I'm retracting my email due to my misunderstanding. It's likely most
item readers will not need a JTA data source. Therefore if you use a
non-JTA data source you can cache the connection for the readItem()
method. Any XA resources need to be opened and closed within the
scope of a single transaction. For example
ItemWriter.writeItems(List<Object> items) the XA resource must
be opened and closed within this method and NOT in the
ItemWriter.open() and ItemWriter.close() methods.
In other words, there are no changes needed. It just needs to be
noted one should not cache an XA data source in the open method and
attempt to reuse it later.
On 02/03/2015 02:21 PM, James R.
Perkins wrote:
In the JSR 352 batch specification there are some issues around
transactions with JCA. These issues would mainly be seen with JDBC
item readers/writers.
Here is kind of a thought dump from a sit down I had with the JCA
team. If anyone has any opinions on how this should be handled
let's talk it out. I would imagine this is a fairly important
issue as generally speaking batch jobs will likely be legacy jobs
and JDBC is probably heavily used.
Batch Transactions with JCA
Problem:
Batch requires that a Transaction.begin() and a
Transaction.commit() for each open, close and chunk processed.
This causes connections from JCA to potentially cross
transactional boundaries.
This requires that the JCA CachedConnectionManager (CCM) is
enabled for the resource in question (Jesper)
Transaction code should be written like:
Connection c
Transaction.begin()
c = DataSource.getConnection()
c.close()
Transaction.commit()
Chunk Processing process:
Transaction.begin()
ItemReader.open()
ItemWriter.open()
Transaction.commit()
repeat until item reader returns null
Transaction.begin()
repeat-on-chunk
ItemReader.readItem()
ItemProcessor.processItem()
ItemWriter.writeItems
Transaction.commit()
Transaction.begin()
ItemReader.close()
ItemWriter.close()
Transaction.commit()
Where seen:
- No errors in 8.1+
- Upstream with the tracking set to true and exception is
thrown;
/subsystem=datasources/data-source=ExampleDS:write-attribute(name=tracking,
value=true)
- https://gist.github.com/jamezp/cf39f92913425c83929f
- This shows where the connection was allocated that is
crossing the transaction boundary, and hence killed (Jesper)
Questions:
- Will the tracking attribute be used often?
- The feature is meant to allow people to find where in
their code they are making assumptions that isn't true
(Jesper)
- The corner case is just the "c.close()" call (Jesper)
Possible Fixes:
- Leave batch as is. If the tracking attribute is set to true
exceptions will be thrown
- Remember that the underlying connection will be killed
(Jesper)
- Add a property to jBeret to use local (fake) transactions.
This is what we currently do and I feel it's just wrong.
- Create a deployment descriptor (or possibly a property that
can be passed when starting the job) to allow different styles
for transactions
Example JBoss Way
repeat until item reader returns null
Transaction.begin()
ItemReader.open()
ItemWriter.open()
repeat-on-chunk
ItemReader.readItem()
ItemProcessor.processItem()
ItemWriter.writeItems()
ItemReader.close()
ItemWriter.close()
Transaction.commit()
--
James R. Perkins
JBoss by Red Hat
--
James R. Perkins
JBoss by Red Hat