[jira] [Comment Edited] (HIVE-21028) get_table_meta should use a fetch plan

["Karthik Manamcheri (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HIVE-21028?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16715880#comment-16715880 ] 

Karthik Manamcheri edited comment on HIVE-21028 at 12/11/18 12:54 AM:
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Thoughts [~vihangk1] [~ngangam] [~pvary]. I also don't know how to test this in an unit test! I have manually tested this by slowing down the get_table_meta call and then dropping the database from another HMS.


was (Author: karthik.manamcheri):
Thoughts [~vihangk1] [~ngangam] [~pvary]. I also don't know how to test this in an unit test! I can manually test this by slowing down the get_table_meta call and then dropping the database from another HMS.

> get_table_meta should use a fetch plan
> --------------------------------------
>
>                 Key: HIVE-21028
>                 URL: https://issues.apache.org/jira/browse/HIVE-21028
>             Project: Hive
>          Issue Type: Bug
>            Reporter: Karthik Manamcheri
>            Assignee: Karthik Manamcheri
>            Priority: Major
>
> The {{getTableMeta}} call retrieves the tables, loops through the tables and during this loop it retrieves the database object to get the containing database name. DataNuclues does a lazy retrieval and so, when the first call to get all the tables is done, it does not retrieve the database objects.
> When this query is executed
> {code}query = pm.newQuery(MTable.class, filterBuilder.toString());
> {code}
> it loads all the tables, and when you do
> {code}
> table.getDatabase().getName()
> {code}
> it then goes and retrieves the database object.
> *However*, there could be another thread which actually has deleted the database!! If this happens, we end up with exceptions such as
> {code}
> 2018-12-04 22:25:06,525 INFO  DataNucleus.Datastore.Retrieve: [pool-7-thread-191]: Object with id "6930391[OID]org.apache.hadoop.hive.metastore.model.MTable" not found !
> 2018-12-04 22:25:06,527 WARN  DataNucleus.Persistence: [pool-7-thread-191]: Exception thrown by StateManager.isLoaded
> No such database row
> org.datanucleus.exceptions.NucleusObjectNotFoundException: No such database row
> {code}
> We see this happen especially with calls which retrieve all the tables in all the databases (basically a call to get_table_meta with dbNames="\*" and tableNames="\*").
> To avoid this, we can define a custom fetch plan and activate it only for the get_table_meta query. This fetch plan would fetch the database object along with the MTable object.
> We would first create a fetch plan on the pmf
> {code}
> pmf.getFetchGroup(MTable.class, "mtable_db_fetch_group").addMember("database");
> {code}
> Then we use it just before calling the query
> {code}
> pm.getFetchPlan().addGroup("mtable_db_fetch_group");
> query = pm.newQuery(MTable.class, filterBuilder.toString());
> Collection<MTable> tables = (Collection<MTable>) query.executeWithArray(...);
> ...
> {code}
> Before the API call ends, we can remove the fetch plan by
> {code}
> pm.getFetchPlan().removeGroup("mtable_db_fetch_group");
> {code}



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