Arjun Mishra commented on HIVE-18885:

[~akolb] At least we have isolated the query. I will look to see if there are 
more such queries. Is the fix to create a single transaction for each alter 
partition call?

> 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.

This message was sent by Atlassian JIRA

Reply via email to