docs/build/plain-html/topics/impala_sync_ddl.html - impala - Git at Google

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   <h1 class="title topictitle1" id="ariaid-title1">SYNC_DDL Query Option</h1>


   <div class="body conbody">

     <p class="p">

       When enabled, causes any DDL operation such as <code class="ph codeph">CREATE TABLE</code> or <code class="ph codeph">ALTER TABLE</code>
       to return only when the changes have been propagated to all other Impala nodes in the cluster by the Impala
       catalog service. That way, if you issue a subsequent <code class="ph codeph">CONNECT</code> statement in
       <span class="keyword cmdname">impala-shell</span> to connect to a different node in the cluster, you can be sure that other
       node will already recognize any added or changed tables. (The catalog service automatically broadcasts the
       DDL changes to all nodes automatically, but without this option there could be a period of inconsistency if
       you quickly switched to another node, such as by issuing a subsequent query through a load-balancing proxy.)
     </p>


     <p class="p"> Although <code class="ph codeph">INSERT</code> is classified as a DML statement, when the
         <code class="ph codeph">SYNC_DDL</code> option is enabled, <code class="ph codeph">INSERT</code> statements also delay
       their completion until all the underlying data and metadata changes are propagated to all
       Impala nodes and this option applies to all filesystem-based tables. Internally, Impala
       inserts have similarities with DDL statements in traditional database systems, because they
       create metadata needed to track HDFS block locations for new files and they potentially add
       new partitions to partitioned tables. </p>


     <div class="note note"><span class="notetitle">Note:</span>
       Because this option can introduce a delay after each write operation, if you are running a sequence of
       <code class="ph codeph">CREATE DATABASE</code>, <code class="ph codeph">CREATE TABLE</code>, <code class="ph codeph">ALTER TABLE</code>,
       <code class="ph codeph">INSERT</code>, and similar statements within a setup script, to minimize the overall delay you can
       enable the <code class="ph codeph">SYNC_DDL</code> query option only near the end, before the final DDL statement.
     </div>


     <p class="p">
         <strong class="ph b">Type:</strong> Boolean; recognized values are 1 and 0, or <code class="ph codeph">true</code> and
         <code class="ph codeph">false</code>; any other value interpreted as <code class="ph codeph">false</code>
       </p>

     <p class="p">
         <strong class="ph b">Default:</strong> <code class="ph codeph">false</code> (shown as 0 in output of <code class="ph codeph">SET</code>
         statement)
       </p>


     <p class="p">
         <strong class="ph b">Related information:</strong>
       </p>

     <p class="p">
       <a class="xref" href="impala_ddl.html#ddl">DDL Statements</a>
     </p>


   </div>

 <div class="related-links">
 <div class="familylinks">
 <div class="parentlink"><strong>Parent topic:</strong> <a class="link" href="../topics/impala_set.html">SET Statement</a></div>
 </div>
 </div></body>
 </html>
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	<!DOCTYPE html
	PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
	<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
	<head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />

	<meta name="copyright" content="(C) Copyright 2023" />
	<meta name="DC.rights.owner" content="(C) Copyright 2023" />
	<meta name="DC.Type" content="concept" />
	<meta name="DC.Title" content="SYNC_DDL Query Option" />
	<meta name="DC.Relation" scheme="URI" content="../topics/impala_set.html" />
	<meta name="prodname" content="Impala" />
	<meta name="prodname" content="Impala" />
	<meta name="version" content="Impala 3.4.x" />
	<meta name="version" content="Impala 3.4.x" />
	<meta name="DC.Format" content="XHTML" />
	<meta name="DC.Identifier" content="sync_ddl" />
	<link rel="stylesheet" type="text/css" href="../commonltr.css" />
	<title>SYNC_DDL Query Option</title>
	</head>
	<body id="sync_ddl">


	<h1 class="title topictitle1" id="ariaid-title1">SYNC_DDL Query Option</h1>




	<div class="body conbody">

	<p class="p">

	When enabled, causes any DDL operation such as <code class="ph codeph">CREATE TABLE</code> or <code class="ph codeph">ALTER TABLE</code>
	to return only when the changes have been propagated to all other Impala nodes in the cluster by the Impala
	catalog service. That way, if you issue a subsequent <code class="ph codeph">CONNECT</code> statement in
	<span class="keyword cmdname">impala-shell</span> to connect to a different node in the cluster, you can be sure that other
	node will already recognize any added or changed tables. (The catalog service automatically broadcasts the
	DDL changes to all nodes automatically, but without this option there could be a period of inconsistency if
	you quickly switched to another node, such as by issuing a subsequent query through a load-balancing proxy.)
	</p>


	<p class="p"> Although <code class="ph codeph">INSERT</code> is classified as a DML statement, when the
	<code class="ph codeph">SYNC_DDL</code> option is enabled, <code class="ph codeph">INSERT</code> statements also delay
	their completion until all the underlying data and metadata changes are propagated to all
	Impala nodes and this option applies to all filesystem-based tables. Internally, Impala
	inserts have similarities with DDL statements in traditional database systems, because they
	create metadata needed to track HDFS block locations for new files and they potentially add
	new partitions to partitioned tables. </p>


	<div class="note note"><span class="notetitle">Note:</span>
	Because this option can introduce a delay after each write operation, if you are running a sequence of
	<code class="ph codeph">CREATE DATABASE</code>, <code class="ph codeph">CREATE TABLE</code>, <code class="ph codeph">ALTER TABLE</code>,
	<code class="ph codeph">INSERT</code>, and similar statements within a setup script, to minimize the overall delay you can
	enable the <code class="ph codeph">SYNC_DDL</code> query option only near the end, before the final DDL statement.
	</div>


	<p class="p">
	<strong class="ph b">Type:</strong> Boolean; recognized values are 1 and 0, or <code class="ph codeph">true</code> and
	<code class="ph codeph">false</code>; any other value interpreted as <code class="ph codeph">false</code>
	</p>

	<p class="p">
	<strong class="ph b">Default:</strong> <code class="ph codeph">false</code> (shown as 0 in output of <code class="ph codeph">SET</code>
	statement)
	</p>




	<p class="p">
	<strong class="ph b">Related information:</strong>
	</p>

	<p class="p">
	<a class="xref" href="impala_ddl.html#ddl">DDL Statements</a>
	</p>


	</div>

	<div class="related-links">
	<div class="familylinks">
	<div class="parentlink"><strong>Parent topic:</strong> <a class="link" href="../topics/impala_set.html">SET Statement</a></div>
	</div>
	</div></body>
	</html>