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Posted to commits@flink.apache.org by uc...@apache.org on 2017/02/22 12:45:38 UTC
flink git commit: [FLINK-5876] [docs] Mention Scala extensions in
queryable state docs
Repository: flink
Updated Branches:
refs/heads/master fcc1efcb0 -> 8e1775afc
[FLINK-5876] [docs] Mention Scala extensions in queryable state docs
Project: http://git-wip-us.apache.org/repos/asf/flink/repo
Commit: http://git-wip-us.apache.org/repos/asf/flink/commit/8e1775af
Tree: http://git-wip-us.apache.org/repos/asf/flink/tree/8e1775af
Diff: http://git-wip-us.apache.org/repos/asf/flink/diff/8e1775af
Branch: refs/heads/master
Commit: 8e1775afc39a525fce334c71af0eafaeb1d882e1
Parents: fcc1efc
Author: Ufuk Celebi <uc...@apache.org>
Authored: Wed Feb 22 13:45:27 2017 +0100
Committer: Ufuk Celebi <uc...@apache.org>
Committed: Wed Feb 22 13:45:27 2017 +0100
----------------------------------------------------------------------
docs/dev/stream/queryable_state.md | 26 +++++++++++++++++++++-----
1 file changed, 21 insertions(+), 5 deletions(-)
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http://git-wip-us.apache.org/repos/asf/flink/blob/8e1775af/docs/dev/stream/queryable_state.md
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diff --git a/docs/dev/stream/queryable_state.md b/docs/dev/stream/queryable_state.md
index 4a63856..62d6a33 100644
--- a/docs/dev/stream/queryable_state.md
+++ b/docs/dev/stream/queryable_state.md
@@ -37,14 +37,14 @@ Flink. For some scenarios, queryable state thus eliminates the need for distribu
operations/transactions with external systems such as key-value stores which are often the
bottleneck in practice.
-<div class="alert alert-danger">
+<div class="alert alert-warning">
<strong>Attention:</strong> Queryable state accesses keyed state from a concurrent thread rather
than synchronizing with the operator and potentially blocking its operation. Since any state
- backend using Java heap space, e.g. <code>MemoryStateBackend</code> or
- <code>FsStateBackend</code>, does not work with copies when retrieving values but instead directly
+ backend using Java heap space, e.g. MemoryStateBackend or
+ FsStateBackend, does not work with copies when retrieving values but instead directly
references the stored values, read-modify-write patterns are unsafe and may cause the
queryable state server to fail due to concurrent modifications.
- The <code>RocksDBStateBackend</code> is safe from these issues.
+ The RocksDBStateBackend is safe from these issues.
</div>
## Making State Queryable
@@ -167,7 +167,7 @@ about any class loading issues etc.
There are some serialization utils for key/namespace and value serialization included in
`KvStateRequestSerializer`.
-## Example
+### Example
The following example extends the `CountWindowAverage` example
(see [Using Managed Keyed State]({{ site.baseurl }}/dev/stream/state.html#using-managed-keyed-state))
@@ -233,6 +233,22 @@ Tuple2<Long, Long> value =
KvStateRequestSerializer.deserializeValue(serializedValue, valueSerializer);
{% endhighlight %}
+### Note for Scala Users
+
+Please use the available Scala extensions when creating the `TypeSerializer` instances. Add the following import:
+
+```scala
+import org.apache.flink.streaming.api.scala._
+```
+
+Now you can create the type serializers as follows:
+
+```scala
+val keySerializer = createTypeInformation[Long]
+ .createSerializer(new ExecutionConfig)
+```
+
+If you don't do this, you can run into mismatches between the serializers used in the Flink job and in your client code, because types like `scala.Long` cannot be caputured at runtime.
## Configuration