listen to colin's advice, avoid the temptation of anti-patterns.
Post by Colin
Use a message bus with a transactional get, get the message, send to
cassandra, upon write success, submit to esp, commit get on bus. Messaging
systems like rabbitmq support this semantic.
Using cassandra as a queuing mechanism is an anti-pattern.
Thank you all for your answers.
It seems I'll have to go with some event-driven processing before/during
the Cassandra write path.
My concern would be that I'd love to first guarantee the disk write of the
Cassandra persistence and then do the event processing (which is mostly
CRUD intercepts at this point), even if slightly delayed, and doing so via
triggers would probably bog down the whole processing pipeline.
What I'd probably do is to write, in trigger, a separate key table with
all the CRUDed elements and to have the ESP process that table.
Thank you for your contribution. Should anyone else have any experiende
experience in these scenarios I'm obviously all ears as well.
Enviado do meu iPhone
I was facing the same kind of requirement from some users. Long story
short, below are the possible strategies with advantages and draw-backs of
1) Put Spark in front of the back-end, every incoming
modification/update/insert goes into Spark first, then Spark will forward
it to Cassandra for persistence. With Spark, you can perform pre or
post-processing and notify external clients of mutation.
The draw back of this solution is that all the incoming mutations must go
through Spark. You may set up a Kafka queue as temporary storage to
distribute the load and consume mutations with Spark but it add ups to the
architecture complexity with additional components & technologies
2) For high availability and resilience, you probably want to have all
mutations saved first into Cassandra then process notifications with Spark.
In this case the only way to have notifications from Cassandra, as of
version 2.1, is to rely on manually coded triggers (which is still
With the triggers you can notify whatever clients you want, not only Spark.
The big draw back of this solution is that playing with triggers is
dangerous if you are not familiar with Cassandra internals. Indeed the
trigger is on the write path and may hurt performance if you are doing
complex and blocking tasks.
That's the 2 solutions I can see, maybe the ML members will propose other
On Sat, Jan 3, 2015 at 11:46 AM, Hugo JosÃ© Pinto <
Post by Hugo JosÃ© Pinto
We're currently using Hazelcast (http://hazelcast.org/) as a distributed
in-memory data grid. That's been working sort-of-well for us, but going
solely in-memory has exhausted its path in our use case, and we're
considering porting our application to a NoSQL persistent store. After the
usual comparisons and evaluations, we're borderline close to picking
Cassandra, plus eventually Spark for analytics.
Nonetheless, there is a gap in our architectural needs that we're still
not grasping how to solve in Cassandra (with or without Spark): Hazelcast
allows us to create a Continuous Query in that, whenever a row is
added/removed/modified from the clause's resultset, Hazelcast calls up back
with the corresponding notification. We use this to continuously update the
clients via AJAX streaming with the new/changed rows.
This is probably a conceptual mismatch we're making, so - how to best
address this use case in Cassandra (with or without Spark's help)? Is there
something in the API that allows for Continuous Queries on key/clause
changes (haven't found it)? Is there some other way to get a stream of
key/clause updates? Events of some sort?
I'm aware that we could, eventually, periodically poll Cassandra, but in
our use case, the client is potentially interested in a large number of
table clause notifications (think "all changes to Ship positions on
California's coastline"), and iterating out of the store would kill the
Hence, the magic question: what are we missing? Is Cassandra the wrong
tool for the job? Are we not aware of a particular part of the API or
external library in/outside the apache realm that would allow for this?
Many thanks for any assistance!