Status

Current state: Under Discussion

Discussion thread: here 

JIRA: KAFKA-4499

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Motivation

Currently, both KTable and windowed-KTable stores can be queried via IQ feature. While ReadOnlyKeyValueStore(for KTable stores) provide method all() to scan the whole store (ie, returns an iterator over all stored key-value pairs), there is no similar API for ReadOnlyWindowStore (for windowed-KTable stores).

This limits the usage of a windowed store, because the user needs to know what keys are stored in order the query it. 

Public Interface

Methods similar to the ones found in ReadOnlyKeyValueStore will be introduced into the ReadOnlyWindowStore interface. They are the following:

     /**
     * Gets the latest window for each distinctive key.
     * 
     * @returns an iterator over windowed key-value pairs {@code <Windowed<K>, value>}
     * @throws InvalidStateStoreException if the store is not initialized
     * @throws NullPointerException if null is used for any key
     */
     Collection<Windowed<K>> range(long timeFrom, long timeTo);
     /**
     * Returns the minimum key in existing windows.
     * 
     * @returns a {@code Windowed<K>} value
     * @throws InvalidStateStoreException if the store is not initialized
     * @throws NullPointerException if null is used for any key
     */
     Windowed<K> minKey();
    
     /**
     * Returns the maximum key in existing windows
     * 
     * @returns a {@code Windowed<K>} value
     * @throws InvalidStateStoreException if the store is not initialized
     * @throws NullPointerException if null is used for any key
     */
     Windowed<K> maxKey();

Proposed Changes

With the need to test the implementation of these methods in mind, the ReadOnlyWindowStoreStub class will implement these additions (i.e. @Override public Collection<Windowed<K>> range(long timeFrom, long timeTo){...}). The corresponding test will also be modified. (e.g. @Test public void testRange(){...}) 

Following the changes in ReadOnlyWindowStore, CachingWindowStore and other WindowStore API will implement these changes accordingly.

Compatibility, Deprecation, and Migration Plan

Rejected Alternatives