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From S Ahmed <sahmed1...@gmail.com>
Subject Re: storing last processed offset, recovery of failed message processing etc.
Date Mon, 09 Dec 2013 20:36:55 GMT
Say am I doing this, a scenerio that I just came up with that demonstrates

Someone signs up on a website, and you have to:

1. create the user profile
2. send email confirmation email
3. resize avatar

Now once a person registers on a website, I write a message to Kafka.

Now I have 3 different things to process (1,2,3), if I get to #2 and then
the server loses power, if I replay, I will re-send the confirmation email
2 times.   Sure in this case its not that big of a deal, but just pretend
it is, what should be done?

I guess I have to keep track of state then per step in ZK right? I mean
that's the only way so I guess I am answering my own question but was
hoping for people with real-life experience to chime in.

I could write 3 messages to kafka, but maybe order is important :)

On Mon, Dec 9, 2013 at 3:31 PM, Philip O'Toole <philip@loggly.com> wrote:

> We use Zookeeper, as is standard with Kafka.
> Our systems are idempotent, so we only store offsets when the message is
> fully processed. If this means we occasionally replay a message due to some
> corner-case, or simply a restart, it doesn't matter.
> Philip
> On Mon, Dec 9, 2013 at 12:28 PM, S Ahmed <sahmed1020@gmail.com> wrote:
> > I was hoping people could comment on how they handle the following
> > scenerios:
> >
> > 1. Storing the last successfully processed messageId/Offset.  Are people
> > using mysql, redis, etc.?  What are the tradeoffs here?
> >
> > 2. How do you handle recovering from an error while processesing a given
> > event?
> >
> > There are various scenerioes for #2, like:
> > 1. Do you mark the start of processing a message somewhere, and then
> update
> > the status to complete and THEN update the last messaged processed for
> #1?
> > 2. Do you only mark the status as complete, and not the start of
> processing
> > it?  I guess this depends of there are intermediate steps and processing
> > the entire message again would result in some duplicated work right?
> >

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