# Can I only keep the last message of each keyed entity?

**URL:** <https://forum.confluent.io/t/can-i-only-keep-the-last-message-of-each-keyed-entity/5293>\
**Category:** Kafka Streams\
**Created:** [14 June 2022 12:47 UTC](https://forum.confluent.io/t/can-i-only-keep-the-last-message-of-each-keyed-entity/5293 "2022-06-14T12:47:51Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![vnadkarni](https://sea1.discourse-cdn.com/flex019/user_avatar/forum.confluent.io/vnadkarni/32/1839_2.png) [@vnadkarni](https://forum.confluent.io/u/vnadkarni)\
**Post date:** [14 June 2022 12:47 UTC](https://forum.confluent.io/t/can-i-only-keep-the-last-message-of-each-keyed-entity/5293/1 "2022-06-14T12:47:51Z")

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**SGiuliani**

> Hi guys, I have a question. I have a kafka cluster with a ktable which gets updated as a results of other tables/streams joined together. This table is then converted to a stream whose elements are pushed into a topic which is growing massively in terms of number of elements/size (maybe I should talk in terms of partitions here if you look at the internals). The stream of elements are keyed and I am really only interested in keeping its last value. From what I can see I can control the retention of messages in terms of bytes and millisecond. I was wondering if there’s a way I can only keep the last message of each keyed entity. I know it’s a log, it’s immutable etc… but I need to understand how I can approach this problem. Thanks guys

**Neil Buesing**

> that is what compacted topics are for; and kafka-streams and tables leverages this.
> 
> However, just because the topic is compacted doesn’t mean there are duplicates (just means that older values can be deleted).
> 
> This is one of the reasons Kafka-Streams will fully read in a topic into rockdb on a restart to make sure it is current value.

**Neil Buesing**

> So by taking a table and converting it into a stream this is where it is going from a compacted topic (provided the streams application configured the topic) to a non compacted topic.

**Neil Buesing**

> typically if I need move data from a topic to a stream, I have the topic backing that stream to have a low retention time as the system of record for data in that stream is maintained in the ktable (compacted topic)

**Neil Buesing**

> so the pieces are there to get you what you need (I believe) but the nuances will take a little more understanding of your business needs. 1) maybe you don’t need to take the table and converted to a stream or 2) maybe that stream could be windowed 3) or you do need a stream and you need to lower its retention hand have means to republish from the source ktable as needed.

**SGiuliani**

> Thanks @nbuesing it’s a very good answer