This document discusses streaming and paging data from Apache Cassandra using observables. It introduces the speaker as an evangelist for Cassandra and describes how server-side paging and combining result sets with observables allows efficient streaming of large result sets without blocking or out of memory errors. Code examples are provided showing how to create an observable from a Cassandra query result set and subscribe to stream result rows.

1. I want my data out: streaming + observable +
paging
Christopher Batey
@chbatey
©2013 DataStax Confidential. Do not distribute without consent.
1

2. Who am I?
•Technical Evangelist for Apache Cassandra
• Founder of Stubbed Cassandra
• Help out Apache Cassandra users
• Previous: Senior software engineer @ BSkyB

3. Cassandra is great because…
• What was once hard is now easy!
• More and more features that aren’t part of
its core competency

4. Your favourite - OutOfMemory
Application C Big Query

5. Your favourite - OutOfMemory
Application C Big Query

6. Your favourite - OutOfMemory
Uh oh, OutOfMemory
Application C Big Query

7. Your favourite - OutOfMemory
Uh oh, OutOfMemory
Application C Big Query

8. Okay so 2 gb queries aren’t
recommended?

9. Manual paging
WEB
Your Application
DAO
Lots of small queries
Super C*
Blocking
Queue

10. Server side paging = awesome

11. Your favourite - OutOfMemory
Uh oh, OutOfMemory
Application C Big Query

12. Not so manual paging
Your Application
Super awesome paging query!
C*

13. ResultSet + Observable = Awesome
public Observable<CustomerEvent> getCustomerEventsObservable(String customerId) {
BoundStatement boundStatement = getEventsForCustomer.bind(customerId);
ListenableFuture<ResultSet> resultSetFuture = session.executeAsync(boundStatement);
Observable<ResultSet> observable =
Observable.from(resultSetFuture, Schedulers.io());
Observable<Row> rowObservable = observable.flatMapIterable(result -> result);
return rowObservable.map(row -> new CustomerEvent(
row.getString("customer_id"),
row.getUUID("time"),
row.getString("staff_id"),
row.getString("store_type"),
row.getString("event_type"),
row.getMap("tags", String.class, String.class)));
}
p

14. ResultSet + Observable = Awesome
Observable<CustomerEvent> chbatey = customerEventDao.getCustomerEventsObservable("chbatey");
chbatey.doOnCompleted(() -> {
try { outputStream.close(); } catch (IOException e) { }
});
chbatey.subscribe(event -> {
try { outputStream.write(event.serialise()); } catch (IOException e) { }
});

15. Manual paging
WEB
Your Application
DAO
Lots of small queries
Super C*
Blocking
Queue

16. Thanks for listening
@chbatey
http://christopher-batey.blogspot.co.uk