[GitHub] [incubator-druid] leventov commented on a change in pull request #8114: Fix race between canHandle() and addSegment() in StorageLocation

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

leventov commented on a change in pull request #8114: Fix race between canHandle() and addSegment() in StorageLocation
URL: https://github.com/apache/incubator-druid/pull/8114#discussion_r306396261
 
 

 ##########
 File path: server/src/main/java/org/apache/druid/segment/loading/StorageLocation.java
 ##########
 @@ -19,28 +19,39 @@
 
 package org.apache.druid.segment.loading;
 
+import com.google.common.annotations.VisibleForTesting;
 import org.apache.commons.io.FileUtils;
-import org.apache.druid.java.util.common.ISE;
 import org.apache.druid.java.util.common.logger.Logger;
 import org.apache.druid.timeline.DataSegment;
+import org.apache.druid.timeline.SegmentId;
 
 import javax.annotation.Nullable;
 import java.io.File;
 import java.util.HashSet;
 import java.util.Set;
 
 /**
+ * This class is a very simple logical representation of a local path. It keeps track of files stored under the
+ * {@link #path} via {@link #reserve}, so that the total size of stored files doesn't exceed the {@link #maxSize} and
+ * available space is always kept smaller than {@link #freeSpaceToKeep}.
+ *
+ * This class is thread-safe, so that multiple threads can update its state at the same time.
+ * One example usage is that a historical can use multiple threads to load different segments in parallel
+ * from deep storage.
 */
 public class StorageLocation
 {
   private static final Logger log = new Logger(StorageLocation.class);
 
   private final File path;
-  private final long maxSize;
+  private final long maxSize; // in bytes
 
 Review comment:
   Can call this field `maxSizeBytes`

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