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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 note_note"><span class="note__title 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>
<nav role="navigation" 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></nav></article></main></body></html>