pvary commented on a change in pull request #2219:
URL: https://github.com/apache/hive/pull/2219#discussion_r620293681



##########
File path: 
ql/src/java/org/apache/hadoop/hive/ql/ddl/table/AbstractAlterTableOperation.java
##########
@@ -138,8 +141,32 @@ private void finalizeAlterTableWithWriteIdOp(Table table, 
Table oldTable, List<P
       
environmentContext.putToProperties(HiveMetaHook.ALTER_TABLE_OPERATION_TYPE, 
desc.getType().name());
       if (partitions == null) {
         long writeId = desc.getWriteId() != null ? desc.getWriteId() : 0;
-        context.getDb().alterTable(desc.getDbTableName(), table, 
desc.isCascade(), environmentContext, true,
-            writeId);
+        try {
+          context.getDb().alterTable(desc.getDbTableName(), table, 
desc.isCascade(), environmentContext, true, writeId);
+        } catch (HiveException ex) {
+          if 
(environmentContext.getProperties().containsKey(HiveMetaHook.INITIALIZE_ROLLBACK_ALTER)
 && Boolean
+              
.valueOf(environmentContext.getProperties().get(HiveMetaHook.INITIALIZE_ROLLBACK_ALTER)))
 {
+            // in case of rollback of alter table do the following:
+            // 1. drop the already altered table but keep the data files
+            // 2. recreate the original table
+            // 3. run msck repair to sync partitions on filesystem with 
metastore

Review comment:
       This could have unexpected result, if we have extra directories in the 
table root, which are not added yet to the HMS. I think it would be good to 
have a way to disable things




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