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https://issues.apache.org/jira/browse/HIVE-21075?focusedWorklogId=602742&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-602742
]
ASF GitHub Bot logged work on HIVE-21075:
-----------------------------------------
Author: ASF GitHub Bot
Created on: 27/May/21 07:19
Start Date: 27/May/21 07:19
Worklog Time Spent: 10m
Work Description: oleksiy-sayankin commented on a change in pull request
#2323:
URL: https://github.com/apache/hive/pull/2323#discussion_r640351626
##########
File path:
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/ObjectStore.java
##########
@@ -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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Issue Time Tracking
-------------------
Worklog Id: (was: 602742)
Time Spent: 50m (was: 40m)
> Metastore: Drop partition performance downgrade with Postgres DB
> ----------------------------------------------------------------
>
> Key: HIVE-21075
> URL: https://issues.apache.org/jira/browse/HIVE-21075
> Project: Hive
> Issue Type: Bug
> Components: Metastore
> Affects Versions: 3.0.0
> Reporter: Yongzhi Chen
> Assignee: Oleksiy Sayankin
> Priority: Major
> Labels: pull-request-available
> Time Spent: 50m
> Remaining Estimate: 0h
>
> In order to workaround oracle not supporting limit statement caused
> performance issue, HIVE-9447 makes all the backend DB run select count(1)
> from SDS where SDS.CD_ID=? to check if the specific CD_ID is referenced in
> SDS table before drop a partition. This select count(1) statement does not
> scale well in Postgres, and there is no index for CD_ID column in SDS table.
> For a SDS table with with 1.5 million rows, select count(1) has average 700ms
> without index, while in 10-20ms with index. But the statement before
> HIVE-9447( SELECT * FROM "SDS" "A0" WHERE "A0"."CD_ID" = $1 limit 1) uses
> less than 10ms .
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