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is #Transactional not sufficient for transaction management

I have been using #Transactional on my spring boot application for transaction management. But today someone told me to use narayana for transaction management.
Why do I have to use narayana if spring itself can do transaction management for me.

There are basically two kind of transaction. Local transactions are specific to a single transactional resource like a JDBC connection, whereas global transactions can span multiple transactional resources like transaction in a distributed system.
If you need transaction management for distributed system, spring transaction management is not sufficient and narayana will come into play.
From Spring boot docs:
Spring Boot supports distributed JTA transactions across multiple XA
resources by using either an Atomikos or Bitronix embedded transaction
manager. JTA transactions are also supported when deploying to a
suitable Java EE Application Server.
When a JTA environment is detected, Spring’s JtaTransactionManager is
used to manage transactions. Auto-configured JMS, DataSource, and JPA
beans are upgraded to support XA transactions. You can use standard
Spring idioms, such as #Transactional, to participate in a distributed
transaction. If you are within a JTA environment and still want to use
local transactions, you can set the spring.jta.enabled property to
false to disable the JTA auto-configuration.

Why use DataSource instead of XADataSource?

As far as I understand there are two types of DataSource connections, javax.sql.DataSource and javax.sql.XADataSource, this tutorial explains that javax.sql.DataSource give the connection the ability to be pooled and javax.sql.XADataSource give the connection distributed transactional behavior.
I understand most XADataSource will implement connection pooling as well as distributed transactions so I don't see the point to use a DataSource when you could use a XADataSource and have both.
Are there any tradeoff when choosing a XADataSource over a DataSource?
I understand is not mandatory for a XADataSource to use pooled connections, is it there a way to find out if a XADataSource uses pooled connections or only relying on the XADataSource provider's documentation?
EDIT:
I am refering to javax.sql.DataSource and javax.sql.XADataSource because those are the types Tomcat 8 factory gives you:
Type should always be javax.sql.DataSource or javax.sql.XADataSource
Depending on the type a org.apache.tomcat.jdbc.pool.DataSource or a
org.apache.tomcat.jdbc.pool.XADataSource will be created.
I do understand that in the end I would be using a DataSource on my code as an API, abstracting the underlying implementation... my question is more related on the decision making process I have to go through when I am configuring Tomcat 8 (or any other server as well).
I want to have pooled connections and there are many XADataSource implementations that will give transactional and pooled connections, so why not always use XADataSource if I will get more? (this of course doesn't applies for a XADataSource that doesn't implements pooled connections)

When to configure XADataSource
As explained in the second section, your code will always use the DataSource interface (which might use a XADataSource). If the question is when should you use a XADataSource (eg configure it in your application server), then the answer is simple:
You use an XADataSource if you need to have distributed transactions: that is ensure a transaction succeeds or fails across multiple resources (eg different databases).
If you don't need distributed transactions, then you can still configure an XADataSource, but this might have some overhead in terms of memory and processing, for example extra objects (eg XAResource) that go unused, and maybe in terms of the 'bookkeeping' done by the data source. This overhead is probably negligible though.
Some data source (eg the Tomcat pool as mentioned in your question), can either use a DataSource or an XADataSource as a factory to create connections (according to the JDBC spec a ConnectionPoolDataSource should also be available as a factory, but it looks like Tomcat ignores that option). This doesn't change the way you decide what to use:
Don't need distributed transactions:
Program --uses--> Tomcat connection pool DataSource --uses--> JDBC driver DataSource
Need distributed transactions:
Program --uses--> Tomcat connection pool DataSource --uses--> JDBC driver XADataSource
In both cases the connection pool is provided by the Tomcat connection pool DataSource, not by the JDBC driver (XA)DataSource. A correct* implementation of XADataSource will not implement connection pooling: that would be the (optional) responsibility of the DataSource implementation that uses the XADataSource as its factory. So that is not a reason to choose (or not choose) an XADataSource.
Your question might stem from the confusing terminology that a XADataSource creates XAConnection which extends PooledConnection. The name PooledConnection doesn't mean it comes from a connection pool, it means that after creation these can be held in a connection pool (which would be inside the DataSource that called XADataSource.getXAConnection).
Responsibilities of DataSource and XADataSource
In JDBC the responsibility of a DataSource is to create connections that can be used by your application. This means that it can be a very basic implementation that does nothing more than go directly to DriverManager, but also an implementation that provides connection pooling, and support for distributed transactions.
The idea is that you can swap one implementation for the other, while your code would be untouched.
So, the code consuming connections should always use a javax.sql.DataSource implementation. The javax.sql.XADataSource (and javax.sql.ConnectionPoolDataSource for that matter) are intended to be used by javax.sql.DataSource implementations that provided advanced features like connection pooling and/or distributed transactions. They should not be used directly in your own program. As the tutorial you link says:
Similarly, when the DataSource implementation is implemented to work with an XADataSource class, all of the connections it produces will automatically be connections that can be used in a distributed transaction.
In other words DataSource is the API you use to obtain a connection, and a XADataSource is used by a data source library that provides distributed transaction support. It obtains the XAConnection, registers it with a distributed transaction manager, and then gives you the logical connection obtained from XAConnection.getConnection().
This is also a described in the JDBC 4.2 specification, section 12.1:
Distributed transactions require an infrastructure that provides these
roles:
Transaction manager — controls transaction boundaries and manages the two-phase commit protocol. This typically will be an
implementation of JTA.
JDBC drivers that implement the XADataSource, XAConnection, and XAResource interfaces. These are described in the next section.
An application-visible implementation of DataSource to “sit on top of” each XADataSource object and interact with the transaction
manager. The DataSource implementation is typically provided by an
application server.
Resource manager(s) to manage the underlying data. In the context of the JDBC API, a resource manager is a DBMS server. The term
“resource manager” is borrowed from JTA to emphasize the point that
distributed transactions using the JDBC API follow the architecture
specified in that document.
TL;DR: You --use--> DataSource --(potentially) uses--> XADataSource
*: Historically there has been some confusion in various JDBC implementations regarding responsibilities, and in some cases connection pools have implemented all three interfaces at the same time.

Transactions in Enterprise level application

I am trying to understand the transactions, and more specifically i am doing it using Spring framework. Going through the material that i have (both internet and books), i see these terminologies:
Container managed transactions (CMT).
Bean Managed transactions (BMT).
Java transaction API (JTA).
Also, for a large enterprise level application, terminologies like "local" and "global" transactions too i have encountered.
What i have understood, is that global transactions is for the cases in which we are managing two or more different resouces (like One Oracle DB, other MySQL etc) and commits/rollback to them happen if both are success/failure. Local transactions is for when we have only one resource to manage (like only one DB connection to MySQL).
I have following doubts:
While writing a simple JDBC standalone program, we can code to commit/rollback. I believe this is example of local transaction, is this correct? And is this transaction taken care by "JDBC" library itself or the drivers?
What is CMT? What i understand is that Container takes care of the transaction management (like Jboss AS). If this is correct, how internally does it manages? Are CMT local or global? Do they use JDBC API's internally to manage the transactions?
What is BMT? This i am not able to understand. We can have application deployed in an App server (and i believe in those cases the transaction would be managed by Container) or i can write an standalone application in which i can use the transaction management code myself (try .. catch block etc). So, which category BMT falls?
While reading Spring framework, i read that Spring framework have its own way of managing the transaction. Down the line, i read Spring Framework uses JTA to manage transactions? I am confused about this. If JTA is API, do we have multiple vendors who implement JTA (like for JPA, we can have multiple vendors who provide the implementation e.g. Hibernate).
Is JTA for local or global transactions? When i write a simple JDBC program to manage transaction, does it use API's which comply JTA? Or is JTA totally different from transaction management which simple JDBC program uses?
Same for CMT, does CMT follow the rules which JTA has in place (the API's primarily)?
It would be great if you answer point-wise, i did search on net, my doubts are still not answered.

Concerning local/global transaction: by global I suppose you are talking about XA transaction (2 phase commits : http://en.wikipedia.org/wiki/X/Open_XA). This is just mandatory when you deal with multiple databases or transactionnal resources.
yes it's a "local transaction", it means only one database is
part of the transaction. The transaction is managed by the database
and controlled by JDBC in that case.
CMT : Container Managed: the container will detect the start and
the end of the transaction and will perform commit/rollback
depending on method return status (successfull return : commit,
exception : rollback). CMT rely on JTA to manage transactions on its
resources. Then it's up to the proper resource adapters (RA) to talk
to jdbc or any other drivers related to your EIS (data). Look at
http://docs.oracle.com/javaee/5/tutorial/doc/bncjx.html
BMT: it means it's up to the bean to control transaction
boundaries. It's pretty rare to use this kind of transaction
management these days. With BMT you control the UserTransaction
object, it's an error to control transaction boundaries directly
with JDBC. Bear in mind also that even if you are in BMT some
framework like JPA (not JTA) will invalidate current transaction on
any error even if you did not explicitely requested a rollback. It
means it's quite hard/dangerous/useless to use BMT.
JTA (I hope you did not mispelled JPA) is at another level: JTA
the API a resource adapter must implement to be part of a container
transaction. Apart from UserTransaction class (what you'll use in
BMT to control transaction boundaries) you have nothing to do with
JTA. There is no multiple implementation of JTA but there is multiple implementation of JTS (Java Transaction Service), each application server vendor implements their own JTS.
JTA is a API for framework designer, JTA impose a contract to the
Resource Adapter RA, and the RA will use JDBC or any other API to
deal with it's EIS (Enterprise Information Storage, let's call it
your DB). JTA works for XA and non XA transactions (if your RA supports XA transactions).
CMT uses JTA, but again JTA is a lowlevel contract between
components of the application server. Application designer should
not care about JTA.

working with JTATransactionManager for transactions?

I am using spring3 and Hibernate4 with Tomcat7.
I have to use JTATransactionManager and i have below configuration.
<bean id="transactionManager"
class="org.springframework.transaction.jta.JtaTransactionManager">
<property name="userTransactionName" value="java:comp/UserTransaction"></property>
</bean>
In above configuration where is java:comp/UserTransaction defined?
Thanks!

It is a JNDI reference to container-supplied user transaction object.
It is not user configurable as such (as in you cannot change the value yourself). The value depends on the EE container you use.
As to what user transaction object really is, see Wikipedia:
UserTransaction interface
The javax.transaction.UserTransaction interface provides the
application the ability to control transaction boundaries
programmatically. This interface may be used by Java client programs
or EJB beans.
The UserTransaction.begin() method starts a global transaction and
associates the transaction with the calling thread. The
transaction-to-thread association is managed transparently by the
Transaction Manager.
Support for nested transactions is not required. The
UserTransaction.begin method throws the NotSupportedException when the
calling thread is already associated with a transaction and the
transaction manager implementation does not support nested
transactions.
Transaction context propagation between application programs is
provided by the underlying transaction manager implementations on the
client and server machines. The transaction context format used for
propagation is protocol dependent and must be negotiated between the
client and server hosts. For example, if the transaction manager is an
implementation of the JTS specification, it will use the transaction
context propagation format as specified in the CORBA OTS 1.1
specification. Transaction propagation is transparent to application
programs..

JTA and associated with it XA transactions are tricky things to implement and support. As #js-nizet said only JEE Application servers have their own transaction managers implementation working out of the box. For lightweight web server like Tomcat or Jetty you have to provide an external implementation and to configure the Spring to work with it. There are a lot of choices so it is up to you. I can recommend you Jboss' Narayana, but it is really up to you. Since it is not so straight-forward to have this running I would recommend you the following blog post which describes everything in a great detail - Configuring Spring and JTA without full Java EE.
Here's another post on how to configure Narayan with Spring and Jetty.

Making datasource in Glassfish

I am creating a JDBC connection pool resource for GlassFish, using the server's Admin Console.
One of the fields on the page to create the pool is labeled 'Resource Type'. This field has four possible values: javax.sql.DataSource, javax.sql.XADataSource, javax.sql.ConnectionPoolDataSource and javax.sql.Driver, but the help text for the Create JDBC connection pool 'wizard' does not have much info about the advantages and disadvantages of these choices.
When prompted to pick a resource type which should I choose?
I am going to connect to a local MySQL server. It would be nice to get an explanation of the differences between the choices in the drop-down as well.

Below are the scenarios where you would need each of the resource types listed. Hope this helps.
DataSource
DataSource A DataSource object is a factory for Connection objects. When using simple DataSource, appserver uses its own pooling instead of native.
ConnectionPoolDataSource
A ConnectionPoolDataSource object is a factory for PooledConnection objects. ConnectionPoolDataSource is used to give access to PooledConnection which implements native pooling by JDBC driver. In this case application server can implement connections pooling using this native interface. Please refer to Java API to know what a PooledConnection is...A ConnectionPoolDataSource can use a third party implementation for pooling - as far as I know for Tomcat, for instance, DBCP connection pooling is used.
XADataSource
You need an XADataSource if you want to execute a Distributed Transaction. You should use XADataSource instead of DataSource if the application
Uses the Java Transaction API (JTA)
Includes multiple database updates within a single transaction
Accesses multiple resources, such as a database and the Java Messaging Service (JMS), during a transaction