[SPARK-12429][Streaming][Doc]Add Accumulator and Broadcast example for Streaming #10385
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@tdas could you take a look before I start to add Java and Python examples? |
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Test build #48018 has finished for PR 10385 at commit
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| ## Accumulator and Broadcast | |||
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| Accumulator and Broadcast cannot be recovered from checkpoint in Streaming. If you enable checkpoint and use Accumulator or Broadcast as well, you have to create lazily instantiated singleton instances for Accumulator and Broadcast so that they can be restarted on driver failures. This is shown in the following example. | |||
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I'd say: "in Spark Streaming. If you enable checkpointing and use an Accumulator or Broadcast as well, you**'ll** have to create ..."
zsxwing
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Test build #48038 has finished for PR 10385 at commit
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zsxwing
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Test build #48120 has finished for PR 10385 at commit
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Added Java and Python examples. |
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lgtm |
| @@ -1415,6 +1415,185 @@ Note that the connections in the pool should be lazily created on demand and tim | |||
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| ## Accumulator and Broadcast | |||
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Accumulators and Broadcast variables
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Small comments, otherwise LGTM. |
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| What is happening here is that the variables within the closure sent to each executor are now copies and thus, when **counter** is referenced within the `foreach` function, it's no longer the **counter** on the driver node. There is still a **counter** in the memory of the driver node but this is no longer visible to the executors! The executors only see the copy from the serialized closure. Thus, the final value of **counter** will still be zero since all operations on **counter** were referencing the value within the serialized closure. | |||
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| To ensure well-defined behavior in these sorts of scenarios one should use an [`Accumulator`](#AccumLink). Accumulators in Spark are used specifically to provide a mechanism for safely updating a variable when execution is split up across worker nodes in a cluster. The Accumulators section of this guide discusses these in more detail. | |||
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I also fixed the broken Accumulator link in programming-guide.md
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Test build #48222 has finished for PR 10385 at commit
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Dec 23, 2015
…or Streaming This PR adds Scala, Java and Python examples to show how to use Accumulator and Broadcast in Spark Streaming to support checkpointing. Author: Shixiong Zhu <[email protected]> Closes #10385 from zsxwing/accumulator-broadcast-example. (cherry picked from commit 20591af) Signed-off-by: Tathagata Das <[email protected]>
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This PR adds Scala, Java and Python examples to show how to use Accumulator and Broadcast in Spark Streaming to support checkpointing.