[GitHub] [ignite] ygerzhedovich commented on a change in pull request #8607: IGNITE-13904 don't use rows buffers for simple one-way reducer

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

ygerzhedovich commented on a change in pull request #8607:
URL: https://github.com/apache/ignite/pull/8607#discussion_r549257424



##########
File path: modules/indexing/src/main/java/org/apache/ignite/internal/processors/query/h2/twostep/UnsortedBaseReducer.java
##########
@@ -0,0 +1,110 @@
+/*
+ * 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.ignite.internal.processors.query.h2.twostep;
+
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Iterator;
+import java.util.List;
+import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import org.apache.ignite.cluster.ClusterNode;
+import org.apache.ignite.internal.GridKernalContext;
+import org.apache.ignite.internal.processors.query.h2.opt.GridH2Cursor;
+import org.h2.index.Cursor;
+import org.h2.result.Row;
+import org.h2.result.SearchRow;
+import org.h2.value.Value;
+import org.jetbrains.annotations.Nullable;
+
+/**
+ * Base unsorted merge index.
+ */
+public abstract class UnsortedBaseReducer extends AbstractReducer {
+    /** */
+    protected final AtomicInteger activeSourcesCnt = new AtomicInteger(-1);
+
+    /** */
+    protected final PollableQueue<ReduceResultPage> queue = new PollableQueue<>();
+
+    /** */
+    protected Iterator<Value[]> iter = Collections.emptyIterator();
+
+    /**
+     * Constructor.
+     *
+     * @param ctx Context.
+     */
+    public UnsortedBaseReducer(GridKernalContext ctx) {
+        super(ctx);
+    }
+
+    /** {@inheritDoc} */
+    @Override public void setSources(Collection<ClusterNode> nodes, int segmentsCnt) {
+        super.setSources(nodes, segmentsCnt);
+
+        int x = srcNodes.size() * segmentsCnt;
+
+        assert x > 0 : x;
+
+        activeSourcesCnt.set(x);
+    }
+
+    /** {@inheritDoc} */
+    @Override public boolean fetchedAll() {
+        int x = activeSourcesCnt.get();
+
+        assert x >= 0 : x; // This method must not be called if the sources were not set.
+
+        return x == 0 && queue.isEmpty();
+    }
+
+    /**
+     * @param page Page.
+     */
+    @Override protected void addPage0(ReduceResultPage page) {
+        assert page.rowsInPage() > 0 || page.isLast() || page.isFail();
+
+        // Do not add empty page to avoid premature stream termination.
+        if (page.rowsInPage() != 0 || page.isFail())
+            queue.add(page);
+
+        if (page.isLast()) {
+            int x = activeSourcesCnt.decrementAndGet();
+
+            assert x >= 0 : x;
+
+            if (x == 0) // Always terminate with empty iterator.
+                queue.add(createDummyLastPage(page));
+        }
+    }
+
+    /** {@inheritDoc} */
+    @Override protected Cursor findAllFetched(List<Row> fetched, @Nullable SearchRow first, @Nullable SearchRow last) {
+        // This index is unsorted: have to ignore bounds.
+        return new GridH2Cursor(fetched.iterator());
+    }
+
+    /**
+     *

Review comment:
       short version of JavaDoc




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