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  1. Apache Drill
  2. DRILL-6735

Enhance the Hash-Join Operator to perform Semi-Join

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      Description

      Currently Drill implements Semi-Join (see DRILL-402) by using a regular join, with a DISTINCT operator under the build upstream side to eliminate duplicates. Typically a physical plan for the Semi uses a hash-join, with a hash-aggr performing the DISTINCT (see example below). 
          This effectively builds the same hash table(s) twice - a big waste of time and memory.

      Improvement: Eliminate the Hash-Aggr from the plan, and notify the Hash-Join to perform a Semi-join. The HJ then would just skip the duplicates in its hash table(s), thus performing a Semi -Join.

      Example: 

      select c.c_first_name, c.c_last_name from dfs.`/data/json/s1/customer` c where c.c_customer_sk in (select s.ss_customer_sk from dfs.`/data/json/s1/store_sales` s) limit 4;
      

      And the result plan (see the HJ at 01-03, and the Hash Agg at 01-05):

      00-00    Screen : rowType = RecordType(ANY c_first_name, ANY c_last_name): rowcount = 4.0, cumulative cost = {4693752.96 rows, 2.3095576720000003E7 cpu, 0.0 io, 2.1598011392E9 network, 3.5895861760000005E7 memory}, id = 1320
      00-01      Project(c_first_name=[$1], c_last_name=[$2]) : rowType = RecordType(ANY c_first_name, ANY c_last_name): rowcount = 4.0, cumulative cost = {4693752.56 rows, 2.3095576320000004E7 cpu, 0.0 io, 2.1598011392E9 network, 3.5895861760000005E7 memory}, id = 1319
      00-02        Project(c_customer_sk=[$1], c_first_name=[$2], c_last_name=[$3], ss_customer_sk=[$0]) : rowType = RecordType(ANY c_customer_sk, ANY c_first_name, ANY c_last_name, ANY ss_customer_sk): rowcount = 4.0, cumulative cost = {4693748.56 rows, 2.3095568320000004E7 cpu, 0.0 io, 2.1598011392E9 network, 3.5895861760000005E7 memory}, id = 1318
      00-03          SelectionVectorRemover : rowType = RecordType(ANY ss_customer_sk, ANY c_customer_sk, ANY c_first_name, ANY c_last_name): rowcount = 4.0, cumulative cost = {4693744.56 rows, 2.3095552320000004E7 cpu, 0.0 io, 2.1598011392E9 network, 3.5895861760000005E7 memory}, id = 1317
      00-04            Limit(fetch=[4]) : rowType = RecordType(ANY ss_customer_sk, ANY c_customer_sk, ANY c_first_name, ANY c_last_name): rowcount = 4.0, cumulative cost = {4693740.56 rows, 2.3095548320000004E7 cpu, 0.0 io, 2.1598011392E9 network, 3.5895861760000005E7 memory}, id = 1316
      00-05              UnionExchange : rowType = RecordType(ANY ss_customer_sk, ANY c_customer_sk, ANY c_first_name, ANY c_last_name): rowcount = 4.0, cumulative cost = {4693736.56 rows, 2.3095532320000004E7 cpu, 0.0 io, 2.1598011392E9 network, 3.5895861760000005E7 memory}, id = 1315
      01-01                SelectionVectorRemover : rowType = RecordType(ANY ss_customer_sk, ANY c_customer_sk, ANY c_first_name, ANY c_last_name): rowcount = 4.0, cumulative cost = {4693732.56 rows, 2.3095500320000004E7 cpu, 0.0 io, 2.1597356032E9 network, 3.5895861760000005E7 memory}, id = 1314
      01-02                  Limit(fetch=[4]) : rowType = RecordType(ANY ss_customer_sk, ANY c_customer_sk, ANY c_first_name, ANY c_last_name): rowcount = 4.0, cumulative cost = {4693728.56 rows, 2.3095496320000004E7 cpu, 0.0 io, 2.1597356032E9 network, 3.5895861760000005E7 memory}, id = 1313
      01-03                    HashJoin(condition=[=($1, $0)], joinType=[inner]) : rowType = RecordType(ANY ss_customer_sk, ANY c_customer_sk, ANY c_first_name, ANY c_last_name): rowcount = 90182.8, cumulative cost = {4693724.56 rows, 2.3095480320000004E7 cpu, 0.0 io, 2.1597356032E9 network, 3.5895861760000005E7 memory}, id = 1312
      01-05                      HashAgg(group=[{0}]) : rowType = RecordType(ANY ss_customer_sk): rowcount = 18036.56, cumulative cost = {4509140.0 rows, 2.1824237600000005E7 cpu, 0.0 io, 1.4775549952E9 network, 3.4918780160000004E7 memory}, id = 1309
      01-06                        Project(ss_customer_sk=[$0]) : rowType = RecordType(ANY ss_customer_sk): rowcount = 180365.6, cumulative cost = {4328774.4 rows, 2.0381312800000004E7 cpu, 0.0 io, 1.4775549952E9 network, 3.17443456E7 memory}, id = 1308
      01-07                          HashToRandomExchange(dist0=[[$0]]) : rowType = RecordType(ANY ss_customer_sk, ANY E_X_P_R_H_A_S_H_F_I_E_L_D): rowcount = 180365.6, cumulative cost = {4148408.8000000003 rows, 2.0200947200000003E7 cpu, 0.0 io, 1.4775549952E9 network, 3.17443456E7 memory}, id = 1307
      02-01                            UnorderedMuxExchange : rowType = RecordType(ANY ss_customer_sk, ANY E_X_P_R_H_A_S_H_F_I_E_L_D): rowcount = 180365.6, cumulative cost = {3968043.2 rows, 1.73150976E7 cpu, 0.0 io, 0.0 network, 3.17443456E7 memory}, id = 1306
      04-01                              Project(ss_customer_sk=[$0], E_X_P_R_H_A_S_H_F_I_E_L_D=[hash32AsDouble($0, 1301011)]) : rowType = RecordType(ANY ss_customer_sk, ANY E_X_P_R_H_A_S_H_F_I_E_L_D): rowcount = 180365.6, cumulative cost = {3787677.6 rows, 1.7134732E7 cpu, 0.0 io, 0.0 network, 3.17443456E7 memory}, id = 1305
      04-02                                HashAgg(group=[{0}]) : rowType = RecordType(ANY ss_customer_sk): rowcount = 180365.6, cumulative cost = {3607312.0 rows, 1.6232904E7 cpu, 0.0 io, 0.0 network, 3.17443456E7 memory}, id = 1304
      04-03                                  Scan(groupscan=[EasyGroupScan [selectionRoot=file:/data/json/s1/store_sales, numFiles=1, columns=[`ss_customer_sk`], files=[file:/data/json/s1/store_sales/0_0_0.json]]]) : rowType = RecordType(ANY ss_customer_sk): rowcount = 1803656.0, cumulative cost = {1803656.0 rows, 1803656.0 cpu, 0.0 io, 0.0 network, 0.0 memory}, id = 1303
      01-04                      BroadcastExchange : rowType = RecordType(ANY c_customer_sk, ANY c_first_name, ANY c_last_name): rowcount = 55516.0, cumulative cost = {111032.0 rows, 610676.0 cpu, 0.0 io, 6.82180608E8 network, 0.0 memory}, id = 1311
      03-01                        Scan(groupscan=[EasyGroupScan [selectionRoot=file:/data/json/s1/customer, numFiles=1, columns=[`c_customer_sk`, `c_first_name`, `c_last_name`], files=[file:/data/json/s1/customer/0_0_0.json]]]) : rowType = RecordType(ANY c_customer_sk, ANY c_first_name, ANY c_last_name): rowcount = 55516.0, cumulative cost = {55516.0 rows, 166548.0 cpu, 0.0 io, 0.0 network, 0.0 memory}, id = 1310
      

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              • Assignee:
                ben-zvi Boaz Ben-Zvi
                Reporter:
                ben-zvi Boaz Ben-Zvi
                Reviewer:
                Timothy Farkas
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