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<li class="md-nav__item"><a href="#optimizer-dictionary-aggregation" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.dictionary-aggregation</span></code></a>
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<li class="md-nav__item"><a href="#optimizer-optimize-hash-generation" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.optimize-hash-generation</span></code></a>
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<li class="md-nav__item"><a href="#optimizer-optimize-metadata-queries" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.optimize-metadata-queries</span></code></a>
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<li class="md-nav__item"><a href="#optimizer-push-aggregation-through-outer-join" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.push-aggregation-through-outer-join</span></code></a>
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<li class="md-nav__item"><a href="#optimizer-push-table-write-through-union" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.push-table-write-through-union</span></code></a>
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<li class="md-nav__item"><a href="#optimizer-join-reordering-strategy" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.join-reordering-strategy</span></code></a>
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<li class="md-nav__item"><a href="#optimizer-max-reordered-joins" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.max-reordered-joins</span></code></a>
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<li class="md-nav__item"><a href="#optimizer-optimize-duplicate-insensitive-joins" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.optimize-duplicate-insensitive-joins</span></code></a>
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<li class="md-nav__item"><a href="#optimizer-use-table-scan-node-partitioning" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.use-table-scan-node-partitioning</span></code></a>
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<li class="md-nav__item"><a href="#optimizer-table-scan-node-partitioning-min-bucket-to-task-ratio" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.table-scan-node-partitioning-min-bucket-to-task-ratio</span></code></a>
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<li class="md-nav__item"><a href="#optimizer-filter-conjunction-independence-factor" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.filter-conjunction-independence-factor</span></code></a>
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<li class="md-nav__item"><a href="#optimizer-join-multi-clause-independence-factor" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.join-multi-clause-independence-factor</span></code></a>
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<li class="md-nav__item"><a href="#optimizer-non-estimatable-predicate-approximation-enabled" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.non-estimatable-predicate-approximation.enabled</span></code></a>
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<li class="md-nav__item"><a href="#optimizer-dictionary-aggregation" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.dictionary-aggregation</span></code></a>
</li>
<li class="md-nav__item"><a href="#optimizer-optimize-hash-generation" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.optimize-hash-generation</span></code></a>
</li>
<li class="md-nav__item"><a href="#optimizer-optimize-metadata-queries" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.optimize-metadata-queries</span></code></a>
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<li class="md-nav__item"><a href="#optimizer-push-aggregation-through-outer-join" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.push-aggregation-through-outer-join</span></code></a>
</li>
<li class="md-nav__item"><a href="#optimizer-push-table-write-through-union" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.push-table-write-through-union</span></code></a>
</li>
<li class="md-nav__item"><a href="#optimizer-join-reordering-strategy" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.join-reordering-strategy</span></code></a>
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<li class="md-nav__item"><a href="#optimizer-max-reordered-joins" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.max-reordered-joins</span></code></a>
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<li class="md-nav__item"><a href="#optimizer-optimize-duplicate-insensitive-joins" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.optimize-duplicate-insensitive-joins</span></code></a>
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<li class="md-nav__item"><a href="#optimizer-use-table-scan-node-partitioning" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.use-table-scan-node-partitioning</span></code></a>
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<li class="md-nav__item"><a href="#optimizer-table-scan-node-partitioning-min-bucket-to-task-ratio" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.table-scan-node-partitioning-min-bucket-to-task-ratio</span></code></a>
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<li class="md-nav__item"><a href="#optimizer-filter-conjunction-independence-factor" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.filter-conjunction-independence-factor</span></code></a>
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<li class="md-nav__item"><a href="#optimizer-join-multi-clause-independence-factor" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.join-multi-clause-independence-factor</span></code></a>
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<li class="md-nav__item"><a href="#optimizer-non-estimatable-predicate-approximation-enabled" class="md-nav__link"><code class="docutils literal notranslate"><span class="pre">optimizer.non-estimatable-predicate-approximation.enabled</span></code></a>
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<article class="md-content__inner md-typeset" role="main">
<h1 id="admin-properties-optimizer--page-root">Optimizer properties<a class="headerlink" href="#admin-properties-optimizer--page-root" title="Permalink to this headline">#</a></h1>
<h2 id="optimizer-dictionary-aggregation"><code class="docutils literal notranslate"><span class="pre">optimizer.dictionary-aggregation</span></code><a class="headerlink" href="#optimizer-dictionary-aggregation" title="Permalink to this headline">#</a></h2>
<ul class="simple">
<li><p><strong>Type:</strong> <a class="reference internal" href="properties.html#prop-type-boolean"><span class="std std-ref">boolean</span></a></p></li>
<li><p><strong>Default value:</strong> <code class="docutils literal notranslate"><span class="pre">false</span></code></p></li>
</ul>
<p>Enables optimization for aggregations on dictionaries. This can also be specified
on a per-query basis using the <code class="docutils literal notranslate"><span class="pre">dictionary_aggregation</span></code> session property.</p>
<h2 id="optimizer-optimize-hash-generation"><code class="docutils literal notranslate"><span class="pre">optimizer.optimize-hash-generation</span></code><a class="headerlink" href="#optimizer-optimize-hash-generation" title="Permalink to this headline">#</a></h2>
<ul class="simple">
<li><p><strong>Type:</strong> <a class="reference internal" href="properties.html#prop-type-boolean"><span class="std std-ref">boolean</span></a></p></li>
<li><p><strong>Default value:</strong> <code class="docutils literal notranslate"><span class="pre">true</span></code></p></li>
</ul>
<p>Compute hash codes for distribution, joins, and aggregations early during execution,
allowing result to be shared between operations later in the query. This can reduce
CPU usage by avoiding computing the same hash multiple times, but at the cost of
additional network transfer for the hashes. In most cases it decreases overall
query processing time. This can also be specified on a per-query basis using the
<code class="docutils literal notranslate"><span class="pre">optimize_hash_generation</span></code> session property.</p>
<p>It is often helpful to disable this property, when using <a class="reference internal" href="../sql/explain.html"><span class="doc">EXPLAIN</span></a> in order
to make the query plan easier to read.</p>
<h2 id="optimizer-optimize-metadata-queries"><code class="docutils literal notranslate"><span class="pre">optimizer.optimize-metadata-queries</span></code><a class="headerlink" href="#optimizer-optimize-metadata-queries" title="Permalink to this headline">#</a></h2>
<ul class="simple">
<li><p><strong>Type:</strong> <a class="reference internal" href="properties.html#prop-type-boolean"><span class="std std-ref">boolean</span></a></p></li>
<li><p><strong>Default value:</strong> <code class="docutils literal notranslate"><span class="pre">false</span></code></p></li>
</ul>
<p>Enable optimization of some aggregations by using values that are stored as metadata.
This allows Trino to execute some simple queries in constant time. Currently, this
optimization applies to <code class="docutils literal notranslate"><span class="pre">max</span></code>, <code class="docutils literal notranslate"><span class="pre">min</span></code> and <code class="docutils literal notranslate"><span class="pre">approx_distinct</span></code> of partition
keys and other aggregation insensitive to the cardinality of the input,including
<code class="docutils literal notranslate"><span class="pre">DISTINCT</span></code> aggregates. Using this may speed up some queries significantly.</p>
<p>The main drawback is that it can produce incorrect results, if the connector returns
partition keys for partitions that have no rows. In particular, the Hive connector
can return empty partitions, if they were created by other systems. Trino cannot
create them.</p>
<h2 id="optimizer-push-aggregation-through-outer-join"><code class="docutils literal notranslate"><span class="pre">optimizer.push-aggregation-through-outer-join</span></code><a class="headerlink" href="#optimizer-push-aggregation-through-outer-join" title="Permalink to this headline">#</a></h2>
<ul class="simple">
<li><p><strong>Type:</strong> <a class="reference internal" href="properties.html#prop-type-boolean"><span class="std std-ref">boolean</span></a></p></li>
<li><p><strong>Default value:</strong> <code class="docutils literal notranslate"><span class="pre">true</span></code></p></li>
</ul>
<p>When an aggregation is above an outer join and all columns from the outer side of the join
are in the grouping clause, the aggregation is pushed below the outer join. This optimization
is particularly useful for correlated scalar subqueries, which get rewritten to an aggregation
over an outer join. For example:</p>
<div class="highlight-sql notranslate"><div class="highlight"><pre><span></span><span class="k">SELECT</span> <span class="o">*</span> <span class="k">FROM</span> <span class="n">item</span> <span class="n">i</span>
<span class="k">WHERE</span> <span class="n">i</span><span class="p">.</span><span class="n">i_current_price</span> <span class="o">></span> <span class="p">(</span>
<span class="k">SELECT</span> <span class="k">AVG</span><span class="p">(</span><span class="n">j</span><span class="p">.</span><span class="n">i_current_price</span><span class="p">)</span> <span class="k">FROM</span> <span class="n">item</span> <span class="n">j</span>
<span class="k">WHERE</span> <span class="n">i</span><span class="p">.</span><span class="n">i_category</span> <span class="o">=</span> <span class="n">j</span><span class="p">.</span><span class="n">i_category</span><span class="p">);</span>
</pre></div>
</div>
<p>Enabling this optimization can substantially speed up queries by reducing
the amount of data that needs to be processed by the join. However, it may slow down some
queries that have very selective joins. This can also be specified on a per-query basis using
the <code class="docutils literal notranslate"><span class="pre">push_aggregation_through_join</span></code> session property.</p>
<h2 id="optimizer-push-table-write-through-union"><code class="docutils literal notranslate"><span class="pre">optimizer.push-table-write-through-union</span></code><a class="headerlink" href="#optimizer-push-table-write-through-union" title="Permalink to this headline">#</a></h2>
<ul class="simple">
<li><p><strong>Type:</strong> <a class="reference internal" href="properties.html#prop-type-boolean"><span class="std std-ref">boolean</span></a></p></li>
<li><p><strong>Default value:</strong> <code class="docutils literal notranslate"><span class="pre">true</span></code></p></li>
</ul>
<p>Parallelize writes when using <code class="docutils literal notranslate"><span class="pre">UNION</span> <span class="pre">ALL</span></code> in queries that write data. This improves the
speed of writing output tables in <code class="docutils literal notranslate"><span class="pre">UNION</span> <span class="pre">ALL</span></code> queries, because these writes do not require
additional synchronization when collecting results. Enabling this optimization can improve
<code class="docutils literal notranslate"><span class="pre">UNION</span> <span class="pre">ALL</span></code> speed, when write speed is not yet saturated. However, it may slow down queries
in an already heavily loaded system. This can also be specified on a per-query basis
using the <code class="docutils literal notranslate"><span class="pre">push_table_write_through_union</span></code> session property.</p>
<h2 id="optimizer-join-reordering-strategy"><code class="docutils literal notranslate"><span class="pre">optimizer.join-reordering-strategy</span></code><a class="headerlink" href="#optimizer-join-reordering-strategy" title="Permalink to this headline">#</a></h2>
<ul class="simple">
<li><p><strong>Type:</strong> <a class="reference internal" href="properties.html#prop-type-string"><span class="std std-ref">string</span></a></p></li>
<li><p><strong>Allowed values:</strong> <code class="docutils literal notranslate"><span class="pre">AUTOMATIC</span></code>, <code class="docutils literal notranslate"><span class="pre">ELIMINATE_CROSS_JOINS</span></code>, <code class="docutils literal notranslate"><span class="pre">NONE</span></code></p></li>
<li><p><strong>Default value:</strong> <code class="docutils literal notranslate"><span class="pre">AUTOMATIC</span></code></p></li>
</ul>
<p>The join reordering strategy to use. <code class="docutils literal notranslate"><span class="pre">NONE</span></code> maintains the order the tables are listed in the
query. <code class="docutils literal notranslate"><span class="pre">ELIMINATE_CROSS_JOINS</span></code> reorders joins to eliminate cross joins, where possible, and
otherwise maintains the original query order. When reordering joins, it also strives to maintain the
original table order as much as possible. <code class="docutils literal notranslate"><span class="pre">AUTOMATIC</span></code> enumerates possible orders, and uses
statistics-based cost estimation to determine the least cost order. If stats are not available, or if
for any reason a cost could not be computed, the <code class="docutils literal notranslate"><span class="pre">ELIMINATE_CROSS_JOINS</span></code> strategy is used. This can
be specified on a per-query basis using the <code class="docutils literal notranslate"><span class="pre">join_reordering_strategy</span></code> session property.</p>
<h2 id="optimizer-max-reordered-joins"><code class="docutils literal notranslate"><span class="pre">optimizer.max-reordered-joins</span></code><a class="headerlink" href="#optimizer-max-reordered-joins" title="Permalink to this headline">#</a></h2>
<ul class="simple">
<li><p><strong>Type:</strong> <a class="reference internal" href="properties.html#prop-type-integer"><span class="std std-ref">integer</span></a></p></li>
<li><p><strong>Default value:</strong> <code class="docutils literal notranslate"><span class="pre">9</span></code></p></li>
</ul>
<p>When optimizer.join-reordering-strategy is set to cost-based, this property determines
the maximum number of joins that can be reordered at once.</p>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p>The number of possible join orders scales factorially with the number of
relations, so increasing this value can cause serious performance issues.</p>
</div>
<h2 id="optimizer-optimize-duplicate-insensitive-joins"><code class="docutils literal notranslate"><span class="pre">optimizer.optimize-duplicate-insensitive-joins</span></code><a class="headerlink" href="#optimizer-optimize-duplicate-insensitive-joins" title="Permalink to this headline">#</a></h2>
<ul class="simple">
<li><p><strong>Type:</strong> <a class="reference internal" href="properties.html#prop-type-boolean"><span class="std std-ref">boolean</span></a></p></li>
<li><p><strong>Default value:</strong> <code class="docutils literal notranslate"><span class="pre">true</span></code></p></li>
</ul>
<p>Reduces number of rows produced by joins when optimizer detects that duplicated
join output rows can be skipped.</p>
<h2 id="optimizer-use-table-scan-node-partitioning"><code class="docutils literal notranslate"><span class="pre">optimizer.use-table-scan-node-partitioning</span></code><a class="headerlink" href="#optimizer-use-table-scan-node-partitioning" title="Permalink to this headline">#</a></h2>
<ul class="simple">
<li><p><strong>Type:</strong> <a class="reference internal" href="properties.html#prop-type-boolean"><span class="std std-ref">boolean</span></a></p></li>
<li><p><strong>Default value:</strong> <code class="docutils literal notranslate"><span class="pre">true</span></code></p></li>
</ul>
<p>Use connector provided table node partitioning when reading tables.
For example, table node partitioning corresponds to Hive table buckets.
When set to <code class="docutils literal notranslate"><span class="pre">true</span></code> and minimal partition to task ratio is matched or exceeded,
each table partition is read by a separate worker. The minimal ratio is defined in
<code class="docutils literal notranslate"><span class="pre">optimizer.table-scan-node-partitioning-min-bucket-to-task-ratio</span></code>.</p>
<p>Partition reader assignments are distributed across workers for
parallel processing. Use of table scan node partitioning can improve
query performance by reducing query complexity. For example,
cluster wide data reshuffling might not be needed when processing an aggregation query.
However, query parallelism might be reduced when partition count is
low compared to number of workers.</p>
<h2 id="optimizer-table-scan-node-partitioning-min-bucket-to-task-ratio"><code class="docutils literal notranslate"><span class="pre">optimizer.table-scan-node-partitioning-min-bucket-to-task-ratio</span></code><a class="headerlink" href="#optimizer-table-scan-node-partitioning-min-bucket-to-task-ratio" title="Permalink to this headline">#</a></h2>
<ul class="simple">
<li><p><strong>Type:</strong> <a class="reference internal" href="properties.html#prop-type-double"><span class="std std-ref">double</span></a></p></li>
<li><p><strong>Default value:</strong> <code class="docutils literal notranslate"><span class="pre">0.5</span></code></p></li>
</ul>
<p>Specifies minimal bucket to task ratio that has to be matched or exceeded in order
to use table scan node partitioning. When the table bucket count is small
compared to the number of workers, then the table scan is distributed across
all workers for improved parallelism.</p>
<h2 id="optimizer-filter-conjunction-independence-factor"><code class="docutils literal notranslate"><span class="pre">optimizer.filter-conjunction-independence-factor</span></code><a class="headerlink" href="#optimizer-filter-conjunction-independence-factor" title="Permalink to this headline">#</a></h2>
<ul class="simple">
<li><p><strong>Type:</strong> <a class="reference internal" href="properties.html#prop-type-double"><span class="std std-ref">double</span></a></p></li>
<li><p><strong>Default value:</strong> <code class="docutils literal notranslate"><span class="pre">0.75</span></code></p></li>
<li><p><strong>Min allowed value:</strong> <code class="docutils literal notranslate"><span class="pre">0</span></code></p></li>
<li><p><strong>Max allowed value:</strong> <code class="docutils literal notranslate"><span class="pre">1</span></code></p></li>
</ul>
<p>Scales the strength of independence assumption for estimating the selectivity of
the conjunction of multiple predicates. Lower values for this property will produce
more conservative estimates by assuming a greater degree of correlation between the
columns of the predicates in a conjunction. A value of <code class="docutils literal notranslate"><span class="pre">0</span></code> results in the
optimizer assuming that the columns of the predicates are fully correlated and only
the most selective predicate drives the selectivity of a conjunction of predicates.</p>
<h2 id="optimizer-join-multi-clause-independence-factor"><code class="docutils literal notranslate"><span class="pre">optimizer.join-multi-clause-independence-factor</span></code><a class="headerlink" href="#optimizer-join-multi-clause-independence-factor" title="Permalink to this headline">#</a></h2>
<ul class="simple">
<li><p><strong>Type:</strong> <a class="reference internal" href="properties.html#prop-type-double"><span class="std std-ref">double</span></a></p></li>
<li><p><strong>Default value:</strong> <code class="docutils literal notranslate"><span class="pre">0.25</span></code></p></li>
<li><p><strong>Min allowed value:</strong> <code class="docutils literal notranslate"><span class="pre">0</span></code></p></li>
<li><p><strong>Max allowed value:</strong> <code class="docutils literal notranslate"><span class="pre">1</span></code></p></li>
</ul>
<p>Scales the strength of independence assumption for estimating the output of a
multi-clause join. Lower values for this property will produce more
conservative estimates by assuming a greater degree of correlation between the
columns of the clauses in a join. A value of <code class="docutils literal notranslate"><span class="pre">0</span></code> results in the optimizer
assuming that the columns of the join clauses are fully correlated and only
the most selective clause drives the selectivity of the join.</p>
<h2 id="optimizer-non-estimatable-predicate-approximation-enabled"><code class="docutils literal notranslate"><span class="pre">optimizer.non-estimatable-predicate-approximation.enabled</span></code><a class="headerlink" href="#optimizer-non-estimatable-predicate-approximation-enabled" title="Permalink to this headline">#</a></h2>
<ul class="simple">
<li><p><strong>Type:</strong> <a class="reference internal" href="properties.html#prop-type-boolean"><span class="std std-ref">boolean</span></a></p></li>
<li><p><strong>Default value:</strong> <code class="docutils literal notranslate"><span class="pre">true</span></code></p></li>
</ul>
<p>Enables approximation of the output row count of filters whose costs cannot be
accurately estimated even with complete statistics. This allows the optimizer to
produce more efficient plans in the presence of filters which were previously
not estimated.</p>
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