Add scaladoc for EventualCassandraConfig

eventual-cassandra/src/main/scala/com/evolutiongaming/kafka/journal/eventual/cassandra/EventualCassandraConfig.scala

@@ -5,7 +5,31 @@ import com.evolutiongaming.scassandra.{CassandraConfig, QueryConfig}
 import pureconfig.generic.semiauto.deriveReader
 import pureconfig.ConfigReader
 
-
+/** Cassandra-specific configuration used by a plugin.
+  *
+  * Specifies long time storage configuration and Cassandra client parameters.
+  *
+  * @param retries
+  *   Number of retries in
+  *   [[com.evolutiongaming.scassandra.NextHostRetryPolicy]]. It will retry
+  *   doing a request on the same host if it timed out, or switch to another
+  *   host if error happened, or the host was not available on a first attempt.
+  * @param segmentSize
+  *   Number of records per one segment. The larger the number, the better the
+  *   chance the recovery will hit the same partition, and be faster, but too
+  *   large numbers are also will make larger Cassandra partitions with all the
+  *   associated issues. See [[SegmentSize]] for more details.
+  * @param client
+  *   Cassandra client configuration, see [[CassandraConfig]] for more details.
+  * @param schema
+  *   Schema of Cassandra database, i.e. keyspace, names of the tables etc. It
+  *   also contains a flag if schema should be automatically created if not
+  *   present, which is useful for integration testing purposes etc.
+  * @param consistencyConfig
+  *   Consistency levels to use for read and for write statements to Cassandra.
+  *   The main reason one may be interested to change it, is for integration
+  *   tests with small number of Cassandra nodes.
+  */
 final case class EventualCassandraConfig(
   retries: Int = 100,
   segmentSize: SegmentSize = SegmentSize.default,
@@ -53,4 +77,4 @@ object EventualCassandraConfig {
       implicit val configReaderWrite: ConfigReader[Write] = ConfigReader[ConsistencyLevel].map { a => Write(a) }
     }
   }
-}
+}