K
- Type of keysV
- Type of valuespublic interface SessionWindowedCogroupedKStream<K,V>
SessionWindowedCogroupKStream
is an abstraction of a windowed record stream of KeyValue
pairs.
It is an intermediate representation of a CogroupedKStream
in order to apply a windowed aggregation operation
on the original KGroupedStream
records resulting in a windowed KTable
(a KTable
is a KTable
with key type Windowed
).
SessionWindows
are dynamic data driven windows.
They have no fixed time boundaries, rather the size of the window is determined by the records.
The result is written into a local SessionStore
(which is basically an ever-updating
materialized view) that can be queried using the name provided in the Materialized
instance.
Furthermore, updates to the store are sent downstream into a windowed KTable
changelog stream, where
"windowed" implies that the KTable
key is a combined key of the original record key and a window ID.
New events are added to sessions until their grace period ends (see SessionWindows.grace(Duration)
).
A SessionWindowedCogroupedKStream
must be obtained from a CogroupedKStream
via
CogroupedKStream.windowedBy(SessionWindows)
.
KStream
,
KGroupedStream
,
SessionWindows
,
CogroupedKStream
Modifier and Type | Method and Description |
---|---|
KTable<Windowed<K>,V> |
aggregate(Initializer<V> initializer,
Merger<? super K,V> sessionMerger)
Aggregate the values of records in these streams by the grouped key and defined sessions.
|
KTable<Windowed<K>,V> |
aggregate(Initializer<V> initializer,
Merger<? super K,V> sessionMerger,
Materialized<K,V,SessionStore<org.apache.kafka.common.utils.Bytes,byte[]>> materialized)
Aggregate the values of records in these streams by the grouped key and defined sessions.
|
KTable<Windowed<K>,V> |
aggregate(Initializer<V> initializer,
Merger<? super K,V> sessionMerger,
Named named)
Aggregate the values of records in these streams by the grouped key and defined sessions.
|
KTable<Windowed<K>,V> |
aggregate(Initializer<V> initializer,
Merger<? super K,V> sessionMerger,
Named named,
Materialized<K,V,SessionStore<org.apache.kafka.common.utils.Bytes,byte[]>> materialized)
Aggregate the values of records in these streams by the grouped key and defined sessions.
|
KTable<Windowed<K>,V> aggregate(Initializer<V> initializer, Merger<? super K,V> sessionMerger)
null
key or value are ignored.
The result is written into a local SessionStore
(which is basically an ever-updating materialized view).
Furthermore, updates to the store are sent downstream into a KTable
changelog stream.
The specified Initializer
is applied directly before the first input record per session is processed to
provide an initial intermediate aggregation result that is used to process the first record per session.
The specified Aggregator
(as specified in KGroupedStream.cogroup(Aggregator)
or
CogroupedKStream.cogroup(KGroupedStream, Aggregator)
) is applied for each input record and computes a new
aggregate using the current aggregate (or for the very first record using the intermediate aggregation result
provided via the Initializer
) and the record's value.
The specified Merger
is used to merge two existing sessions into one, i.e., when the windows overlap,
they are merged into a single session and the old sessions are discarded.
Thus, aggregate()
can be used to compute aggregate functions like count or sum etc.
The default key and value serde from the config will be used for serializing the result.
If a different serde is required then you should use aggregate(Initializer, Merger, Materialized)
.
Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to
the same window and key.
The rate of propagated updates depends on your input data rate, the number of distinct keys, the number of
parallel running Kafka Streams instances, and the configuration
parameters for
cache size
, and
commit interval
.
For failure and recovery the store will be backed by an internal changelog topic that will be created in Kafka.
The changelog topic will be named "${applicationId}-${internalStoreName}-changelog", where "applicationId" is
user-specified in StreamsConfig
via parameter
APPLICATION_ID_CONFIG
, "internalStoreName" is an internal name
and "-changelog" is a fixed suffix.
Note that the internal store name may not be queryable through Interactive Queries.
You can retrieve all generated internal topic names via Topology.describe()
.
initializer
- an Initializer
that computes an initial intermediate aggregation result. Cannot be null
.sessionMerger
- a Merger
that combines two aggregation results. Cannot be null
.KTable
that contains "update" records with unmodified keys, and values that represent
the latest (rolling) aggregate for each key per sessionKTable<Windowed<K>,V> aggregate(Initializer<V> initializer, Merger<? super K,V> sessionMerger, Named named)
null
key or value are ignored.
The result is written into a local SessionStore
(which is basically an ever-updating materialized view).
Furthermore, updates to the store are sent downstream into a KTable
changelog stream.
The specified Initializer
is applied directly before the first input record per session is processed to
provide an initial intermediate aggregation result that is used to process the first record per session.
The specified Aggregator
(as specified in KGroupedStream.cogroup(Aggregator)
or
CogroupedKStream.cogroup(KGroupedStream, Aggregator)
) is applied for each input record and computes a new
aggregate using the current aggregate (or for the very first record using the intermediate aggregation result
provided via the Initializer
) and the record's value.
The specified Merger
is used to merge two existing sessions into one, i.e., when the windows overlap,
they are merged into a single session and the old sessions are discarded.
Thus, aggregate()
can be used to compute aggregate functions like count or sum etc.
The default key and value serde from the config will be used for serializing the result.
If a different serde is required then you should use
aggregate(Initializer, Merger, Named, Materialized)
.
Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to
the same window and key.
The rate of propagated updates depends on your input data rate, the number of distinct
keys, the number of parallel running Kafka Streams instances, and the configuration
parameters for cache size
, and
commit interval
.
For failure and recovery the store will be backed by an internal changelog topic that will be created in Kafka.
The changelog topic will be named "${applicationId}-${internalStoreName}-changelog", where "applicationId" is
user-specified in StreamsConfig
via parameter
APPLICATION_ID_CONFIG
, "internalStoreName" is an internal name
and "-changelog" is a fixed suffix.
Note that the internal store name may not be queryable through Interactive Queries.
You can retrieve all generated internal topic names via Topology.describe()
.
initializer
- an Initializer
that computes an initial intermediate aggregation result. Cannot be null
.sessionMerger
- a Merger
that combines two aggregation results. Cannot be null
.named
- a Named
config used to name the processor in the topology. Cannot be null
.KTable
that contains "update" records with unmodified keys, and values that represent
the latest (rolling) aggregate for each key per sessionKTable<Windowed<K>,V> aggregate(Initializer<V> initializer, Merger<? super K,V> sessionMerger, Materialized<K,V,SessionStore<org.apache.kafka.common.utils.Bytes,byte[]>> materialized)
null
key or value are ignored.
The result is written into a local SessionStore
(which is basically an ever-updating materialized view)
that can be queried using the store name as provided with Materialized
.
Furthermore, updates to the store are sent downstream into a KTable
changelog stream.
The specified Initializer
is applied directly before the first input record (per key) in each window is
processed to provide an initial intermediate aggregation result that is used to process the first record for
the session (per key).
The specified Aggregator
(as specified in KGroupedStream.cogroup(Aggregator)
or
CogroupedKStream.cogroup(KGroupedStream, Aggregator)
) is applied for each input record and computes a new
aggregate using the current aggregate (or for the very first record using the intermediate aggregation result
provided via the Initializer
) and the record's value.
The specified Merger
is used to merge two existing sessions into one, i.e., when the windows overlap,
they are merged into a single session and the old sessions are discarded.
Thus, aggregate()
can be used to compute aggregate functions like count or sum etc.
Not all updates might get sent downstream, as an internal cache is used to deduplicate consecutive updates to
the same window and key if caching is enabled on the Materialized
instance.
When caching is enabled the rate of propagated updates depends on your input data rate, the number of distinct keys, the number of
parallel running Kafka Streams instances, and the configuration
parameters for
cache size
, and
commit interval
.
To query the local SessionStore
it must be obtained via
KafkaStreams#store(...)
:
KafkaStreams streams = ... // counting words
Store queryableStoreName = ... // the queryableStoreName should be the name of the store as defined by the Materialized instance
StoreQueryParameters<ReadOnlySessionStore<String, Long>> storeQueryParams = StoreQueryParameters.fromNameAndType(queryableStoreName, QueryableStoreTypes.sessionStore());
ReadOnlySessionStore<String,Long> localWindowStore = streams.store(storeQueryParams);
String key = "some-word";
long fromTime = ...;
long toTime = ...;
WindowStoreIterator<Long> aggregateStore = localWindowStore.fetch(key, timeFrom, timeTo); // key must be local (application state is shared over all running Kafka Streams instances)
For non-local keys, a custom RPC mechanism must be implemented using KafkaStreams.metadataForAllStreamsClients()
to
query the value of the key on a parallel running instance of your Kafka Streams application.
For failure and recovery the store will be backed by an internal changelog topic that will be created in Kafka.
Therefore, the store name defined by the Materialized
instance must be a valid Kafka topic name and
cannot contain characters other than ASCII alphanumerics, '.', '_' and '-'.
The changelog topic will be named "${applicationId}-${storeName}-changelog", where "applicationId" is
user-specified in StreamsConfig
via parameter
APPLICATION_ID_CONFIG
, "storeName" is the
provide store name defined in Materialized
, and "-changelog" is a fixed suffix.
You can retrieve all generated internal topic names via Topology.describe()
.
initializer
- an Initializer
that computes an initial intermediate aggregation result. Cannot be null
.sessionMerger
- a Merger
that combines two aggregation results. Cannot be null
.materialized
- a Materialized
config used to materialize a state store. Cannot be null
.KTable
that contains "update" records with unmodified keys, and values that represent
the latest (rolling) aggregate for each key within a windowKTable<Windowed<K>,V> aggregate(Initializer<V> initializer, Merger<? super K,V> sessionMerger, Named named, Materialized<K,V,SessionStore<org.apache.kafka.common.utils.Bytes,byte[]>> materialized)
null
key or value are ignored.
The result is written into a local SessionStore
(which is basically an ever-updating materialized view)
that can be queried using the store name as provided with Materialized
.
Furthermore, updates to the store are sent downstream into a KTable
changelog stream.
The specified Initializer
is applied directly before the first input record (per key) in each window is
processed to provide an initial intermediate aggregation result that is used to process the first record for
the session (per key).
The specified Aggregator
(as specified in KGroupedStream.cogroup(Aggregator)
or
CogroupedKStream.cogroup(KGroupedStream, Aggregator)
) is applied for each input record and computes a new
aggregate using the current aggregate (or for the very first record using the intermediate aggregation result
provided via the Initializer
) and the record's value.
The specified Merger
is used to merge two existing sessions into one, i.e., when the windows overlap,
they are merged into a single session and the old sessions are discarded.
Thus, aggregate()
can be used to compute aggregate functions like count or sum etc.
Not all updates might get sent downstream, as an internal cache will be used to deduplicate consecutive updates
to the same window and key if caching is enabled on the Materialized
instance.
When caching is enabled the rate of propagated updates depends on your input data rate, the number of distinct
keys, the number of parallel running Kafka Streams instances, and the configuration
parameters for cache size
, and
commit interval
.
To query the local SessionStore
it must be obtained via
KafkaStreams.store(StoreQueryParameters)
KafkaStreams#store(...)}:
KafkaStreams streams = ... // some windowed aggregation on value type double
Sting queryableStoreName = ... // the queryableStoreName should be the name of the store as defined by the Materialized instance
StoreQueryParameters<ReadOnlySessionStore<String, Long>> storeQueryParams = StoreQueryParameters.fromNameAndType(queryableStoreName, QueryableStoreTypes.sessionStore());
ReadOnlySessionStore<String,Long> localWindowStore = streams.store(storeQueryParams);
String key = "some-key";
KeyValueIterator<Windowed<String>, Long> aggForKeyForSession = localWindowStore.fetch(key); // key must be local (application state is shared over all running Kafka Streams instances)
For non-local keys, a custom RPC mechanism must be implemented using KafkaStreams.metadataForAllStreamsClients()
to
query the value of the key on a parallel running instance of your Kafka Streams application.
For failure and recovery the store will be backed by an internal changelog topic that will be created in Kafka.
Therefore, the store name defined by the Materialized
instance must be a valid Kafka topic name and
cannot contain characters other than ASCII alphanumerics, '.', '_' and '-'.
The changelog topic will be named "${applicationId}-${storeName}-changelog", where "applicationId" is
user-specified in StreamsConfig
via parameter
APPLICATION_ID_CONFIG
, "storeName" is the
provide store name defined in Materialized
, and "-changelog" is a fixed suffix.
You can retrieve all generated internal topic names via Topology.describe()
.
initializer
- an Initializer
that computes an initial intermediate aggregation result. Cannot be null
.sessionMerger
- a Merger
that combines two aggregation results. Cannot be null
.named
- a Named
config used to name the processor in the topology. Cannot be null
.materialized
- a Materialized
config used to materialize a state store. Cannot be null
.KTable
that contains "update" records with unmodified keys, and values that represent
the latest (rolling) aggregate for each key per session