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https://issues.apache.org/jira/browse/HIVE-18885?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16390493#comment-16390493
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Alexander Kolbasov commented on HIVE-18885:
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[~vihangk1] Something like this would work in general but it allows for missed
notifications since creating notification and storing it may fail. This means
that there is some chance that certain operations succeed but do not have
corresponding notifications.
Another issue is that we have bulk operations which create many notifications.
This means that the code should be restructured to save all these notification
after transaction completes rather then inline.
> Cascaded alter table + notifications = disaster
> -----------------------------------------------
>
> Key: HIVE-18885
> URL: https://issues.apache.org/jira/browse/HIVE-18885
> Project: Hive
> Issue Type: Bug
> Components: Hive, Metastore
> Affects Versions: 3.0.0
> Reporter: Alexander Kolbasov
> 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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