cascading.redshift

Provides an optimised Cascading sink for Amazon Redshift; String data will be checked for invalid codepoints, output files will be Gzip compressed automatically etc.

Data is sunk using an s3 path before a JDBC connection issues the DROP/CREATE/COPY statements.

Installing

cascading-redshift is hosted on conjars.org. You can add conjars.org as a maven repository and install the latest release:

<dependency>
  <groupId>cascading</groupId>
  <artifactId>cascading-redshift</artifactId>
  <version>0.15</version>
</dependency>

Using

Java

The wordcount example from Cascading with a sink to send data to Redshift.

HadoopFlowConnector flowConnector = new HadoopFlowConnector(properties);

Tap inTap = new Hfs(new TextDelimited(new Fields("line"), false, "\t"), inputPath);

String tableName = "cascading_redshift_sample";
String[] columnNames = {"word", "freq"};
String[] columnDefinitions = {"VARCHAR(500)", "SMALLINT"};
String distributionKey = "word";
String[] sortKeys = {"freq"};

String outputPath = "s3n://mybucket/data"

AWSCredentials credentials = new AWSCredentials(accessKey, secretKey);

RedshiftScheme scheme = new RedshiftScheme(Fields.ALL, new Fields("word", "count"), tableName, columnNames, columnDefinitions, distributionKey, sortKeys, new String[] {}, "\001");
Tap outTap = new RedshiftTap(outputPath, credentials, redshiftJdbcUrl, redshiftUsername, redshiftPassword, scheme, SinkMode.REPLACE);

Pipe assembly = new Pipe("wordcount");
String wordSplitRegex = "(?<!\\pL)(?=\\pL)[^ ]*(?<=\\pL)(?!\\pL)";

assembly = new Each(assembly, new Fields("line"), new RegexGenerator(new Fields("word"), wordSplitRegex));
assembly = new GroupBy(assembly, new Fields("word"));
assembly = new Every(assembly, new Fields("word"), new Count(new Fields("count")), new Fields("word", "count"));

flowConnector.connect("word-count", inTap, outTap, assembly).complete();

Lingual

The sink can also be used from within lingual, if you use the fatJar produced by the build. If you have followed the lingual introduction, this should be straight forward. If you haven't followed the tutorial, might be a bit to terse for you. If you are intersted in using the redshift tap from lingual, follow the tutorial first.

Please note that the redshift provider only supports the hadoop platform of lingual, the local platform is not supported. To simplify the interaction with the lingual catalog, you can set the platform as an evironment variable:

export LINGUAL_PLATFORM=hadoop

The provder name is redshift and the format and protocol are defined as redshift-s3, since this provider uses amazon S3 as intermediate storage. Redshift also allows you to read from a dynamo db instead of S3, however that is currently not supported.

To register the sink within lingual, you first have to build the provider compliant jar file in this project:

gradle build

The register the provider-jar, use lingual catalog:

lingual catalog --provider -add ./build/libs/cascading-redshift-0.15.0-provider.jar

Next add a schema called working:

lingual catalog --schema working --add

Next we define a stereotype:

lingual catalog --schema working --stereotype titles -add --columns TITLE,CNT --types string,int

lingual catalog --schema working --format redshift-s3 --add --properties-file redshift-format.properties --provider redshift

The redshift-format.properties contains information about the table structure for redshift:

tableName=title_counts
columnNames=title:cnt
columnDefs=varchar(100):int
distributionKey=title
sortKeys=title
copyOptions=

Next we register the redshift-s3 protocol in the working schema:

lingual catalog --schema working --protocol redshift-s3 --add --properties-file redshift-protocol.properties  --provider redshift

The redshift-protocol.properties looks like this:

s3OutputPath=s3n://<bucketName>/<path>/
jdbcUser=redshift-master-user
jdbcPassword=redshift-master-user-password
copyTimeout=5

And finally register the table in lingual. You can find the jdbc-url to use in the redshift cluster details in your aws console:

lingual catalog --schema working --table title_counts --add "jdbc:postgresql://<cluster-name>.<random>.<region>.redshift.amazonaws.com:<port>/<database>" --stereotype titles --protocol redshift-s3  --format redshift-s3

Before you write into the table, make sure, that the security group is correctly configured.

After this, we can directly select into redshift from the lingual shell:

(lingual shell) insert into "working"."title_counts" select title, count( title) as cnt  from employees.titles group by title;
    +-----------+
    | ROWCOUNT  |
    +-----------+
    | 7         |
    +-----------+

The data has now been written into the redshift table title_counts.

AWS credentials

Since redshift reads the data initially from S3, you have to provide a valid aws access-key/secret-key combination. There are multiple options to do that:

put them in the redshift-protocol.properties file as awsAccessKey and awsSecretKey
set them as the environment variables AWS_ACCESS_KEY and AWS_SECRET_KEY
put them in the your mapred-site.xml file as fs.s3n.awsAccessKeyId and fs.s3n.awsSecretAccessKey