IMPROVING SPARK SQL PERFORMANCE Keiji Yoshida - LINE Corporation 

OASIS 

Agenda 1. Issue 2. Gathering Statistics 3. Injecting Custom Optimization Rules 4. Cost-based Optimizer 

Agenda 1. Issue 2. Gathering Statistics 3. Injecting Custom Optimization Rules 4. Cost-based Optimizer 

Users / Day 1,300+ Spark Apps / Day 7,000+ Spark Jobs / Day 200+ USAGE 

SPARK VERSION AND CONFIGURATION • 2.4.0 • spark.sql.cbo.enabled = false 

SLOW QUERIES Rank Query Count Average Time (min) Total Time (min) 1 Query A 335 20 6,842 2 Query B 28 85 2,380 3 Query C 109 20 2,182 4 Query D 4028 0 1,543 5 Query E 14 105 1,480 

IMPACTS • Speed of data analysis and decision making • Usage efficiency of computing resources 

CHALLENGES FOR END USERS • Acquiring knowledge and skills of data engineering • Taking care of queries’ performances • Changing queries and tables in the production environment 

SOLUTION • Improving queries’ performances on the platform side 

Agenda 1. Issue 2. Gathering Statistics 3. Injecting Custom Optimization Rules 4. Cost-based Optimizer 

GATHERING STATISTICS • 1,500 sec → 60 sec 

QUERY select t.dt, m.name, count(1) from ( select dt, key from db.transaction where dt between '20190211' and '20190217' ) t inner join db.master m on m.key = t.key group by t.dt, m.name 

QUERY select t.dt, m.name, count(1) from ( select dt, key from db.transaction where dt between '20190211' and '20190217' ) t inner join db.master m on m.key = t.key group by t.dt, m.name 1,800,000,000 records 200 records 

PHYSICAL PLAN *(6) HashAggregate(keys=[dt#958, name#970], functions=[count(1)]) +- Exchange hashpartitioning(dt#958, name#970, 200) +- *(5) HashAggregate(keys=[dt#958, name#970], functions=[partial_count(1)]) +- *(5) Project [dt#958, name#970] +- *(5) SortMergeJoin [key#937], [key#960], Inner :- *(2) Sort [key#937 ASC NULLS FIRST], false, 0 : +- Exchange hashpartitioning(key#937, 200) : +- *(1) Project [dt#958, key#937] : +- *(1) Filter isnotnull(key#937) : +- *(1) FileScan orc transaction[key#937,dt#958] Batched: true, Format: ORC, Location:… +- *(4) Sort [key#960 ASC NULLS FIRST], false, 0 +- Exchange hashpartitioning(key#960, 200) +- *(3) Project [key#960, name#970] +- *(3) Filter isnotnull(key#960) +- *(3) FileScan orc master[key#960,name#970] Batched: true, Format: ORC, Location:… 

SORT MERGE JOIN 

BROADCAST HASH JOIN 

AUTO BROADCASTJOIN THRESHOLD • spark.sql.autoBroadcastJoinThreshold = 10 MB 

QUERY select t.dt, m.name, count(1) from ( select dt, key from db.transaction where dt between '20190211' and '20190217' ) t inner join db.master m on m.key = t.key group by t.dt, m.name 1,800,000,000 records 200 records 

PHYSICAL PLAN *(6) HashAggregate(keys=[dt#958, name#970], functions=[count(1)]) +- Exchange hashpartitioning(dt#958, name#970, 200) +- *(5) HashAggregate(keys=[dt#958, name#970], functions=[partial_count(1)]) +- *(5) Project [dt#958, name#970] +- *(5) SortMergeJoin [key#937], [key#960], Inner :- *(2) Sort [key#937 ASC NULLS FIRST], false, 0 : +- Exchange hashpartitioning(key#937, 200) : +- *(1) Project [dt#958, key#937] : +- *(1) Filter isnotnull(key#937) : +- *(1) FileScan orc db.transaction[key#937,dt#958] Batched: true, Format: ORC +- *(4) Sort [key#960 ASC NULLS FIRST], false, 0 +- Exchange hashpartitioning(key#960, 200) +- *(3) Project [key#960, name#970] +- *(3) Filter isnotnull(key#960) +- *(3) FileScan orc db.master[key#960,name#970] Batched: true, Format: ORC 

STATS val q = "select * from db.master” spark.sql(q).queryExecution.optimizedPlan.stats.sizeInBytes → 9223372036854775807 

OASIS.INSERTOVERWRITE spark.sql(q).repartition(filesNum).write().mode(“overwrite”).insertInto(“db.master”) 

OASIS.INSERTOVERWRITE spark.sql(q).repartition(filesNum).write().mode(“overwrite”).insertInto(“db.master”) spark.sql(“analyze table db.master compute statistics noscan”) 

STATS 

STATS val q = "select * from db.master” spark.sql(q).queryExecution.optimizedPlan.stats.sizeInBytes → 8239 

PHYSICAL PLAN *(3) HashAggregate(keys=[dt#149, name#161], functions=[count(1)]) +- Exchange hashpartitioning(dt#149, name#161, 200) +- *(2) HashAggregate(keys=[dt#149, name#161], functions=[partial_count(1)]) +- *(2) Project [dt#149, name#161] +- *(2) BroadcastHashJoin [key#128], [key#151], Inner, BuildRight :- *(2) Project [dt#149, key#128] : +- *(2) Filter isnotnull(key#128) : +- *(2) FileScan orc db.transaction[key#128,dt#149] Batched: true, Format:… +- BroadcastExchange HashedRelationBroadcastMode(List(input[0, string, true])) +- *(1) Project [key#151, name#161] +- *(1) Filter isnotnull(key#151) +- *(1) FileScan orc db.master[key#151,name#161] Batched: true, Format:… 

RESULT • 1,500 sec → 60 sec 

Agenda 1. Issue 2. Gathering Statistics 3. Injecting Custom Optimization Rules 4. Cost-based Optimizer 

INJECTING CUSTOM OPTIMIZATION RULES • 6,000 sec → 200 sec 

QUERY select t.dt, a.area_name, count(distinct uid) from ( select dt, area_code, uid from db.transaction where dt between '20180818' and '20190217' ) t inner join (select * from db.area where dt = ‘20190217’) a on a.area_code = t.area_code group by t.dt, a.area_name 

QUERY select t.dt, a.area_name, count(distinct uid) from ( select dt, area_code, uid from db.transaction where dt between '20180818' and '20190217' ) t inner join (select * from db.area where dt = ‘20190217’) a on a.area_code = t.area_code group by t.dt, a.area_name 4,500,000,000 records 90 records 

PHYSICAL PLAN +- *(5) HashAggregate(...) +- *(5) HashAggregate(...) +- *(5) HashAggregate(...) +- *(5) Project [...] +- *(5) SortMergeJoin [...], Inner :- *(2) Sort [...], false, 0 : +- Exchange hashpartitioning(...) : +- *(1) Project [...] : +- *(1) Filter (...) : +- *(1) FileScan orc db.transaction[...] Batched: true, Format: ORC +- *(4) Sort [...], false, 0 +- Exchange hashpartitioning(...) +- *(3) Filter (...) +- Scan hive db.area [...], HiveTableRelation 

HIVE.STATS.AUTOGATHER 

BROADCAST HINT select /*+ broadcast(r) */ * from records r join src s on r.key = s.key 

CUSTOMIZE OPTIMIZATION spark.experimental.extraOptimizations = MyOptimization :: Nil 

CUSTOMIZE OPTIMIZATION object InsertBroadcastHints extends Rule[LogicalPlan] { val targets = Map(("db", "area") -> "dt") override def apply(plan: LogicalPlan): LogicalPlan = plan transform { case join: Join if isSelectFromTarget(join.left) => join.copy(left = ResolvedHint(join.left, HintInfo(true))) case join: Join if isSelectFromTarget(join.right) => join.copy(right = ResolvedHint(join.right, HintInfo(true))) } private def isSelectFromTarget(plan: LogicalPlan): Boolean = plan match { case p: Project => p.child match { case f: Filter => f.child match { case rel: HiveTableRelation => targets.get(rel.tableMeta.database, rel.tableMeta.identifier.table) match { case Some(pt) => isFilteredByLiteral(f.condition, pt) case None => false } … } private def isFilteredByLiteral(expr: Expression, pt: String): Boolean = ... } spark.experimental.extraOptimizations = InsertBroadcastHints :: Nil 

OPTIMIZED LOGICAL PLAN Aggregate [...] +- Project [...] +- Join Inner, (...) :- Project [...] : +- Filter (...) : +- Relation[...] orc +- ResolvedHint (broadcast) +- Project [...] +- Filter (...) +- HiveTableRelation `db`.`area`, ... 

PHYSICAL PLAN *(4) HashAggregate(...) +- Exchange hashpartitioning(...) +- *(3) HashAggregate(...) +- *(3) HashAggregate(...) +- Exchange hashpartitioning(...) +- *(2) HashAggregate(...) +- *(2) Project [...] +- *(2) BroadcastHashJoin [...], [...], Inner, BuildRight :- *(2) Project [...] : +- *(2) Filter (...) : +- *(2) FileScan orc db.transaction[...] Batched: true, Format: ORC +- BroadcastExchange HashedRelationBroadcastMode(...) +- *(1) Filter (...) +- Scan hive db.area [...], HiveTableRelation 

RESULT • 6,000 sec → 200 sec 

Agenda 1. Issue 2. Gathering Statistics 3. Injecting Custom Optimization Rules 4. Cost-based Optimizer 

COST-BASED OPTIMIZATION • Apache Spark 2.2.0~ • Statistics, Cost • Advanced Optimizations 1. Broadcast Hash Join Based on Column Statistics 2. Join Reordering 

COST-BASED OPTIMIZATION • Apache Spark 2.2.0~ • Statistics, Cost • Advanced Optimizations 1. Broadcast Hash Join Based on Column Statistics 2. Join Reordering 

QUERY select a.* from db.a inner join db.b on a.id = b.id inner join db.c on b.key = c.key 

QUERY select a.* from db.a inner join db.b on a.id = b.id inner join db.c on b.key = c.key 1,500,000,000 records 400,000,000 records 1 records 

JOIN ORDER db.a (1,500,000,000 records) db.b (400,000,000 records) db.c (1 record) 

db.a db.b db.c 

CBO • set spark.sql.cbo.enabled = true • set spark.sql.cbo.joinReorder.enabled = true 

db.b db.c db.a 

RESULT • 1,000 sec → 100 sec 

COST • cost = weight * numOfRows + (1.0 - weight) * dataSize 

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