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https://issues.apache.org/jira/browse/SPARK-23650?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16404198#comment-16404198
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Felix Cheung commented on SPARK-23650:
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Is there a reason for the broadcast?
Could you instead distribute the .rds to all the executor and then call readRDS
from within your UDF?
I understand this approach has been done quite a bit.
> Slow SparkR udf (dapply)
> ------------------------
>
> Key: SPARK-23650
> URL: https://issues.apache.org/jira/browse/SPARK-23650
> Project: Spark
> Issue Type: Improvement
> Components: Spark Shell, SparkR, Structured Streaming
> Affects Versions: 2.2.0
> Reporter: Deepansh
> Priority: Major
> Attachments: sparkR_log2.txt, sparkRlag.txt
>
>
> For eg, I am getting streams from Kafka and I want to implement a model made
> in R for those streams. For this, I am using dapply.
> My code is:
> iris_model <- readRDS("./iris_model.rds")
> randomBr <- SparkR:::broadcast(sc, iris_model)
> kafka <- read.stream("kafka",subscribe = "source", kafka.bootstrap.servers =
> "localhost:9092", topic = "source")
> lines<- select(kafka, cast(kafka$value, "string"))
> schema<-schema(lines)
> df1<-dapply(lines,function(x){
> i_model<-SparkR:::value(randomMatBr)
> for (row in 1:nrow(x))
> { y<-fromJSON(as.character(x[row,"value"])) y$predict=predict(i_model,y)
> y<-toJSON(y) x[row,"value"] = y }
> x
> },schema)
> Every time when Kafka streams are fetched the dapply method creates new
> runner thread and ships the variables again, which causes a huge lag(~2s for
> shipping model) every time. I even tried without broadcast variables but it
> takes same time to ship variables. Can some other techniques be applied to
> improve its performance?
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