does @Transactional annotation merge new transaction into exisiting transaction-CodePudding

i am having a simple controller /hello which internally calls Repository layer for a transaction using the default propagation level i.e Propagation.REQUIRED.

@Controller
public void hello(data) -> doTransaction(data)

@Repository
@Transactional
public void doTransaction(data){
  jdbcTemplateInsertA(data);
  Thread.sleep(15*1000);
  jdbcTemplateUpdateB(data);
}

as per online docs

REQUIRED is the default propagation. Spring checks if there is an active transaction, and if nothing exists, it creates a new one. Otherwise, the business logic appends to the currently active transaction:

now let's say i hit the API 2 times, with data1 and then data2, before request 1 was finished API was hit 2nd time.
would there be only a single transaction or two separate independent transactions?

Also, i want to know is using @Transactional with jdbcTemplate valid? i am having doubt on how jdbcTemplate internally gets the same connection object that was used by @Transactional annotation considering pool size >=2.

UPDATE:
You will have a transaction per thread. -> any docs/resources where i can find this?
For 2nd part, let me rephrase my question.
Let's say using hikari pool with size as 5 as per my understanding @Transactional would pick some connection from pool, let's say it picked up connectionId1554 now, when i call jdbc.execute(), how spring ensure that it uses connectionId1554 and not any other available connection from the pool

CodePudding user response：

You will have a transaction per thread. If you have two requests, then you will have two threads (from your web container, like Tomcat), and therefore you'll have two separate transactions.

Based on the code and (lack of) configuration it is hard to tell how you setup your JdbcTemplate. Most likely the connection used by the JdbcTemplate comes from a database connection pool. If you've configured two connections then you can only use two connections and the usage of those connections will block other requests to the database if they are in use. Now, that being said, database connection pools are generally programmed to be super smart and one database connection can be used between multiple database requests/transactions depending on configuration settings.

CodePudding user response：

let's say i hit the API 2 times, with data1 and then data2, before request 1 was finished API was hit 2nd time. would there be only a single transaction or two separate independent transactions?

Each incoming request to your api will result in an independent transaction being started. If you think this through this makes sense: if you have 2 users each making a request at the same time, you would want each of their requests to be handled independently, it would be odd if both of their requests joined and were handled as a single transaction.

i want to know is using @Transactional with jdbcTemplate valid? i am having doubt on how jdbcTemplate internally gets the same connection object that was used by @Transactional annotation

This depends on how you have configured a Datasource and a connection pool. Are you running this on an appserver like Webpshere, Weblogic or WildFly? They provide Datasource connection pooling integrated with a TransactionManager too.