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diff --git a/site/trunk/site-publish/rdb-das-transaction-control.html b/site/trunk/site-publish/rdb-das-transaction-control.html new file mode 100644 index 0000000000..26c0a65abd --- /dev/null +++ b/site/trunk/site-publish/rdb-das-transaction-control.html @@ -0,0 +1,268 @@ + +<!-- + + Licensed to the Apache Software Foundation (ASF) under one or more + contributor license agreements. See the NOTICE file distributed with + this work for additional information regarding copyright ownership. + The ASF licenses this file to You under the Apache License, Version 2.0 + (the "License"); you may not use this file except in compliance with + the License. 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Data integrity is <BR> +the most essential aspect of correct business functioning. Transactions control the concurrent access of data <BR> +by multiple programs. In the event of a system failure, transactions make sure that after recovery the data will<BR> + be in a consistent state. This document helps to understand transaction management in RDB DAS.</P> + +<P>One DAS instance is always associated with one database and one Connection. DAS participates in <BR> +<B>A> DAS managed and B> Externally managed transactions</B>.</P> + +<H3><A name="RDBDAS-TransactionControl-DASmanagedtransactions"></A><A name="RDBDAS-TransactionControl-DASmanagedtransactions"></A>DAS managed transactions</H3> + +<P>By default, the RDB DAS assumes responsibility for managing transaction boundaries by executing commit and <BR> +rollback operations against the database. A configuration attribute managedtx is assumed with default value <BR> +TRUE. This signals DAS to control the transaction. The boundaries of these transactions are as follows:</P> + +<P><B>Reading Data</B><BR> +Queries to the database are always made by calling DAS command's "executeQuery()" method. The associated <BR> +transaction lives for the duration of this method execution. That is, the transaction can be thought to start <BR> +when control is transferred to "executeQuery" and the transaction ends just prior to return from this method.</P> + +<P><B>Writing Data</B><BR> +Writes can be accomplished by two DAS APIs. First is calling the DAS "execute()" command against a command the <BR> +will perform write operations and, in this case, the transaction boundaries are the same as read queries. That <BR> +is the transaction life matches the life of the "execute" processing. If the method returns without exception <BR> +then the application can assume that any changes were successfully committed to the database. If an exception is <BR> +returned then the changes will have all been rolled back.</P> + +<P>The second API used by clients is the DAS applyChanges() method (see ChangeSummaryProcessing). Again, the <BR> +boundaries of the transaction match the boundaries of the call to the method. The DAS will create a set of <BR> +INSERT/UPDATE and DELETE statements to flush the graph changes to the database and all of these statements <BR> +will be executed as part of a single transaction. If the method returns without exception then the application <BR> +can assume that all changes were successfully committed to the database. If an exception is returned then the changes <BR> +will have all been rolled back.</P> + +<P><B>Use</B></P> + +<P>This mode is useful for simple data operations, where there is no need of having group of SQL statements or group of DAS <BR> +Commands in one transaction unit. At the maximum one applyChanges() call having multiple INSERT/UPDATE/DELETE executes <BR> +under one transaction. Cases where multiple applyChanges() method calls or multiple executeQuery() method calls are <BR> +required to be part of one transaction, this mode is not useful. In this mode, the database Connection can be internally <BR> +obtained using DAS Config ConnectionInfo settings or database Connection can also be passed from the client to DAS instance. <BR> +When DAS obtains database Connection internally, in Config ConnectionInfo, settings can either specify DataSource name or <BR> +Database Driver related information. Typical examples - </P> +<UL> + <LI>When using Tomcat based web app with DAS, Tomcat configured DataSource name is set in the DAS Config.</LI> + <LI>When using J2SE application client with DAS, Database Driver related information from DAS Config is used to form a database Connection.</LI> +</UL> + + +<P>When multiple SQL statements/DAS commands need to be part of one transaction and also when multiple DAS instances need to participate <BR> +in one transaction, the other mode "Externally managed transactions" is useful.</P> + +<H3><A name="RDBDAS-TransactionControl-Externallymanagedtransactions"></A><A name="RDBDAS-TransactionControl-Externallymanagedtransactions"></A>Externally managed transactions</H3> + +<P>The RDB DAS provides a straightforward mechanism for working with external transactions. In this mode, DAS is configured to not issue <BR> +commit/rollback. This behavior is needed to have the DAS participate in a larger transaction since some external party is responsible <BR> +for these actions. </P> + +<P><B>Use</B></P> + +<P>The scope of transaction support is a blend of <B>Supports</B> and <B>Mandatory</B> transaction attributes in J2EE scenario. i.e. DAS will use the <BR> +client's transaction if it is available. DAS does not throw exception if external client transaction is not available, but the end result <BR> +without external transaction is unpredictable. So, when using DAS in this mode, client needs to ensure availability of external transaction <BR> +encompassing required DAS/s commands. External transaction can be JDBC transaction or JTA transaction. </P> + +<P>When JDBC transaction, it is possible to group multiple Commands from single DAS instance in one transaction. Also nested transactions using <BR> +multiple DAS instances can be carried out. AS JTA does not support nested transactions, if <B>nested transactions</B> is the requirement, JDBC <BR> +Transactions should be used. For example:-</P> + +<DIV class="preformatted panel" style="border-width: 1px;"><DIV class="preformattedContent panelContent"> +<PRE>Das1 = DAS.FACTORY.createDAS(jdbcconn1); +Das2 = DAS.FACTORY.createDAS(jdbcconn2); + +try { + doSomeDAS1Stuff(); + doSomeDAS2Stuff(); + jdbcconn2.commit(); + doSomeDAS1Stuff(); + jdbcconn1.commit(); +} catch (AnyException ex) { + jdbcconn1.rollback(); + jdbcconn2.rollback(); +} +</PRE> +</DIV></DIV> + +<P>When JTA transaction, multiple units like JMS, DAS1(derbydatabase1), DAS2(derbydatabase2/mysqldatabase2) can be part of single transaction. <BR> +See example:-</P> + +<DIV class="preformatted panel" style="border-width: 1px;"><DIV class="preformattedContent panelContent"> +<PRE>tx.begin(); +try { + doSomeJMSStuff(); + doSomeDAS1Stuff(); + doSomeDAS2Stuff(); + tx.commit(); +} catch (AnyException ex) { + tx.rollback(); +} +</PRE> +</DIV></DIV> + +<P>In both the examples above, the DAS1 and DAS2 have been configured to not manage transactions since this is handled by the calling program.<BR> +The DAS is set to behave this way by a piece of configuration (typically via a configuration xml file). The following config file snippet <BR> +illustrates this setting:</P> + +<DIV class="preformatted panel" style="border-width: 1px;"><DIV class="preformattedContent panelContent"> +<PRE><Config xsi:noNamespaceSchemaLocation="http:///org.apache.tuscany.das.rdb/config.xsd" + xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"> + + <ConnectionInfo managedtx="false"/> + +</Config> +</PRE> +</DIV></DIV> + +<P><B>Note</B> When using DAS with "Externally managed transactions", it is required by the client to pass appropriate Connection object to DAS <BR> +instance. There is no meaning to forming Connection internally in DAS using Config info, as such Connections will not be part of external <BR> +Transaction Control.</P> + +<P><B>Methods Not Used in Externally managed transactions</B><BR> +DAS does not invoke any method that might interfere with the transaction boundaries set by the Transaction Manager. The list of prohibited <BR> +methods follows: </P> +<UL> + <LI>The commit, setAutoCommit, and rollback methods of java.sql.Connection</LI> + <LI>The getUserTransaction method of javax.ejb.EJBContext</LI> + <LI>Any method of javax.transaction.UserTransaction</LI> +</UL> + + +<P><B>Note</B> DAS never allows AutoCommit(TRUE) for the Connection it is using and throws Exception if this mode is detected.</P> +</TD></TR></TBODY></TABLE> + </DIV> + </DIV> + </DIV> + <!-- pageContent macro end --> + + </TD> + </TR> + </TABLE> + + <!-- footer macro --> + <SCRIPT src="http://www.google-analytics.com/urchin.js" type="text/javascript"> + </SCRIPT> + <SCRIPT type="text/javascript"> + _uacct = "UA-1174707-5"; + urchinTracker(); + </SCRIPT> + + <A href="http://www.statcounter.com/" target="_blank"><IMG src="http://c26.statcounter.com/counter.php?sc_project=2619156&java=0&security=94bd7e7d&invisible=0" alt="website stats" border="0"></A> + + <DIV class="footer"> + Copyright � 2003-2012, The Apache Software Foundation </BR> + Apache Tuscany and the Apache Tuscany project logo are trademarks of The Apache Software Foundation. + </DIV> + <!-- footer macro end --> + + </BODY> +</HTML> |