[SPARK-24025] Join of bucketed and non-bucketed tables can give two exchanges and sorts for non-bucketed side

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Incomplete
• Affects Version/s: 2.3.0, 2.3.1
• Component/s: SQL
• Labels: bulk-closed

Environment

./bin/spark-shell --version
Welcome to
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/ __/__ ___ _____/ /__
_\ \/ _ \/ _ `/ __/ '_/
/___/ .__/\_,_/_/ /_/\_\ version 2.3.0
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Using Scala version 2.11.8, Java HotSpot(TM) 64-Bit Server VM, 1.8.0_162
Branch master
Compiled by user sameera on 2018-02-22T19:24:29Z
Revision a0d7949896e70f427e7f3942ff340c9484ff0aab
Url [e-mail]:sameeragarwal/spark.git
Type --help for more information.

• Assignee: Unassigned
• Reporter: Jacek Laskowski
• Created: 19/Apr/18 11:27
• Updated: 12/Dec/22 18:11
• Resolved: 08/Oct/19 05:41

Description

While exploring bucketing I found the following join query of non-bucketed and bucketed tables that ends up with two exchanges and two sorts in the physical plan for the non-bucketed join side.

// Make sure that you don't end up with a BroadcastHashJoin and a BroadcastExchange
// Disable auto broadcasting
spark.conf.set("spark.sql.autoBroadcastJoinThreshold", -1)

val bucketedTableName = "bucketed_4_id"
val large = spark.range(1000000)
large.write
  .bucketBy(4, "id")
  .sortBy("id")
  .mode("overwrite")
  .saveAsTable(bucketedTableName)

// Describe the table and include bucketing spec only
val descSQL = sql(s"DESC FORMATTED $bucketedTableName").filter($"col_name".contains("Bucket") || $"col_name" === "Sort Columns")
scala> descSQL.show(truncate = false)
+--------------+---------+-------+
|col_name      |data_type|comment|
+--------------+---------+-------+
|Num Buckets   |4        |       |
|Bucket Columns|[`id`]   |       |
|Sort Columns  |[`id`]   |       |
+--------------+---------+-------+

val bucketedTable = spark.table(bucketedTableName)
val t1 = spark.range(4)
  .repartition(2, $"id")  // Use just 2 partitions
  .sortWithinPartitions("id") // sort partitions

val q = t1.join(bucketedTable, "id")
// Note two exchanges and sorts
scala> q.explain
== Physical Plan ==
*(5) Project [id#79L]
+- *(5) SortMergeJoin [id#79L], [id#77L], Inner
   :- *(3) Sort [id#79L ASC NULLS FIRST], false, 0
   :  +- Exchange hashpartitioning(id#79L, 4)
   :     +- *(2) Sort [id#79L ASC NULLS FIRST], false, 0
   :        +- Exchange hashpartitioning(id#79L, 2)
   :           +- *(1) Range (0, 4, step=1, splits=8)
   +- *(4) Sort [id#77L ASC NULLS FIRST], false, 0
      +- *(4) Project [id#77L]
         +- *(4) Filter isnotnull(id#77L)
            +- *(4) FileScan parquet default.bucketed_4_id[id#77L] Batched: true, Format: Parquet, Location: InMemoryFileIndex[file:/Users/jacek/dev/oss/spark/spark-warehouse/bucketed_4_id], PartitionFilters: [], PushedFilters: [IsNotNull(id)], ReadSchema: struct<id:bigint>

q.foreach(_ => ())

Issue Links

• is related to: SPARK-17570 Avoid Hash and Exchange in Sort Merge join if bucketing factor is multiple for tables