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https://issues.apache.org/jira/browse/KAFKA-4212?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16882449#comment-16882449
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James Ritt commented on KAFKA-4212:
-----------------------------------
Thanks [~ableegoldman] & [~mjsax]! So I took a look at
[`RocksDBConfigSetter`|https://github.com/apache/kafka/blob/trunk/streams/src/main/java/org/apache/kafka/streams/state/RocksDBConfigSetter.java#L45]
and my current understanding is that its `setConfig` method is used to mutate
the provided `org.rocksdb.Options` before it's subsequently passed into the
rocks DB constructor. Unfortunately, ttl doesn't seem to be configurable within
`org.rocksdb.Options`, and instead, as far as I can tell, the usage of the
TtlDB would instead need to be enacted by using the appropriate constructor
[here|https://github.com/apache/kafka/blob/trunk/streams/src/main/java/org/apache/kafka/streams/state/internals/RocksDBStore.java#L191].
Please let me know if I'm missing something, but given the above, the next
approach I was considering was adding a StreamsConfig rocksDbTtl setting
similar to [here;|https://github.com/apache/kafka/pull/2159/files] your
thoughts?
> Add a key-value store that is a TTL persistent cache
> ----------------------------------------------------
>
> Key: KAFKA-4212
> URL: https://issues.apache.org/jira/browse/KAFKA-4212
> Project: Kafka
> Issue Type: Improvement
> Components: streams
> Affects Versions: 0.10.0.1
> Reporter: Elias Levy
> Priority: Major
> Labels: api
>
> Some jobs needs to maintain as state a large set of key-values for some
> period of time. I.e. they need to maintain a TTL cache of values potentially
> larger than memory.
> Currently Kafka Streams provides non-windowed and windowed key-value stores.
> Neither is an exact fit to this use case.
> The {{RocksDBStore}}, a {{KeyValueStore}}, stores one value per key as
> required, but does not support expiration. The TTL option of RocksDB is
> explicitly not used.
> The {{RocksDBWindowsStore}}, a {{WindowsStore}}, can expire items via segment
> dropping, but it stores multiple items per key, based on their timestamp.
> But this store can be repurposed as a cache by fetching the items in reverse
> chronological order and returning the first item found.
> KAFKA-2594 introduced a fixed-capacity in-memory LRU caching store, but here
> we desire a variable-capacity memory-overflowing TTL caching store.
> Although {{RocksDBWindowsStore}} can be repurposed as a cache, it would be
> useful to have an official and proper TTL cache API and implementation.
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