Author: christian.bauer(a)jboss.com Date: 2009-04-06 03:20:49 -0400 (Mon, 06 Apr 2009) New Revision: 10309 Added: trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetFlushEventListener.java trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetLockTimeoutException.java Removed: trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetMonitor.java Modified: trunk/examples/wiki/src/etc/META-INF/persistence-dev-war.xml trunk/examples/wiki/src/etc/META-INF/persistence-prod-war.xml trunk/examples/wiki/src/etc/META-INF/persistence-test-war.xml trunk/examples/wiki/src/etc/WEB-INF/pages.xml trunk/examples/wiki/src/etc/i18n/messages_en.properties trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/action/Pager.java trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetOperation.java trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetPostDeleteEventListener.java trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetPostInsertEventListener.java trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/package.html trunk/examples/wiki/view/includes/pager.xhtml Log: JBSEAM-4069, new approach to nested set locking Modified: trunk/examples/wiki/src/etc/META-INF/persistence-dev-war.xml =================================================================== --- trunk/examples/wiki/src/etc/META-INF/persistence-dev-war.xml 2009-04-06 04:49:46 UTC (rev 10308) +++ trunk/examples/wiki/src/etc/META-INF/persistence-dev-war.xml 2009-04-06 07:20:49 UTC (rev 10309) @@ -76,6 +76,8 @@ value="read-write, WikiFeedEntryCollection"/> <!-- Nested Set handling through special Hibernate event listeners --> + <property name="hibernate.ejb.event.flush" + value="org.jboss.seam.wiki.core.nestedset.listener.NestedSetFlushEventListener"/> <property name="hibernate.ejb.event.post-insert" value="org.jboss.seam.wiki.core.nestedset.listener.NestedSetPostInsertEventListener"/> <property name="hibernate.ejb.event.post-delete" Modified: trunk/examples/wiki/src/etc/META-INF/persistence-prod-war.xml =================================================================== --- trunk/examples/wiki/src/etc/META-INF/persistence-prod-war.xml 2009-04-06 04:49:46 UTC (rev 10308) +++ trunk/examples/wiki/src/etc/META-INF/persistence-prod-war.xml 2009-04-06 07:20:49 UTC (rev 10309) @@ -73,6 +73,8 @@ value="read-write, WikiFeedEntryCollection"/> <!-- Nested Set handling through special Hibernate event listeners --> + <property name="hibernate.ejb.event.flush" + value="org.jboss.seam.wiki.core.nestedset.listener.NestedSetFlushEventListener"/> <property name="hibernate.ejb.event.post-insert" value="org.jboss.seam.wiki.core.nestedset.listener.NestedSetPostInsertEventListener"/> <property name="hibernate.ejb.event.post-delete" Modified: trunk/examples/wiki/src/etc/META-INF/persistence-test-war.xml =================================================================== --- trunk/examples/wiki/src/etc/META-INF/persistence-test-war.xml 2009-04-06 04:49:46 UTC (rev 10308) +++ trunk/examples/wiki/src/etc/META-INF/persistence-test-war.xml 2009-04-06 07:20:49 UTC (rev 10309) @@ -48,6 +48,8 @@ <property name="hibernate.session_factory_name" value="SessionFactories/lacewikiSF"/> <!-- Nested Set handling through special Hibernate event listeners --> + <property name="hibernate.ejb.event.flush" + value="org.jboss.seam.wiki.core.nestedset.listener.NestedSetFlushEventListener"/> <property name="hibernate.ejb.event.post-insert" value="org.jboss.seam.wiki.core.nestedset.listener.NestedSetPostInsertEventListener"/> <property name="hibernate.ejb.event.post-delete" Modified: trunk/examples/wiki/src/etc/WEB-INF/pages.xml =================================================================== --- trunk/examples/wiki/src/etc/WEB-INF/pages.xml 2009-04-06 04:49:46 UTC (rev 10308) +++ trunk/examples/wiki/src/etc/WEB-INF/pages.xml 2009-04-06 07:20:49 UTC (rev 10309) @@ -335,6 +335,21 @@ </redirect> </exception> + <exception class="org.jboss.seam.wiki.core.nestedset.listener.NestedSetLockTimeoutException"> + <end-conversation/> + <redirect view-id="/wiki.xhtml"> + <message severity="WARN">#{messages['lacewiki.msg.LockTimeoutError']}</message> + </redirect> + </exception> + + <!-- This occurs on concurrent delete of comments --> + <exception class="javax.persistence.EntityNotFoundException"> + <end-conversation/> + <redirect view-id="/wiki.xhtml"> + <message severity="WARN">#{messages['lacewiki.msg.EntityNotFound']}</message> + </redirect> + </exception> + <exception class="org.jboss.seam.security.AuthorizationException"> <end-conversation/> <redirect view-id="/message.xhtml"> Modified: trunk/examples/wiki/src/etc/i18n/messages_en.properties =================================================================== --- trunk/examples/wiki/src/etc/i18n/messages_en.properties 2009-04-06 04:49:46 UTC (rev 10308) +++ trunk/examples/wiki/src/etc/i18n/messages_en.properties 2009-04-06 07:20:49 UTC (rev 10309) @@ -267,10 +267,6 @@ lacewiki.label.dirDisplay.ReadAccess=Read Access lacewiki.label.dirDisplay.WriteAccess=Write Access lacewiki.label.dirDisplay.DirectoryIsEmpty=This directory is empty. -lacewiki.label.dirDisplay.PagerShowing= -lacewiki.label.dirDisplay.PagerTo=to -lacewiki.label.dirDisplay.PagerOf=of -lacewiki.label.dirDisplay.PagerElements= lacewiki.label.dirDisplay.ShowItems=Show items lacewiki.label.dirDisplay.All=All lacewiki.button.dirDisplay.Refresh=Re<u>f</u>resh @@ -652,6 +648,9 @@ lacewiki.msg.Clipboard.DuplicatePasteName=The name '{0}' was already in use in this area, renamed item to '{1}'. lacewiki.msg.Clipboard.DuplicatePasteNameFailure=The name '{0}' was already in use in this area and is too long to be renamed, skipping paste. +# Pager +lacewiki.label.pagerTo=to +lacewiki.label.pagerOf=of # Entity update/delete/persist @@ -717,6 +716,8 @@ lacewiki.msg.TrashAreaNotFound=Could not find trash area with name {0} - your configuration is broken, please change it. lacewiki.msg.HelpAreaNotFound=Could not find help area with name {0} - your configuration is broken, please change it. lacewiki.msg.OptimisticLockError=Someone modified the same record while you were editing it. Your workspace has been closed. +lacewiki.msg.LockTimeoutError=Your action conflicted with the action of another user, please try again in a few seconds. +lacewiki.msg.EntityNotFound=The requested entity was not found. lacewiki.msg.AccessDenied=Access Denied lacewiki.msg.FatalError=Request failed, please check the application log or contact the administrator lacewiki.msg.RequestError=Request failed, most likely because a request parameter was missing Modified: trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/action/Pager.java =================================================================== --- trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/action/Pager.java 2009-04-06 04:49:46 UTC (rev 10308) +++ trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/action/Pager.java 2009-04-06 07:20:49 UTC (rev 10309) @@ -14,6 +14,7 @@ @AutoCreate public class Pager implements Serializable { + private String pagerEventName = "Pager"; private Long numOfRecords = 0l; private Integer page = 0; private Long pageSize = 15l; @@ -24,6 +25,15 @@ this.pageSize = pageSize; } + public Pager(String pagerEventName) { + this.pagerEventName = pagerEventName; + } + + public Pager(String pagerEventName, Long pageSize) { + this.pagerEventName = pagerEventName; + this.pageSize = pageSize; + } + public Long getNumOfRecords() { return numOfRecords; } @@ -103,22 +113,22 @@ public void setFirstPage() { setPage(getFirstPage()); - Events.instance().raiseEvent("Pager.pageChanged"); + Events.instance().raiseEvent(pagerEventName + "pageChanged"); } public void setPreviousPage() { setPage(getPreviousPage()); - Events.instance().raiseEvent("Pager.pageChanged"); + Events.instance().raiseEvent(pagerEventName + ".pageChanged"); } public void setNextPage() { setPage(getNextPage()); - Events.instance().raiseEvent("Pager.pageChanged"); + Events.instance().raiseEvent(pagerEventName + ".pageChanged"); } public void setLastPage() { setPage(new Long(getLastPage()).intValue()); - Events.instance().raiseEvent("Pager.pageChanged"); + Events.instance().raiseEvent(pagerEventName + ".pageChanged"); } public String toString() { Added: trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetFlushEventListener.java =================================================================== --- trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetFlushEventListener.java (rev 0) +++ trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetFlushEventListener.java 2009-04-06 07:20:49 UTC (rev 10309) @@ -0,0 +1,105 @@ +/* + * JBoss, Home of Professional Open Source + * + * Distributable under LGPL license. + * See terms of license at gnu.org. + */ +package org.jboss.seam.wiki.core.nestedset.listener; + +import org.apache.commons.logging.Log; +import org.apache.commons.logging.LogFactory; +import org.hibernate.HibernateException; +import org.hibernate.ejb.event.EJB3FlushEventListener; +import org.hibernate.event.EventSource; + +import java.util.concurrent.TimeUnit; +import java.util.concurrent.locks.Lock; +import java.util.concurrent.locks.ReentrantLock; + +/** + * <p> + * TODO: This is really the issue why a nice nested set implementation with Hibernate and MySQL is impossible! + * </p> + * <p> + * Any nested set tree modification potentially updates all rows in a database table. This + * requires several <tt>UPDATE</tt> statements, and also <tt>INSERT</tt> and <tt>DELETE</tt>. + * Any concurrent insertion or deletion to the rows betwen <tt>UPDATE</tt> statements would be fatal and + * corrupt the tree information. Transactions that modify nested set data should be serialized. + * </p> + * <p> + * For example, without any additional locking we'd run into the following deadlock situation with MySQL. Consider + * the following threads and the required modifications when two nested set node are deleted concurrently: + * </p> + * + * <pre> + * Thread I Nested Set Nodes Thread II + * --- 1. DELETE ---> A + * + * B <--- 2. DELETE --- + * + * --- 2. UPDATE ---> B + * (Waits for lock) + * A <--- 3. UPDATE --- + * (Waits for lock) + * + * </pre> + * + * <p> + * This results in a MySQL deadlock detection exception and a rollback of the transaction in Thread II. + * The usual solution is to lock the whole table(s) to force serialized execution of threads that modify + * nested set tree state. + * </p> + * <p> + * However, because MySQL has an unusable locking system (locking a table commits the current transaction, you + * need to lock all tables you are going to use from that point on, etc.), and because portability is + * a concern of this nested set implementation, we work around the problem with an in-memory exclusive lock. + * </p> + * <p> + * The situation is further complicated by Hibernate's flushing/eventing behavior. There is no way how we can + * only lock for nested set updates, we need to lock on every execution of a flush. WARNING: This severely + * degrades performance of your application, as any automatic or manual flush of the Hibernate persistence context + * will be serialized application-wide! Luckily, we can only lock when deletions or insertions are queued so + * flushing with no modifications in the persistence context (e.g. before a query) is not affected. + * </p> + * <p> + * <b>NOTE:</b> This does NOT work if several applications modify the nested set tree on the same database tables! + * </p> + * + * @author Christian Bauer + */ +public class NestedSetFlushEventListener extends EJB3FlushEventListener { + + private static final Log log = LogFactory.getLog(NestedSetFlushEventListener.class); + + private static final int LOCK_TIMEOUT_SECONDS = 15; + + private static final Lock lock = new ReentrantLock(true); + + @Override + protected void performExecutions(EventSource eventSource) throws HibernateException { + + if (eventSource.getActionQueue().areInsertionsOrDeletionsQueued()) { + try { + log.debug("######################### trying to obtain exclusive lock for " + LOCK_TIMEOUT_SECONDS + + " seconds before performing database modifications during flush"); + if (lock.tryLock(LOCK_TIMEOUT_SECONDS, TimeUnit.SECONDS)) { + log.debug("successfully obtained lock, executing flush"); + try { + super.performExecutions(eventSource); + } finally { + log.debug("releasing exclusive lock after flush execution"); + lock.unlock(); + } + } else { + throw new NestedSetLockTimeoutException("Could not aquire exclusive lock during database flush"); + } + } catch (InterruptedException ex) { + throw new NestedSetLockTimeoutException("Current thread could not aquire lock, has been interrupted"); + } + } else { + super.performExecutions(eventSource); + } + + } + +} \ No newline at end of file Added: trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetLockTimeoutException.java =================================================================== --- trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetLockTimeoutException.java (rev 0) +++ trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetLockTimeoutException.java 2009-04-06 07:20:49 UTC (rev 10309) @@ -0,0 +1,23 @@ +package org.jboss.seam.wiki.core.nestedset.listener; + +/** + * @author Christian Bauer + */ +public class NestedSetLockTimeoutException extends RuntimeException { + + public NestedSetLockTimeoutException() { + super(); + } + + public NestedSetLockTimeoutException(String s) { + super(s); + } + + public NestedSetLockTimeoutException(String s, Throwable throwable) { + super(s, throwable); + } + + public NestedSetLockTimeoutException(Throwable throwable) { + super(throwable); + } +} Deleted: trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetMonitor.java =================================================================== --- trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetMonitor.java 2009-04-06 04:49:46 UTC (rev 10308) +++ trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetMonitor.java 2009-04-06 07:20:49 UTC (rev 10309) @@ -1,49 +0,0 @@ -package org.jboss.seam.wiki.core.nestedset.listener; - -import org.hibernate.event.EventSource; - -import java.util.concurrent.locks.ReentrantLock; -import java.util.concurrent.locks.Lock; -import java.util.concurrent.TimeUnit; - -/** - * An alternative to table locking, we serialize nested set insert/updates in memory. - * - * <p> - * Any nested set tree modification potentially updates all rows in a database table. This - * requires several <tt>UPDATE</tt> statements, and also <tt>INSERT</tt> and <tt>DELETE</tt>. - * Any concurrent commit to the rows betwen <tt>UPDATE</tt> statements would be fatal and - * corrupt the tree information. The usual solution is to lock the whole table(s). Because - * MySQL has a compleltey unusable locking system (locking a table commits the current transaction, you - * need to lock all tables you are going to use from that point on, etc.), and because portability is - * a concern of this Nested Set implementation, we work around the problem with an in-memory exclusive lock. - * </p> - * <p> - * <b>NOTE:</b> This does NOT work if several applications modify the nested set - * tree in the same tables! - * </p> - * - * @author Christian Bauer - */ -public class NestedSetMonitor { - - private static final int LOCK_TIMEOUT_SECONDS = 10; - - private static final Lock lock = new ReentrantLock(true); - - public static void executeOperation(NestedSetOperation operation, EventSource session) { - try { - if (lock.tryLock(LOCK_TIMEOUT_SECONDS, TimeUnit.SECONDS)) { - try { - operation.execute(session); - } finally { - lock.unlock(); - } - } else { - throw new RuntimeException("Could not aquire lock to update nested set tree"); - } - } catch (InterruptedException ex) { - throw new RuntimeException("Current thread could not aquire lock, has been interrupted"); - } - } -} Modified: trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetOperation.java =================================================================== --- trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetOperation.java 2009-04-06 04:49:46 UTC (rev 10308) +++ trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetOperation.java 2009-04-06 07:20:49 UTC (rev 10309) @@ -43,8 +43,6 @@ * for the deprecated <tt>Session#connection()</tt> method. * </p> * - * TODO: We should lock the tables! Instead we are using the NestedSetMonitor as a workaround... - * * @author Christian Bauer */ public class NestedSetOperation { Modified: trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetPostDeleteEventListener.java =================================================================== --- trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetPostDeleteEventListener.java 2009-04-06 04:49:46 UTC (rev 10308) +++ trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetPostDeleteEventListener.java 2009-04-06 07:20:49 UTC (rev 10309) @@ -26,10 +26,7 @@ if ( NestedSetNode.class.isAssignableFrom(event.getEntity().getClass())) { log.debug("executing nested set delete operation, recalculating the tree"); - NestedSetMonitor.executeOperation( - new DeleteNestedSetOperation( (NestedSetNode)event.getEntity() ), - event.getSession() - ); + new DeleteNestedSetOperation( (NestedSetNode)event.getEntity() ).execute(event.getSession()); } } Modified: trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetPostInsertEventListener.java =================================================================== --- trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetPostInsertEventListener.java 2009-04-06 04:49:46 UTC (rev 10308) +++ trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/listener/NestedSetPostInsertEventListener.java 2009-04-06 07:20:49 UTC (rev 10309) @@ -26,10 +26,7 @@ if ( NestedSetNode.class.isAssignableFrom(event.getEntity().getClass())) { log.debug("executing nested set insert operation, recalculating the tree"); - NestedSetMonitor.executeOperation( - new InsertNestedSetOperation((NestedSetNode)event.getEntity()), - event.getSession() - ); + new InsertNestedSetOperation((NestedSetNode)event.getEntity()).execute(event.getSession()); } } Modified: trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/package.html =================================================================== --- trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/package.html 2009-04-06 04:49:46 UTC (rev 10308) +++ trunk/examples/wiki/src/main/org/jboss/seam/wiki/core/nestedset/package.html 2009-04-06 07:20:49 UTC (rev 10309) @@ -59,7 +59,7 @@ <p> <b>Manual Recursion</b>: Select all the children of node <tt>C</tt>, and if these nodes have children, recursively query until the whole subtree is loaded. This can be implemented with a stored procedure in SQL or by - recursively exeucting <tt>SELECT</tt> statements in the application language. This strategy does not scale. + recursively executing <tt>SELECT</tt> statements in the application language. This strategy does not scale. </p> </li> <li> @@ -201,7 +201,7 @@ </pre> <p> - This implementation is based on mix-in and delegates. The <tt>ITEM</tt> table of the <tt>Item</tt> class will + This implementation is based on mix-in and delegates. The <tt>ITEM</tt> table of the <tt>Item</tt> class does not carry the left, right, and thread values. This job is delegated to an additional <tt>ItemNestedSetDelegate</tt> class: </p> @@ -280,11 +280,12 @@ &lt;persistence-unit ...> ... &lt;properties> + &lt;property name="hibernate.ejb.event.flush" + value="nestedset.NestedSetFlushEventListener"/> &lt;property name="hibernate.ejb.event.post-insert" value="nestedset.NestedSetPostInsertEventListener"/> &lt;property name="hibernate.ejb.event.post-delete" value="nestedset.NestedSetPostDeleteEventListener"/> - &lt;/properties> &lt;/persistence-unit> </pre> @@ -296,6 +297,12 @@ </p> <p> + Note that concurrent nested set tree modifications need to be serialized. This implementation locks flush events + in-memory with a <tt>ReentrantLock</tt> and a timeout of 15 seconds. See <tt>NestedSetFlushEventListener.java</tt> + for more information. +</p> + +<p> To query for a subtree, use the <tt>NestedSetWrapper</tt> and <tt>NestedSetResultTransformer</tt> convenience classes. An example, loading the whole subtree starting at <tt>startNode</tt> (which would be an instance of <tt>Item</tt> you have already loaded): Modified: trunk/examples/wiki/view/includes/pager.xhtml =================================================================== --- trunk/examples/wiki/view/includes/pager.xhtml 2009-04-06 04:49:46 UTC (rev 10308) +++ trunk/examples/wiki/view/includes/pager.xhtml 2009-04-06 07:20:49 UTC (rev 10309) @@ -48,10 +48,10 @@ </s:fragment> <s:fragment> - <h:outputText value="#{messages['lacewiki.label.dirDisplay.PagerShowing']} - #{pager.firstRecord} #{messages['lacewiki.label.dirDisplay.PagerTo']} - #{pager.lastRecord} #{messages['lacewiki.label.dirDisplay.PagerOf']} - #{pager.numOfRecords} #{messages['lacewiki.label.dirDisplay.PagerElements']}"/> + <h:outputText value="#{pager.firstRecord} #{messages['lacewiki.label.pagerTo']} + #{pager.lastRecord} #{messages['lacewiki.label.pagerOf']} + #{pager.numOfRecords} + #{pager.numOfRecords > 1 ? pagerPluralLabel : pagerSingularLabel}"/> </s:fragment> <s:fragment>