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133 lines
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<meta name="DC.Title" content="Vote reliable effect on flow of commit processing" />
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<meta name="abstract" content="Vote reliable is an optimization that improves performance by returning earlier to the initiator application after a commit operation and eliminating one message during a commit operation." />
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<title>Vote reliable effect on flow of commit processing</title>
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<body id="rzakjvotereliable"><a name="rzakjvotereliable"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Vote reliable effect on flow of commit processing</h1>
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<div><p>Vote reliable is an optimization that improves performance by returning
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earlier to the initiator application after a commit operation and eliminating
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one message during a commit operation. </p>
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<p>There is no explicit vote reliable optimization for DRDA<sup>®</sup> distributed
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unit of work over TCP/IP. However, i5/OS™ never requests a reset (forget) confirmation
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for TCP/IP connections. Therefore, a reset (forget) is always implied for
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TCP/IP connections.</p>
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<p>After you start commitment control, you can use the Change Commitment Options
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(QTNCHGCO) API to change the <samp class="codeph">Accept vote reliable</samp> option
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to Y.</p>
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<p>Vote reliable can be thought of as a promise by an agent to its initiator
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that no heuristic decisions will be made at the agent if communications failure
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occurs while the agent is in doubt. An agent that is using the vote reliable
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optimization sends an indicator to the initiator during the prepare wave of
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the commit. If the initiator is also using the vote reliable optimization,
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it then sends an indicator to the agent that no reset is required in response
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to the commit message. This eliminates the reset message, and allows the transaction
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manager to return to the application at the initiator as soon as the commit
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message is sent.</p>
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<p>Consider using the vote reliable optimization if the following conditions
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are true:</p>
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<ul><li>It is unlikely that a heuristic decision will be made at an in doubt agent
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in the event of a systems or communications failure unless the failure cannot
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be repaired.</li>
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<li>Your program logic does not need the results of previous transactions
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to ensure that your database files remain synchronized.</li>
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</ul>
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<p>The vote reliable optimization is used by i5/OS only if <em>all</em> the
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following conditions are true:</p>
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<ul><li>The initiator and agent locations support the presumed abort level of
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commitment control.</li>
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<li>The initiator location accepts the vote reliable
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indication from the agent. On i5/OS initiators, this depends on the value
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of two commitment options: <ul><li>The value of the Wait for outcome commitment option must be No (Yes is
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the default).</li>
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<li>The value of the Accept vote reliable commitment option must be Yes (Yes
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is the default).</li>
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</ul>
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</li>
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<li>The agent location votes reliable during the prepare
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wave. i5/OS agents
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always vote reliable. This is because heuristic decisions can be made only
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through a manual procedure that warns of the possible negative side-effects
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of making a heuristic decision.</li>
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</ul>
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<div class="section" xml:lang="en-us" id="rzakjvotereliable__flowcommitprocvotereliableopt"><a name="rzakjvotereliable__flowcommitprocvotereliableopt"><!-- --></a><h4 class="sectiontitle">Flow of
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commit processing with vote reliable optimization</h4><p>The following
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figure shows the flow of messages among the application programs and the transaction
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managers when the vote reliable optimization is used. Both the initiator application
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program and the agent application programs are unaware of the two-phase commit
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processing. The numbers in parentheses () in the figure correspond to the
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numbered items in the description that follows.</p>
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<br /><img src="rzakj516.gif" alt="Flow of commit processing with vote reliable optimization" /><br /><p>The following
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list describes the events for normal processing without last agent optimization
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when the agent votes reliable. This describes a basic flow. The sequence of
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events can become much more complex when the transaction program network has
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multiple levels or when errors occur.</p>
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<ol><li>Application program A does a receive request to indicate that it is ready
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to receive a request from program I.</li>
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<li>The initiator application (I) issues a commit instruction.</li>
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<li>The transaction manager for the initiator (TM-I) takes the role of initiator
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for this transaction. It starts the prepare wave by sending a prepare message
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to all the other locations that are participating in the transaction.</li>
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<li>The transaction managers for every other location take the role of agent
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(TM-A). The application program A is notified by TM-A that a request to commit
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has been received. For ICF files, the notification is in the form of the Receive
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Take Commit (RCVTKCMT) ICF indicator being set on.</li>
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<li>The application program A responds by issuing a commit instruction (or
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a rollback instruction). This is the application program's vote.</li>
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<li>The agent (TM-A) responds to the initiator (TM-I)
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with a request commit message. i5/OS systems send a vote reliable indicator
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with the request commit.</li>
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<li id="rzakjvotereliable__step7"><a name="rzakjvotereliable__step7"><!-- --></a>When the initiator (TM-I) receives all the votes, the TM-I
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sends a commit message. If the Wait for outcome commitment option is N (No)
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and the Accept vote reliable commitment option is Y (Yes), a no reset indicator
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is sent with the commit message. This tells the agent that no reset message
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is required in response to the commit.</li>
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<li>The transaction is complete. A return is sent to the application
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programs (I and A). This return indicates that the commit operation was successful.
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If a heuristic damage occurs at system A due to a heuristic decision being
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made before the committed message is received, application I is not informed.
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Instead, a message is sent to the QSYSOPR message queue. However, application
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A receives the heuristic damage indication.</li>
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<li>The next time the agent (TM-A) sends any message to the initiator (TM-I),
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either a data flow or a commitment instruction, an implied reset indicator
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is sent with the message to inform TM-I that TM-A completed the commit successfully.
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The reason for this is that TM-I must retain information about the completed
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transaction until it has confirmed that TM-A successfully received the commit
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message in step <a href="#rzakjvotereliable__step7">7</a></li>
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</ol>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzakjcommitdefs_tp.htm" title="After you start commitment control, you can use the Change Commitment Options (QTNCHGCO) API to change the commitment options for your transaction.">Commitment definitions for two-phase commitment control</a></div>
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</div>
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<div class="relref"><strong>Related reference</strong><br />
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<div><a href="../apis/QTNCHGCO.htm">Change Commitment Options (QTNCHGCO) API</a></div>
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</div>
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</div>
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