[GitHub] [accumulo] keith-turner commented on a diff in pull request #3232: Proof of Concept for adding conditional mutation support to Ample

["keith-turner (via GitHub)" <gi...@apache.org>]

keith-turner commented on code in PR #3232:
URL: https://github.com/apache/accumulo/pull/3232#discussion_r1143346453


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core/src/main/java/org/apache/accumulo/core/metadata/TabletOperation.java:
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@@ -0,0 +1,24 @@
+/*
+ * 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
+ *
+ *   https://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.accumulo.core.metadata;
+
+// TODO where should this go, maybe in MetadataSchema class?
+public enum TabletOperation {
+  NONE, SPLITTING, MERGING, DELETING

Review Comment:
   The way this is used is in flux at the moment.  I created them at first thinking it would prevent a split and merge operation from running on the same tablet.  While working on it I realized that two concurrent splits operations also need to be prevented from running on the same tablet.  Like if two operations try to split the same tablet with different split points at the same time.  So the operation id column with a uuid was added to prevent this.  I think the operation id is all that is needed and the operation column that uses this enum could be dropped. 
   
   Also thinking of changing the column name from operation id to lock id.  Split, merge, and delete operations need to prevent any changes from being made to the tablet.  So maybe lock is a better name for the column in the metadata table.  
   
   This lock column in the metadata table could have a structure like `lock=<manager id>:<operation type>:<operation uuid>`.  The operation uuid would identify the specific task that holds the lock and manager id would identify where its currently running. When a manger process dies, another will need to take over running the operation.  The operation type would be SPLIT, MERGE, or DELETE as those are the current operations that need exclusive tablet access.



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