Spark没有将负载均匀地分配给任务
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【中文标题】Spark没有将负载均匀地分配给任务【英文标题】：Spark not distributing load to tasks evenly 【发布时间】：2015-12-02 16:49:27 【问题描述】：RDD.saveAsTextFile 最后阶段很慢。我怀疑记录没有均匀分布在分区和任务中的问题。有什么办法可以强制吗？
public static JavaRDD<String> getJsonUserIdVideoIdRDD(JavaRDD<Rating> cachedRating,
JavaPairRDD<Integer, Integer> userIdClusterId,
int numPartitions, String outDir)
/*
convert the JavaRDD<Rating> to JavaPairRDD<Integer,DmRating>
*/
JavaPairRDD<Integer,DmRating> userIdDmRating = cachedRating.mapToPair(new PairFunction<Rating, Integer, DmRating>()
public Tuple2<Integer, DmRating> call(Rating dmRating) throws Exception
return new Tuple2<>(dmRating.user(), (DmRating)dmRating);
);
/*
join this RDD with userIdClusterID RDD by key
*/
JavaPairRDD<Integer, Tuple2<Integer, DmRating>> userId_T_clusterIdDmRating = userIdClusterId.join(userIdDmRating, numPartitions);
// extract the clusterId to videoId map
JavaPairRDD<Integer, Integer> clusterIdVideoId = userId_T_clusterIdDmRating.mapToPair(new PairFunction<Tuple2<Integer, Tuple2<Integer,DmRating>>, Integer, Integer>()
public Tuple2<Integer, Integer> call(Tuple2<Integer, Tuple2<Integer, DmRating>> userIdDmRatingClusterId ) throws Exception
Integer userId = userIdDmRatingClusterId._1();
Tuple2<Integer, DmRating> dmRatingClusterId = userIdDmRatingClusterId._2();
return new Tuple2<Integer, Integer>(dmRatingClusterId._1(), dmRatingClusterId._2().product());
);
//////
/// Count the popularity of a video in a cluster
JavaPairRDD<String, Integer> clusterIdVideoIdStrInt = clusterIdVideoId.mapToPair(new PairFunction<Tuple2<Integer, Integer>, String, Integer>()
@Override
public Tuple2<String, Integer> call(Tuple2<Integer, Integer> videoIdClusterId) throws Exception
return new Tuple2<>(String.format("%d:%d", videoIdClusterId._1(), videoIdClusterId._2()), 1);
);
JavaPairRDD<String, Integer> clusterIdVideoIdStrCount = clusterIdVideoIdStrInt.reduceByKey(new Function2<Integer, Integer, Integer>()
@Override
public Integer call(Integer v1, Integer v2) throws Exception
return v1+v2;
);
///
JavaPairRDD<Integer, Tuple2<Integer, Integer>> clusterId_T_videoIdCount = clusterIdVideoIdStrCount.mapToPair(new PairFunction<Tuple2<String, Integer>, Integer, Tuple2<Integer, Integer>>()
@Override
public Tuple2<Integer, Tuple2<Integer, Integer>> call(Tuple2<String, Integer> clusterIdVideoIdStrCount) throws Exception
String[] splits = clusterIdVideoIdStrCount._1().split(":");
try
if(splits.length==2)
int clusterId = Integer.parseInt(splits[0]);
int videoId = Integer.parseInt(splits[1]);
return new Tuple2<>(clusterId, new Tuple2<>(videoId, clusterIdVideoIdStrCount._2()));
else
//Should never occur
LOGGER.error("Could not split into two with : as the separator!", clusterIdVideoIdStrCount._1());
catch (NumberFormatException ex)
LOGGER.error(ex.getMessage());
return new Tuple2<>(-1, new Tuple2<>(-1,-1));
);
JavaPairRDD<Integer, Iterable<Tuple2<Integer, Integer>>> clusterIdVideoIdGrouped = clusterId_T_videoIdCount.groupByKey();
JavaPairRDD<Integer, DmRating> clusterIdDmRating = userId_T_clusterIdDmRating.mapToPair(new PairFunction<Tuple2<Integer, Tuple2<Integer, DmRating>>, Integer, DmRating>()
@Override
public Tuple2<Integer, DmRating> call(Tuple2<Integer, Tuple2<Integer, DmRating>> userId_T_clusterIdDmRating) throws Exception
return userId_T_clusterIdDmRating._2();
);
JavaPairRDD<Integer, Tuple2<DmRating, Iterable<Tuple2<Integer, Integer>>>> clusterId_T_DmRatingVideoIds = clusterIdDmRating.join(clusterIdVideoIdGrouped, numPartitions);
JavaPairRDD<Integer, String> userIdStringRDD = clusterId_T_DmRatingVideoIds.mapToPair(new PairFunction<Tuple2<Integer, Tuple2<DmRating, Iterable<Tuple2<Integer, Integer>>>>, Integer, String>()
@Override
public Tuple2<Integer, String> call(Tuple2<Integer, Tuple2<DmRating, Iterable<Tuple2<Integer, Integer>>>> v1) throws Exception
int clusterId = v1._1();
Tuple2<DmRating, Iterable<Tuple2<Integer, Integer>>> tuple = v1._2();
DmRating rating = tuple._1();
Iterable<Tuple2<Integer, Integer>> videosCounts= tuple._2();
StringBuilder recosStr = new StringBuilder();
boolean appendComa = false;
for(Tuple2<Integer, Integer> videoCount : videosCounts)
if(appendComa) recosStr.append(",");
recosStr.append("");
recosStr.append("\"video_id\":");
recosStr.append(videoCount._1());
recosStr.append(",");
recosStr.append("\"count\":");
recosStr.append(videoCount._2());
recosStr.append("");
appendComa = true;
String val = String.format("\"user_id\":\"%s\",\"v1st\":\"%s\",\"redis_uid\":%s,\"cluster_id\": %d,\"recommendations\":[ %s ]", rating.dmUserId, rating.dmV1stStr, rating.user(), clusterId, recosStr);
return new Tuple2<Integer, String>(rating.user(), val);
);
JavaPairRDD<Integer, Iterable<String>> groupedRdd = userIdStringRDD.groupByKey(numPartitions);
JavaRDD<String> jsonStringRdd = groupedRdd.map(new Function<Tuple2<Integer, Iterable<String>>, String>()
@Override
public String call(Tuple2<Integer, Iterable<String>> v1) throws Exception
for(String str : v1._2())
return str;
LOGGER.error("Could not fetch a string from iterable so returning empty");
return "";
);
//LOGGER.info("Number of items in RDD: ", jsonStringRDD.count());
//return jsonStringRDD.persist(StorageLevel.MEMORY_ONLY_SER_2());
LOGGER.info("Repartitioning the data into ", numPartitions );
jsonStringRdd.cache().saveAsTextFile(outDir);
return jsonStringRdd;
集群大小： 1. 主控：16 CPU，32GB 2. Workers 4 : 32CPU, 102GB, 4X375GB SSD 驱动器
我将代码更改为使用 DataFrames。还是一样的问题
public static void saveAlsKMeansRecosAsParquet(JavaPairRDD<Integer, Tuple2<DmRating, Integer>> userIdRatingClusterIdRDD,
int numPartitions,
JavaSparkContext javaSparkContext,
String outdir)
JavaRDD<DmRating> dmRatingJavaRDD = userIdRatingClusterIdRDD.map(new Function<Tuple2<Integer, Tuple2<DmRating, Integer>>, DmRating>()
public DmRating call(Tuple2<Integer, Tuple2<DmRating, Integer>> v1) throws Exception
//Integer userId = v1._1();
Tuple2<DmRating, Integer> values = v1._2();
DmRating rating = values._1();
Integer clusterId = values._2();
rating.setClusterId(clusterId);
rating.setVideoId(rating.product());
rating.setV1stOrUserId((rating.userId== null || rating.userId.isEmpty())? rating.v1stId : rating.userId);
rating.setRedisId(rating.user());
return rating;
//return String.format("\"clusterId\": %s,\"userId\": %s, \"userId\":\"%s\", \"videoId\": %s", clusterId, userId, rating.userId, rating.product());
);
SQLContext sqlContext = new SQLContext(javaSparkContext);
DataFrame dmRatingDF = sqlContext.createDataFrame(dmRatingJavaRDD, DmRating.class);
dmRatingDF.registerTempTable("dmrating");
DataFrame clusterIdVideoIdDF = sqlContext.sql("SELECT clusterId, videoId FROM dmrating").cache();
DataFrame rolledupClusterIdVideoIdDF = clusterIdVideoIdDF.rollup("clusterId","videoId").count().cache();
DataFrame clusterIdUserIdDF = sqlContext.sql("SELECT clusterId, userId, redisId, v1stId FROM dmrating").distinct().cache();
JavaRDD<Row> rolledUpRDD = rolledupClusterIdVideoIdDF.toJavaRDD();
JavaRDD<Row> filteredRolledUpRDD = rolledUpRDD.filter(new Function<Row, Boolean>()
@Override
public Boolean call(Row v1) throws Exception
//make sure the size and values of the properties are correct
return !(v1.size()!=3 || v1.isNullAt(0) || v1.isNullAt(1) || v1.isNullAt(2));
);
JavaPairRDD<Integer, Tuple2<Integer, Integer>> clusterIdVideoIdCount = filteredRolledUpRDD.mapToPair(new PairFunction<Row, Integer, Tuple2<Integer, Integer>>()
@Override
public Tuple2<Integer, Tuple2<Integer, Integer>> call(Row row) throws Exception
Tuple2<Integer, Integer> videoIdCount = new Tuple2<Integer, Integer>(row.getInt(1), Long.valueOf(row.getLong(2)).intValue());
return new Tuple2<Integer, Tuple2<Integer, Integer>>(row.getInt(0),videoIdCount);
).cache();
JavaPairRDD<Integer, Iterable<Tuple2<Integer, Integer>>> groupedPair = clusterIdVideoIdCount.groupByKey(numPartitions).cache();
JavaRDD<ClusterIdVideos> groupedFlat = groupedPair.map(new Function<Tuple2<Integer, Iterable<Tuple2<Integer, Integer>>>, ClusterIdVideos>()
@Override
public ClusterIdVideos call(Tuple2<Integer, Iterable<Tuple2<Integer, Integer>>> v1) throws Exception
ClusterIdVideos row = new ClusterIdVideos();
Iterable<Tuple2<Integer, Integer>> videosCounts= v1._2();
StringBuilder recosStr = new StringBuilder();
recosStr.append("[");
boolean appendComa = false;
for(Tuple2<Integer, Integer> videoCount : videosCounts)
if(appendComa) recosStr.append(",");
recosStr.append("");
recosStr.append("\"video_id\":");
recosStr.append(videoCount._1());
recosStr.append(",");
recosStr.append("\"count\":");
recosStr.append(videoCount._2());
recosStr.append("");
appendComa = true;
recosStr.append("]");
row.setClusterId(v1._1());
row.setVideos(recosStr.toString());
return row;
).cache();
DataFrame groupedClusterId = sqlContext.createDataFrame(groupedFlat, ClusterIdVideos.class);
DataFrame recosDf = clusterIdUserIdDF.join(groupedClusterId, "clusterId");
recosDf.write().parquet(outdir);
【问题讨论】：
使用“好的，找到了问题。罪魁祸首是 groupBy 和 join 操作。 Spark 网站上的文档说
在 Spark 中，数据通常不会跨分区分布在特定操作的必要位置。在计算过程中，单个任务将在单个分区上操作 - 因此，为了组织单个 reduceByKey 减少任务执行的所有数据，Spark 需要执行 all-to-all 操作。它必须从所有分区中读取以找到所有键的所有值，然后将跨分区的值汇总以计算每个键的最终结果 - 这称为 shuffle。
要优化任何 join/groupByKey 操作，目标应该是减少 shuffle。我发现this deck 对诊断问题很有帮助。尤其是幻灯片12。
我知道集群 ids 数据非常小，每次运行 100 个集群，所以我为较小的表创建了一个广播变量并将其广播给所有执行程序，并使用该变量进行连接。这很有效，将计算时间从 2 小时缩短到 10 分钟。
//convert json string to DF
DataFrame groupedClusterId = sqlContext.read().json(groupedFlat.rdd());
Broadcast<DataFrame> broadcastDataFrame= javaSparkContext.broadcast(groupedClusterId);
DataFrame recosDf = clusterIdUserIdDF.join(broadcastDataFrame.value(),"clusterId");
recosDf.write().parquet(outdir);
【讨论】：
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