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From "Alan Gates (JIRA)" <>
Subject [jira] [Commented] (HIVE-17714) move custom SerDe schema considerations into metastore from QL
Date Mon, 13 Nov 2017 21:26:03 GMT


Alan Gates commented on HIVE-17714:

bq. We can remove the logic that avoids storing schema in metastore entirely, and always store
the schema, like before.
No, -1.  For the reasons I gave above.  I'm fine with working on ways at write and alter time
to make sure things are in sync.  I am not ok with complicating the read path.

> move custom SerDe schema considerations into metastore from QL
> --------------------------------------------------------------
>                 Key: HIVE-17714
>                 URL:
>             Project: Hive
>          Issue Type: Bug
>            Reporter: Sergey Shelukhin
>            Assignee: Alan Gates
> Columns in metastore for tables that use external schema don't have the type information
(since HIVE-11985) and may be entirely inconsistent (since forever, due to issues like HIVE-17713;
or for SerDes that allow an URL for the schema, due to a change in the underlying file).
> Currently, if you trace the usage of ConfVars.SERDESUSINGMETASTOREFORSCHEMA, and to MetaStoreUtils.getFieldsFromDeserializer,
you'd see that the code in QL handles this in Hive. So, for the most part metastore just returns
whatever is stored for columns in the database.
> One exception appears to be get_fields_with_environment_context, which is interesting...
so getTable will return incorrect columns (potentially), but get_fields/get_schema will return
correct ones from SerDe as far as I can tell.
> As part of separating the metastore, we should make sure all the APIs return the correct
schema for the columns; it's not a good idea to have everyone reimplement getFieldsFromDeserializer.
> Note: this should also remove a flag introduced in HIVE-17731

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