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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-11825" style="color: #3b73af; text-decoration: none"><img src="cid:jira-generated-image-avatar-cbb5e53e-43c7-45a5-8d78-c49fb8a3bd52" height="16" width="16" border="0" align="absmiddle" alt="Bug" style="vertical-align: text-bottom"></a> <a href="https://hibernate.atlassian.net/browse/HHH-11825" style="color: #3b73af; text-decoration: none">HHH-11825</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-11825" style="color: #3b73af; text-decoration: none">Deadlock using sequence ID generator in MySQL</a> </span> </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-avatar-cbb5e53e-43c7-45a5-8d78-c49fb8a3bd52" height="16" width="16" border="0" align="absmiddle" alt="Bug" style="vertical-align: text-bottom"> Bug </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"> 5.2.10 </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"> hibernate-core </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"> 19/Jun/2017 09:34 AM </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-5d310757-e4aa-4129-9738-3588b50883ea" height="16" width="16" border="0" align="absmiddle" alt="Major" style="vertical-align: text-bottom"> Major </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"> <a class="user-hover" rel="jamesagnew" id="email_jamesagnew" href="https://hibernate.atlassian.net/secure/ViewProfile.jspa?name=jamesagnew" style="color:#6c797f;; color: #3b73af; text-decoration: none">James Agnew</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">When using a sequence ID generator with MySQL Dialect, it seems to be possible to get the system to lock up completely.</p> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0">This behaviour is triggered if a large number of threads are all creating entities in the table with the sequence generator at the same time.</p> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0">After poring over stack traces, the problem seems to be as follows: </p>
<ul>
<li>The TableStructure generator is used on MySQL since there is no native support for sequences</li>
<li>This generator makes an SQL call, but does this in a separate connection from the currently executing connection (see here: <a href="https://github.com/hibernate/hibernate-orm/blob/master/hibernate-core/src/main/java/org/hibernate/id/enhanced/TableGenerator.java#L530" class="external-link" rel="nofollow" style="color: #3b73af; text-decoration: none">https://github.com/hibernate/hibernate-orm/blob/master/hibernate-core/src/main/java/org/hibernate/id/enhanced/TableGenerator.java#L530</a> )</li>
<li>If no connection is available because other entity creation threads have consumed all available connections, the generator will hang indefinitely while waiting for a connection</li>
<li>Since the ID generator is hung, all of the connection threads hang too leading to a deadlock</li>
</ul> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0">The relevant portion of the stack trace seems to be:</p> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0">```<br> at sun.misc.Unsafe.park(boolean, long)<br> at java.util.concurrent.locks.LockSupport.park(java.lang.Object) (line: 175)<br> at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await() (line: 2039)<br> at org.apache.commons.pool2.impl.LinkedBlockingDeque.takeFirst() (line: 583)<br> at org.apache.commons.pool2.impl.GenericObjectPool.borrowObject(long) (line: 442)<br> at org.apache.commons.pool2.impl.GenericObjectPool.borrowObject() (line: 363)<br> at org.apache.commons.dbcp2.PoolingDataSource.getConnection() (line: 134)<br> at org.apache.commons.dbcp2.BasicDataSource.getConnection() (line: 1533)<br> at org.hibernate.engine.jdbc.connections.internal.DatasourceConnectionProviderImpl.getConnection() (line: 122)<br> at org.hibernate.internal.NonContextualJdbcConnectionAccess.obtainConnection() (line: 35)<br> at org.hibernate.resource.transaction.backend.jdbc.internal.JdbcIsolationDelegate.delegateWork(org.hibernate.jdbc.WorkExecutorVisitable, boolean) (line: 48)<br> at org.hibernate.id.enhanced.TableStructure$1.getNextValue() (line: 125)<br> at org.hibernate.id.enhanced.PooledOptimizer.generate(org.hibernate.id.enhanced.AccessCallback) (line: 73)<br> at org.hibernate.id.enhanced.SequenceStyleGenerator.generate(org.hibernate.engine.spi.SharedSessionContractImplementor, java.lang.Object) (line: 432)<br> at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(java.lang.Object, java.lang.String, java.lang.Object, org.hibernate.event.spi.EventSource, boolean) (line: 105)<br> at org.hibernate.jpa.event.internal.core.JpaPersistEventListener.saveWithGeneratedId(java.lang.Object, java.lang.String, java.lang.Object, org.hibernate.event.spi.EventSource, boolean) (line: 67)<br> ```</p> <p style="margin-top:0;margin-bottom:10px;; margin: 10px 0 0">I guess the question on my mind is why does this operation need to proceed in a separate connection? That just seems ripe for this kind of deadlock.</p> </td>
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