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= Apache Cassandra Acceleration With Apache Ignite

== Overview

The Ignite Cassandra integration implements the link:persistence/external-storage#overview[CacheStore] interface allowing
to deploy Ignite as a high-performance caching layer on top of Cassandra.

Some observations in regards to the integration:

. The integration uses Cassandra http://www.datastax.com/dev/blog/java-driver-async-queries[asynchronous queries, window=_blank]
for `CacheStore` batch operations such as such as `loadAll()`, `writeAll()` and `deleteAll()` to provide extremely high performance.
. The integration automatically creates all necessary tables (and keyspaces) in Cassandra if they are absent. Also, it
automatically detects all the necessary fields for Ignite key-value tuples that will be stored as POJOs, and creates an
appropriate table structure. Thus you don't need to care about the Cassandra DDL syntax for table creation and Java to
Cassandra type mapping details.
. You can optionally specify the settings (replication factor, replication strategy, bloom filter and etc.) for Cassandra
tables and keyspaces which should be created.
. Combines functionality of BLOB and POJO storage, allowing to specify how you prefer to store (as a BLOB or as a POJO)
key-value tuples from your Ignite cache.
. Supports standard https://docs.oracle.com/javase/tutorial/jndi/objects/serial.html[Java, window=_blank] and
https://github.com/EsotericSoftware/kryo[Kryo, window=_blank] serialization for key-values which should be stored as BLOBs in Cassandra
. Supports Cassandra http://docs.datastax.com/en/cql/3.0/cql/cql_reference/create_index_r.html[secondary indexes, window=_blank] (including custom indexes)
through persistence configuration settings for particular Ignite cache or such settings could be detected automatically
if you configured link:SQL/indexes#configuring-indexes-using-annotations[SQL Indexes by Annotations] by using `@QuerySqlField(index = true)` annotation
. Supports sort order for Cassandra cluster key fields through persistence configuration settings or such settings could be
detected automatically if you are using `@QuerySqlField(descending = true)` annotation.
. Supports link:data-modeling/affinity-collocation[affinity co-location] for the POJO key classes having one of their fields
annotated by `@AffinityKeyMapped`. In such a way, key-values tuples which were stored on one node in an Ignite cache will
be also stored (co-located) on one node in Cassandra.

[CAUTION]
====
[discrete]
=== Ignite SQL Queries and Cassandra
Note that in order to execute SQL queries you need to have all the data loaded from Cassandra into an Ignite cluster.
The Ignite SQL engine doesn't assumes that all the records are available in memory and won't try to query Cassandra.

An alternative would be to use Ignite Native Persistence - a distributed, ACID, and SQL-compliant disk store that allows
performing SQL queries on the data stored in-memory as well as on disk.
====