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new 7bd8ada MINOR: Docs on state store instantiation (#5698)
7bd8ada is described below
commit 7bd8ada8e21cd9717eea6916a5a55274a49fdeda
Author: Guozhang Wang <wangg...@gmail.com>
AuthorDate: Wed Oct 3 11:20:47 2018 -0700
MINOR: Docs on state store instantiation (#5698)
Reviewers: Bill Bejeck <b...@confluent.io>, Matthias J. Sax
<matth...@confluent.io>
---
docs/streams/developer-guide/processor-api.html | 3 +++
.../java/org/apache/kafka/streams/processor/StateStore.java | 13 ++++++++++++-
2 files changed, 15 insertions(+), 1 deletion(-)
diff --git a/docs/streams/developer-guide/processor-api.html
b/docs/streams/developer-guide/processor-api.html
index cb45cd9..ae43360 100644
--- a/docs/streams/developer-guide/processor-api.html
+++ b/docs/streams/developer-guide/processor-api.html
@@ -347,6 +347,9 @@
The primary interface to implement for the store is
<code class="docutils literal"><span
class="pre">org.apache.kafka.streams.processor.StateStore</span></code>. Kafka
Streams also has a few extended interfaces such
as <code class="docutils literal"><span
class="pre">KeyValueStore</span></code>.</p>
+ <p>Note that your customized <code class="docutils
literal"><span
class="pre">org.apache.kafka.streams.processor.StateStore</span></code>
implementation also needs to provide the logic on how to restore the state
+ via the <code class="docutils literal"><span
class="pre">org.apache.kafka.streams.processor.StateRestoreCallback</span></code>
or <code class="docutils literal"><span
class="pre">org.apache.kafka.streams.processor.BatchingStateRestoreCallback</span></code>
interface.
+ Details on how to instantiate these interfaces can be
found in the <a class="reference external"
href="../../../javadoc/org/apache/kafka/streams/processor/StateStore.html">javadocs</a>.</p>
<p>You also need to provide a “builder” for the
store by implementing the
<code class="docutils literal"><span
class="pre">org.apache.kafka.streams.state.StoreBuilder</span></code>
interface, which Kafka Streams uses to create instances of
your store.</p>
diff --git
a/streams/src/main/java/org/apache/kafka/streams/processor/StateStore.java
b/streams/src/main/java/org/apache/kafka/streams/processor/StateStore.java
index f098cd0..df53ee2 100644
--- a/streams/src/main/java/org/apache/kafka/streams/processor/StateStore.java
+++ b/streams/src/main/java/org/apache/kafka/streams/processor/StateStore.java
@@ -46,7 +46,18 @@ public interface StateStore {
String name();
/**
- * Initializes this state store
+ * Initializes this state store.
+ * <p>
+ * The implementation of this function must register the root store in the
context via the
+ * {@link ProcessorContext#register(StateStore, StateRestoreCallback)}
function, where the
+ * first {@link StateStore} parameter should always be the passed-in
{@code root} object, and
+ * the second parameter should be an object of user's implementation
+ * of the {@link StateRestoreCallback} interface used for restoring the
state store from the changelog.
+ * <p>
+ * Note that if the state store engine itself supports bulk writes, users
can implement another
+ * interface {@link BatchingStateRestoreCallback} which extends {@link
StateRestoreCallback} to
+ * let users implement bulk-load restoration logic instead of restoring
one record at a time.
+ *
* @throws IllegalStateException If store gets registered after
initialized is already finished
* @throws StreamsException if the store's change log does not contain the
partition
*/
