[GitHub] [incubator-druid] leventov commented on a change in pull request #8564: Fix ambiguity about IndexerSQLMetadataStorageCoordinator.getUsedSegmentsForInterval() returning only non-overshadowed or all used segments

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leventov commented on a change in pull request #8564: Fix ambiguity about IndexerSQLMetadataStorageCoordinator.getUsedSegmentsForInterval() returning only non-overshadowed or all used segments
URL: https://github.com/apache/incubator-druid/pull/8564#discussion_r342938668
 
 

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 File path: server/src/main/java/org/apache/druid/indexing/overlord/Segments.java
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 @@ -0,0 +1,50 @@
+/*
+ * 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.druid.indexing.overlord;
+
+/**
+ * This enum is used as a parameter for several methods in {@link IndexerMetadataStorageCoordinator}, specifying whether
+ * only visible segments, or visible as well as overshadowed segments should be included in results.
+ *
+ * Visibility (and overshadowness - these terms are antonyms) may be defined on an interval (or a series of intervals).
+ * Consider the following example:
+ *
+ * |----| I
+ *   |----| S'
+ *   |-------| S
+ *
+ * Here, I denotes an interval in question, S and S' are segments. S' is newer (has a higher version) than S.
+ * Segment S is overshadowed (by S') on the interval I, though it's visible (non-overshadowed) outside of I: more
+ * specifically, it's visible on the interval [end of S', end of S].
+ *
+ * A segment is considered visible on a series of intervals if it's visible on any of the intervals in the series. A
+ * segment is considered (fully) overshadowed on a series of intervals if it's overshadowed (= non-visible) on all of
+ * the intervals in the series.
+ *
+ * If not specified otherwise, visibility (or overshadowness) should be assumed on the interval (-inf, +inf). This
+ * visibility may also be called "global" or "general" visibility.
 
 Review comment:
   Ok, removed the last sentence.

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