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https://issues.apache.org/jira/browse/GEARPUMP-24?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15242429#comment-15242429
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Manu Zhang edited comment on GEARPUMP-24 at 4/15/16 4:50 AM:
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Hi [~whjiang],
For KafkaSource, we already have an internal queue for messages asyncly fetched
from Kafka. I feel more like allowing users to access the internal queue
directly than copy messages to another in memory queue. This may be applied to
other sources and I think an iterator like interface is more general and safer.
Hi [~clockfly],
Users still do a batch of reads in one Task invocation and data sources are
free to pull in data in batch or not. I'll perform a benchmark on KafkaSource.
was (Author: mauzhang):
Hi [~whjiang],
For KafkaSource, we already have an internal queue for messages asyncly fetched
from Kafka. I feel more like allowing users to access the internal queue
directly than copy messages to another in memory queue. This may be applied to
other sources.
Hi [~clockfly],
Users still do a batch of reads in one Task invocation and data sources are
free to pull in data in batch or not. I'll perform a benchmark on KafkaSource.
> refactor DataSource API
> -----------------------
>
> Key: GEARPUMP-24
> URL: https://issues.apache.org/jira/browse/GEARPUMP-24
> Project: Apache Gearpump
> Issue Type: Improvement
> Components: streaming
> Affects Versions: 0.8.0
> Reporter: Manu Zhang
> Assignee: Manu Zhang
> Fix For: 0.8.1
>
>
> From [https://github.com/gearpump/gearpump/issues/2013]:
> The current DataSource API
> {code}
> trait DataSource extends java.io.Serializable {
> /**
> * open connection to data source
> * invoked in onStart() method of
> [[io.gearpump.streaming.source.DataSourceTask]]
> * @param context is the task context at runtime
> * @param startTime is the start time of system
> */
> def open(context: TaskContext, startTime: Option[TimeStamp]): Unit
> /**
> * read a number of messages from data source.
> * invoked in each onNext() method of
> [[io.gearpump.streaming.source.DataSourceTask]]
> * @param batchSize max number of messages to read
> * @return a list of messages wrapped in [[io.gearpump.Message]]
> */
> def read(batchSize: Int): List[Message]
> /**
> * close connection to data source.
> * invoked in onStop() method of
> [[io.gearpump.streaming.source.DataSourceTask]]
> */
> def close(): Unit
> }
> {code}
> has several issues
> 1. read returns a scala list of Message which is unfriendly to Java
> DataSources. Same for Option parameter in open
> 2. the number of read messages may not be the same as the passed in batchSize
> which leaves uncertainty to users (users may access out of boundary list
> positions)
> 3. to return a list an extra buffer could be needed in read (e.g.
> KafkaSource) which is not best for performance
> Update:
> I'd like to add a "getWatermark" interface that helps to fix GEARPUMP-32
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