forked from docs/doc-exports
Lu, Huayi
a24ca60074
Reviewed-by: Hasko, Vladimir <vladimir.hasko@t-systems.com> Co-authored-by: Lu, Huayi <luhuayi@huawei.com> Co-committed-by: Lu, Huayi <luhuayi@huawei.com>
31 lines
4.0 KiB
HTML
31 lines
4.0 KiB
HTML
<a name="EN-US_TOPIC_0000001098974946"></a><a name="EN-US_TOPIC_0000001098974946"></a>
|
|
|
|
<h1 class="topictitle1">Stream Operation Hints</h1>
|
|
<div id="body1534471018690"><div class="section" id="EN-US_TOPIC_0000001098974946__section290819468377"><h4 class="sectiontitle">Function</h4><p id="EN-US_TOPIC_0000001098974946__p6952105124120">These hints specify a stream operation, which can be <strong id="EN-US_TOPIC_0000001098974946__b4971143352713">broadcast</strong> or <strong id="EN-US_TOPIC_0000001098974946__b1767375122620">redistribute</strong>.</p>
|
|
</div>
|
|
<div class="section" id="EN-US_TOPIC_0000001098974946__section17783121184117"><h4 class="sectiontitle">Syntax</h4><div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001098974946__screen682272534119"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal">1</span></pre></div></td><td class="code"><div><pre><span></span><span class="p">[</span><span class="k">no</span><span class="p">]</span><span class="w"> </span><span class="n">broadcast</span><span class="o">|</span><span class="n">redistribute</span><span class="p">(</span><span class="n">table_list</span><span class="p">)</span><span class="w"></span>
|
|
</pre></div></td></tr></table></div>
|
|
|
|
</div>
|
|
</div>
|
|
<div class="section" id="EN-US_TOPIC_0000001098974946__section3914251214383"><h4 class="sectiontitle">Parameter Description</h4><ul id="EN-US_TOPIC_0000001098974946__ul14347162691914"><li id="EN-US_TOPIC_0000001098974946__li143471926121911"><strong id="EN-US_TOPIC_0000001098974946__b1032416913113">no</strong> indicates that the specified hint will not be used for a join.</li></ul>
|
|
</div>
|
|
<ul id="EN-US_TOPIC_0000001098974946__ul1334719263193"><li id="EN-US_TOPIC_0000001098974946__li1734719264194"><em id="EN-US_TOPIC_0000001098974946__i25311812172811">table_list</em> specifies the tables to be joined. For details, see <a href="dws_04_0457.html#EN-US_TOPIC_0000001099134840__section35948678143011">Parameter Description</a>.</li></ul>
|
|
<div class="section" id="EN-US_TOPIC_0000001098974946__section1127715590585"><h4 class="sectiontitle">Examples</h4><p id="EN-US_TOPIC_0000001098974946__p1698632723710">Hint the query plan in <a href="dws_04_0455.html#EN-US_TOPIC_0000001098974750__section671421102912">Examples</a> as follows:</p>
|
|
</div>
|
|
<div class="codecoloring" codetype="Sql" id="EN-US_TOPIC_0000001098974946__screen19749123984117"><div class="highlight"><table class="highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre><span class="normal">1</span>
|
|
<span class="normal">2</span></pre></div></td><td class="code"><div><pre><span></span><span class="k">explain</span><span class="w"></span>
|
|
<span class="k">select</span><span class="w"> </span><span class="cm">/*+ no redistribute(store_sales store_returns item store) leading(((store_sales store_returns item store) customer)) */</span><span class="w"> </span><span class="n">i_product_name</span><span class="w"> </span><span class="n">product_name</span><span class="w"> </span><span class="p">...</span><span class="w"></span>
|
|
</pre></div></td></tr></table></div>
|
|
|
|
</div>
|
|
<p id="EN-US_TOPIC_0000001098974946__p35873872152236">In the original plan, the join result of <strong id="EN-US_TOPIC_0000001098974946__b5894843191114">store_sales</strong>, <strong id="EN-US_TOPIC_0000001098974946__b10600048201114">store_returns</strong>, <strong id="EN-US_TOPIC_0000001098974946__b85071452131112">item</strong>, and <strong id="EN-US_TOPIC_0000001098974946__b1289405515119">store</strong> is redistributed before it is joined with <strong id="EN-US_TOPIC_0000001098974946__b1942114567234">customer</strong>. After the hinting, the redistribution is disabled and the join order is retained. The optimized plan is as follows:</p>
|
|
<p id="EN-US_TOPIC_0000001098974946__p981419333811"><span><img id="EN-US_TOPIC_0000001098974946__image781353143813" src="figure/en-us_image_0000001145495247.png"></span></p>
|
|
</div>
|
|
<div>
|
|
<div class="familylinks">
|
|
<div class="parentlink"><strong>Parent topic:</strong> <a href="dws_04_0454.html">Hint-based Tuning</a></div>
|
|
</div>
|
|
</div>
|
|
|