That information is not accurate. Trident can have exactly once semantics with *any* external database. See this page for the details: https://storm.apache.org/documentation/Trident-state.html
On Tue, Jan 12, 2016 at 3:55 AM, Matthias J. Sax <mj...@apache.org> wrote: > Hi, > > Storm does only guarantee exactly once *within* the system. If you write > to an external consumer you need to ensure that writes are idempotent or > de-duplicate externally. > > About Tridents internals, start to read the documentation here: > > https://storm.apache.org/documentation/Transactional-topologies.html > > If you have further questions, don't hesitate to follow up on this thread. > > -Matthias > > > On 01/12/2016 06:26 AM, Ajay wrote: > > Hi, > > > > We are evaluating storm with Trident to process events from Kafka in an > > exactly once manner so that the consumer application need not worry > > about the de-duplication logic. > > > > > > One of the sample use case could be as below: > > > > 1) Read an event from Kafka > > 2) Parse the JSON > > 3) Process the data > > 4) Write it to dynamo db and Apache solr > > > > So I want to understand how does the Trident handles exactly once > > semantics when the processing updates one or more distributed systems > > like in this case. What happens if write to one of them fails. > > > > Also wish to know the implementation details of how Trident supports > > exactly once semantics. > > > > Thanks > > Ajay > > -- Twitter: @nathanmarz http://nathanmarz.com
