Yu Zhong created SPARK-33933:
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Summary: Broadcast timeout happened unexpectedly in AQE
Key: SPARK-33933
URL: https://issues.apache.org/jira/browse/SPARK-33933
Project: Spark
Issue Type: Bug
Components: SQL
Affects Versions: 3.0.1, 3.0.0
Reporter: Yu Zhong
In Spark 3.0, when AQE is enabled, there is often broadcast timeout in normal
queries as below.
{code:java}
Could not execute broadcast in 300 secs. You can increase the timeout for
broadcasts via spark.sql.broadcastTimeout or disable broadcast join by setting
spark.sql.autoBroadcastJoinThreshold to -1
{code}
This is usually happens when broadcast join(with or without hint) after a long
running shuffle (more than 5 minutes). By disable AQE, the issues disappear.
The workaround is to increase spark.sql.broadcastTimeout and it works. But
because the data to broadcast is very small, that doesn't make sense.
After investigation, the root cause should be like this: when enable AQE, in
getFinalPhysicalPlan, spark traversal the physical plan bottom up and create
query stage for materialized part by createQueryStages and materialize those
new created query stages to submit map stages or broadcasting. When
ShuffleQueryStage are materializing before BroadcastQueryStage, the map job and
broadcast job are submitted almost at the same time, but map job will hold all
the computing resources. If the map job runs slow (when lots of data needs to
process and the resource is limited), the broadcast job cannot be started(and
finished) before spark.sql.broadcastTimeout, thus cause whole job failed
(introduced in SPARK-31475).
Code to reproduce:
{code:java}
import java.util.UUID
import scala.util.Random
import org.apache.spark.sql.functions._
import org.apache.spark.sql.SparkSession
val spark = SparkSession.builder()
.master("local[2]")
.appName("Test Broadcast").getOrCreate()
import spark.implicits._
val sc = spark.sparkContext
sc.setLogLevel("INFO")
val uuid = UUID.randomUUID
val df = sc.parallelize(Range(0, 10000), 10000).flatMap(x => {
for (i <- Range(0, 10000 + Random.nextInt(10000)))
yield (x % 26, x, Random.nextInt(10), UUID.randomUUID.toString)
}).toDF("index", "part", "pv", "uuid")
.withColumn("md5", md5($"uuid"))
val dim_data = Range(0, 26).map(x => (('a' + x).toChar.toString, x))
val dim = dim_data.toDF("name", "index")
val result = df.groupBy("index")
.agg(sum($"pv").alias("pv"), countDistinct("uuid").alias("uv"))
.join(dim, Seq("index"))
.collect(){code}
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