K
- Type of primary keysV
- Type of value changespublic interface GlobalKTable<K,V>
GlobalKTable
is an abstraction of a changelog stream from a primary-keyed table.
Each record in this changelog stream is an update on the primary-keyed table with the record key as the primary key.
GlobalKTable
can only be used as right-hand side input for stream
-table joins.
In contrast to a KTable
that is partitioned over all KafkaStreams
instances, a GlobalKTable
is fully replicated per KafkaStreams
instance.
Every partition of the underlying topic is consumed by each GlobalKTable
, such that the full set of data is
available in every KafkaStreams
instance.
This provides the ability to perform joins with KStream
without having to repartition the input stream.
All joins with the GlobalKTable
require that a KeyValueMapper
is provided that can map from the
KeyValue
of the left hand side KStream
to the key of the right hand side GlobalKTable
.
A GlobalKTable
is created via a StreamsBuilder
. For example:
builder.globalTable("topic-name", "queryable-store-name");
all GlobalKTable
s are backed by a ReadOnlyKeyValueStore
and are therefore queryable via the
interactive queries API.
For example:
final GlobalKTable globalOne = builder.globalTable("g1", "g1-store");
final GlobalKTable globalTwo = builder.globalTable("g2", "g2-store");
...
final KafkaStreams streams = ...;
streams.start()
...
ReadOnlyKeyValueStore view = streams.store("g1-store", QueryableStoreTypes.timestampedKeyValueStore());
view.get(key); // can be done on any key, as all keys are present
Note that in contrast to KTable
a GlobalKTable
's state holds a full copy of the underlying topic,
thus all keys can be queried locally.
Records from the source topic that have null keys are dropped.
Modifier and Type | Method and Description |
---|---|
String |
queryableStoreName()
Get the name of the local state store that can be used to query this
GlobalKTable . |
String queryableStoreName()
GlobalKTable
.null
if this GlobalKTable
cannot be queried.