Added: samza/site/learn/documentation/0.10/introduction/background.html URL: http://svn.apache.org/viewvc/samza/site/learn/documentation/0.10/introduction/background.html?rev=1721445&view=auto ============================================================================== --- samza/site/learn/documentation/0.10/introduction/background.html (added) +++ samza/site/learn/documentation/0.10/introduction/background.html Tue Dec 22 19:01:05 2015 @@ -0,0 +1,247 @@ +<!DOCTYPE html> +<!-- + Licensed to the Apache Software Foundation (ASF) under one or more + contributor license agreements. See the NOTICE file distributed with + this work for additional information regarding copyright ownership. + The ASF licenses this file to You under the Apache License, Version 2.0 + (the "License"); you may not use this file except in compliance with + the License. You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. +--> +<html lang="en"> + <head> + <meta charset="utf-8"> + <title>Samza - Background</title> + <link href='/css/ropa-sans.css' rel='stylesheet' type='text/css'/> + <link href="/css/bootstrap.min.css" rel="stylesheet"/> + <link href="/css/font-awesome.min.css" rel="stylesheet"/> + <link href="/css/main.css" rel="stylesheet"/> + <link href="/css/syntax.css" rel="stylesheet"/> + <link rel="icon" type="image/png" href="/img/samza-icon.png"> + <script src="/js/jquery-1.11.1.min.js"></script> + </head> + <body> + <div class="wrapper"> + <div class="wrapper-content"> + + <div class="masthead"> + <div class="container"> + <div class="masthead-logo"> + <a href="/" class="logo">samza</a> + </div> + <div class="masthead-icons"> + <div class="pull-right"> + <a href="/startup/download"><i class="fa fa-arrow-circle-o-down masthead-icon"></i></a> + <a href="https://git-wip-us.apache.org/repos/asf?p=samza.git;a=tree"; target="_blank"><i class="fa fa-code masthead-icon" style="font-weight: bold;"></i></a> + <a href="https://twitter.com/samzastream"; target="_blank"><i class="fa fa-twitter masthead-icon"></i></a> + <!-- this icon only shows in versioned pages --> + + + + + <a href="http://samza.apache.org/learn/documentation/latest/introduction/background.html";><i id="switch-version-button"></i></a> + <!-- links for the navigation bar --> + + + </div> + </div> + </div><!-- /.container --> + </div> + + <div class="container"> + <div class="menu"> + <h1><i class="fa fa-rocket"></i> Getting Started</h1> + <ul> + <li><a href="/startup/hello-samza/0.10">Hello Samza</a></li> + <li><a href="/startup/download">Download</a></li> + </ul> + + <h1><i class="fa fa-book"></i> Learn</h1> + <ul> + <li><a href="/learn/documentation/0.10">Documentation</a></li> + <li><a href="/learn/documentation/0.10/jobs/configuration-table.html">Configuration</a></li> + <li><a href="/learn/documentation/0.10/api/javadocs/">Javadocs</a></li> + <li><a href="/learn/tutorials/0.10">Tutorials</a></li> + <li><a href="https://cwiki.apache.org/confluence/display/SAMZA/FAQ";>FAQ</a></li> + <li><a href="https://cwiki.apache.org/confluence/display/SAMZA/Apache+Samza";>Wiki</a></li> + <li><a href="https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=51812876";>Papers & Talks</a></li> + <li><a href="http://blogs.apache.org/samza";>Blog</a></li> + </ul> + + <h1><i class="fa fa-comments"></i> Community</h1> + <ul> + <li><a href="/community/mailing-lists.html">Mailing Lists</a></li> + <li><a href="/community/irc.html">IRC</a></li> + <li><a href="https://issues.apache.org/jira/browse/SAMZA";>Bugs</a></li> + <li><a href="https://cwiki.apache.org/confluence/display/SAMZA/Powered+By";>Powered by</a></li> + <li><a href="https://cwiki.apache.org/confluence/display/SAMZA/Ecosystem";>Ecosystem</a></li> + <li><a href="/community/committers.html">Committers</a></li> + </ul> + + <h1><i class="fa fa-code"></i> Contribute</h1> + <ul> + <li><a href="/contribute/rules.html">Rules</a></li> + <li><a href="/contribute/coding-guide.html">Coding Guide</a></li> + <li><a href="/contribute/projects.html">Projects</a></li> + <li><a href="/contribute/design-documents.html">Design Documents</a></li> + <li><a href="/contribute/code.html">Code</a></li> + <li><a href="https://reviews.apache.org/groups/samza";>Review Board</a></li> + <li><a href="/contribute/tests.html">Tests</a></li> + </ul> + + <h1><i class="fa fa-history"></i> Archive</h1> + <ul> + <li><a href="/archive/index.html#latest">latest</a></li> + <li><a href="/archive/index.html#09">0.9</a></li> + <li><a href="/archive/index.html#08">0.8</a></li> + <li><a href="/archive/index.html#07">0.7</a></li> + </ul> + </div> + + <div class="content"> + <!-- + Licensed to the Apache Software Foundation (ASF) under one or more + contributor license agreements. See the NOTICE file distributed with + this work for additional information regarding copyright ownership. + The ASF licenses this file to You under the Apache License, Version 2.0 + (the "License"); you may not use this file except in compliance with + the License. You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. +--> + +<h2>Background</h2> + +<!-- + Licensed to the Apache Software Foundation (ASF) under one or more + contributor license agreements. See the NOTICE file distributed with + this work for additional information regarding copyright ownership. + The ASF licenses this file to You under the Apache License, Version 2.0 + (the "License"); you may not use this file except in compliance with + the License. You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. +--> + +<p>This page provides some background about stream processing, describes what Samza is, and why it was built.</p> + +<h3 id="what-is-messaging?">What is messaging?</h3> + +<p>Messaging systems are a popular way of implementing near-realtime asynchronous computation. Messages can be added to a message queue (ActiveMQ, RabbitMQ), pub-sub system (Kestrel, Kafka), or log aggregation system (Flume, Scribe) when something happens. Downstream <em>consumers</em> read messages from these systems, and process them or take actions based on the message contents.</p> + +<p>Suppose you have a website, and every time someone loads a page, you send a “user viewed page” event to a messaging system. You might then have consumers which do any of the following:</p> + +<ul> +<li>Store the message in Hadoop for future analysis</li> +<li>Count page views and update a dashboard</li> +<li>Trigger an alert if a page view fails</li> +<li>Send an email notification to another user</li> +<li>Join the page view event with the user’s profile, and send the message back to the messaging system</li> +</ul> + +<p>A messaging system lets you decouple all of this work from the actual web page serving.</p> + +<h3 id="what-is-stream-processing?">What is stream processing?</h3> + +<p>A messaging system is a fairly low-level piece of infrastructure—it stores messages and waits for consumers to consume them. When you start writing code that produces or consumes messages, you quickly find that there are a lot of tricky problems that have to be solved in the processing layer. Samza aims to help with these problems.</p> + +<p>Consider the counting example, above (count page views and update a dashboard). What happens when the machine that your consumer is running on fails, and your current counter values are lost? How do you recover? Where should the processor be run when it restarts? What if the underlying messaging system sends you the same message twice, or loses a message? (Unless you are careful, your counts will be incorrect.) What if you want to count page views grouped by the page URL? How do you distribute the computation across multiple machines if it’s too much for a single machine to handle?</p> + +<p>Stream processing is a higher level of abstraction on top of messaging systems, and it’s meant to address precisely this category of problems.</p> + +<h3 id="samza">Samza</h3> + +<p>Samza is a stream processing framework with the following features:</p> + +<ul> +<li><strong>Simple API:</strong> Unlike most low-level messaging system APIs, Samza provides a very simple callback-based “process message” API comparable to MapReduce.</li> +<li><strong>Managed state:</strong> Samza manages snapshotting and restoration of a stream processor’s state. When the processor is restarted, Samza restores its state to a consistent snapshot. Samza is built to handle large amounts of state (many gigabytes per partition).</li> +<li><strong>Fault tolerance:</strong> Whenever a machine in the cluster fails, Samza works with YARN to transparently migrate your tasks to another machine.</li> +<li><strong>Durability:</strong> Samza uses Kafka to guarantee that messages are processed in the order they were written to a partition, and that no messages are ever lost.</li> +<li><strong>Scalability:</strong> Samza is partitioned and distributed at every level. Kafka provides ordered, partitioned, replayable, fault-tolerant streams. YARN provides a distributed environment for Samza containers to run in.</li> +<li><strong>Pluggable:</strong> Though Samza works out of the box with Kafka and YARN, Samza provides a pluggable API that lets you run Samza with other messaging systems and execution environments.</li> +<li><strong>Processor isolation:</strong> Samza works with Apache YARN, which supports Hadoop’s security model, and resource isolation through Linux CGroups.</li> +</ul> + +<h3 id="alternatives">Alternatives</h3> + +<p>The available open source stream processing systems are actually quite young, and no single system offers a complete solution. New problems in this area include: how a stream processor’s state should be managed, whether or not a stream should be buffered remotely on disk, what to do when duplicate messages are received or messages are lost, and how to model underlying messaging systems.</p> + +<p>Samza’s main differentiators are:</p> + +<ul> +<li>Samza supports fault-tolerant local state. State can be thought of as tables that are split up and co-located with the processing tasks. State is itself modeled as a stream. If the local state is lost due to machine failure, the state stream is replayed to restore it.</li> +<li>Streams are ordered, partitioned, replayable, and fault tolerant.</li> +<li>YARN is used for processor isolation, security, and fault tolerance.</li> +<li>Jobs are decoupled: if one job goes slow and builds up a backlog of unprocessed messages, the rest of the system is not affected.</li> +</ul> + +<p>For a more in-depth discussion on Samza, and how it relates to other stream processing systems, have a look at Samza’s <a href="../comparisons/introduction.html">Comparisons</a> documentation.</p> + +<h2 id="concepts-»"><a href="concepts.html">Concepts »</a></h2> + + + </div> + </div> + + </div><!-- /.wrapper-content --> + </div><!-- /.wrapper --> + + <div class="footer"> + <div class="container"> + <!-- nothing for now. --> + </div> + </div> + + + <script> + $( document ).ready(function() { + if ( $.fn.urlExists( "/learn/documentation/latest/introduction/background.html" ) ) { + $("#switch-version-button").addClass("fa fa-history masthead-icon"); + } + }); + + /* a function to test whether the url exists or not */ + (function( $ ) { + $.fn.urlExists = function(url) { + var http = new XMLHttpRequest(); + http.open('HEAD', url, false); + http.send(); + return http.status != 404; + }; + }( jQuery )); + </script> + + + <!-- Google Analytics --> + <script> + (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){ + (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o), + m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m) + })(window,document,'script','//www.google-analytics.com/analytics.js','ga'); + + ga('create', 'UA-43122768-1', 'apache.org'); + ga('send', 'pageview'); + + </script> + </body> +</html>
Added: samza/site/learn/documentation/0.10/introduction/concepts.html URL: http://svn.apache.org/viewvc/samza/site/learn/documentation/0.10/introduction/concepts.html?rev=1721445&view=auto ============================================================================== --- samza/site/learn/documentation/0.10/introduction/concepts.html (added) +++ samza/site/learn/documentation/0.10/introduction/concepts.html Tue Dec 22 19:01:05 2015 @@ -0,0 +1,242 @@ +<!DOCTYPE html> +<!-- + Licensed to the Apache Software Foundation (ASF) under one or more + contributor license agreements. See the NOTICE file distributed with + this work for additional information regarding copyright ownership. + The ASF licenses this file to You under the Apache License, Version 2.0 + (the "License"); you may not use this file except in compliance with + the License. You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. +--> +<html lang="en"> + <head> + <meta charset="utf-8"> + <title>Samza - Concepts</title> + <link href='/css/ropa-sans.css' rel='stylesheet' type='text/css'/> + <link href="/css/bootstrap.min.css" rel="stylesheet"/> + <link href="/css/font-awesome.min.css" rel="stylesheet"/> + <link href="/css/main.css" rel="stylesheet"/> + <link href="/css/syntax.css" rel="stylesheet"/> + <link rel="icon" type="image/png" href="/img/samza-icon.png"> + <script src="/js/jquery-1.11.1.min.js"></script> + </head> + <body> + <div class="wrapper"> + <div class="wrapper-content"> + + <div class="masthead"> + <div class="container"> + <div class="masthead-logo"> + <a href="/" class="logo">samza</a> + </div> + <div class="masthead-icons"> + <div class="pull-right"> + <a href="/startup/download"><i class="fa fa-arrow-circle-o-down masthead-icon"></i></a> + <a href="https://git-wip-us.apache.org/repos/asf?p=samza.git;a=tree"; target="_blank"><i class="fa fa-code masthead-icon" style="font-weight: bold;"></i></a> + <a href="https://twitter.com/samzastream"; target="_blank"><i class="fa fa-twitter masthead-icon"></i></a> + <!-- this icon only shows in versioned pages --> + + + + + <a href="http://samza.apache.org/learn/documentation/latest/introduction/concepts.html";><i id="switch-version-button"></i></a> + <!-- links for the navigation bar --> + + + </div> + </div> + </div><!-- /.container --> + </div> + + <div class="container"> + <div class="menu"> + <h1><i class="fa fa-rocket"></i> Getting Started</h1> + <ul> + <li><a href="/startup/hello-samza/0.10">Hello Samza</a></li> + <li><a href="/startup/download">Download</a></li> + </ul> + + <h1><i class="fa fa-book"></i> Learn</h1> + <ul> + <li><a href="/learn/documentation/0.10">Documentation</a></li> + <li><a href="/learn/documentation/0.10/jobs/configuration-table.html">Configuration</a></li> + <li><a href="/learn/documentation/0.10/api/javadocs/">Javadocs</a></li> + <li><a href="/learn/tutorials/0.10">Tutorials</a></li> + <li><a href="https://cwiki.apache.org/confluence/display/SAMZA/FAQ";>FAQ</a></li> + <li><a href="https://cwiki.apache.org/confluence/display/SAMZA/Apache+Samza";>Wiki</a></li> + <li><a href="https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=51812876";>Papers & Talks</a></li> + <li><a href="http://blogs.apache.org/samza";>Blog</a></li> + </ul> + + <h1><i class="fa fa-comments"></i> Community</h1> + <ul> + <li><a href="/community/mailing-lists.html">Mailing Lists</a></li> + <li><a href="/community/irc.html">IRC</a></li> + <li><a href="https://issues.apache.org/jira/browse/SAMZA";>Bugs</a></li> + <li><a href="https://cwiki.apache.org/confluence/display/SAMZA/Powered+By";>Powered by</a></li> + <li><a href="https://cwiki.apache.org/confluence/display/SAMZA/Ecosystem";>Ecosystem</a></li> + <li><a href="/community/committers.html">Committers</a></li> + </ul> + + <h1><i class="fa fa-code"></i> Contribute</h1> + <ul> + <li><a href="/contribute/rules.html">Rules</a></li> + <li><a href="/contribute/coding-guide.html">Coding Guide</a></li> + <li><a href="/contribute/projects.html">Projects</a></li> + <li><a href="/contribute/design-documents.html">Design Documents</a></li> + <li><a href="/contribute/code.html">Code</a></li> + <li><a href="https://reviews.apache.org/groups/samza";>Review Board</a></li> + <li><a href="/contribute/tests.html">Tests</a></li> + </ul> + + <h1><i class="fa fa-history"></i> Archive</h1> + <ul> + <li><a href="/archive/index.html#latest">latest</a></li> + <li><a href="/archive/index.html#09">0.9</a></li> + <li><a href="/archive/index.html#08">0.8</a></li> + <li><a href="/archive/index.html#07">0.7</a></li> + </ul> + </div> + + <div class="content"> + <!-- + Licensed to the Apache Software Foundation (ASF) under one or more + contributor license agreements. See the NOTICE file distributed with + this work for additional information regarding copyright ownership. + The ASF licenses this file to You under the Apache License, Version 2.0 + (the "License"); you may not use this file except in compliance with + the License. You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. +--> + +<h2>Concepts</h2> + +<!-- + Licensed to the Apache Software Foundation (ASF) under one or more + contributor license agreements. See the NOTICE file distributed with + this work for additional information regarding copyright ownership. + The ASF licenses this file to You under the Apache License, Version 2.0 + (the "License"); you may not use this file except in compliance with + the License. You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. +--> + +<p>This page gives an introduction to the high-level concepts in Samza.</p> + +<h3 id="streams">Streams</h3> + +<p>Samza processes <em>streams</em>. A stream is composed of immutable <em>messages</em> of a similar type or category. For example, a stream could be all the clicks on a website, or all the updates to a particular database table, or all the logs produced by a service, or any other type of event data. Messages can be appended to a stream or read from a stream. A stream can have any number of <em>consumers</em>, and reading from a stream doesn’t delete the message (so each message is effectively broadcast to all consumers). Messages can optionally have an associated key which is used for partitioning, which we’ll talk about in a second.</p> + +<p>Samza supports pluggable <em>systems</em> that implement the stream abstraction: in <a href="https://kafka.apache.org/";>Kafka</a> a stream is a topic, in a database we might read a stream by consuming updates from a table, in Hadoop we might tail a directory of files in HDFS.</p> + +<p><img src="/img/0.10/learn/documentation/introduction/job.png" alt="job"></p> + +<h3 id="jobs">Jobs</h3> + +<p>A Samza <em>job</em> is code that performs a logical transformation on a set of input streams to append output messages to set of output streams.</p> + +<p>If scalability were not a concern, streams and jobs would be all we need. However, in order to scale the throughput of the stream processor, we chop streams and jobs up into smaller units of parallelism: <em>partitions</em> and <em>tasks</em>.</p> + +<h3 id="partitions">Partitions</h3> + +<p>Each stream is broken into one or more partitions. Each partition in the stream is a totally ordered sequence of messages.</p> + +<p>Each message in this sequence has an identifier called the <em>offset</em>, which is unique per partition. The offset can be a sequential integer, byte offset, or string depending on the underlying system implementation.</p> + +<p>When a message is appended to a stream, it is appended to only one of the stream’s partitions. The assignment of the message to its partition is done with a key chosen by the writer. For example, if the user ID is used as the key, that ensures that all messages related to a particular user end up in the same partition.</p> + +<p><img src="/img/0.10/learn/documentation/introduction/stream.png" alt="stream"></p> + +<h3 id="tasks">Tasks</h3> + +<p>A job is scaled by breaking it into multiple <em>tasks</em>. The <em>task</em> is the unit of parallelism of the job, just as the partition is to the stream. Each task consumes data from one partition for each of the job’s input streams.</p> + +<p>A task processes messages from each of its input partitions sequentially, in the order of message offset. There is no defined ordering across partitions. This allows each task to operate independently. The YARN scheduler assigns each task to a machine, so the job as a whole can be distributed across many machines.</p> + +<p>The number of tasks in a job is determined by the number of input partitions (there cannot be more tasks than input partitions, or there would be some tasks with no input). However, you can change the computational resources assigned to the job (the amount of memory, number of CPU cores, etc.) to satisfy the job’s needs. See notes on <em>containers</em> below.</p> + +<p>The assignment of partitions to tasks never changes: if a task is on a machine that fails, the task is restarted elsewhere, still consuming the same stream partitions.</p> + +<p><img src="/img/0.10/learn/documentation/introduction/job_detail.png" alt="job-detail"></p> + +<h3 id="dataflow-graphs">Dataflow Graphs</h3> + +<p>We can compose multiple jobs to create a dataflow graph, where the nodes are streams containing data, and the edges are jobs performing transformations. This composition is done purely through the streams the jobs take as input and output. The jobs are otherwise totally decoupled: they need not be implemented in the same code base, and adding, removing, or restarting a downstream job will not impact an upstream job.</p> + +<p>These graphs are often acyclic—that is, data usually doesn’t flow from a job, through other jobs, back to itself. However, it is possible to create cyclic graphs if you need to.</p> + +<p><img src="/img/0.10/learn/documentation/introduction/dag.png" width="430" alt="Directed acyclic job graph"></p> + +<h3 id="containers">Containers</h3> + +<p>Partitions and tasks are both <em>logical</em> units of parallelism—they don’t correspond to any particular assignment of computational resources (CPU, memory, disk space, etc). Containers are the unit of physical parallelism, and a container is essentially a Unix process (or Linux <a href="http://en.wikipedia.org/wiki/Cgroups";>cgroup</a>). Each container runs one or more tasks. The number of tasks is determined automatically from the number of partitions in the input and is fixed, but the number of containers (and the CPU and memory resources associated with them) is specified by the user at run time and can be changed at any time.</p> + +<h2 id="architecture-»"><a href="architecture.html">Architecture »</a></h2> + + + </div> + </div> + + </div><!-- /.wrapper-content --> + </div><!-- /.wrapper --> + + <div class="footer"> + <div class="container"> + <!-- nothing for now. --> + </div> + </div> + + + <script> + $( document ).ready(function() { + if ( $.fn.urlExists( "/learn/documentation/latest/introduction/concepts.html" ) ) { + $("#switch-version-button").addClass("fa fa-history masthead-icon"); + } + }); + + /* a function to test whether the url exists or not */ + (function( $ ) { + $.fn.urlExists = function(url) { + var http = new XMLHttpRequest(); + http.open('HEAD', url, false); + http.send(); + return http.status != 404; + }; + }( jQuery )); + </script> + + + <!-- Google Analytics --> + <script> + (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){ + (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o), + m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m) + })(window,document,'script','//www.google-analytics.com/analytics.js','ga'); + + ga('create', 'UA-43122768-1', 'apache.org'); + ga('send', 'pageview'); + + </script> + </body> +</html>
