[jira] [Created] (KAFKA-9551) Alternate WindowKeySchema Implementations

["Michael Viamari (Jira)" <ji...@apache.org>]

Michael Viamari created KAFKA-9551:
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             Summary: Alternate WindowKeySchema Implementations
                 Key: KAFKA-9551
                 URL: https://issues.apache.org/jira/browse/KAFKA-9551
             Project: Kafka
          Issue Type: Improvement
            Reporter: Michael Viamari


Currently, the {{WindowKeySchema}} used by all {{WindowStore}} implementations serializes the key with window information as {{keyBytes + timestampBytes + seqNumByte}}. This is optimal for iterations and queries that have a fixed key with a variable time window (which I think is leveraged in KStream-KStream join windows).

 

In cases where the time-window is fixed, but the key range is variable, there is a significant overhead for iteration: all time-windows for a given key must be traversed. The iteration only uses 1 out of every N keys, where N is the number of windows.

A key serialization format that is structured as {{timestampBytes}} + {{keyBytes + seqNumByte}} would be much more efficient when iterating over keys in a fixed window.

Implementing a custom {{KeySchema}} is not easy at the moment. Currently, {{WindowKeySchema}} is instantiated when supplying a RocksDB instance in {{RocksDbWindowBytesStoreSupplier}}, but most/all other references to a {{KeySchema}} use static functions on {{WindowKeySchema}}. This makes supporting an alternate {{KeySchema}} very challenging. Additionally, making a custom implementation of {{KeySchema}} is complicated by the fact that although {{RocksDBSegmentedBytesStore.KeySchema}} is a public interface, the interface depends on {{HasNextCondition}} which is package-private to {{org.apache.kafka.streams.state.internals}}.



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