Leah Thomas created KAFKA-13811:
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             Summary: Investigate sliding windows performance
                 Key: KAFKA-13811
                 URL: https://issues.apache.org/jira/browse/KAFKA-13811
             Project: Kafka
          Issue Type: Task
          Components: streams
            Reporter: Leah Thomas


We recently fixed a bug in sliding windows so that a grace period of 0ms is 
properly calculated, see https://issues.apache.org/jira/browse/KAFKA-13739. 
Before this patch, sliding windows with a grace period of 0ms would just skip 
all records so nothing would get put into the store.

When we ran benchmarks for the 3.2 release we saw a significant drop in 
performance for sliding windows on both the 3.2 and trunk branches, see the 
`sliding windows` results 
[here|[http://kstreams-benchmark-results.s3-website-us-west-2.amazonaws.com/summaries/process-cumulative-rate/graph.html].]
 These benchmarks use a sliding window with a 0ms grace period, which means 
until now we weren't sending any values to the state store when running these 
benchmarks.

I ran benchmarks on the 
[commit|https://github.com/apache/kafka/commit/430f9c99012d1585aa544d4dadf449963296c1fd]
 before KAFKA-13739 and changed the grace period to 2 seconds to see if the bug 
fix changed anything. The performance was still low for [this 
run|[http://kstreams-benchmark-results.s3-website-us-west-2.amazonaws.com/experiments/sliding1min-3-5-3-3-0-430f9c9901-leah-20220408084241-streamsbench/].]

Given this, it seems like the performance for sliding windows has always been 
low but we didn't realize it because the bug fixed in KAFKA-13739 was present 
in the benchmarks we were running. We should investigate why the current 
algorithm is slow and see if improvements can be made



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