kafka-streams-internals-CachingKeyValueStore.adoc

CachingKeyValueStore

CachingKeyValueStore is a concrete KeyValueStore of Bytes keys and byte[] values (i.e. KeyValueStore<Bytes, byte[]>).

CachingKeyValueStore is also a concrete WrappedStateStore of KeyValueStore of Bytes keys and byte[] values (i.e. WrappedStateStore<KeyValueStore<Bytes, byte[]>, byte[], byte[]>).

CachingKeyValueStore is a concrete CachedStateStore.

CachingKeyValueStore is created when:

• KeyValueStoreBuilder is requested to build a KeyValueStore with caching enabled

• TimestampedKeyValueStoreBuilder is requested to build a TimestampedKeyValueStore with caching enabled

CachingKeyValueStore takes a single KeyValueStore (underlying state store) to be created.

Initializing State Store — init Method

void init(
  ProcessorContext context,
  StateStore root)

Note	init is part of the StateStore Contract to initialize the state store.

init initInternal with the ProcessorContext.

init then requests the underlying KeyValueStore to initialize.

In the end, init saves the current thread as the streamThread internal registry.

initInternal Internal Method

void initInternal(ProcessorContext context)

initInternal saves the ProcessorContext as the context internal registry.

initInternal requests the InternalProcessorContext for a ThreadCache that is saved as the cache internal registry.

initInternal creates the name of the cache for the task ID and the store name and that is saved as the cacheName internal registry.

In the end, initInternal requests the ThreadCache to addDirtyEntryFlushListener with the cache name and a DirtyEntryFlushListener that simply putAndMaybeForward the DirtyEntries.

Note	initInternal is used exclusively when CachingKeyValueStore is requested to initialize.

putAndMaybeForward Internal Method

void putAndMaybeForward(
  ThreadCache.DirtyEntry entry,
  InternalProcessorContext context)

putAndMaybeForward…​FIXME

Note	putAndMaybeForward is used exclusively when CachingKeyValueStore is requested to initialize (via initInternal).

remove Method

void remove(final Windowed<Bytes> sessionKey)

Note	remove is part of SessionStore Contract to…​FIXME.

remove…​FIXME

Closing State Store — close Method

void close()

Note	close is part of…​FIXME

close…​FIXME

Internal Properties

Name	Description
cache	ThreadCache Used when…​FIXME
cacheName
context	InternalProcessorContext Used when…​FIXME
streamThread	Thread Used when…​FIXME