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.68-.57.33-.87L12.67 3.6c-.38-.34-.96-.34-1.34 0l-8.36 7.53c-.34.3-.13.87.33.87H5v7c0 .55.45 1 1 1h3c.55 0 1-.45 1-1z" fill="currentColor"></path></svg></a></li><li itemscope="" itemprop="itemListElement" itemtype="https://schema.org/ListItem" class="breadcrumbs__item"><a class="breadcrumbs__link" itemprop="item" href="/docs/next/reference-landing/"><span itemprop="name">Reference</span></a><meta itemprop="position" content="1"></li><li itemscope="" itemprop="itemListElement" itemtype="https://schema.org/ListItem" class="breadcrumbs__item breadcrumbs__item--active"><span class="breadcrumbs__link" itemprop="name">Terminology</span><meta itemprop="position" content="2"></li></ul></nav><span class="theme-doc-version-badge badge badge--secondary">Version: Next</span><div class="tocCollapsible_ETCw theme-doc-toc-mobile tocMobile_ITEo"><button type="button" class="clean-btn tocCollapsibleButton_TO0P">On this page</button></div><div class="theme-doc-markdown markdown"><header><h1>Pulsar Terminology</h1></header><p>Here is a glossary of terms related to Apache Pulsar:</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="concepts">Concepts<a href="#concepts" class="hash-link" aria-label="Direct link to Concepts" title="Direct link to Concepts"></a></h2><h3 class="anchor anchorWithStickyNavbar_LWe7" id="pulsar">Pulsar<a href="#pulsar" class="hash-link" aria-label="Direct link to Pulsar" title="Direct link to Pulsar"></a></h3><p>Pulsar is a distributed messaging system originally created by Yahoo but now under the stewardship of the Apache Software Foundation.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="namespace-bundle">Namespace Bundle<a href="#namespace-bundle" class="hash-link" aria-label="Direct link to Namespace Bundle" title="Direct link to Namespace Bundle"></a></h3><p>Namespace bundle is a virtual group of <a href="/docs/next/concepts-messaging/#topics">topics</a> that belong to the same <a href="/docs/next/concepts-multi-tenancy/#namespaces">namespace</a>. A namespace bundle |
| is defined as a range between two 32-bit hashes, such as 0x00000000 and 0xffffffff.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="namespace">Namespace<a href="#namespace" class="hash-link" aria-label="Direct link to Namespace" title="Direct link to Namespace"></a></h3><p>Namespace is a virtual grouping of <a href="/docs/next/concepts-messaging/#topics">topics</a>, under a specific |
| <a href="/docs/next/concepts-multi-tenancy/#tenants">tenant</a>. A namespace is defined |
| by a string name, such as <code>my-tenant/my-namespace</code>.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="pub-sub">Pub-Sub<a href="#pub-sub" class="hash-link" aria-label="Direct link to Pub-Sub" title="Direct link to Pub-Sub"></a></h3><p>Pub-sub is a messaging pattern in which <a href="/docs/next/concepts-clients/#producer">producer</a> processes publish messages on <a href="/docs/next/concepts-messaging/#topics">topics</a> that |
| are then consumed (processed) by <a href="/docs/next/concepts-clients/#consumer">consumer</a> processes.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="reader">Reader<a href="#reader" class="hash-link" aria-label="Direct link to Reader" title="Direct link to Reader"></a></h3><p>Pulsar readers are message processors much like Pulsar <a href="/docs/next/concepts-clients/#consumer">consumers</a> but with two crucial differences:</p><ul><li>you can specify <em>where</em> on a topic readers begin processing messages (consumers always begin with the latest |
| available unacked message);</li><li>readers don't retain data or acknowledge messages.</li></ul><h3 class="anchor anchorWithStickyNavbar_LWe7" id="cursor">Cursor<a href="#cursor" class="hash-link" aria-label="Direct link to Cursor" title="Direct link to Cursor"></a></h3><p>Cursor is the subscription position for a <a href="/docs/next/concepts-clients/#consumer">consumer</a>.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="unacknowledged">Unacknowledged<a href="#unacknowledged" class="hash-link" aria-label="Direct link to Unacknowledged" title="Direct link to Unacknowledged"></a></h3><p>Unacknowledged means a message that has been delivered to a consumer for processing but not yet confirmed as processed by the consumer.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="retention-policy">Retention Policy<a href="#retention-policy" class="hash-link" aria-label="Direct link to Retention Policy" title="Direct link to Retention Policy"></a></h3><p>Retention policy is the size and time limits that you can set on a <a href="/docs/next/concepts-multi-tenancy/#namespaces">namespace</a> to configure retention of <a href="/docs/next/concepts-messaging/#messages">messages</a> |
| that have already been <a href="/docs/next/concepts-messaging/#acknowledgment">acknowledged</a>.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="multi-tenancy">Multi-Tenancy<a href="#multi-tenancy" class="hash-link" aria-label="Direct link to Multi-Tenancy" title="Direct link to Multi-Tenancy"></a></h3><p>Multi-tenancy is the ability to isolate <a href="/docs/next/concepts-multi-tenancy/#namespaces">namespaces</a>, specify quotas, and configure authentication and authorization |
| on a per-<a href="/docs/next/concepts-multi-tenancy/#tenants">tenant</a> basis.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="failure-domain">Failure Domain<a href="#failure-domain" class="hash-link" aria-label="Direct link to Failure Domain" title="Direct link to Failure Domain"></a></h3><p>Failure domain is a logical domain under a Pulsar cluster. Each logical domain contains a pre-configured list of brokers.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="anti-affinity-namespaces">Anti-Affinity Namespaces<a href="#anti-affinity-namespaces" class="hash-link" aria-label="Direct link to Anti-Affinity Namespaces" title="Direct link to Anti-Affinity Namespaces"></a></h3><p>Anti-affinity namespaces are a group of namespaces that have anti-affinity to each other.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="architecture">Architecture<a href="#architecture" class="hash-link" aria-label="Direct link to Architecture" title="Direct link to Architecture"></a></h2><h3 class="anchor anchorWithStickyNavbar_LWe7" id="standalone">Standalone<a href="#standalone" class="hash-link" aria-label="Direct link to Standalone" title="Direct link to Standalone"></a></h3><p>Standalone is a lightweight Pulsar broker in which all components run in a single Java Virtual Machine (JVM) process. Standalone |
| clusters can be run on a single machine and are useful for development purposes.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="topic-lookup">Topic Lookup<a href="#topic-lookup" class="hash-link" aria-label="Direct link to Topic Lookup" title="Direct link to Topic Lookup"></a></h3><p>Topic lookup is a service provided by Pulsar <a href="/docs/next/concepts-architecture-overview/#brokers">brokers</a> that enables connecting clients to automatically determine |
| which Pulsar <a href="/docs/next/concepts-architecture-overview/#clusters">cluster</a> is responsible for a <a href="/docs/next/concepts-messaging/#topics">topic</a> (and thus where message traffic for |
| the topic needs to be routed).</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="dispatcher">Dispatcher<a href="#dispatcher" class="hash-link" aria-label="Direct link to Dispatcher" title="Direct link to Dispatcher"></a></h3><p>Dispatcher is an asynchronous TCP server used for all data transfers in and out of a Pulsar <a href="/docs/next/concepts-architecture-overview/#brokers">broker</a>. The Pulsar |
| dispatcher uses a custom binary protocol for all communications.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="broker">Broker<a href="#broker" class="hash-link" aria-label="Direct link to Broker" title="Direct link to Broker"></a></h3><p>Broker is a Pulsar server that receives, acknowledges, and delivers messages to consumers. |
| A Pulsar cluster can have one or more brokers.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="storage">Storage<a href="#storage" class="hash-link" aria-label="Direct link to Storage" title="Direct link to Storage"></a></h2><h3 class="anchor anchorWithStickyNavbar_LWe7" id="bookie">Bookie<a href="#bookie" class="hash-link" aria-label="Direct link to Bookie" title="Direct link to Bookie"></a></h3><p>Bookie is the name of an individual BookKeeper server. It is effectively the storage server of Pulsar.</p></div><footer class="theme-doc-footer docusaurus-mt-lg"><div class="theme-doc-footer-edit-meta-row row"><div class="col"><a href="https://github.com/apache/pulsar-site/edit/main/docs/reference-terminology.md" target="_blank" rel="noreferrer noopener" class="theme-edit-this-page"><svg fill="currentColor" height="20" width="20" viewBox="0 0 40 40" class="iconEdit_Z9Sw" aria-hidden="true"><g><path d="m34.5 11.7l-3 3.1-6.3-6.3 3.1-3q0.5-0.5 1.2-0.5t1.1 0.5l3.9 3.9q0.5 0.4 0.5 1.1t-0.5 1.2z m-29.5 17.1l18.4-18.5 6.3 6.3-18.4 18.4h-6.3v-6.2z"></path></g></svg>Edit this page</a></div><div class="col lastUpdated_vwxv"></div></div></footer></article><nav class="pagination-nav docusaurus-mt-lg" aria-label="Docs pages navigation"><a class="pagination-nav__link pagination-nav__link--prev" href="/docs/next/reference-rest-api-overview/"><div class="pagination-nav__sublabel">Previous</div><div class="pagination-nav__label">REST APIs</div></a><a 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