[jira] Commented: (OPENJPA-1248) LOB streaming does not work as expected

["Jeremy Bauer (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/OPENJPA-1248?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12775126#action_12775126 ] 

Jeremy Bauer commented on OPENJPA-1248:
---------------------------------------

These tests are two of the few remaining failures in the o-j-p project when running on Oracle.  (Version XE/10 using the 11.2.0.1 driver)  I found a few issues and came up with a couple of options for fixing them.

First, when inserting a LOB OpenJPA currently inserts a null value into the LOB column.  When this value is retrieved from the result set (res.getBlob) it is null - and not an updatable blob.  This is currently causing an NPE.  If an Oracle empty_[b,c]lob() is inserted, the rs will return an updatable lob.  However, this changes behavior a bit since null != empty and some of the test assertions that assert a persistent stream attribute is NULL will fail.  Another option is to continue to insert a NULL value then when doing the update, create a temporary lob (using Oracle APIs) and do the update.  I've found this to be troublesome - especially when connection pooling is used - since the Oracle APIs assert that the connection they are provided is an Oracle connection.  I put together a DBCP/JDBC 4 reflection-based solution but it is cumbersome.   Worse yet, DBCP requires a special property be set to get access to the underlying connection.

I think the cleanest solution would be to use empty_lob() and change the behavior of the tests to expect an empty stream when using Oracle.  A hybrid solution would handle cases where an existing value is null...  but this might be overkill.

The second issue (after correcting the first) was that the test was failing with an exception indicating that the connection is closed when reading from the updated BLOB.  This issue is related to OpenJPA connection management and the need for Oracle streaming LOBs to maintain an open connection.  The issue was corrected on Oracle by setting the property openjpa.ConnectionRetainMode=transaction, indicating that em should use the same connection for the duration of the transaction.  Some applications may need to use mode "always", depending on transactional patterns and when the LOB is accessed - but that can result in an inefficient use of connections in a pooled environment.  This needs to be documented in the OpenJPA manual as part of this JIRA.  Unfortunately, this did not correct similar test failures on SQL Server.  SQL Server will require additional investigation.

Unless someone(s) is/are in strong disagreement, I'll be committing code to trunk which fixes the Oracle failures by using empty_[c,b]lob() instead of inserting null. The tests will be modified to assert that the stream is empty (instead of null) when running with Oracle.  I'll also attach a patch to OPENJPA-1249 (since the patch is Oracle specific) that uses native Oracle methods to handle null LOBs as an alternative solution.  Finally, the Oracle section of the manual will be updated to include the ConnectionRetainMode requirement for streaming LOBs.  

> LOB streaming does not work as expected
> ---------------------------------------
>
>                 Key: OPENJPA-1248
>                 URL: https://issues.apache.org/jira/browse/OPENJPA-1248
>             Project: OpenJPA
>          Issue Type: Bug
>          Components: jdbc
>    Affects Versions: 1.1.0, 1.2.0, 1.2.1, 1.3.0, 2.0.0
>         Environment: Oracle, MySQL, PostgreSQL, SQL Server
>            Reporter: Milosz Tylenda
>         Attachments: failures.txt, TestReaderLob_oracle.log
>
>
> TestReaderLob does not pass with any of the databases indicated in the test case: Oracle, MySQL, PostgreSQL, SQL Server. TestInputStreamLob passes only with MySQL and PostgreSQL.

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