THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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Status
Current state: Under Discussion Accepted
Discussion thread: here
JIRA: here KAFKA-4490
Released: 0.10.2
Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).
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A new interface to represent the GlobalKTable. This interface is deliberately restrictive as its primary purpose is to enable non-key joins without having to do any re-partitioning.
The joins between GlobalKTables are never materialized to a Physical StateStore, and aren't backed by another change-log topic. Instead they are just a view on top of the joined GlobalKTables and the joins are resolved on demand.
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// Represents a Table that is fully replicated on each KafkaStreams instance
public interface GlobalKTable<K, V> {
<K1, V1, R> GlobalKTable<K, R> join(final GlobalKTable<K1, V1> other,
final KeyValueMapper<K, V, K1> keyMapper,
final ValueJoiner<V, V1, R> joiner
final String queryableViewName);
<K1, V1, R> GlobalKTable<K, R> leftJoin(final GlobalKTable<K1, V1> other,
final KeyValueMapper<K, V, K1> keyMapper,
final ValueJoiner<V, V1, R> joiner,
final String queryableViewName);
}
}
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KStream
Add overloaded methods for joining with GlobalKTable
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/** * perform a left join with a GlobalKTable using the provided KeyValueMapper * to map from the (key, value) of the KStream to the key of the GlobalKTable */ <K1, V1, R> KStream<K, R> leftJoin(final GlobalKTable<K1, V1> replicatedTable, final KeyValueMapper<K, V, K1> keyValueMapper, final ValueJoiner<V, V1, R> valueJoiner); /** * perform a join with a GlobalKTable using the provided KeyValueMapper * to map from the (key, value) of the KStream to the key of the GlobalKTable */ <K1, V1, V2> KStream<K, V2> join(final GlobalKTable<K1, V1> table, final KeyValueMapper<K, V, K1> keyValueMapper, final ValueJoiner<V, V1, V2> joiner); |
KTable
Add overloaded methods for joining with GlobalKTable
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/**
* perform a join with a GlobalKTable using the provided KeyValueMapper
* to map from the (key, value) of the KTable to the key of the GlobalKTable
*/
<K1, V1, R> KTable<K, R> join(final GlobalKTable<K1, V1> globalTable,
final KeyValueMapper<K, V, K1> keyMapper,
final ValueJoiner<V, V1, R> joiner);
/**
* perform a left join with a GlobalKTable using the provided KeyValueMapper
* to map from the (key, value) of the KTable to the key of the GlobalKTable
*/
<K1, V1, R> KTable<K, R> leftJoin(final GlobalKTable<K1, V1> globalTable,
final KeyValueMapper<K, V, K1> keyMapper,
final ValueJoiner<V, V1, R> joiner); |
KStreamBuilder
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/**
* Add a GlobalKTable to the topology using the provided Serdes
*/
public <K, V> GlobalKTable<K, V> globalTable(final Serde<K> keySerde,
final Serde<V> valSerde,
final String topic,
final String storeName)
/**
* Add a GlobalKTable to the topology using default Serdes
*/
public <K, V> GlobalKTable<K, V> globalTable(final String topic,
final String storeName) |
TopologyBuilder
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// add a Global Store that is backed by a source topic to the TopologyBuilder public synchronized TopologyBuilder addGlobalStore(final StateStore store, final String sourceName, final Deserializer keyDeserializer, final DeserializerString valueDeserializersourceName, final StringDeserializer topickeyDeserializer, final StringDeserializer processorNamevalueDeserializer, final ProcessorSupplier stateUpdateSupplier) // A method to add Global Stores that are not backed by afinal sourceString topic, i.e., the view that is the result of a join between two GlobalKTables public synchronized TopologyBuilder addGlobalStore(final StateStore store) final String processorName, final ProcessorSupplier stateUpdateSupplier) // All Global State Stores will be part of a single ProcessorTopology // this provides an easy way to build that topology public synchronized ProcessorTopology buildGlobalStateTopology(); // Retrieve the Global State Stores from the builder. public synchronized Map<String, StateStore> builder.globalStateStores() |
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On close of the GlobalKTable, we will write out a checkpoint file to the global table’s state directory, located under the global sub-directory of StreamsConfig.STATE_DIR_CONFIG, i.e, /state.dir/appId/global, containing the current offset for each partition in the GlobalKTable. The checkpoint file will be used to recover during restarts. On restart we will first check for the existence of the checkpoint file, if it exists we will read in the current offsets for each partition and seek to those offsets and start consuming. In the event the checkpoint file doesn’t exist, we will restore from the earliest offset.
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Replicating per thread: Doesn’t provide any benefit beyond per instance, but adds additional replication overhead
- Introduce a broadcastJoin() API that uses the existing KTable interface and automatically converts it, internally, to a global table. The feeling is that this would muddy the API, i.e. it is better to be explicit with the type.
- Supporting GlobalKTable to GlobalKTable outerJoin: There are many constraints around outerJoin that we cannot check during the building of the outerJoin at runtime. Further this would require KeyValueMappers in both directionsjoins: In order to fully support bi-directional joins would require KeyValueMappers , and either materializing the outerJoin join in a Physical StateStore, i.e., RocksDB, or by having yet another interface to Map from the key of the outerJoin join table to the keys of both input tables. We decided that for now we will not support outerJoin GlobalKTable/GlobalKTable joins, but revisit in the future should the need arise.