Chapter 22. Cassandra CQL Both producer and consumer are supported Apache Cassandra is an open source NoSQL database designed to handle large amounts on commodity hardware. Like Amazon's DynamoDB, Cassandra has a peer-to-peer and master-less architecture to avoid single point of failure and garanty high availability. Like Google's BigTable, Cassandra data is structured using column families which can be accessed through the Thrift RPC API or a SQL-like API called CQL. Note This component aims at integrating Cassandra 2.0+ using the CQL3 API (not the Thrift API). It's based on Cassandra Java Driver provided by DataStax. 22.1. Dependencies When using cql with Red Hat build of Camel Spring Boot make sure to use the following Maven dependency to have support for auto configuration: <dependency> <groupId>org.apache.camel.springboot</groupId> <artifactId>camel-cassandraql-starter</artifactId> </dependency> 22.2. Configuring Options Camel components are configured on two separate levels: component level endpoint level 22.2.1. Configuring Component Options At the component level, you set general and shared configurations that are, then, inherited by the endpoints. It is the highest configuration level. For example, a component may have security settings, credentials for authentication, urls for network connection and so forth. Some components only have a few options, and others may have many. Because components typically have pre-configured defaults that are commonly used, then you may often only need to configure a few options on a component; or none at all. You can configure components using: the Component DSL . in a configuration file (application.properties, *.yaml files, etc). directly in the Java code. 22.2.2. Configuring Endpoint Options You usually spend more time setting up endpoints because they have many options. These options help you customize what you want the endpoint to do. The options are also categorized into whether the endpoint is used as a consumer (from), as a producer (to), or both. Configuring endpoints is most often done directly in the endpoint URI as path and query parameters. You can also use the Endpoint DSL and DataFormat DSL as a type safe way of configuring endpoints and data formats in Java. A good practice when configuring options is to use Property Placeholders . Property placeholders provide a few benefits: They help prevent using hardcoded urls, port numbers, sensitive information, and other settings. They allow externalizing the configuration from the code. They help the code to become more flexible and reusable. The following two sections list all the options, firstly for the component followed by the endpoint. 22.3. Component Options The Cassandra CQL component supports 3 options, which are listed below. Name Description Default Type bridgeErrorHandler (consumer) Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions occurred while the consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions, that will be logged at WARN or ERROR level and ignored. false boolean lazyStartProducer (producer) Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel's routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing. false boolean autowiredEnabled (advanced) Whether autowiring is enabled. This is used for automatic autowiring options (the option must be marked as autowired) by looking up in the registry to find if there is a single instance of matching type, which then gets configured on the component. This can be used for automatic configuring JDBC data sources, JMS connection factories, AWS Clients, etc. true boolean 22.4. Endpoint Options The Cassandra CQL endpoint is configured using URI syntax: with the following path and query parameters: 22.4.1. Path Parameters (4 parameters) Name Description Default Type beanRef (common) beanRef is defined using bean:id. String hosts (common) Hostname(s) Cassandra server(s). Multiple hosts can be separated by comma. String port (common) Port number of Cassandra server(s). Integer keyspace (common) Keyspace to use. String 22.4.2. Query Parameters (30 parameters) Name Description Default Type clusterName (common) Cluster name. String consistencyLevel (common) Consistency level to use. Enum values: ANY ONE TWO THREE QUORUM ALL LOCAL_ONE LOCAL_QUORUM EACH_QUORUM SERIAL LOCAL_SERIAL DefaultConsistencyLevel cql (common) CQL query to perform. Can be overridden with the message header with key CamelCqlQuery. String datacenter (common) Datacenter to use. datacenter1 String loadBalancingPolicyClass (common) To use a specific LoadBalancingPolicyClass. String password (common) Password for session authentication. String prepareStatements (common) Whether to use PreparedStatements or regular Statements. true boolean resultSetConversionStrategy (common) To use a custom class that implements logic for converting ResultSet into message body ALL, ONE, LIMIT_10, LIMIT_100... ResultSetConversionStrategy session (common) To use the Session instance (you would normally not use this option). CqlSession username (common) Username for session authentication. String bridgeErrorHandler (consumer) Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions occurred while the consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions, that will be logged at WARN or ERROR level and ignored. false boolean sendEmptyMessageWhenIdle (consumer) If the polling consumer did not poll any files, you can enable this option to send an empty message (no body) instead. false boolean exceptionHandler (consumer (advanced)) To let the consumer use a custom ExceptionHandler. Notice if the option bridgeErrorHandler is enabled then this option is not in use. By default the consumer will deal with exceptions, that will be logged at WARN or ERROR level and ignored. ExceptionHandler exchangePattern (consumer (advanced)) Sets the exchange pattern when the consumer creates an exchange. Enum values: InOnly InOut InOptionalOut ExchangePattern pollStrategy (consumer (advanced)) A pluggable org.apache.camel.PollingConsumerPollingStrategy allowing you to provide your custom implementation to control error handling usually occurred during the poll operation before an Exchange have been created and being routed in Camel. PollingConsumerPollStrategy lazyStartProducer (producer) Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel's routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing. false boolean backoffErrorThreshold (scheduler) The number of subsequent error polls (failed due some error) that should happen before the backoffMultipler should kick-in. int backoffIdleThreshold (scheduler) The number of subsequent idle polls that should happen before the backoffMultipler should kick-in. int backoffMultiplier (scheduler) To let the scheduled polling consumer backoff if there has been a number of subsequent idles/errors in a row. The multiplier is then the number of polls that will be skipped before the actual attempt is happening again. When this option is in use then backoffIdleThreshold and/or backoffErrorThreshold must also be configured. int delay (scheduler) Milliseconds before the poll. 500 long greedy (scheduler) If greedy is enabled, then the ScheduledPollConsumer will run immediately again, if the run polled 1 or more messages. false boolean initialDelay (scheduler) Milliseconds before the first poll starts. 1000 long repeatCount (scheduler) Specifies a maximum limit of number of fires. So if you set it to 1, the scheduler will only fire once. If you set it to 5, it will only fire five times. A value of zero or negative means fire forever. 0 long runLoggingLevel (scheduler) The consumer logs a start/complete log line when it polls. This option allows you to configure the logging level for that. Enum values: TRACE DEBUG INFO WARN ERROR OFF TRACE LoggingLevel scheduledExecutorService (scheduler) Allows for configuring a custom/shared thread pool to use for the consumer. By default each consumer has its own single threaded thread pool. ScheduledExecutorService scheduler (scheduler) To use a cron scheduler from either camel-spring or camel-quartz component. Use value spring or quartz for built in scheduler. none Object schedulerProperties (scheduler) To configure additional properties when using a custom scheduler or any of the Quartz, Spring based scheduler. Map startScheduler (scheduler) Whether the scheduler should be auto started. true boolean timeUnit (scheduler) Time unit for initialDelay and delay options. Enum values: NANOSECONDS MICROSECONDS MILLISECONDS SECONDS MINUTES HOURS DAYS MILLISECONDS TimeUnit useFixedDelay (scheduler) Controls if fixed delay or fixed rate is used. See ScheduledExecutorService in JDK for details. true boolean 22.5. Endpoint Connection Syntax The endpoint can initiate the Cassandra connection or use an existing one. URI Description cql:localhost/keyspace Single host, default port, usual for testing cql:host1,host2/keyspace Multi host, default port cql:host1,host2:9042/keyspace Multi host, custom port cql:host1,host2 Default port and keyspace cql:bean:sessionRef Provided Session reference cql:bean:clusterRef/keyspace Provided Cluster reference To fine tune the Cassandra connection (SSL options, pooling options, load balancing policy, retry policy, reconnection policy... ), create your own Cluster instance and give it to the Camel endpoint. 22.6. Messages 22.6.1. Incoming Message The Camel Cassandra endpoint expects a bunch of simple objects ( Object or Object[] or Collection<Object> ) which will be bound to the CQL statement as query parameters. If message body is null or empty, then CQL query will be executed without binding parameters. Headers CamelCqlQuery (optional, String or RegularStatement ) CQL query either as a plain String or built using the QueryBuilder . 22.6.2. Outgoing Message The Camel Cassandra endpoint produces one or many a Cassandra Row objects depending on the resultSetConversionStrategy : List<Row> if resultSetConversionStrategy is ALL or LIMIT_[0-9]+ Single` Row` if resultSetConversionStrategy is ONE Anything else, if resultSetConversionStrategy is a custom implementation of the ResultSetConversionStrategy 22.7. Repositories Cassandra can be used to store message keys or messages for the idempotent and aggregation EIP. Cassandra might not be the best tool for queuing use cases yet, read Cassandra anti-patterns queues and queue like datasets . It's advised to use LeveledCompaction and a small GC grace setting for these tables to allow tombstoned rows to be removed quickly. 22.8. Idempotent repository The NamedCassandraIdempotentRepository stores messages keys in a Cassandra table like this: CAMEL_IDEMPOTENT.cql CREATE TABLE CAMEL_IDEMPOTENT ( NAME varchar, -- Repository name KEY varchar, -- Message key PRIMARY KEY (NAME, KEY) ) WITH compaction = {'class':'LeveledCompactionStrategy'} AND gc_grace_seconds = 86400; This repository implementation uses lightweight transactions (also known as Compare and Set) and requires Cassandra 2.0.7+. Alternatively, the CassandraIdempotentRepository does not have a NAME column and can be extended to use a different data model. Option Default Description table CAMEL_IDEMPOTENT Table name pkColumns NAME ,` KEY` Primary key columns name Repository name, value used for NAME column ttl Key time to live writeConsistencyLevel Consistency level used to insert/delete key: ANY , ONE , TWO , QUORUM , LOCAL_QUORUM ... readConsistencyLevel Consistency level used to read/check key: ONE , TWO , QUORUM , LOCAL_QUORUM ... 22.9. Aggregation repository The NamedCassandraAggregationRepository stores exchanges by correlation key in a Cassandra table like this: CAMEL_AGGREGATION.cql CREATE TABLE CAMEL_AGGREGATION ( NAME varchar, -- Repository name KEY varchar, -- Correlation id EXCHANGE_ID varchar, -- Exchange id EXCHANGE blob, -- Serialized exchange PRIMARY KEY (NAME, KEY) ) WITH compaction = {'class':'LeveledCompactionStrategy'} AND gc_grace_seconds = 86400; Alternatively, the CassandraAggregationRepository does not have a NAME column and can be extended to use a different data model. Option Default Description table CAMEL_AGGREGATION Table name pkColumns NAME , KEY Primary key columns exchangeIdColumn EXCHANGE_ID Exchange Id column exchangeColumn EXCHANGE Exchange content column name Repository name, value used for NAME column ttl Exchange time to live writeConsistencyLevel Consistency level used to insert/delete exchange: ANY , ONE , TWO , QUORUM , LOCAL_QUORUM ... readConsistencyLevel Consistency level used to read/check exchange: ONE , TWO , QUORUM , LOCAL_QUORUM ... 22.10. Examples To insert something on a table you can use the following code: String CQL = "insert into camel_user(login, first_name, last_name) values (?, ?, ?)"; from("direct:input") .to("cql://localhost/camel_ks?cql=" + CQL); At this point you should be able to insert data by using a list as body Arrays.asList("davsclaus", "Claus", "Ibsen") The same approach can be used for updating or querying the table. 22.11. Spring Boot Auto-Configuration The component supports 4 options, which are listed below. Name Description Default Type camel.component.cql.autowired-enabled Whether autowiring is enabled. This is used for automatic autowiring options (the option must be marked as autowired) by looking up in the registry to find if there is a single instance of matching type, which then gets configured on the component. This can be used for automatic configuring JDBC data sources, JMS connection factories, AWS Clients, etc. true Boolean camel.component.cql.bridge-error-handler Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions occurred while the consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions, that will be logged at WARN or ERROR level and ignored. false Boolean camel.component.cql.enabled Whether to enable auto configuration of the cql component. This is enabled by default. Boolean camel.component.cql.lazy-start-producer Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel's routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing. false Boolean

Commands:
<dependency> <groupId>org.apache.camel.springboot</groupId> <artifactId>camel-cassandraql-starter</artifactId> </dependency>
cql:beanRef:hosts:port/keyspace
CREATE TABLE CAMEL_IDEMPOTENT ( NAME varchar, -- Repository name KEY varchar, -- Message key PRIMARY KEY (NAME, KEY) ) WITH compaction = {'class':'LeveledCompactionStrategy'} AND gc_grace_seconds = 86400;
CREATE TABLE CAMEL_AGGREGATION ( NAME varchar, -- Repository name KEY varchar, -- Correlation id EXCHANGE_ID varchar, -- Exchange id EXCHANGE blob, -- Serialized exchange PRIMARY KEY (NAME, KEY) ) WITH compaction = {'class':'LeveledCompactionStrategy'} AND gc_grace_seconds = 86400;
String CQL = "insert into camel_user(login, first_name, last_name) values (?, ?, ?)"; from("direct:input") .to("cql://localhost/camel_ks?cql=" + CQL);
Arrays.asList("davsclaus", "Claus", "Ibsen")