[teiid-issues] [JBoss JIRA] Commented: (TEIID-1648) Reading CLOB's from Teradata has issues and produces exception when stream is read from a different thread than what the clob was read from the resultset

[Van Halbert (JIRA)]

    [ https://issues.jboss.org/browse/TEIID-1648?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12610100#comment-12610100 ] 

Van Halbert commented on TEIID-1648:
------------------------------------

Note: The Teradata Database does not support more than one active request per session. If
the user attempts to do this, then the Teradata JDBC Driver blocks until the previous request
has returned. This may negatively impact performance.

Table 12 contains JDBC Object Thread safety information.
Table 12: JDBC Object Thread Safety
JDBC Object            Thread Safety
Connection             Connection objects are fully thread-safe, and can be used by multiple
threads. However, only one request is executed at a time. Subsequent
requests block until the previous request completes executing.
Statement,
PreparedStatement,
CallableStatement      Statement and its subclass objects are generally not thread-safe. One
specific case is supported. A second thread can call the cancel()
method to interrupt an executing request.
ResultSet              ResultSet objects are not thread-safe. A ResultSet object should only
be used by a single thread. A ResultSet object contains state
information that is not thread-safe, such as the wasNull state to
indicate whether the most recently called getter method returned a
NULL.

> Reading CLOB's from Teradata has issues and produces exception when stream is read from a different thread than what the clob was read from the resultset
> ---------------------------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: TEIID-1648
>                 URL: https://issues.jboss.org/browse/TEIID-1648
>             Project: Teiid
>          Issue Type: Bug
>          Components: Misc. Connectors
>    Affects Versions: 7.4.1
>            Reporter: Van Halbert
>            Assignee: Steven Hawkins
>            Priority: Critical
>         Attachments: JDBCQueryServlet.java
>
>
> The initial problem was seen when running BQT testing against the teradata source.   However, when debugging, the exception was occurring on the initial client read of the stream.    After reading teradata jdbc driver doc, it talks about how its not thread safe and has issues when different threads are handling blobs/clobs.   Which lead me to do a simple client test.   2 tests where run run thru a servlet that obtains the teradata connenction via jndi.   Thet are as follows (attached is the sample code after the changes used for #2):
> 1.   simple execute/select:   execute select intkey, objectvalue from bqt1.smalla,  for each row, obtain the clob and read the stream (no exception is seen)
> 2.   execute select and read clob in a different thread:     a new thread is created, passing in the clob, thread is started and then proceeds to try to read the stream, exceptions are seen
> I'll attach the sample code.

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