[GitHub] [ignite] timoninmaxim commented on a change in pull request #9081: IGNITE-14703. Add MergeSort distributed cache query reducer.

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timoninmaxim commented on a change in pull request #9081:
URL: https://github.com/apache/ignite/pull/9081#discussion_r642922363



##########
File path: modules/core/src/main/java/org/apache/ignite/internal/processors/cache/query/UnsortedDistributedCacheQueryReducer.java
##########
@@ -0,0 +1,211 @@
+/*
+ * 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.cache.query;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.UUID;
+import java.util.concurrent.CountDownLatch;
+import org.apache.ignite.IgniteCheckedException;
+import org.apache.ignite.cluster.ClusterNode;
+import org.apache.ignite.internal.IgniteInterruptedCheckedException;
+import org.apache.ignite.internal.processors.cache.GridCacheContext;
+import org.apache.ignite.internal.util.typedef.F;
+import org.apache.ignite.internal.util.typedef.P1;
+import org.apache.ignite.internal.util.typedef.internal.U;
+import org.jetbrains.annotations.Nullable;
+
+/**
+ * Reducer of distributed query, fetch pages from remote nodes. All pages go in single page stream so no ordering is provided.
+ */
+class UnsortedDistributedCacheQueryReducer<R> extends AbstractCacheQueryReducer<R> implements DistributedCacheQueryReducer<R> {
+    /**
+     * Whether it is allowed to send cache query result requests to nodes.
+     * It is set to {@code false} if a query finished or failed.
+     */
+    protected volatile boolean loadAllowed;
+
+    /** Query request ID. */
+    protected final long reqId;
+
+    /**
+     * Dynamic collection of nodes that run this query. If a node finishes this query then remove it from this colleciton.
+     */
+    protected final Collection<UUID> subgrid = new HashSet<>();
+
+    /**
+     * List of nodes that respons with cache query result pages. This collection should be cleaned before sending new
+     * cache query request.
+     */
+    protected final Collection<UUID> rcvd = new HashSet<>();
+
+    /** Requester of cache query result pages. */
+    protected final CacheQueryPageRequester pageRequester;
+
+    /** Cache context. */
+    protected final GridCacheContext cctx;
+
+    /** Count down this latch when every node responses on initial cache query request. */
+    private final CountDownLatch firstPageLatch = new CountDownLatch(1);
+
+    /** Single page stream. */
+    private final PageStream pageStream;
+
+    /** Query future. */
+    protected final GridCacheQueryFutureAdapter fut;
+
+    /**
+     * @param reqId Cache query request ID.
+     * @param pageRequester Provides a functionality to request pages from remote nodes.
+     * @param nodes Collection of nodes this query applies to.
+     */
+    UnsortedDistributedCacheQueryReducer(GridCacheQueryFutureAdapter fut, long reqId, CacheQueryPageRequester pageRequester,
+        Collection<ClusterNode> nodes) {
+        super(fut);
+
+        this.reqId = reqId;
+        this.pageRequester = pageRequester;
+
+        synchronized (queueLock()) {
+            for (ClusterNode node : nodes)
+                subgrid.add(node.id());
+        }
+
+        cctx = fut.cctx;
+
+        pageStream = new PageStream();
+
+        this.fut = fut;
+    }
+
+    /** {@inheritDoc} */
+    @Override public boolean hasNext() throws IgniteCheckedException {
+        return pageStream.hasNext();
+    }
+
+    /** {@inheritDoc} */
+    @Override public R next() throws IgniteCheckedException {
+        return pageStream.next();
+    }
+
+    /** {@inheritDoc} */
+    @Override public void addPage(@Nullable UUID nodeId, Collection<R> data) {
+        pageStream.addPage(data);
+    }
+
+    /** {@inheritDoc} */
+    @Override public void onLastPage() {
+        super.onLastPage();
+
+        loadAllowed = false;
+
+        firstPageLatch.countDown();
+    }
+
+    /** {@inheritDoc} */
+    @Override public void cancel() {

Review comment:
       No, as `cancel()` always prefaced with `onLastPage()` call. 
   
   Also, I checked that actually the `awaitFirstItem()` used only for ScanQuery only in case user specified partitions to enable retry this query if first page loading failed. Looks too narrow case, and I think there should be a separate activity to investigate this functionality.




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