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https://issues.apache.org/jira/browse/HIVE-18940?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16405155#comment-16405155
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Andrew Sherman commented on HIVE-18940:
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The restriction that the EVENT_ID has to be in the order of commit is
presumably having a major impact on concurrency in the HMS DBMS. It effectively
serializes avery transaction. Has there been any thought to relaxing this
restriction?
> Hive notifications serialize all write DDL operations
> -----------------------------------------------------
>
> Key: HIVE-18940
> URL: https://issues.apache.org/jira/browse/HIVE-18940
> Project: Hive
> Issue Type: Bug
> Components: Metastore
> Affects Versions: 3.0.0
> Reporter: Alexander Kolbasov
> Priority: Major
>
> The implementation of DbNotificationListener uses a single row to store
> current notification ID and uses {{SELECT FOR UPDATE}} to lock the row. This
> serializes all write DDL operations which isn't good.
> We should consider using database auto-increment for notification ID instead.
> Especially on mMySQL/innoDb it is supported natively with relatively
> light-weight locking.
> This creates potential issue for consumers though because such IDs may have
> holes. There are two types of holes - transient hole for a transaction which
> have not committed yet and will be committed shortly and permanent holes for
> transactions that fail. Consumers need to deal with it. It may be useful to
> add DB-generated timestamp as well to assist in recovery from holes.
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