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<div class="section" id="distributedlog-operations">
<h1>DistributedLog Operations<a class="headerlink" href="#distributedlog-operations" title="Permalink to this headline">¶</a></h1>
<div class="section" id="feature-provider">
<h2>Feature Provider<a class="headerlink" href="#feature-provider" title="Permalink to this headline">¶</a></h2>
<p>DistributedLog uses a <cite>feature-provider</cite> library provided by Apache BookKeeper for managing features
dynamically at runtime. It is a <a class="reference external" href="https://en.wikipedia.org/wiki/Feature_toggle">feature-flag</a> system used to proportionally control what features
are enabled for the system. In other words, it is a way of altering the control in a system without
restarting it. It can be used during all stages of development, its most visible use case is on
production. For instance, during a production release, you can enable or disable individual features,
control the data flow through the system, thereby minimizing risk of system failure in real time.</p>
<p>This <cite>feature-provider</cite> interface is pluggable and easy to integrate with any configuration management
system.</p>
<div class="section" id="api">
<h3>API<a class="headerlink" href="#api" title="Permalink to this headline">¶</a></h3>
<p><cite>FeatureProvider</cite> is a provider that manages features under different scopes. The provider is responsible
for loading features dynamically at runtime. A <cite>Feature</cite> is a numeric flag that control how much percentage
of this feature will be available to the system - the number is called <cite>availability</cite>.</p>
<div class="highlight-python"><pre>Feature.name() =&gt; returns the name of this feature
Feature.availability() =&gt; returns the availability of this feature
Feature.isAvailable() =&gt; returns true if its availability is larger than 0; otherwise false</pre>
<div style='display:none;' class='raw-code'><pre>Feature.name() =&gt; returns the name of this feature
Feature.availability() =&gt; returns the availability of this feature
Feature.isAvailable() =&gt; returns true if its availability is larger than 0; otherwise false</pre>
</div></div>
<p>It is easy to obtain a feature from the provider by just providing a feature name.</p>
<div class="highlight-python"><pre>FeatureProvider provider = ...;
Feature feature = provider.getFeature("feature1"); // returns the feature named 'feature1'</pre>
<div style='display:none;' class='raw-code'><pre>FeatureProvider provider = ...;
Feature feature = provider.getFeature("feature1"); // returns the feature named 'feature1'</pre>
</div></div>
<p>The <cite>FeatureProvider</cite> is scopable to allow creating features in a hierarchical way. For example, if a system
is comprised of two subsystems, one is <em>cache</em>, while the other one is <em>storage</em>. so the features belong to
different subsystems can be created under different scopes.</p>
<div class="highlight-python"><pre>FeatureProvider provider = ...;
FeatureProvider cacheFeatureProvider = provider.scope("cache");
FeatureProvider storageFeatureProvider = provider.scope("storage");
Feature writeThroughFeature = cacheFeatureProvider.getFeature("write_through");
Feature duralWriteFeature = storageFeatureProvider.getFeature("dural_write");
// so the available features under `provider` are: (assume scopes are separated by '.')
// - 'cache.write_through'
// - 'storage.dural_write'</pre>
<div style='display:none;' class='raw-code'><pre>FeatureProvider provider = ...;
FeatureProvider cacheFeatureProvider = provider.scope("cache");
FeatureProvider storageFeatureProvider = provider.scope("storage");
Feature writeThroughFeature = cacheFeatureProvider.getFeature("write_through");
Feature duralWriteFeature = storageFeatureProvider.getFeature("dural_write");
// so the available features under `provider` are: (assume scopes are separated by '.')
// - 'cache.write_through'
// - 'storage.dural_write'</pre>
</div></div>
<p>The feature provider could be passed to <cite>DistributedLogNamespaceBuilder</cite> when building the namespace,
thereby it would be used for controlling the features exposed under <cite>DistributedLogNamespace</cite>.</p>
<div class="highlight-python"><pre>FeatureProvider rootProvider = ...;
FeatureProvider dlFeatureProvider = rootProvider.scope("dlog");
DistributedLogNamespace namespace = DistributedLogNamespaceBuilder.newBuilder()
.uri(uri)
.conf(conf)
.featureProvider(dlFeatureProvider)
.build();</pre>
<div style='display:none;' class='raw-code'><pre>FeatureProvider rootProvider = ...;
FeatureProvider dlFeatureProvider = rootProvider.scope("dlog");
DistributedLogNamespace namespace = DistributedLogNamespaceBuilder.newBuilder()
.uri(uri)
.conf(conf)
.featureProvider(dlFeatureProvider)
.build();</pre>
</div></div>
<p>The feature provider is loaded by reflection on distributedlog write proxy server. You could specify
the feature provider class name as below. Otherwise it would use <cite>DefaultFeatureProvider</cite>, which disables
all the features by default.</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="n">featureProviderClass</span><span class="o">=</span><span class="n">com</span><span class="o">.</span><span class="n">twitter</span><span class="o">.</span><span class="n">distributedlog</span><span class="o">.</span><span class="n">feature</span><span class="o">.</span><span class="n">DynamicConfigurationFeatureProvider</span>
</pre></div>
<div style='display:none;' class='raw-code'><pre>featureProviderClass=com.twitter.distributedlog.feature.DynamicConfigurationFeatureProvider</pre>
</div></div>
</div>
<div class="section" id="configuration-based-feature-provider">
<h3>Configuration Based Feature Provider<a class="headerlink" href="#configuration-based-feature-provider" title="Permalink to this headline">¶</a></h3>
<p>Beside <cite>DefaultFeatureProvider</cite>, distributedlog also provides a file-based feature provider - it loads
the features from properties files.</p>
<p>All the features and their availabilities are configured in properties file format. For example,</p>
<div class="highlight-python"><div class="highlight"><pre><span></span><span class="n">cache</span><span class="o">.</span><span class="n">write_through</span><span class="o">=</span><span class="mi">100</span>
<span class="n">storage</span><span class="o">.</span><span class="n">dural_write</span><span class="o">=</span><span class="mi">0</span>
</pre></div>
<div style='display:none;' class='raw-code'><pre>cache.write_through=100
storage.dural_write=0</pre>
</div></div>
<p>You could configure <cite>featureProviderClass</cite> in distributedlog configuration file by setting it to
<cite>com.twitter.distributedlog.feature.DynamicConfigurationFeatureProvider</cite> to enable file-based feature
provider. The feature provider will load the features from two files, one is base config file configured
by <cite>fileFeatureProviderBaseConfigPath</cite>, while the other one is overlay config file configured by
<cite>fileFeatureProviderOverlayConfigPath</cite>. Current implementation doesn't differentiate these two files
too much other than the <cite>overlay</cite> config will override the settings in <cite>base</cite> config. It is recommended
to have a base config file for storing the default availability values for your system and dynamically
adjust the availability values in overlay config file.</p>
<div class="highlight-python"><pre>featureProviderClass=com.twitter.distributedlog.feature.DynamicConfigurationFeatureProvider
fileFeatureProviderBaseConfigPath=/path/to/base/config
fileFeatureProviderOverlayConfigPath=/path/to/overlay/config
// how frequent we reload the config files
dynamicConfigReloadIntervalSec=60</pre>
<div style='display:none;' class='raw-code'><pre>featureProviderClass=com.twitter.distributedlog.feature.DynamicConfigurationFeatureProvider
fileFeatureProviderBaseConfigPath=/path/to/base/config
fileFeatureProviderOverlayConfigPath=/path/to/overlay/config
// how frequent we reload the config files
dynamicConfigReloadIntervalSec=60</pre>
</div></div>
</div>
<div class="section" id="available-features">
<h3>Available Features<a class="headerlink" href="#available-features" title="Permalink to this headline">¶</a></h3>
<p>Check the <a class="reference internal" href="../references/features.html"><em>Features</em></a> reference page for the features exposed by DistributedLog.</p>
</div>
</div>
<div class="section" id="dlog">
<h2><cite>dlog</cite><a class="headerlink" href="#dlog" title="Permalink to this headline">¶</a></h2>
<p>A CLI is provided for inspecting DistributedLog streams and metadata.</p>
<div class="highlight-bash"><div class="highlight"><pre><span></span>dlog
JMX enabled by default
Usage: dlog &lt;command&gt;
where <span class="nb">command</span> is one of:
<span class="nb">local</span> Run distributedlog sandbox
example Run distributedlog example
tool Run distributedlog tool
proxy_tool Run distributedlog proxy tool to interact with proxies
balancer Run distributedlog balancer
admin Run distributedlog admin tool
<span class="nb">help</span> This <span class="nb">help</span> message
or <span class="nb">command</span> is the full name of a class with a defined main<span class="o">()</span> method.
Environment variables:
DLOG_LOG_CONF Log4j configuration file <span class="o">(</span>default <span class="nv">$HOME</span>/src/distributedlog/distributedlog-service/conf/log4j.properties<span class="o">)</span>
DLOG_EXTRA_OPTS Extra options to be passed to the jvm
DLOG_EXTRA_CLASSPATH Add extra paths to the dlog classpath
</pre></div>
<div style='display:none;' class='raw-code'><pre>dlog
JMX enabled by default
Usage: dlog &lt;command&gt;
where command is one of:
local Run distributedlog sandbox
example Run distributedlog example
tool Run distributedlog tool
proxy_tool Run distributedlog proxy tool to interact with proxies
balancer Run distributedlog balancer
admin Run distributedlog admin tool
help This help message
or command is the full name of a class with a defined main() method.
Environment variables:
DLOG_LOG_CONF Log4j configuration file (default $HOME/src/distributedlog/distributedlog-service/conf/log4j.properties)
DLOG_EXTRA_OPTS Extra options to be passed to the jvm
DLOG_EXTRA_CLASSPATH Add extra paths to the dlog classpath</pre>
</div></div>
<p>These variable can also be set in conf/dlogenv.sh</p>
<div class="section" id="create-a-stream">
<h3>Create a stream<a class="headerlink" href="#create-a-stream" title="Permalink to this headline">¶</a></h3>
<p>To create a stream:</p>
<div class="highlight-bash"><div class="highlight"><pre><span></span>dlog tool create -u &lt;DL URI&gt; -r &lt;STREAM PREFIX&gt; -e &lt;STREAM EXPRESSION&gt;
</pre></div>
<div style='display:none;' class='raw-code'><pre>dlog tool create -u &lt;DL URI&gt; -r &lt;STREAM PREFIX&gt; -e &lt;STREAM EXPRESSION&gt;</pre>
</div></div>
</div>
<div class="section" id="list-the-streams">
<h3>List the streams<a class="headerlink" href="#list-the-streams" title="Permalink to this headline">¶</a></h3>
<p>To list all the streams under a given DistributedLog namespace:</p>
<div class="highlight-bash"><div class="highlight"><pre><span></span>dlog tool list -u &lt;DL URI&gt;
</pre></div>
<div style='display:none;' class='raw-code'><pre>dlog tool list -u &lt;DL URI&gt;</pre>
</div></div>
</div>
<div class="section" id="show-stream-s-information">
<h3>Show stream's information<a class="headerlink" href="#show-stream-s-information" title="Permalink to this headline">¶</a></h3>
<p>To view the metadata associated with a stream:</p>
<div class="highlight-bash"><div class="highlight"><pre><span></span>dlog tool show -u &lt;DL URI&gt; -s &lt;STREAM NAME&gt;
</pre></div>
<div style='display:none;' class='raw-code'><pre>dlog tool show -u &lt;DL URI&gt; -s &lt;STREAM NAME&gt;</pre>
</div></div>
</div>
<div class="section" id="dump-a-stream">
<h3>Dump a stream<a class="headerlink" href="#dump-a-stream" title="Permalink to this headline">¶</a></h3>
<p>To dump the items inside a stream:</p>
<div class="highlight-bash"><div class="highlight"><pre><span></span>dlog tool dump -u &lt;DL URI&gt; -s &lt;STREAM NAME&gt; -o &lt;START TXN ID&gt; -l &lt;NUM RECORDS&gt;
</pre></div>
<div style='display:none;' class='raw-code'><pre>dlog tool dump -u &lt;DL URI&gt; -s &lt;STREAM NAME&gt; -o &lt;START TXN ID&gt; -l &lt;NUM RECORDS&gt;</pre>
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<div class="section" id="delete-a-stream">
<h3>Delete a stream<a class="headerlink" href="#delete-a-stream" title="Permalink to this headline">¶</a></h3>
<p>To delete a stream, run:</p>
<div class="highlight-bash"><div class="highlight"><pre><span></span>dlog tool delete -u &lt;DL URI&gt; -s &lt;STREAM NAME&gt;
</pre></div>
<div style='display:none;' class='raw-code'><pre>dlog tool delete -u &lt;DL URI&gt; -s &lt;STREAM NAME&gt;</pre>
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<div class="section" id="truncate-a-stream">
<h3>Truncate a stream<a class="headerlink" href="#truncate-a-stream" title="Permalink to this headline">¶</a></h3>
<p>Truncate the streams under a given DistributedLog namespace. You could specify a filter to match the streams that you want to truncate.</p>
<p>There is a difference between the <tt class="docutils literal"><span class="pre">truncate</span></tt> and <tt class="docutils literal"><span class="pre">delete</span></tt> command. When you issue a <tt class="docutils literal"><span class="pre">truncate</span></tt>, the data will be purge without removing the streams. A <tt class="docutils literal"><span class="pre">delete</span></tt> will delete the stream. You can pass the flag <tt class="docutils literal"><span class="pre">-delete</span></tt> to the <tt class="docutils literal"><span class="pre">truncate</span></tt> command to also delete the streams.</p>
<div class="highlight-bash"><div class="highlight"><pre><span></span>dlog tool truncate -u &lt;DL URI&gt;
</pre></div>
<div style='display:none;' class='raw-code'><pre>dlog tool truncate -u &lt;DL URI&gt;</pre>
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