[GitHub] afs commented on a change in pull request #527: SDB Transform - improve performance of OPTIONAL, MINUS

[GitBox <gi...@apache.org>]

afs commented on a change in pull request #527: SDB Transform - improve performance of OPTIONAL, MINUS
URL: https://github.com/apache/jena/pull/527#discussion_r255914151
 
 

 ##########
 File path: jena-sdb/src/main/java/org/apache/jena/sdb/compiler/TransformOptimizeSubqueryFragments.java
 ##########
 @@ -0,0 +1,435 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.jena.sdb.compiler;
+
+import org.apache.jena.graph.Triple;
+import org.apache.jena.sparql.algebra.Op;
+import org.apache.jena.sparql.algebra.OpVisitor;
+import org.apache.jena.sparql.algebra.OpVisitorBase;
+import org.apache.jena.sparql.algebra.TransformCopy;
+import org.apache.jena.sparql.algebra.Transformer;
+import org.apache.jena.sparql.algebra.op.Op1;
+import org.apache.jena.sparql.algebra.op.Op2;
+import org.apache.jena.sparql.algebra.op.OpBGP;
+import org.apache.jena.sparql.algebra.op.OpGraph;
+import org.apache.jena.sparql.algebra.op.OpJoin;
+import org.apache.jena.sparql.algebra.op.OpLeftJoin;
+import org.apache.jena.sparql.algebra.op.OpMinus;
+import org.apache.jena.sparql.algebra.op.OpTable;
+import org.apache.jena.sparql.algebra.op.OpUnion;
+import org.apache.jena.sparql.core.BasicPattern;
+
+import java.util.ArrayDeque;
+import java.util.Deque;
+import java.util.HashSet;
+import java.util.Iterator;
+import java.util.Set;
+
+/**
+ * For large datasets, the performance of the OPTIONAL joins and MINUS in SQL can suffer, as the subqueries
+ * generate large views which are expensive to join.
+ *
+ * This optimizer transforms the algebra to insert the restrictions from outside of the optional subquery,
+ * reducing the amount of data that has to be joined.
+ *
+ * By reducing the amount of data that is considered in the LEFT JOIN/MINUS operations, the
+ * efficiency and performance of such constructs is greatly improved in most cases.
+ */
+public class TransformOptimizeSubqueryFragments extends TransformCopy {
+    private Deque<Op> tracker;
+
+    /**
+     * Static method to run the transformer (needs to keep track of visited nodes)
+     * @param op The algebra to rewrite
+     */
+    public static Op transform(Op op) {
+        final Deque<Op> stack = new ArrayDeque<>();
+        OpVisitor before = new Pusher(stack);
+        OpVisitor after = new Popper(stack);
+        return Transformer.transform(new TransformOptimizeSubqueryFragments(stack), op, before, after);
+    }
+
+    private TransformOptimizeSubqueryFragments(Deque<Op> tracker) {
+        this.tracker = tracker;
+    }
+
+    /**
+     * Run transformation on joins
+     *
+     * @param opJoin
+     * @param opLeft
+     * @param opRight
+     * @return
 
 Review comment:
   This is a javadoc warning on `@return`.   Either remove the `@return` here and everywhere else or put the type in (there are 4 instances of this)

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