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| <title>ACID Transactions - Apache Ignite</title> |
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| distributed ACID transactions. The consistency guarantees are met for both memory and disk tiers."/> |
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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 can operate in a strongly consistent mode with full support for |
| distributed ACID transactions. The consistency guarantees are met for both memory and disk tiers. |
| </p> |
| <p> |
| Distributed transactions in Apache Ignite can span multiple cluster nodes, caches/tables, and |
| partitions. Both pessimistic and optimistic locking is available for applications. |
| </p> |
| </div> |
| <div class="col-sm-6 col-md-4 col-xs-12" style="padding-right:0"> |
| <img class="img-responsive" src="/images/in_memory_data.png" width="500" style="float:right;"/> |
| </div> |
| </div> |
| |
| <div class="page-heading">Two-Phase-Commit Protocol</div> |
| <p> |
| In distributed systems, a transaction usually spans across multiple cluster nodes. This requires |
| transactional engines to handle possible distributed failures properly to avoid data inconsistencies |
| cluster-wide. One of the widely-used approaches to ensure data consistency in such a scenario |
| is the two-phase commit protocol (2PC). |
| </p> |
| <p> |
| Ignite transactional engine implements the 2PC protocol. Whenever the records get 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 primary or backup copies of the data participate in the transaction. Moreover, if a transaction is |
| mapped to a single node, then Ignite optimizes the transaction execution by switching to the |
| one-phase-commit (1PC) protocol. |
| </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, |
| which 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 goes 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 for an external database, such as |
| RDBMS, Ignite transactions span both the cached data in Ignite as well as the data persisted in a database |
| supporting transactional APIs. For instance, if a relational database is configured as the disk tier, |
| Ignite writes the transactional changes to the database before sending a commit message to participating |
| cluster nodes. This way, if a transaction fails at the database level, Ignite can still send the rollback |
| message to the cluster nodes, keeping the data consistent across memory and disk tiers. |
| </p> |
| |
| <div class="page-heading">Learn More</div> |
| <p> |
| <a href="https://apacheignite.readme.io/docs/transactions" target="docs"> |
| <b>Ignite Transactions <i class="fa fa-angle-double-right"></i></b> |
| </a> |
| </p> |
| <p> |
| <a href="https://apacheignite.readme.io/docs/transactions#section-two-phase-commit-2pc" target="docs"> |
| <b>Two-phase commit protocol <i class="fa fa-angle-double-right"></i></b> |
| </a> |
| </p> |
| <p> |
| <a href="https://apacheignite.readme.io/docs/transactions#section-deadlock-detection" target="docs"> |
| <b>Deadlock-free transactions and detection <i class="fa fa-angle-double-right"></i></b> |
| </a> |
| </p> |
| <p> |
| <a href="https://apacheignite.readme.io/docs/transactions#section-integration-with-jta" target="docs"> |
| <b>JTA Support <i class="fa fa-angle-double-right"></i></b> |
| </a> |
| </p> |
| </section> |
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