><code> <property> - <name>trace.span.receivers</name> - <value>org.apache.accumulo.tracer.ZooTraceClient,org.apache.htrace.impl.ZipkinSpanReceiver</value> - </property> -</code></pre> - </div> - </li> - <li> - <p>Restart your Accumulo tablet servers.</p> - </li> -</ol> - -<p>In order to use ZipkinSpanReceiver from a client as well as the Accumulo server,</p> - -<ol> - <li> - <p>Ensure your client can see the ZipkinSpanReceiver class at runtime. For Maven projects, -this is easily done by adding to your clientâs pom.xml (taking care to specify a good version)</p> - - <div class="highlighter-rouge"><pre class="highlight"><code> <dependency> - <groupId>org.apache.htrace</groupId> - <artifactId>htrace-zipkin</artifactId> - <version>3.1.0-incubating</version> - <scope>runtime</scope> - </dependency> -</code></pre> - </div> - </li> - <li> - <p>Add the following to your client configuration.</p> - - <div class="highlighter-rouge"><pre class="highlight"><code> trace.span.receivers=org.apache.accumulo.tracer.ZooTraceClient,org.apache.htrace.impl.ZipkinSpanReceiver -</code></pre> - </div> - </li> - <li> - <p>Instrument your client as in the next section.</p> - </li> -</ol> - -<p>Your SpanReceiver may require additional properties, and if so these should likewise -be placed in the ClientConfiguration (if applicable) and Accumuloâs <code class="highlighter-rouge">accumulo-site.xml</code>. -Two such properties for ZipkinSpanReceiver, listed with their default values, are</p> - -<div class="language-xml highlighter-rouge"><pre class="highlight"><code> <span class="nt"><property></span> - <span class="nt"><name></span>trace.span.receiver.zipkin.collector-hostname<span class="nt"></name></span> - <span class="nt"><value></span>localhost<span class="nt"></value></span> - <span class="nt"></property></span> - <span class="nt"><property></span> - <span class="nt"><name></span>trace.span.receiver.zipkin.collector-port<span class="nt"></name></span> - <span class="nt"><value></span>9410<span class="nt"></value></span> - <span class="nt"></property></span> -</code></pre> -</div> - -<h4 id="instrumenting-a-client">Instrumenting a Client</h4> - -<p>Tracing can be used to measure a client operation, such as a scan, as -the operation traverses the distributed system. To enable tracing for -your application call</p> - -<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="kn">import</span> <span class="nn">org.apache.accumulo.core.trace.DistributedTrace</span><span class="o">;</span> -<span class="o">...</span> -<span class="n">DistributedTrace</span><span class="o">.</span><span class="na">enable</span><span class="o">(</span><span class="n">hostname</span><span class="o">,</span> <span class="s">"myApplication"</span><span class="o">);</span> -<span class="c1">// do some tracing</span> -<span class="o">...</span> -<span class="n">DistributedTrace</span><span class="o">.</span><span class="na">disable</span><span class="o">();</span> -</code></pre> -</div> - -<p>Once tracing has been enabled, a client can wrap an operation in a trace.</p> - -<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="kn">import</span> <span class="nn">org.apache.htrace.Sampler</span><span class="o">;</span> -<span class="kn">import</span> <span class="nn">org.apache.htrace.Trace</span><span class="o">;</span> -<span class="kn">import</span> <span class="nn">org.apache.htrace.TraceScope</span><span class="o">;</span> -<span class="o">...</span> -<span class="n">TraceScope</span> <span class="n">scope</span> <span class="o">=</span> <span class="n">Trace</span><span class="o">.</span><span class="na">startSpan</span><span class="o">(</span><span class="s">"Client Scan"</span><span class="o">,</span> <span class="n">Sampler</span><span class="o">.</span><span class="na">ALWAYS</span><span class="o">);</span> -<span class="n">BatchScanner</span> <span class="n">scanner</span> <span class="o">=</span> <span class="n">conn</span><span class="o">.</span><span class="na">createBatchScanner</span><span class="o">(...);</span> -<span class="c1">// Configure your scanner</span> -<span class="k">for</span> <span class="o">(</span><span class="n">Entry</span> <span class="n">entry</span> <span class="o">:</span> <span class="n">scanner</span><span class="o">)</span> <span class="o">{</span> -<span class="o">}</span> -<span class="n">scope</span><span class="o">.</span><span class="na">close</span><span class="o">();</span> -</code></pre> -</div> - -<p>The user can create additional Spans within a Trace.</p> - -<p>The sampler (such as <code class="highlighter-rouge">Sampler.ALWAYS</code>) for the trace should only be specified with a top-level span, -and subsequent spans will be collected depending on whether that first span was sampled. -Donât forget to specify a Sampler at the top-level span -because the default Sampler only samples when part of a pre-existing trace, -which will never occur in a client that never specifies a Sampler.</p> - -<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="n">TraceScope</span> <span class="n">scope</span> <span class="o">=</span> <span class="n">Trace</span><span class="o">.</span><span class="na">startSpan</span><span class="o">(</span><span class="s">"Client Update"</span><span class="o">,</span> <span class="n">Sampler</span><span class="o">.</span><span class="na">ALWAYS</span><span class="o">);</span> -<span class="o">...</span> -<span class="n">TraceScope</span> <span class="n">readScope</span> <span class="o">=</span> <span class="n">Trace</span><span class="o">.</span><span class="na">startSpan</span><span class="o">(</span><span class="s">"Read"</span><span class="o">);</span> -<span class="o">...</span> -<span class="n">readScope</span><span class="o">.</span><span class="na">close</span><span class="o">();</span> -<span class="o">...</span> -<span class="n">TraceScope</span> <span class="n">writeScope</span> <span class="o">=</span> <span class="n">Trace</span><span class="o">.</span><span class="na">startSpan</span><span class="o">(</span><span class="s">"Write"</span><span class="o">);</span> -<span class="o">...</span> -<span class="n">writeScope</span><span class="o">.</span><span class="na">close</span><span class="o">();</span> -<span class="n">scope</span><span class="o">.</span><span class="na">close</span><span class="o">();</span> -</code></pre> -</div> - -<p>Like Dapper, Accumulo tracing supports user defined annotations to associate additional data with a Trace. -Checking whether currently tracing is necessary when using a sampler other than Sampler.ALWAYS.</p> - -<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="o">...</span> -<span class="kt">int</span> <span class="n">numberOfEntriesRead</span> <span class="o">=</span> <span class="mi">0</span><span class="o">;</span> -<span class="n">TraceScope</span> <span class="n">readScope</span> <span class="o">=</span> <span class="n">Trace</span><span class="o">.</span><span class="na">startSpan</span><span class="o">(</span><span class="s">"Read"</span><span class="o">);</span> -<span class="c1">// Do the read, update the counter</span> -<span class="o">...</span> -<span class="k">if</span> <span class="o">(</span><span class="n">Trace</span><span class="o">.</span><span class="na">isTracing</span><span class="o">)</span> - <span class="n">readScope</span><span class="o">.</span><span class="na">getSpan</span><span class="o">().</span><span class="na">addKVAnnotation</span><span class="o">(</span><span class="s">"Number of Entries Read"</span><span class="o">.</span><span class="na">getBytes</span><span class="o">(</span><span class="n">StandardCharsets</span><span class="o">.</span><span class="na">UTF_8</span><span class="o">),</span> - <span class="n">String</span><span class="o">.</span><span class="na">valueOf</span><span class="o">(</span><span class="n">numberOfEntriesRead</span><span class="o">).</span><span class="na">getBytes</span><span class="o">(</span><span class="n">StandardCharsets</span><span class="o">.</span><span class="na">UTF_8</span><span class="o">));</span> -</code></pre> -</div> - -<p>It is also possible to add timeline annotations to your spans. -This associates a string with a given timestamp between the start and stop times for a span.</p> - -<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="o">...</span> -<span class="n">writeScope</span><span class="o">.</span><span class="na">getSpan</span><span class="o">().</span><span class="na">addTimelineAnnotation</span><span class="o">(</span><span class="s">"Initiating Flush"</span><span class="o">);</span> -</code></pre> -</div> - -<p>Some client operations may have a high volume within your -application. As such, you may wish to only sample a percentage of -operations for tracing. As seen below, the CountSampler can be used to -help enable tracing for 1-in-1000 operations</p> - -<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="kn">import</span> <span class="nn">org.apache.htrace.impl.CountSampler</span><span class="o">;</span> -<span class="o">...</span> -<span class="n">Sampler</span> <span class="n">sampler</span> <span class="o">=</span> <span class="k">new</span> <span class="n">CountSampler</span><span class="o">(</span><span class="n">HTraceConfiguration</span><span class="o">.</span><span class="na">fromMap</span><span class="o">(</span> - <span class="n">Collections</span><span class="o">.</span><span class="na">singletonMap</span><span class="o">(</span><span class="n">CountSampler</span><span class="o">.</span><span class="na">SAMPLER_FREQUENCY_CONF_KEY</span><span class="o">,</span> <span class="s">"1000"</span><span class="o">)));</span> -<span class="o">...</span> -<span class="n">TraceScope</span> <span class="n">readScope</span> <span class="o">=</span> <span class="n">Trace</span><span class="o">.</span><span class="na">startSpan</span><span class="o">(</span><span class="s">"Read"</span><span class="o">,</span> <span class="n">sampler</span><span class="o">);</span> -<span class="o">...</span> -<span class="n">readScope</span><span class="o">.</span><span class="na">close</span><span class="o">();</span> -</code></pre> -</div> - -<p>Remember to close all spans and disable tracing when finished.</p> - -<div class="language-java highlighter-rouge"><pre class="highlight"><code><span class="n">DistributedTrace</span><span class="o">.</span><span class="na">disable</span><span class="o">();</span> -</code></pre> -</div> - -<h3 id="viewing-collected-traces">Viewing Collected Traces</h3> - -<p>To view collected traces, use the âRecent Tracesâ link on the Monitor -UI. You can also programmatically access and print traces using the -<code class="highlighter-rouge">TraceDump</code> class.</p> - -<h4 id="trace-table-format">Trace Table Format</h4> - -<p>This section is for developers looking to use data recorded in the trace table -directly, above and beyond the default services of the Accumulo monitor. -Please note the trace table format and its supporting classes -are not in the public API and may be subject to change in future versions.</p> - -<p>Each span received by a tracerâs ZooTraceClient is recorded in the trace table -in the form of three entries: span entries, index entries, and start time entries. -Span and start time entries record full span information, -whereas index entries provide indexing into span information -useful for quickly finding spans by type or start time.</p> - -<p>Each entry is illustrated by a description and sample of data. -In the description, a token in quotes is a String literal, -whereas other other tokens are span variables. -Parentheses group parts together, to distinguish colon characters inside the -column family or qualifier from the colon that separates column family and qualifier. -We use the format <code class="highlighter-rouge">row columnFamily:columnQualifier columnVisibility value</code> -(omitting timestamp which records the time an entry is written to the trace table).</p> - -<p>Span entries take the following form:</p> - -<div class="highlighter-rouge"><pre class="highlight"><code>traceId "span":(parentSpanId:spanId) [] spanBinaryEncoding -63b318de80de96d1 span:4b8f66077df89de1:3778c6739afe4e1 [] %18;%09;... -</code></pre> -</div> - -<p>The parentSpanId is ââ for the root span of a trace. -The spanBinaryEncoding is a compact Apache Thrift encoding of the original Span object. -This allows clients (and the Accumulo monitor) to recover all the details of the original Span -at a later time, by scanning the trace table and decoding the value of span entries -via <code class="highlighter-rouge">TraceFormatter.getRemoteSpan(entry)</code>.</p> - -<p>The trace table has a formatter class by default (org.apache.accumulo.tracer.TraceFormatter) -that changes how span entries appear from the Accumulo shell. -Normal scans to the trace table do not use this formatter representation; -it exists only to make span entries easier to view inside the Accumulo shell.</p> - -<p>Index entries take the following form:</p> - -<div class="highlighter-rouge"><pre class="highlight"><code>"idx":service:startTime description:sender [] traceId:elapsedTime -idx:tserver:14f3828f58b startScan:localhost [] 63b318de80de96d1:1 -</code></pre> -</div> - -<p>The service and sender are set by the first call of each Accumulo process -(and instrumented client processes) to <code class="highlighter-rouge">DistributedTrace.enable(...)</code> -(the sender is autodetected if not specified). -The description is specified in each span. -Start time and the elapsed time (start - stop, 1 millisecond in the example above) -are recorded in milliseconds as long values serialized to a string in hex.</p> - -<p>Start time entries take the following form:</p> - -<div class="highlighter-rouge"><pre class="highlight"><code>"start":startTime "id":traceId [] spanBinaryEncoding -start:14f3828a351 id:63b318de80de96d1 [] %18;%09;... -</code></pre> -</div> - -<p>The following classes may be run while Accumulo is running to provide insight into trace statistics. These require -accumulo-trace-VERSION.jar to be provided on the Accumulo classpath (<code class="highlighter-rouge">lib/ext</code> is fine).</p> - -<div class="highlighter-rouge"><pre class="highlight"><code>$ accumulo org.apache.accumulo.tracer.TraceTableStats -u username -p password -i instancename -$ accumulo org.apache.accumulo.tracer.TraceDump -u username -p password -i instancename -r -</code></pre> -</div> - -<h3 id="tracing-from-the-shell">Tracing from the Shell</h3> -<p>You can enable tracing for operations run from the shell by using the -<code class="highlighter-rouge">trace on</code> and <code class="highlighter-rouge">trace off</code> commands.</p> - -<div class="highlighter-rouge"><pre class="highlight"><code>root@test test> trace on - -root@test test> scan -a b:c [] d - -root@test test> trace off -Waiting for trace information -Waiting for trace information -Trace started at 2013/08/26 13:24:08.332 -Time Start Service@Location Name - 3628+0 shell@localhost shell:root - 8+1690 shell@localhost scan - 7+1691 shell@localhost scan:location - 6+1692 tserver@localhost startScan - 5+1692 tserver@localhost tablet read ahead 6 -</code></pre> -</div> - -<h2 id="logging">Logging</h2> - -<p>Accumulo processes each write to a set of log files. By default, these logs are found at directory -set by <code class="highlighter-rouge">ACCUMULO_LOG_DIR</code> in <code class="highlighter-rouge">accumulo-env.sh</code>.</p> - -<h2 id="recovery">Recovery</h2> - -<p>In the event of TabletServer failure or error on shutting Accumulo down, some -mutations may not have been minor compacted to HDFS properly. In this case, -Accumulo will automatically reapply such mutations from the write-ahead log -either when the tablets from the failed server are reassigned by the Master (in the -case of a single TabletServer failure) or the next time Accumulo starts (in the event of -failure during shutdown).</p> - -<p>Recovery is performed by asking a tablet server to sort the logs so that tablets can easily find their missing -updates. The sort status of each file is displayed on -Accumulo monitor status page. Once the recovery is complete any -tablets involved should return to an ``onlineââ state. Until then those tablets will be -unavailable to clients.</p> - -<p>The Accumulo client library is configured to retry failed mutations and in many -cases clients will be able to continue processing after the recovery process without -throwing an exception.</p> - -<h2 id="migrating-accumulo-from-non-ha-namenode-to-ha-namenode">Migrating Accumulo from non-HA Namenode to HA Namenode</h2> - -<p>The following steps will allow a non-HA instance to be migrated to an HA instance. Consider an HDFS URL -<code class="highlighter-rouge">hdfs://namenode.example.com:8020</code> which is going to be moved to <code class="highlighter-rouge">hdfs://nameservice1</code>.</p> - -<p>Before moving HDFS over to the HA namenode, use <code class="highlighter-rouge">accumulo admin volumes</code> to confirm -that the only volume displayed is the volume from the current namenodeâs HDFS URL.</p> - -<div class="highlighter-rouge"><pre class="highlight"><code>Listing volumes referenced in zookeeper - Volume : hdfs://namenode.example.com:8020/accumulo - -Listing volumes referenced in accumulo.root tablets section - Volume : hdfs://namenode.example.com:8020/accumulo -Listing volumes referenced in accumulo.root deletes section (volume replacement occurrs at deletion time) - -Listing volumes referenced in accumulo.metadata tablets section - Volume : hdfs://namenode.example.com:8020/accumulo - -Listing volumes referenced in accumulo.metadata deletes section (volume replacement occurrs at deletion time) -</code></pre> -</div> - -<p>After verifying the current volume is correct, shut down the cluster and transition HDFS to the HA nameservice.</p> - -<p>Edit <code class="highlighter-rouge">accumulo-site.xml</code> to notify accumulo that a volume is being replaced. First, -add the new nameservice volume to the <code class="highlighter-rouge">instance.volumes</code> property. Next, add the -<code class="highlighter-rouge">instance.volumes.replacements</code> property in the form of <code class="highlighter-rouge">old new</code>. Itâs important to not include -the volume thatâs being replaced in <code class="highlighter-rouge">instance.volumes</code>, otherwise itâs possible accumulo could continue -to write to the volume.</p> - -<div class="language-xml highlighter-rouge"><pre class="highlight"><code><span class="c"><!-- instance.dfs.uri and instance.dfs.dir should not be set--></span> -<span class="nt"><property></span> - <span class="nt"><name></span>instance.volumes<span class="nt"></name></span> - <span class="nt"><value></span>hdfs://nameservice1/accumulo<span class="nt"></value></span> -<span class="nt"></property></span> -<span class="nt"><property></span> - <span class="nt"><name></span>instance.volumes.replacements<span class="nt"></name></span> - <span class="nt"><value></span>hdfs://namenode.example.com:8020/accumulo hdfs://nameservice1/accumulo<span class="nt"></value></span> -<span class="nt"></property></span> -</code></pre> -</div> - -<p>Run <code class="highlighter-rouge">accumulo init --add-volumes</code> and start up the accumulo cluster. Verify that the -new nameservice volume shows up with <code class="highlighter-rouge">accumulo admin volumes</code>.</p> - -<div class="highlighter-rouge"><pre class="highlight"><code>Listing volumes referenced in zookeeper - Volume : hdfs://namenode.example.com:8020/accumulo - Volume : hdfs://nameservice1/accumulo - -Listing volumes referenced in accumulo.root tablets section - Volume : hdfs://namenode.example.com:8020/accumulo - Volume : hdfs://nameservice1/accumulo -Listing volumes referenced in accumulo.root deletes section (volume replacement occurrs at deletion time) - -Listing volumes referenced in accumulo.metadata tablets section - Volume : hdfs://namenode.example.com:8020/accumulo - Volume : hdfs://nameservice1/accumulo -Listing volumes referenced in accumulo.metadata deletes section (volume replacement occurrs at deletion time) -</code></pre> -</div> - -<p>Some erroneous GarbageCollector messages may still be seen for a small period while data is transitioning to -the new volumes. This is expected and can usually be ignored.</p> - -<h2 id="achieving-stability-in-a-vm-environment">Achieving Stability in a VM Environment</h2> - -<p>For testing, demonstration, and even operation uses, Accumulo is often -installed and run in a virtual machine (VM) environment. The majority of -long-term operational uses of Accumulo are on bare-metal cluster. However, the -core design of Accumulo and its dependencies do not preclude running stably for -long periods within a VM. Many of Accumuloâs operational robustness features to -handle failures like periodic network partitioning in a large cluster carry -over well to VM environments. This guide covers general recommendations for -maximizing stability in a VM environment, including some of the common failure -modes that are more common when running in VMs.</p> - -<h3 id="known-failure-modes-setup-and-troubleshooting">Known failure modes: Setup and Troubleshooting</h3> - -<p>In addition to the general failure modes of running Accumulo, VMs can introduce a -couple of environmental challenges that can affect process stability. Clock -drift is something that is more common in VMs, especially when VMs are -suspended and resumed. Clock drift can cause Accumulo servers to assume that -they have lost connectivity to the other Accumulo processes and/or lose their -locks in Zookeeper. VM environments also frequently have constrained resources, -such as CPU, RAM, network, and disk throughput and capacity. Accumulo generally -deals well with constrained resources from a stability perspective (optimizing -performance will require additional tuning, which is not covered in this -section), however there are some limits.</p> - -<h4 id="physical-memory">Physical Memory</h4> - -<p>One of those limits has to do with the Linux out of memory killer. A common -failure mode in VM environments (and in some bare metal installations) is when -the Linux out of memory killer decides to kill processes in order to avoid a -kernel panic when provisioning a memory page. This often happens in VMs due to -the large number of processes that must run in a small memory footprint. In -addition to the Linux core processes, a single-node Accumulo setup requires a -Hadoop Namenode, a Hadoop Secondary Namenode a Hadoop Datanode, a Zookeeper -server, an Accumulo Master, an Accumulo GC and an Accumulo TabletServer. -Typical setups also include an Accumulo Monitor, an Accumulo Tracer, a Hadoop -ResourceManager, a Hadoop NodeManager, provisioning software, and client -applications. Between all of these processes, it is not uncommon to -over-subscribe the available RAM in a VM. We recommend setting up VMs without -swap enabled, so rather than performance grinding to a halt when physical -memory is exhausted the kernel will randomly* select processes to kill in order -to free up memory.</p> - -<p>Calculating the maximum possible memory usage is essential in creating a stable -Accumulo VM setup. Safely engineering memory allocation for stability is a -matter of then bringing the calculated maximum memory usage under the physical -memory by a healthy margin. The margin is to account for operating system-level -operations, such as managing process, maintaining virtual memory pages, and -file system caching. When the java out-of-memory killer finds your process, you -will probably only see evidence of that in /var/log/messages. Out-of-memory -process kills do not show up in Accumulo or Hadoop logs.</p> - -<p>To calculate the max memory usage of all java virtual machine (JVM) processes -add the maximum heap size (often limited by a -Xmx⦠argument, such as in -accumulo-site.xml) and the off-heap memory usage. Off-heap memory usage -includes the following:</p> - -<ul> - <li>âPermanent Spaceâ, where the JVM stores Classes, Methods, and other code elements. This can be limited by a JVM flag such as <code class="highlighter-rouge">-XX:MaxPermSize:100m</code>, and is typically tens of megabytes.</li> - <li>Code generation space, where the JVM stores just-in-time compiled code. This is typically small enough to ignore</li> - <li>Socket buffers, where the JVM stores send and receive buffers for each socket.</li> - <li>Thread stacks, where the JVM allocates memory to manage each thread.</li> - <li>Direct memory space and JNI code, where applications can allocate memory outside of the JVM-managed space. For Accumulo, this includes the native in-memory maps that are allocated with the memory.maps.max parameter in accumulo-site.xml.</li> - <li>Garbage collection space, where the JVM stores information used for garbage collection.</li> -</ul> - -<p>You can assume that each Hadoop and Accumulo process will use ~100-150MB for -Off-heap memory, plus the in-memory map of the Accumulo TServer process. A -simple calculation for physical memory requirements follows:</p> - -<div class="highlighter-rouge"><pre class="highlight"><code> Physical memory needed - = (per-process off-heap memory) + (heap memory) + (other processes) + (margin) -
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