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From "Jay Kreps (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (KAFKA-3777) Extract the LRU cache out of RocksDBStore
Date Fri, 03 Jun 2016 00:20:59 GMT

    [ https://issues.apache.org/jira/browse/KAFKA-3777?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15313382#comment-15313382
] 

Jay Kreps commented on KAFKA-3777:
----------------------------------

Probably everyone already knows but just want to capture a couple of goals of that cache originally:
1. Avoid serialization and deserialization with the read AND write to/from RocksDB
2. Avoid the write to kafka and rocksdb for duplicate updates
3. Allow doing larger batch writes to rocksdb which seemed to significantly cut down on overhead

A long time ago in Samza we had done some benchmarking of each of these. At that time (3)
was a big across the board impact, and (1) and (2) really depend on the cachability of the
read and write stream.

I also think that this was done originally with leveldb and then an early version of rocksdb
and many things may have changed since then, particularly, (a) I am not sure if the batch
write thing matters any more, (b) I think they added a way to disable logging entirely which
should be a big win as long as we handle recovery from kafka in cases of unclean shutdown.

> Extract the LRU cache out of RocksDBStore
> -----------------------------------------
>
>                 Key: KAFKA-3777
>                 URL: https://issues.apache.org/jira/browse/KAFKA-3777
>             Project: Kafka
>          Issue Type: Sub-task
>          Components: streams
>    Affects Versions: 0.10.1.0
>            Reporter: Eno Thereska
>             Fix For: 0.10.1.0
>
>
> The LRU cache that is currently inside the RocksDbStore class. As part of KAFKA-3776
it needs to come outside of RocksDbStore and be a separate component used in:
> 1. KGroupedStream.aggregate() / reduce(), 
> 2. KStream.aggregateByKey() / reduceByKey(),
> 3. KTable.to() (this will be done in KAFKA-3779).
> As all of the above operators can have a cache on top to deduplicate the materialized
state store in RocksDB.
> The scope of this JIRA is to extract out the cache of RocksDBStore, and keep them as
item 1) and 2) above; and it should be done together / after KAFKA-3780.



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