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https://issues.apache.org/jira/browse/SPARK-3376?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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uncleGen updated SPARK-3376:
----------------------------
Component/s: Shuffle
> Memory-based shuffle strategy to reduce overhead of disk I/O
> ------------------------------------------------------------
>
> Key: SPARK-3376
> URL: https://issues.apache.org/jira/browse/SPARK-3376
> Project: Spark
> Issue Type: Planned Work
> Components: Shuffle
> Affects Versions: 1.1.0
> Reporter: uncleGen
> Priority: Trivial
>
> I think a memory-based shuffle can reduce some overhead of disk I/O. I just
> want to know is there any plan to do something about it. Or any suggestion
> about it. Base on the work (SPARK-2044), it is feasible to have several
> implementations of shuffle.
> ----------------------------------------------------------------------------------------------------------------------------------------------------------------
> Currently, there are two implementions of shuffle manager, i.e. SORT and
> HASH. Both of them will use disk in some stages. For examples, in the map
> side, all the intermediate data will be written into temporary files. In the
> reduce side, Spark will use external sort sometimes. In any case, disk I/O
> will bring some performance loss. Maybe，we can provide a pure-memory shuffle
> manager. In this shuffle manager, intermediate data will only go through
> memory. In some of scenes, it can improve performance. Experimentally, I
> implemented a in-memory shuffle manager upon SPARK-2044. Following is my
> testing result:
> | data size | partitions | resources |
> | 5131859218 | 2000 | 50 executors/ 4 cores/ 4GB |
> | settings | operation1 |
> operation2 |
> | shuffle spill & lz4 | repartition+flatMap+groupByKey | repartition +
> groupByKey |
> |memory | 38s | 16s |
> |sort | 45s | 28s |
> |hash | 46s | 28s |
> |no shuffle spill & lz4 | | |
> | memory | 16s | 16s |
> | | | |
> |shuffle spill & lzf | | |
> |memory| 28s | 27s |
> |sort | 29s | 29s |
> |hash | 41s | 30s |
> |no shuffle spill & lzf | | |
> | memory | 15s | 16s |
> In my implementation, I simply reused the "BlockManager" in the map-side and
> set the "spark.shuffle.spill" false in the reduce-side. All the intermediate
> data is cached in memory store. Future work include but not only:
> - memory usage management in "InMemory Shuffle" mode
> - data management when intermediate data can not fit in memory
> Test code：
> {code: borderStyle=solid}
> val conf = new SparkConf().setAppName("InMemoryShuffleTest")
> val sc = new SparkContext(conf)
> val dataPath = args(0)
> val partitions = args(1).toInt
> val rdd1 = sc.textFile(dataPath).cache()
> rdd1.count()
> val startTime = System.currentTimeMillis()
> val rdd2 = rdd1.repartition(partitions)
> .flatMap(_.split(",")).map(s => (s, s))
> .groupBy(e => e._1)
> rdd2.count()
> val endTime = System.currentTimeMillis()
> println("time: " + (endTime - startTime) / 1000 )
> {code}
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