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new 59676a1 [BUG] fix 4149, add sessionVariable to choose broadcastjoin
first when cardinality cannot be estimated (#4150)
59676a1 is described below
commit 59676a11170da90b2a9e883ca02f1af6dc2d659b
Author: wutiangan <wutian...@gmail.com>
AuthorDate: Wed Jul 29 12:28:52 2020 +0800
[BUG] fix 4149, add sessionVariable to choose broadcastjoin first when
cardinality cannot be estimated (#4150)
---
docs/en/administrator-guide/variables.md | 6 ++++++
docs/zh-CN/administrator-guide/variables.md | 5 +++++
.../org/apache/doris/planner/DistributedPlanner.java | 16 +++++++++++++++-
.../java/org/apache/doris/qe/SessionVariable.java | 8 ++++++++
.../main/java/org/apache/doris/qe/VariableMgr.java | 6 ++++++
.../java/org/apache/doris/planner/QueryPlanTest.java | 19 +++++++++++++++++++
6 files changed, 59 insertions(+), 1 deletion(-)
diff --git a/docs/en/administrator-guide/variables.md
b/docs/en/administrator-guide/variables.md
index 5091be4..a41396a 100644
--- a/docs/en/administrator-guide/variables.md
+++ b/docs/en/administrator-guide/variables.md
@@ -338,3 +338,9 @@ SET forward_to_master = concat('tr', 'u', 'e');
* `rewrite_count_distinct_to_bitmap_hll`
Whether to rewrite count distinct queries of bitmap and HLL types as
bitmap_union_count and hll_union_agg.
+
+* `prefer_join_method`
+
+ When choosing the join method(broadcast join or shuffle join), if the
broadcast join cost and shuffle join cost are equal, which join method should
we prefer.
+
+ Currently, the optional values for this variable are "broadcast" or
"shuffle".
diff --git a/docs/zh-CN/administrator-guide/variables.md
b/docs/zh-CN/administrator-guide/variables.md
index 3d21575..f9e6654 100644
--- a/docs/zh-CN/administrator-guide/variables.md
+++ b/docs/zh-CN/administrator-guide/variables.md
@@ -338,3 +338,8 @@ SET forward_to_master = concat('tr', 'u', 'e');
是否将 bitmap 和 hll 类型的 count distinct 查询重写为 bitmap_union_count 和
hll_union_agg 。
+* `prefer_join_method`
+
+ 在选择join的具体实现方式是broadcast join还是shuffle join时，如果broadcast join cost和shuffle
join cost相等时，优先选择哪种join方式。
+
+ 目前该变量的可选值为"broadcast" 或者 "shuffle"。
diff --git
a/fe/fe-core/src/main/java/org/apache/doris/planner/DistributedPlanner.java
b/fe/fe-core/src/main/java/org/apache/doris/planner/DistributedPlanner.java
index 25be3af..88775e1 100644
--- a/fe/fe-core/src/main/java/org/apache/doris/planner/DistributedPlanner.java
+++ b/fe/fe-core/src/main/java/org/apache/doris/planner/DistributedPlanner.java
@@ -281,6 +281,20 @@ public class DistributedPlanner {
}
/**
+ * When broadcastCost and partitionCost are equal, there is no uniform
standard for which join implementation is better.
+ * Some scenarios are suitable for broadcast join, and some scenarios are
suitable for shuffle join.
+ * Therefore, we add a SessionVariable to help users choose a better join
implementation.
+ */
+ private boolean isBroadcastCostSmaller(long broadcastCost, long
partitionCost) {
+ String joinMethod =
ConnectContext.get().getSessionVariable().getPreferJoinMethod();
+ if (joinMethod.equalsIgnoreCase("broadcast")) {
+ return broadcastCost <= partitionCost;
+ } else {
+ return broadcastCost < partitionCost;
+ }
+ }
+
+ /**
* Creates either a broadcast join or a repartitioning join, depending on
the expected cost. If any of the inputs to
* the cost computation is unknown, it assumes the cost will be 0. Costs
being equal, it'll favor partitioned over
* broadcast joins. If perNodeMemLimit > 0 and the size of the hash table
for a broadcast join is expected to exceed
@@ -351,7 +365,7 @@ public class DistributedPlanner {
&& (perNodeMemLimit == 0 || Math.round(
(double) rhsDataSize * PlannerContext.HASH_TBL_SPACE_OVERHEAD)
<= perNodeMemLimit)
&& (node.getInnerRef().isBroadcastJoin() ||
(!node.getInnerRef().isPartitionJoin()
- && broadcastCost < partitionCost))) {
+ && isBroadcastCostSmaller(broadcastCost, partitionCost)))) {
doBroadcast = true;
} else {
doBroadcast = false;
diff --git a/fe/fe-core/src/main/java/org/apache/doris/qe/SessionVariable.java
b/fe/fe-core/src/main/java/org/apache/doris/qe/SessionVariable.java
index 393cdb0..c2a0b88 100644
--- a/fe/fe-core/src/main/java/org/apache/doris/qe/SessionVariable.java
+++ b/fe/fe-core/src/main/java/org/apache/doris/qe/SessionVariable.java
@@ -74,6 +74,7 @@ public class SessionVariable implements Serializable,
Writable {
public static final String PARALLEL_FRAGMENT_EXEC_INSTANCE_NUM =
"parallel_fragment_exec_instance_num";
public static final String ENABLE_INSERT_STRICT = "enable_insert_strict";
public static final String ENABLE_SPILLING = "enable_spilling";
+ public static final String PREFER_JOIN_METHOD = "prefer_join_method";
public static final int MIN_EXEC_INSTANCE_NUM = 1;
public static final int MAX_EXEC_INSTANCE_NUM = 32;
// if set to true, some of stmt will be forwarded to master FE to get
result
@@ -209,6 +210,9 @@ public class SessionVariable implements Serializable,
Writable {
@VariableMgr.VarAttr(name = DISABLE_COLOCATE_JOIN)
private boolean disableColocateJoin = false;
+ @VariableMgr.VarAttr(name = PREFER_JOIN_METHOD)
+ private String preferJoinMethod = "broadcast";
+
/*
* the parallel exec instance num for one Fragment in one BE
* 1 means disable this feature
@@ -397,6 +401,10 @@ public class SessionVariable implements Serializable,
Writable {
return disableColocateJoin;
}
+ public String getPreferJoinMethod() {return preferJoinMethod; }
+
+ public void setPreferJoinMethod(String preferJoinMethod)
{this.preferJoinMethod = preferJoinMethod; }
+
public int getParallelExecInstanceNum() {
return parallelExecInstanceNum;
}
diff --git a/fe/fe-core/src/main/java/org/apache/doris/qe/VariableMgr.java
b/fe/fe-core/src/main/java/org/apache/doris/qe/VariableMgr.java
index 3574ae5..b48fbdc 100644
--- a/fe/fe-core/src/main/java/org/apache/doris/qe/VariableMgr.java
+++ b/fe/fe-core/src/main/java/org/apache/doris/qe/VariableMgr.java
@@ -244,6 +244,12 @@ public class VariableMgr {
}
}
+ if (setVar.getVariable().toLowerCase().equals("prefer_join_method")) {
+ if (!value.toLowerCase().equals("broadcast") &&
!value.toLowerCase().equals("shuffle")) {
+
ErrorReport.reportDdlException(ErrorCode.ERR_WRONG_VALUE_FOR_VAR,
"prefer_join_method", value);
+ }
+ }
+
if (setVar.getType() == SetType.GLOBAL) {
wlock.lock();
try {
diff --git
a/fe/fe-core/src/test/java/org/apache/doris/planner/QueryPlanTest.java
b/fe/fe-core/src/test/java/org/apache/doris/planner/QueryPlanTest.java
index 95fa585..433671e 100644
--- a/fe/fe-core/src/test/java/org/apache/doris/planner/QueryPlanTest.java
+++ b/fe/fe-core/src/test/java/org/apache/doris/planner/QueryPlanTest.java
@@ -907,4 +907,23 @@ public class QueryPlanTest {
explainString = UtFrameUtils.getSQLPlanOrErrorMsg(connectContext,
queryStr);
Assert.assertFalse(explainString.contains("INNER JOIN (PARTITIONED)"));
}
+
+ @Test
+ public void testPreferBroadcastJoin() throws Exception {
+ connectContext.setDatabase("default_cluster:test");
+ String queryStr = "explain select * from (select k1 from jointest
group by k1)t2, jointest t1 where t1.k1 = t2.k1";
+
+ // default set PreferBroadcastJoin true
+ String explainString =
UtFrameUtils.getSQLPlanOrErrorMsg(connectContext, queryStr);
+ Assert.assertTrue(explainString.contains("INNER JOIN (BROADCAST)"));
+
+ connectContext.getSessionVariable().setPreferJoinMethod("shuffle");
+ explainString = UtFrameUtils.getSQLPlanOrErrorMsg(connectContext,
queryStr);
+ Assert.assertTrue(explainString.contains("INNER JOIN (PARTITIONED)"));
+
+
+ connectContext.getSessionVariable().setPreferJoinMethod("broadcast");
+ explainString = UtFrameUtils.getSQLPlanOrErrorMsg(connectContext,
queryStr);
+ Assert.assertTrue(explainString.contains("INNER JOIN (BROADCAST)"));
+ }
}
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