Repository: spark Updated Branches: refs/heads/branch-1.5 165be9ad1 -> 30f0f7e4e
[DOCS] [STREAMING] [KAFKA] Fix typo in exactly once semantics Fix Typo in exactly once semantics [Semantics of output operations] link Author: Moussa Taifi <mouta...@gmail.com> Closes #8468 from moutai/patch-3. (cherry picked from commit 9625d13d575c97bbff264f6a94838aae72c9202d) Signed-off-by: Sean Owen <so...@cloudera.com> Project: http://git-wip-us.apache.org/repos/asf/spark/repo Commit: http://git-wip-us.apache.org/repos/asf/spark/commit/30f0f7e4 Tree: http://git-wip-us.apache.org/repos/asf/spark/tree/30f0f7e4 Diff: http://git-wip-us.apache.org/repos/asf/spark/diff/30f0f7e4 Branch: refs/heads/branch-1.5 Commit: 30f0f7e4e39b58091e0a10199b6da81d14fa7fdb Parents: 165be9a Author: Moussa Taifi <mouta...@gmail.com> Authored: Thu Aug 27 10:34:47 2015 +0100 Committer: Sean Owen <so...@cloudera.com> Committed: Thu Aug 27 10:35:32 2015 +0100 ---------------------------------------------------------------------- docs/streaming-kafka-integration.md | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) ---------------------------------------------------------------------- http://git-wip-us.apache.org/repos/asf/spark/blob/30f0f7e4/docs/streaming-kafka-integration.md ---------------------------------------------------------------------- diff --git a/docs/streaming-kafka-integration.md b/docs/streaming-kafka-integration.md index 7571e22..5db39ae 100644 --- a/docs/streaming-kafka-integration.md +++ b/docs/streaming-kafka-integration.md @@ -82,7 +82,7 @@ This approach has the following advantages over the receiver-based approach (i.e - *Efficiency:* Achieving zero-data loss in the first approach required the data to be stored in a Write Ahead Log, which further replicated the data. This is actually inefficient as the data effectively gets replicated twice - once by Kafka, and a second time by the Write Ahead Log. This second approach eliminates the problem as there is no receiver, and hence no need for Write Ahead Logs. As long as you have sufficient Kafka retention, messages can be recovered from Kafka. -- *Exactly-once semantics:* The first approach uses Kafka's high level API to store consumed offsets in Zookeeper. This is traditionally the way to consume data from Kafka. While this approach (in combination with write ahead logs) can ensure zero data loss (i.e. at-least once semantics), there is a small chance some records may get consumed twice under some failures. This occurs because of inconsistencies between data reliably received by Spark Streaming and offsets tracked by Zookeeper. Hence, in this second approach, we use simple Kafka API that does not use Zookeeper. Offsets are tracked by Spark Streaming within its checkpoints. This eliminates inconsistencies between Spark Streaming and Zookeeper/Kafka, and so each record is received by Spark Streaming effectively exactly once despite failures. In order to achieve exactly-once semantics for output of your results, your output operation that saves the data to an external data store must be either idempotent, or an atomic transa ction that saves results and offsets (see [Semanitcs of output operations](streaming-programming-guide.html#semantics-of-output-operations) in the main programming guide for further information). +- *Exactly-once semantics:* The first approach uses Kafka's high level API to store consumed offsets in Zookeeper. This is traditionally the way to consume data from Kafka. While this approach (in combination with write ahead logs) can ensure zero data loss (i.e. at-least once semantics), there is a small chance some records may get consumed twice under some failures. This occurs because of inconsistencies between data reliably received by Spark Streaming and offsets tracked by Zookeeper. Hence, in this second approach, we use simple Kafka API that does not use Zookeeper. Offsets are tracked by Spark Streaming within its checkpoints. This eliminates inconsistencies between Spark Streaming and Zookeeper/Kafka, and so each record is received by Spark Streaming effectively exactly once despite failures. In order to achieve exactly-once semantics for output of your results, your output operation that saves the data to an external data store must be either idempotent, or an atomic transa ction that saves results and offsets (see [Semantics of output operations](streaming-programming-guide.html#semantics-of-output-operations) in the main programming guide for further information). Note that one disadvantage of this approach is that it does not update offsets in Zookeeper, hence Zookeeper-based Kafka monitoring tools will not show progress. However, you can access the offsets processed by this approach in each batch and update Zookeeper yourself (see below). --------------------------------------------------------------------- To unsubscribe, e-mail: commits-unsubscr...@spark.apache.org For additional commands, e-mail: commits-h...@spark.apache.org
