[GitHub] [iotdb] cornmonster commented on a change in pull request #5294: [IOTDB-2726][IOTDB-2727] Basic interfaces definition of mpp scheduling and memory control

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cornmonster commented on a change in pull request #5294:
URL: https://github.com/apache/iotdb/pull/5294#discussion_r830890274



##########
File path: server/src/main/java/org/apache/iotdb/db/mpp/memory/MemoryPool.java
##########
@@ -0,0 +1,90 @@
+/*
+ * 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.iotdb.db.mpp.memory;
+
+import org.apache.commons.lang3.Validate;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/** Manages certain amount of memory. */
+public class MemoryPool {
+
+  private final String id;
+  private final long maxBytes;
+
+  private long reservedBytes = 0L;
+  private final Map<String, Long> queryMemoryReservations = new HashMap<>();
+
+  public MemoryPool(String id, long maxBytes) {
+    this.id = Validate.notNull(id);
+    Validate.isTrue(maxBytes > 0L);
+    this.maxBytes = maxBytes;
+  }
+
+  public String getId() {
+    return id;
+  }
+
+  public long getMaxBytes() {
+    return maxBytes;
+  }
+
+  public boolean tryReserve(String queryId, long bytes) {
+    Validate.notNull(queryId);
+    Validate.isTrue(bytes > 0L);
+
+    synchronized (this) {

Review comment:
       Good catch! I guess it can be optimized like
   
   ```
   if (maxBytes - reservedBytes < bytes) {
           return false;
   }
   synchronized (this) {
       if (maxBytes - reservedBytes < bytes) {
           return false;
       }
       reservedBytes += bytes;
       queryMemoryReservations.merge(queryId, bytes, Long::sum);
   }
   ```




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