[GitHub] [incubator-doris] vagetablechicken commented on a change in pull request #4771: [LoadBalance] make BeLoadRebalancer extends from base class Rebalancer

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

vagetablechicken commented on a change in pull request #4771:
URL: https://github.com/apache/incubator-doris/pull/4771#discussion_r515766101



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File path: fe/fe-core/src/main/java/org/apache/doris/clone/Rebalancer.java
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@@ -0,0 +1,96 @@
+// 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.doris.clone;
+
+import org.apache.doris.catalog.TabletInvertedIndex;
+import org.apache.doris.clone.TabletScheduler.PathSlot;
+import org.apache.doris.system.SystemInfoService;
+import org.apache.doris.task.AgentBatchTask;
+import org.apache.doris.thrift.TStorageMedium;
+
+import com.google.common.collect.Lists;
+
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+
+/*
+ * Rebalancer is responsible for
+ * 1. selectAlternativeTablets: selecting alternative tablets by one rebalance strategy,
+ * and return them to tablet scheduler(maybe contains the concrete moves, or maybe not).
+ * 2. createBalanceTask: given a tablet, try to create a clone task for this tablet.
+ * 3. getToDeleteReplicaId: if the rebalance strategy wants to delete the specified replica,
+ * override this func to let TabletScheduler know in handling redundant replica.
+ * NOTICE:
+ * 1. Adding the selected tablets by TabletScheduler may not succeed at all. And the move may be failed in some other places.
+ * So the thing you need to know is, Rebalancer cannot know when the move is failed.
+ * 2. If you want to make sure the move is succeed, you can assume that it's succeed when getToDeleteReplicaId called.
+ */
+public abstract class Rebalancer {
+    // When Rebalancer init, the statisticMap is usually empty. So it's no need to be an arg.
+    // Only use updateLoadStatistic() to load stats.
+    protected Map<String, ClusterLoadStatistic> statisticMap = new HashMap<>();
+    protected TabletInvertedIndex invertedIndex;
+    protected SystemInfoService infoService;
+
+    public Rebalancer(SystemInfoService infoService, TabletInvertedIndex invertedIndex) {
+        this.infoService = infoService;
+        this.invertedIndex = invertedIndex;
+    }
+
+    public List<TabletSchedCtx> selectAlternativeTablets() {
+        List<TabletSchedCtx> alternativeTablets = Lists.newArrayList();
+        for (Map.Entry<String, ClusterLoadStatistic> entry : statisticMap.entrySet()) {
+            for (TStorageMedium medium : TStorageMedium.values()) {
+                alternativeTablets.addAll(selectAlternativeTabletsForCluster(entry.getKey(),
+                        entry.getValue(), medium));
+            }
+        }
+        return alternativeTablets;
+    }
+
+    // The return TabletSchedCtx should have the tablet id at least. {srcReplica, destBe} can be complete here or
+    // later(when createBalanceTask called).
+    protected abstract List<TabletSchedCtx> selectAlternativeTabletsForCluster(
+            String clusterName, ClusterLoadStatistic clusterStat, TStorageMedium medium);
+
+
+    public void createBalanceTask(TabletSchedCtx tabletCtx, Map<Long, PathSlot> backendsWorkingSlots,
+                                  AgentBatchTask batchTask) throws SchedException {
+        completePlan(tabletCtx, backendsWorkingSlots);
+        batchTask.addTask(tabletCtx.createCloneReplicaAndTask());
+    }
+
+    // Before createCloneReplicaAndTask, we need to complete the TabletSchedCtx.
+    // 1. If you generate {tabletId, srcReplica, destBe} in selectAlternativeTablets(), it may be invalid at
+    // this point(it may have a long interval between selectAlternativeTablets & createBalanceTask).
+    // You should check the moves' validation.
+    // 2. If you want to generate {srcReplica, destBe} here, just do it.
+    // 3. You should check the path slots of src & dest.
+    protected abstract void completePlan(TabletSchedCtx tabletCtx, Map<Long, PathSlot> backendsWorkingSlots)

Review comment:
       👌




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