diff options
Diffstat (limited to 'site/trunk/site-publish/optimisticconcurrencycontrol.html')
| -rw-r--r-- | site/trunk/site-publish/optimisticconcurrencycontrol.html | 129 |
1 files changed, 129 insertions, 0 deletions
diff --git a/site/trunk/site-publish/optimisticconcurrencycontrol.html b/site/trunk/site-publish/optimisticconcurrencycontrol.html new file mode 100644 index 0000000000..98e0da9979 --- /dev/null +++ b/site/trunk/site-publish/optimisticconcurrencycontrol.html @@ -0,0 +1,129 @@ + +<!-- + + 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. You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE- 2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. +--> + + +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<HTML> + <HEAD> + <!-- generateKeywords macro --> + <META name="description" content="Apache Tuscany"> + <META name="keywords" content="apache, apache tuscany, tuscany, service, services, fabric, soa, service oriented architecture, sca, service component architecture, das, sdo, csa, ruby, opensource"> + <!-- generateKeywords macro end --> + + <LINK type="text/css" rel="stylesheet" href="http://tuscany.apache.org/stylesheets/default.css"> + <LINK rel="SHORTCUT ICON" href="https://cwiki.apache.org/confluence/display/TUSCANY/$images/favicon.ico"> + <TITLE>Apache Tuscany : OptimisticConcurrencyControl</TITLE> + <META http-equiv="Content-Type" content="text/html;charset=UTF-8"></HEAD> + + <BODY onload="init()"> + <!-- topNav macro --> + <TABLE valign="top" border="0" cellspacing="0" cellpadding="0" width="100%" background="http://tuscany.apache.org/images/TuscanyLogoNEW_Text_120px_bg.jpg"> + <TR> + <TD valing="top" align="left"> + <A href="https://cwiki.apache.org/confluence/pages/viewpage.action?spaceKey=TUSCANY&title=$siteroot"><IMG src="http://tuscany.apache.org/images/TuscanyLogoNEW_Text_120px_bg.jpg" height="91" width="25" border="0"></A> + </TD> + <TD> + <A href="http://tuscany.apache.org/"><IMG src="http://tuscany.apache.org/images/TuscanyLogo.jpg" border="0"></A> + </TD> + + <TD width="100%"> + + </TD> + + <!-- Adds the edit page link to the top banner--> + <TD valign="bottom"> + <DIV style="padding: 2px 10px; margin: 0px;"> + <A href="https://cwiki.apache.org/confluence/pages/editpage.action?pageId=52822"> + <IMG src="http://tuscany.apache.org/images/notep_16.gif" height="16" width="16" border="0" align="absmiddle" title="Edit Page"></A> + </DIV> + </TD> + + </TR> + </TABLE> + <!-- topNav macro end --> + + <!-- breadCrumbs macro --> + <TABLE border="0" cellpadding="2" cellspacing="0" width="100%"> + <TR class="topBar"> + <TD align="left" valign="middle" class="topBarDiv" nowrap="true" width="100%"> + <A href="home.html" title="Apache Tuscany">Apache Tuscany</A> > <A href="home.html" title="Home">Home</A> > <A href="das-overview.html" title="DAS Overview">DAS Overview</A> > <A href="das-java.html" title="DAS Java">DAS Java</A> > <A href="das-java-documentation-menu.html" title="DAS Java Documentation Menu">DAS Java Documentation Menu</A> > <A href="das-java-developer-guide.html" title="DAS Java Developer Guide">DAS Java Developer Guide</A> > <A href="rdb-das-java.html" title="RDB DAS Java">RDB DAS Java</A> > <A href="rdb-das-user-guide.html" title="RDB DAS - User Guide">RDB DAS - User Guide</A> > <A href="" title="OptimisticConcurrencyControl">OptimisticConcurrencyControl</A> + </TD> + + <TD align="right" valign="middle" class="topBarDiv" align="left" nowrap="true"> + <A href="http://mail-archives.apache.org/mod_mbox/tuscany-user">User List</A> | <A href="http://mail-archives.apache.org/mod_mbox/tuscany-dev">Dev List</A> | <A href="http://issues.apache.org/jira/browse/Tuscany">Issue Tracker</A> + </TD> + </TR> + </TABLE> + <!-- breadCrumbs macro end --> + + + <TABLE border="0" cellpadding="0" width="100%" bgcolor="#FFFFFF"> + <TR> + <TD align="left" valign="top"> + + <!-- pageContent macro --> + <DIV id="PageContent"> + + <DIV class="pagecontent"> + <DIV class="wiki-content"> + <H1><A name="OptimisticConcurrencyControl-OptimisticConcurrencyControl"></A>OptimisticConcurrencyControl</H1> + + +<P>The RDB DAS is intended for use in disconnected scenarios. When the DAS returns a graph of SDO DataObjects as the result of a query, there are no locks held on the underlying database and the data is no longer associated with any database connection or transaction. However, although locks are not held, the DAS does employ a mechanism called <A href="http://en.wikipedia.org/wiki/Optimistic_locking" class="external-link" rel="nofollow">Optimistic Concurrency Control</A> (OCC) to manage concurrency.</P> + +<P>Basically, when OCC is being utilized, the DAS checks whether the state of the database has changed since the original data was read before applying any writes to the same location. For example, suppose that a DAS client reads a set of Customers, modifies one Customer and then attempts to write the change back to the database:</P> +<DIV class="panel" style="border-width: 1px;"><DIV class="panelContent"> +<P> Command select = das.createCommand("Select * from CUSTOMER where LASTNAME = 'Williams'");<BR> + DataObject root = select.executeQuery();</P> + +<P> DataObject customer = (DataObject) root.get("CUSTOMER[1]");<BR> + customer.set("LASTNAME", "Pavick");</P> + +<P> //Some period of time passes in which "CUSTOMER[1]" could be modified by another process or application</P> + +<P> das.applyChanges(root);</P> +</DIV></DIV> +<P>If OCC is enabled then as part of "applyChanges" processing the DAS will ensure that the table row representing "CUSTOMER[1]" has not been changed since it was read. This is possible because a feature of the original SDO graph is to "remember" its original state along with any changes that have been made. The DAS has access to this original state and uses it to create an "overqualified" update statement. When the DAS executes this update statement against the database, it will fail if the underlying data has been modified (a collision has occurred) and, if so, an exception will be thrown and the transaction rolled back. If there is no collision then the update statement execution succeeds and the change is applied. </P> + </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> |