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    <title>ACID Transactions</title>
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            <h1 class="first">ACID Transactions</h1>
            <div class="col-sm-12 col-md-12 col-xs-12" style="padding:0 0 20px 0;">
                <div class="col-sm-6 col-md-8 col-xs-12" style="padding-left:0; padding-right:0">
                    <p>
                        Apache Ignite is a strongly consistent platform that fully supports distributed ACID transactions.
                        The consistency guarantees are met for both memory and disk tiers.
                    </p>
                    <p>
                        Transactions in Apache Ignite can span multiple cluster nodes, caches (aka. tables) and partitions.
                        Both pessimistic and optimistic locking are available for applications. The optimistic mode
                        also supports deadlock-free transactions that help avoid distributed deadlocks in user code.
                    </p>
                </div>
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            </div>

            <div class="page-heading">Two-Phase-Commit Protocol</div>
            <p>
                In a distributed system, a transaction may span multiple cluster nodes. Obviously, this poses some
                challenges when we want to ensure that the data is consistent across all the participating nodes.
                For example, in the event of a cluster node failure, the transaction may not have fully committed on
                the lost node. A widely-used approach to ensuring data consistency in this type of scenario is the
                two-phase commit protocol (2PC).
            </p>
            <p>
                Ignite comes with one the fastest implementations of 2PC protocol. Moreover,
                often when transactions span only one node or one partition, Ignite will utilize a much faster
                one-phase-commit (1PC) protocol. Whenever the data is updated within a transaction,
                Ignite will keep the transactional state in a local transaction map until the changes are committed,
                at which point the data is transferred to the participating remote nodes. Only the nodes that hold the
                primary or backup copies of the data will participate in the transaction.
            </p>
            <div class="page-heading">Consistency and Ignite Persistence</div>
            <p>
                If Ignite native persistence is used then all the updates are written to the write-ahead log (WAL) file
                that guarantees data consistency, even if the cluster or individual nodes go down in the middle
                of a transaction.
            </p>
            <p>
                The purpose of the WAL is to propagate updates to the disk in the append-only mode, which is the fastest
                way to persist data to disk. WAL provides a recovery mechanism for failure scenarios when a single node
                or the whole cluster go down. A cluster can always be recovered to the
                latest successfully committed transaction.
            </p>
            <div class="page-heading">Consistency and 3rd Party Persistence</div>
            <p>
                In scenarios when Ignite is used as a caching layer on top of 3rd party databases, such as
                RDBMS, Ignite transactions will span both, the cached data and the external database.
                For instance, when an RDBMS is used as a persistence layer, Ignite will write the
                transactional changes to the database before it sends the commit message to participating cluster nodes.
                This way, if a transaction fails at the database level, Ignite can still send the rollback message
                to every node involved, keeping the data consistent between the in-memory cache and the external database.
            </p>

            <div class="code-examples">
                <div class="page-heading">Code Examples</div>
                <!-- Nav tabs -->
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                    <li class="active"><a href="#java-ex" aria-controls="home" data-toggle="tab">Java</a></li>
                    <li><a href="#dotnet-ex" aria-controls="profile" data-toggle="tab">.NET</a></li>
                    <li><a href="#cpp-ex" aria-controls="profile" data-toggle="tab">C++</a></li>
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                <div class="tab-content">
                    <div class="tab-pane active" id="java-ex">
                        <pre class="brush:java">
                            try (Transaction tx = transactions.txStart()) {
                                Integer hello = cache.get("Hello");

                                if (hello == 1)
                                    cache.put("Hello", 11);

                                    cache.put("World", 22);

                                tx.commit();
                            }
                        </pre>
                    </div>
                    <div class="tab-pane" id="dotnet-ex">
                        <pre class="brush:csharp">
                            using (ITransaction tx = transactions.TxStart())
                            {
                                var hello = cache.Get(1);

                                if (hello != "Hello")
                                    cache.Put(1, "Hello");

                                    cache.Put(2, "World");

                                tx.Commit();
                            }
                        </pre>
                    </div>
                    <div class="tab-pane" id="cpp-ex">
                        <pre class="brush:cpp">
                        Transaction tx = transactions.TxStart();

                        int hello = cache.Get("Hello");

                        if (hello == 1)
                            cache.Put("Hello", 11);

                        cache.Put("World", 22);

                        tx.Commit();
                        </pre>
                    </div>
                </div>
            </div>

            <div class="page-heading">More on Ignite Transactions</div>
            <table class="formatted" name="More on Ignite Transactions">
                <thead>
                <tr>
                    <th width="35%" class="left">Feature</th>
                    <th>Description</th>
                </tr>
                </thead>
                <tbody>
                <tr>
                    <td class="features-left">ACID Transactions</td>
                    <td>
                        <p>
                            Ignite provides fully ACID compliant distributed transactions that ensure guaranteed consistency.
                        </p>
                        <div  class="page-links">
                            <a href="https://apacheignite.readme.io/docs/transactions" target="docs">Docs for this feature <i class="fa fa-angle-double-right"></i></a>
                        </div>
                    </td>
                </tr>
                <tr>
                    <td class="features-left">2-Phase-Commit</td>
                    <td>
                        <p>
                            Ignite utilizes a Two-Phase-Commit (2PC) protocol for its transactions and optimizes
                            to one-phase-commit whenever possible:
                        </p>
                        <div  class="page-links">
                            <a href="https://apacheignite.readme.io/docs/transactions#two-phase-commit-2pc" target="docs">Docs for this feature <i class="fa fa-angle-double-right"></i></a>
                        </div>
                    </td>
                </tr>
                <tr>
                    <td class="features-left">Write-Ahead Log</td>
                    <td>
                        <p>
                            Ignite persistence maintains the WAL that propagates updates to disk in the fastest way possible and
                            provides a recovery mechanism for scenarios where a single node or the whole cluster goes down:
                        </p>
                        <div  class="page-links">
                            <a href="https://apacheignite.readme.io/docs/write-ahead-log" target="docs">Docs for this feature <i class="fa fa-angle-double-right"></i></a>
                        </div>
                    </td>
                </tr>
                <tr>
                    <td class="features-left">Deadlock-Free Transactions</td>
                    <td>
                        <p>
                            Ignite supports deadlock-free, optimistic transactions, which do not acquire any locks.
                        </p>
                        <div  class="page-links">
                            <a href="https://apacheignite.readme.io/docs/transactions#deadlock-free-transactions" target="docs">Docs for this feature <i class="fa fa-angle-double-right"></i></a>
                        </div>
                    </td>
                </tr>
                <tr>
                    <td class="features-left">Deadlocks Detection</td>
                    <td>
                        <p>
                            Debugging and troubleshooting distributed deadlocks in Ignite:
                        </p>
                        <div  class="page-links">
                            <a href="https://apacheignite.readme.io/docs/transactions#deadlock-detection" target="docs">Docs for this feature <i class="fa fa-angle-double-right"></i></a>
                        </div>
                    </td>
                </tr>
                <tr>
                    <td class="left" width="35%">Transactional Entry Processor</td>
                    <td>
                        <p>
                            Ignite transactional entry processor allows executing collocated user logic on the server
                            side within a transaction:
                        </p>
                        <div  class="page-links">
                            <a href="https://apacheignite.readme.io/docs/affinity-collocation#ignitecompute-vs-entryprocessor" target="docs">Docs for this feature <i class="fa fa-angle-double-right"></i></a>
                        </div>
                    </td>
                </tr>
                <tr>
                    <td class="left" width="35%">Cross-Partition Transactions</td>
                    <td>
                        <p>
                            In Ignite, transactions can be performed on all partitions of a cache across the whole
                            cluster:
                        </p>
                        <div  class="page-links">
                            <a href="https://apacheignite.readme.io/docs/transactions#ignitetransactions" target="docs">Docs for this feature <i class="fa fa-angle-double-right"></i></a>
                        </div>
                    </td>
                </tr>
                <tr>
                    <td class="left" width="35%">Locks</td>
                    <td>
                        <p>
                            Ignite allows developers to define explicit locks enforcing mutual exclusion on cached objects:
                        </p>
                        <div  class="page-links">
                            <a href="https://apacheignite.readme.io/docs/distributed-locks" target="docs">Docs for this feature <i class="fa fa-angle-double-right"></i></a>
                        </div>
                    </td>
                </tr>
                <tr>
                    <td class="left">XA/JTA</td>
                    <td>
                        <p>
                            Ignite can be configured with a Java Transaction API (JTA) transaction manager lookup class.
                        </p>
                        <div  class="page-links">
                            <a href="https://apacheignite.readme.io/docs/transactions#integration-with-jta" target="docs">Docs for this feature <i class="fa fa-angle-double-right"></i></a>
                        </div>
                    </td>
                </tr>
                </tbody>
            </table>
        </section>
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