pvary commented on a change in pull request #2323:
URL: https://github.com/apache/hive/pull/2323#discussion_r640364312
##########
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:
Transactions could be used also to prevent other queries modifying the
data which was read by another transaction depending on the isolation level
used (for SERIALIZABLE isolation level). [One good
description](https://www.sqlservercentral.com/articles/isolation-levels-in-sql-server)
If there are concurrent transactions that could be an issue:
- T1 reads the data - decides that the CD is not used anymore
- T2 inserts a new row
- T1 drops the CD
The previous version of the code read the data inside the transaction, we
can change the behavior if we decide so, but that has to be a conscious
decision.
IMHO this is all theoretical since if I remember correctly the
`openTransaction()` is called before this method call, so in our case the new
`openTranscation()` call just increments a counter.
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