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        <span>Presto 0.181 Documentation</span></a></h1>
    <h2 class="heading"><span>8.14. EXPLAIN</span></h2>
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  <div class="section" id="explain">
<h1>8.14. EXPLAIN</h1>
<div class="section" id="synopsis">
<h2>Synopsis</h2>
<div class="highlight-none"><div class="highlight"><pre><span></span>EXPLAIN [ ( option [, ...] ) ] statement

where option can be one of:

    FORMAT { TEXT | GRAPHVIZ }
    TYPE { LOGICAL | DISTRIBUTED | VALIDATE }
</pre></div>
</div>
</div>
<div class="section" id="description">
<h2>Description</h2>
<p>Show the logical or distributed execution plan of a statement, or validate the statement.
Use <code class="docutils literal"><span class="pre">TYPE</span> <span class="pre">DISTRIBUTED</span></code> option to display fragmented plan. Each plan fragment is executed by
a single or multiple Presto nodes. Fragments separation represent the data exchange between Presto nodes.
Fragment type specifies how the fragment is executed by Presto nodes and how the data is
distributed between fragments:</p>
<dl class="docutils">
<dt><code class="docutils literal"><span class="pre">SINGLE</span></code></dt>
<dd>Fragment is executed on a single node.</dd>
<dt><code class="docutils literal"><span class="pre">HASH</span></code></dt>
<dd>Fragment is executed on a fixed number of nodes with the input data
distributed using a hash function.</dd>
<dt><code class="docutils literal"><span class="pre">ROUND_ROBIN</span></code></dt>
<dd>Fragment is executed on a fixed number of nodes with the input data
distributed in a round-robin fashion.</dd>
<dt><code class="docutils literal"><span class="pre">BROADCAST</span></code></dt>
<dd>Fragment is executed on a fixed number of nodes with the input data
broadcasted to all nodes.</dd>
<dt><code class="docutils literal"><span class="pre">SOURCE</span></code></dt>
<dd>Fragment is executed on nodes where input splits are accessed.</dd>
</dl>
</div>
<div class="section" id="examples">
<h2>Examples</h2>
<p>Logical plan:</p>
<div class="highlight-none"><div class="highlight"><pre><span></span>presto:tiny&gt; EXPLAIN SELECT regionkey, count(*) FROM nation GROUP BY 1;
                                                Query Plan
----------------------------------------------------------------------------------------------------------
 - Output[regionkey, _col1] =&gt; [regionkey:bigint, count:bigint]
         _col1 := count
     - RemoteExchange[GATHER] =&gt; regionkey:bigint, count:bigint
         - Aggregate(FINAL)[regionkey] =&gt; [regionkey:bigint, count:bigint]
                count := &quot;count&quot;(&quot;count_8&quot;)
             - LocalExchange[HASH][$hashvalue] (&quot;regionkey&quot;) =&gt; regionkey:bigint, count_8:bigint, $hashvalue:bigint
                 - RemoteExchange[REPARTITION][$hashvalue_9] =&gt; regionkey:bigint, count_8:bigint, $hashvalue_9:bigint
                     - Project[] =&gt; [regionkey:bigint, count_8:bigint, $hashvalue_10:bigint]
                             $hashvalue_10 := &quot;combine_hash&quot;(BIGINT &#39;0&#39;, COALESCE(&quot;$operator$hash_code&quot;(&quot;regionkey&quot;), 0))
                         - Aggregate(PARTIAL)[regionkey] =&gt; [regionkey:bigint, count_8:bigint]
                                 count_8 := &quot;count&quot;(*)
                             - TableScan[tpch:tpch:nation:sf0.1, originalConstraint = true] =&gt; [regionkey:bigint]
                                     regionkey := tpch:regionkey
</pre></div>
</div>
<p>Distributed plan:</p>
<div class="highlight-none"><div class="highlight"><pre><span></span>presto:tiny&gt; EXPLAIN (TYPE DISTRIBUTED) SELECT regionkey, count(*) FROM nation GROUP BY 1;
                                          Query Plan
----------------------------------------------------------------------------------------------
 Fragment 0 [SINGLE]
     Output layout: [regionkey, count]
     Output partitioning: SINGLE []
     - Output[regionkey, _col1] =&gt; [regionkey:bigint, count:bigint]
             _col1 := count
         - RemoteSource[1] =&gt; [regionkey:bigint, count:bigint]

 Fragment 1 [HASH]
     Output layout: [regionkey, count]
     Output partitioning: SINGLE []
     - Aggregate(FINAL)[regionkey] =&gt; [regionkey:bigint, count:bigint]
             count := &quot;count&quot;(&quot;count_8&quot;)
         - LocalExchange[HASH][$hashvalue] (&quot;regionkey&quot;) =&gt; regionkey:bigint, count_8:bigint, $hashvalue:bigint
             - RemoteSource[2] =&gt; [regionkey:bigint, count_8:bigint, $hashvalue_9:bigint]

 Fragment 2 [SOURCE]
     Output layout: [regionkey, count_8, $hashvalue_10]
     Output partitioning: HASH [regionkey][$hashvalue_10]
     - Project[] =&gt; [regionkey:bigint, count_8:bigint, $hashvalue_10:bigint]
             $hashvalue_10 := &quot;combine_hash&quot;(BIGINT &#39;0&#39;, COALESCE(&quot;$operator$hash_code&quot;(&quot;regionkey&quot;), 0))
         - Aggregate(PARTIAL)[regionkey] =&gt; [regionkey:bigint, count_8:bigint]
                 count_8 := &quot;count&quot;(*)
             - TableScan[tpch:tpch:nation:sf0.1, originalConstraint = true] =&gt; [regionkey:bigint]
                     regionkey := tpch:regionkey
</pre></div>
</div>
<p>Validate:</p>
<div class="highlight-none"><div class="highlight"><pre><span></span>presto:tiny&gt; EXPLAIN (TYPE VALIDATE) SELECT regionkey, count(*) FROM nation GROUP BY 1;
 Valid
-------
 true
</pre></div>
</div>
</div>
<div class="section" id="see-also">
<h2>See Also</h2>
<p><a class="reference internal" href="explain-analyze.html"><span class="doc">EXPLAIN ANALYZE</span></a></p>
</div>
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