Thanks Maciek,
It looks like my initial issue had another problem with a bad interface that
was being used (or an improper one), but after changing that and ensuring all
of the fields were implemented it worked as expected.
I know in my particular case, I'm planning on writing to Kafka, however my
wrapped function isn't a process function and thus it isn't as simple as
supplying a side-output and sending those to Kafka. I'm guessing in this
scenario, it'd be sufficient to have a plain Kafka producer (created within the
open() function) and just use that as opposed to constructing a sink and
explicitly invoking it.
```
catch (exception: Exception) {
// I'd imagine that the context here would require a second level of
mapping to ensure that
// we have the proper context for the sink itself
dlqSink.invoke(value, context)
// Or this would be the alternative
dlqProducer.send(..., value)
}
```
I don't know if you have the same scenario (or are leveraging Kafka), but if
so, I'd be curious of the approach that you took.
Thanks much,
Rion
On 2021/08/03 08:45:07, Maciej Obuchowski <[email protected]> wrote:
> Hey.
>
> As far as I see, you're not overriding functions like open,
> setRuntimeContext, snapshotState, initializeState - the calls needs to
> be passed to the inner sink function.
>
> pon., 2 sie 2021 o 19:31 Rion Williams <[email protected]> napisał(a):
> >
> > Hi again Maciek (and all),
> >
> > I just recently returned to start investigating this approach, however I
> > can't seem to get the underlying invocation to work as I would normally
> > expect. I'll try to share a bit more as what I currently have and perhaps
> > I'm just missing something minor that someone may be able to spot.
> >
> > To reiterate - what I'm attempting to do is take a stream of events flowing
> > through, specific types of entities are extracted from these events into
> > multiple side-outputs, and these side-outputs are passed to a sync that
> > will write them via JDBC using logic specific to that entity. What I am
> > aiming to achieve is being able to capture a single record that may be
> > problematic and avoid a poison pill to throw onto a dead-letter queue
> > (Kafka). I understand this would mean limiting batching sizes to a single
> > record, however I'm assuming that the connections themselves could be
> > pooled possibly to avoid opening up a new connection per call. If this
> > isn't the case, is there a way to handle that (or would I need to implement
> > my own sync).
> >
> > ```
> > val users = Tags.users
> > parsedChangelogs
> > .getSideOutput(users)
> > .addSink(PostgresSink.fromEntityType(users.typeInfo,
> > parameters))
> > .uid("sync-${users.id}-to-postgres")
> > .name("sync-${users.id}-to-postgres")
> >
> > val addresses = Tags.addresses
> > parsedChangelogs
> > .getSideOutput(addresses)
> > .addSink(PostgresSink.fromEntityType(addresses.typeInfo,
> > parameters))
> > .uid("sync-${addresses.id}-to-postgres")
> > .name("sync-${addresses.id}-to-postgres")
> > ```
> >
> > And the dynamic sink (that would associate a given entity to the necessary
> > calls made to the database) looks a bit like this:
> >
> > ```
> > fun <T: Any> fromEntityType(typeInfo: TypeInformation<T>, parameters:
> > ParameterTool): SinkFunction<T> {
> > val metadata = getQueryMetadataFromType(typeInfo)
> >
> > return JdbcSink
> > .sink(
> > metadata.query,
> > metadata.statement,
> > getJdbcExecutionOptions(parameters),
> > JdbcConnectionOptions.JdbcConnectionOptionsBuilder()
> > .withDriverName("org.postgresql.Driver")
> > .withUrl(buildConnectionString(parameters))
> > .build(),
> > )
> > }
> > ```
> >
> > I've tried several, a naive wrapper approach that I attempted looked
> > something like this:
> >
> > ```
> > class DlqWrapper<T>(private val sink: SinkFunction<T>, val parameters:
> > ParameterTool): SinkFunction<T> {
> > private val logger = LoggerFactory.getLogger(DlqSink::class.java)
> > private val dlqSink: SinkFunction<String> = ...
> >
> > override fun invoke(value: T, context: SinkFunction.Context) {
> > try {
> > sink.invoke(value, context)
> > }
> > catch (ex: Exception) {
> > logger.error("Encountered sink exception. Sending message to
> > dead letter queue. Value: $value. Exception: ${ex.message}")
> > val payload = Gson().toJsonTree(value).asJsonObject
> > payload.addProperty("exception", ex.message)
> >
> > dlqSink.invoke("$payload", context)
> > }
> > }
> > }
> > ```
> >
> > After doing this, it doesn't look like when the invoke calls are made that
> > it's actually attempting to perform the JDBC calls to insert the records
> > into those sources. I'm not entirely sure if this is related specifically
> > for how the JdbcSink is wrapped (via the GenericJdbcSink, etc.).
> >
> > I had seen several posts around involving the use of an
> > InvocationHandler/Proxy, etc. but I'm not sure if that should be necessary
> > for handling this type of functionality. Any ideas/thoughts/examples would
> > be greatly appreciated.
> >
> > Thanks,
> >
> > Rion
> >
> > On 2021/07/14 15:47:18, Maciej Bryński <[email protected]> wrote:
> > > This is the idea.
> > > Of course you need to wrap more functions like: open, close,
> > > notifyCheckpointComplete, snapshotState, initializeState and
> > > setRuntimeContext.
> > >
> > > The problem is that if you want to catch problematic record you need
> > > to set batch size to 1, which gives very bad performance.
> > >
> > > Regards,
> > > Maciek
> > >
> > > śr., 14 lip 2021 o 17:31 Rion Williams <[email protected]> napisał(a):
> > > >
> > > > Hi Maciej,
> > > >
> > > > Thanks for the quick response. I wasn't aware of the idea of using a
> > > > SinkWrapper, but I'm not quite certain that it would suit this specific
> > > > use case (as a SinkFunction / RichSinkFunction doesn't appear to
> > > > support side-outputs). Essentially, what I'd hope to accomplish would
> > > > be to pick up when a bad record could not be written to the sink and
> > > > then offload that via a side-output somewhere else.
> > > >
> > > > Something like this, which is a very, very naive idea:
> > > >
> > > > class PostgresSinkWrapper<T>(private val sink: SinkFunction<T>):
> > > > RichSinkFunction<T>() {
> > > > private val logger =
> > > > LoggerFactory.getLogger(PostgresSinkWrapper::class.java)
> > > >
> > > > override fun invoke(value: T, context: SinkFunction.Context) {
> > > > try {
> > > > sink.invoke(value, context)
> > > > }
> > > > catch (exception: Exception){
> > > > logger.error("Encountered a bad record, offloading to
> > > > dead-letter-queue")
> > > > // Offload bad record to DLQ
> > > > }
> > > > }
> > > > }
> > > >
> > > > But I think that's basically the gist of it. I'm just not sure how I
> > > > could go about doing this aside from perhaps writing a custom process
> > > > function that wraps another sink function (or just completely rewriting
> > > > my own JdbcSink?)
> > > >
> > > > Thanks,
> > > >
> > > > Rion
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > On Wed, Jul 14, 2021 at 9:56 AM Maciej Bryński <[email protected]>
> > > > wrote:
> > > >>
> > > >> Hi Rion,
> > > >> We have implemented such a solution with Sink Wrapper.
> > > >>
> > > >>
> > > >> Regards,
> > > >> Maciek
> > > >>
> > > >> śr., 14 lip 2021 o 16:21 Rion Williams <[email protected]>
> > > >> napisał(a):
> > > >> >
> > > >> > Hi all,
> > > >> >
> > > >> > Recently I've been encountering an issue where some external
> > > >> > dependencies or process causes writes within my JDBCSink to fail
> > > >> > (e.g. something is being inserted with an explicit constraint that
> > > >> > never made it's way there). I'm trying to see if there's a pattern
> > > >> > or recommendation for handling this similar to a dead-letter queue.
> > > >> >
> > > >> > Basically - if I experience a given number of failures (> max retry
> > > >> > attempts) when writing to my JDBC destination, I'd like to take the
> > > >> > record that was attempted and throw it into a Kafka topic or some
> > > >> > other destination so that it can be evaluated at a later time.
> > > >> >
> > > >> > Are there any well defined patterns or recommended approaches around
> > > >> > this?
> > > >> >
> > > >> > Thanks,
> > > >> >
> > > >> > Rion
> > > >>
> > > >>
> > > >>
> > > >> --
> > > >> Maciek Bryński
> > >
> > >
> > >
> > > --
> > > Maciek Bryński
> > >
>
