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<td class="page-title-pattern-first-line " style="padding: 0; border-collapse: collapse; font-family: Arial, sans-serif; font-size: 14px; padding-top: 10px"> <a href="https://hibernate.atlassian.net/browse/HHH" style="color: #3b73af; text-decoration: none">Hibernate ORM</a> / <a href="https://hibernate.atlassian.net/browse/HHH-11260" style="color: #3b73af; text-decoration: none"><img src="cid:jira-generated-image-avatar-8e11713d-7ead-4811-8540-18ab781ad6fc" height="16" width="16" border="0" align="absmiddle" alt="Improvement" style="vertical-align: text-bottom"></a> <a href="https://hibernate.atlassian.net/browse/HHH-11260" style="color: #3b73af; text-decoration: none">HHH-11260</a> </td>
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<td style="vertical-align: top;; padding: 0; border-collapse: collapse; padding-right: 5px; font-size: 20px; line-height: 30px; mso-line-height-rule: exactly" class="page-title-pattern-header-container"> <span class="page-title-pattern-header" style="font-family: Arial, sans-serif; padding: 0; font-size: 20px; line-height: 30px; mso-text-raise: 2px; mso-line-height-rule: exactly; vertical-align: middle"> <a href="https://hibernate.atlassian.net/browse/HHH-11260" style="color: #3b73af; text-decoration: none">Apply fetch-size optimization for result streaming with MySQL</a> </span> </td>
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<th style="color: #707070; font: normal 14px/20px Arial, sans-serif; text-align: left; vertical-align: top; padding: 2px 0">Issue Type:</th>
<td class="has-icon" style="padding: 0; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> <img src="cid:jira-generated-image-avatar-8e11713d-7ead-4811-8540-18ab781ad6fc" height="16" width="16" border="0" align="absmiddle" alt="Improvement" style="vertical-align: text-bottom"> Improvement </td>
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<th style="color: #707070; font: normal 14px/20px Arial, sans-serif; text-align: left; vertical-align: top; padding: 2px 0">Affects Versions:</th>
<td style="padding: 0; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> 5.2.0 </td>
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<td style="padding: 0; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> Unassigned </td>
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<th style="color: #707070; font: normal 14px/20px Arial, sans-serif; text-align: left; vertical-align: top; padding: 2px 0">Components:</th>
<td style="padding: 0; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> query-hql </td>
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<th style="color: #707070; font: normal 14px/20px Arial, sans-serif; text-align: left; vertical-align: top; padding: 2px 0">Created:</th>
<td style="padding: 0; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> 18/Nov/2016 07:46 AM </td>
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<th style="color: #707070; font: normal 14px/20px Arial, sans-serif; text-align: left; vertical-align: top; padding: 2px 0">Environment:</th>
<td style="padding: 0; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> MySQL, Forward-only resultsets, Read-only statements </td>
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<td class="has-icon" style="padding: 0; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> <img src="cid:jira-generated-image-static-major-463438ea-f2fd-43b7-bdfe-879d20350737" height="16" width="16" border="0" align="absmiddle" alt="Major" style="vertical-align: text-bottom"> Major </td>
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<th style="color: #707070; font: normal 14px/20px Arial, sans-serif; text-align: left; vertical-align: top; padding: 2px 0">Reporter:</th>
<td style="padding: 0; border-collapse: collapse; font: normal 14px/20px Arial, sans-serif; padding: 2px 0 2px 5px; vertical-align: top"> <a class="user-hover" rel="mp911de" id="email_mp911de" href="https://hibernate.atlassian.net/secure/ViewProfile.jspa?name=mp911de" style="color:#6c797f;; color: #3b73af; text-decoration: none">Mark Paluch</a> </td>
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<td class="text-paragraph-pattern-container mobile-resize-text " style="padding: 0; border-collapse: collapse; padding: 0 0 10px"> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0; margin-top: 0">Hibernate 5.2 introduced <tt>Query.stream</tt> to consume results as stream. A user wanting to benefit from iterative streaming is required to set <tt>Query.setFetchSize(Integer.MIN_VALUE)</tt> otherwise the <tt>ResultSet</tt> is entirely stored in memory:</p> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0">Quote from MySQL JDBC docs:</p>
<blockquote style="margin: 10px 0 0; border-left: 1px solid #cccccc; color: #707070; margin-left: 19px; padding: 10px 20px">
<p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0; margin-top: 0">By default, ResultSets are completely retrieved and stored in memory. In most cases this is the most efficient way to operate and, due to the design of the MySQL <span class="error">[...]</span> If you are working with ResultSets that have a large number of rows <span class="error">[...]</span> you can tell the driver to stream the results back one row at a time.</p>
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<pre class="code-java" style="margin: 10px 0 0; margin-top: 0; max-height: 30em; overflow: auto; white-space: pre-wrap; word-wrap: normal">
stmt = conn.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY,java.sql.ResultSet.CONCUR_READ_ONLY);
stmt.setFetchSize(<span class="code-object" style="color: #910091">Integer</span>.MIN_VALUE);
</pre>
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</div> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0">Users could participate from this optimization if the query yields to a Read-Only cursor and Forward-Only result set by defaulting to <tt>Query.setFetchSize(Integer.MIN_VALUE)</tt> (on query level) if no other fetch size settings are applied.</p> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0">Doing so imposes a caveat:</p>
<blockquote style="margin: 10px 0 0; border-left: 1px solid #cccccc; color: #707070; margin-left: 19px; padding: 10px 20px">
<p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0; margin-top: 0">There are some caveats with this approach. You must read all of the rows in the result set (or close it) before you can issue any other queries on the connection, or an exception will be thrown.</p>
</blockquote> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0">This issue could be addressed by applying close actions to the stream.</p> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0">Reference</p>
<ul>
<li><a href="https://knes1.github.io/blog/2015/2015-10-19-streaming-mysql-results-using-java8-streams-and-spring-data.html" class="external-link" rel="nofollow" style="color: #3b73af; text-decoration: none">https://knes1.github.io/blog/2015/2015-10-19-streaming-mysql-results-using-java8-streams-and-spring-data.html</a></li>
<li><a href="https://dev.mysql.com/doc/connector-j/6.0/en/connector-j-reference-implementation-notes.html" class="external-link" rel="nofollow" style="color: #3b73af; text-decoration: none">https://dev.mysql.com/doc/connector-j/6.0/en/connector-j-reference-implementation-notes.html</a></li>
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