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https://issues.apache.org/jira/browse/HIVE-18885?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16400820#comment-16400820
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Alexander Kolbasov commented on HIVE-18885:
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[~anishek] One serious issue is that the lock may be held for relatively long
time when there are many partitions involved in the operations. Combining
multiple events into one event helps with that.
> DbNotificationListener has a deadlock between Java and DB locks
> ---------------------------------------------------------------
>
> Key: HIVE-18885
> URL: https://issues.apache.org/jira/browse/HIVE-18885
> Project: Hive
> Issue Type: Bug
> Components: Hive, Metastore
> Affects Versions: 2.3.2
> Reporter: Alexander Kolbasov
> Assignee: Vihang Karajgaonkar
> Priority: Major
>
> You can see the problem from looking at the code, but it actually created
> severe problems for real life Hive user.
> When {{alter table}} has {{cascade}} option it does the following:
> {code:java}
> msdb.openTransaction()
> ...
> List<Partition> parts = msdb.getPartitions(dbname, name, -1);
> for (Partition part : parts) {
> List<FieldSchema> oldCols = part.getSd().getCols();
> part.getSd().setCols(newt.getSd().getCols());
> String oldPartName =
> Warehouse.makePartName(oldt.getPartitionKeys(), part.getValues());
> updatePartColumnStatsForAlterColumns(msdb, part, oldPartName,
> part.getValues(), oldCols, part);
> msdb.alterPartition(dbname, name, part.getValues(), part);
> }
> {code}
> So it walks all partitions (and this may be huge list) and does some
> non-trivial operations in one single uber-transaction.
> When DbNotificationListener is enabled, it adds an event for each partition,
> all while
> holding a row lock on NOTIFICATION_SEQUENCE table. As a result, while this is
> happening no other write DDL can proceed. This can sometimes cause DB lock
> timeouts which cause HMS level operation retries which make things even worse.
> In one particular case this pretty much made HMS unusable.
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