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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Presto | FAQ</title>
<link rel="stylesheet" href="static/presto.css" type="text/css"/>
<meta name="viewport" content="width=device-width">
<meta property="og:type" content="website">
<meta property="og:title" content="Presto | FAQ">
<meta property="og:description" content="Distributed SQL Query Engine for Big Data">
<meta property="og:image" content="static/presto-og.png">
</head>
<body>
<header class="topbar clearfix">
<nav class="width">
<a href="."><h1>Presto</h1></a>
<ul class="nav">
<li><a href="overview.html">Overview</a></li>
<li><a href="docs/current/">Docs</a></li>
<li><a href="faq.html">FAQ</a></li>
<li><a href="community.html">Community</a></li>
<li><a href="resources.html">Resources</a></li>
<li><a href="https://github.com/facebook/presto">GitHub</a>
</ul>
</nav>
</header>
<header class="hero clearfix">
<div class="width">
<h1>Presto FAQ</h1>
</div>
</header>
<div class="content homecontent width clearfix">
<div class="leftcol widecol faq">
<h2 id="running">Running Presto</h2>
<h3 id="memory">How much memory should I give a worker node?</h3>
<p>
The answer to this question will depend on the size of the data
sets you are working with and the nature of the queries you are
running, but Facebook typically runs Presto with a 16 GB heap
(this is the amount specified by the example JVM config file
in the deployment instructions).
</p>
<h2 id="compatibility">Compatibility and Support</h2>
<h3 id="hadoopversion">What versions of Hadoop does Presto support?</h3>
<p>
The <a href="docs/current/connector/hive.html">Hive Connector</a>
supports all popular versions of Hadoop.
</p>
<h3>Does Presto connect to Cassandra?</h3>
<p>
Yes, via the <a href="docs/current/connector/cassandra.html">Cassandra Connector</a>.
</p>
<h3>Does Presto connect to MySQL or PostgreSQL?</h3>
<p>
Yes, via the
<a href="docs/current/connector/mysql.html">MySQL Connector</a> or
<a href="docs/current/connector/postgresql.html">PostgreSQL Connector</a>.
Both of these connectors extend a base JDBC connector that is
easy to extend to connect other databases. Presto also includes a
<a href="docs/current/installation/jdbc.html">JDBC Driver</a>
that allows Java applications to connect to Presto.
</p>
<h2 id="errors">Common Errors and Troubleshooting</h2>
<h3>Why can I run <tt>SHOW TABLES</tt> but I can't <tt>SELECT</tt> from any of them?</h3>
<p>
If you can run metadata commands like <code>SHOW TABLES</code>
but can't read from them, this means that Presto is able to
access your Hive metastore but not your HDFS cluster. You
might see one of these error messages:
</p>
<ul>
<li><code>java.io.IOException: Response is null</code></li>
<li><code>InvalidProtocolBufferException: Message missing required fields</code></li>
</ul>
<p>
There is probably a mismatch between your Hadoop version and the
<a href="docs/current/connector/hive.html">Hive Connector</a>
version you have selected. Make sure that you set the
catalog property <code>connector.name</code> appropriately for
your version of Hadoop.
</p>
<h3>Why do I see a "<i>Cannot connect to discovery server for refresh</i>" error on startup?</h3>
<p>
This is usually not a problem. The error message appears because
the discovery client starts before the embedded discovery server
is ready. You will see a <code>succeeded for refresh</code> message
shortly after the error message in the logs which shows that
everything is working. We will fix the log message eventually
but it is purely a cosmetic issue.
</p>
<h3>Queries are running slower than expected. What are the factors that influence Presto performance?</h3>
<p>
The first things to check are the basic machine stats for
your workers and coordinators. Measure the load, network,
and disk utilization over time to understand where Presto
is running out of resources.
</p>
<ul>
<li>If the Presto process is mostly idle, this means that
Presto can not retrieve data fast enough from the HDFS
data node. This could be caused by network or disk
bandwidth or CPU on the data node.</li>
<li>If the Presto process is using 100% cpu, it might be
caused by the use of an expensive to parse input format.
For example, the Textfile is a very expensive input format
to parse.</li>
<li>If neither of the above are true, the Presto process
may have some sort of internal resource starvation. If
this is the case you should take a thread dump of your
coordinators and workers with a tool like jstack as a
starting point for your investigation.</li>
</ul>
<h2 id="querying">Running Presto Queries</h2>
<h3>Is there a user-friendly interface for running Presto queries?</h3>
<p>
The <a href="resources.html">resources page</a> lists
several external projects designed to provide a
user-friendly GUI interface for Presto queries.
</p>
<h2 id="support">Enterprise Support for Presto</h2>
<h3>Is there enterprise support available for Presto?<br/>
Is there an enterprise distribution of Presto?</h3>
<p>
<a href="https://www.starburstdata.com/">Starburst Data</a> described
on the <a href="resources.html#support">resources page</a> provides a
wide variety of
<a href="https://www.starburstdata.com/presto-enterprise/">services around Presto</a>.
From enterprise support for Presto clusters, through configuration and
custom Presto development, to trainings. Starburst also provides an
<a href="https://www.starburstdata.com/our-offerings/">enterprise ready
distribution of Presto</a>.
</p>
</div>
<div class="rightcol">
<h3>Presto FAQs</h3>
<ul>
<li><a href="#running">Running Presto</a></li>
<li><a href="#compatibility">Compatibility</a></li>
<li><a href="#errors">Common Errors</a></li>
<li><a href="#querying">Running Presto Queries</a></li>
<li><a href="#support">Enterprise Support for Presto</a></li>
</ul>
</div>
</div>
<div class="footer">© Copyright 2013-2016, Facebook</div>
</body>
</html>