[GitHub] [hive] oleksiy-sayankin commented on a change in pull request #2323: HIVE-21075 : Metastore: Drop partition performance downgrade with Pos…

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oleksiy-sayankin commented on a change in pull request #2323:
URL: https://github.com/apache/hive/pull/2323#discussion_r640351626



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File path: standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/ObjectStore.java
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@@ -5269,6 +5293,32 @@ private void preDropStorageDescriptor(MStorageDescriptor msd) {
     removeUnusedColumnDescriptor(mcd);
   }
 
+  /**
+   * Get a list of storage descriptors that reference a particular Column Descriptor
+   * @param oldCD the column descriptor to get storage descriptors for
+   * @return a list of storage descriptors
+   */
+  private List<MStorageDescriptor> listStorageDescriptorsWithCD(MColumnDescriptor oldCD, Query query) {
+    boolean success = false;
+    List<MStorageDescriptor> sds = null;
+    try {
+      openTransaction();

Review comment:
       In my understanding transactions are usually used when one has CREATE, UPDATE or DELETE statements and one wants to have the atomic behavior, that is, either commit everything or commit nothing. Consider all queries we have here
   
   1. Query for postgres
   
           SELECT * FROM "SDS" "A0" WHERE "A0"."CD_ID" = $1 limit 1)
   
   2. Query for all DBs except postgres
   
           select count(1) from org.apache.hadoop.hive.metastore.model.MStorageDescriptor where (this.cd == inCD)
   
   3. Constraint deletion
   
           pm.deletePersistentAll(mConstraintsList);
   
   4. CD deletion
   
           pm.deletePersistent(oldCD);
   
   IMHO we need transaction only for items 3 and 4 and it should look this way:
   
           1. SELECT * FROM "SDS" "A0" WHERE "A0"."CD_ID" = $1 limit 1)
           2. select count(1) from org.apache.hadoop.hive.metastore.model.MStorageDescriptor where (this.cd == inCD)
           openTransaction()
           3. pm.deletePersistentAll(mConstraintsList);
           4. pm.deletePersistent(oldCD);
           commitTransaction()
   
   whilst the old implementation was
   
           openTransaction()        
           1. select count(1) from org.apache.hadoop.hive.metastore.model.MStorageDescriptor where (this.cd == inCD)        
           2. pm.deletePersistentAll(mConstraintsList);
           3. pm.deletePersistent(oldCD);
           commitTransaction()  
   
   which seems to me redundant. Make sense?




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