JPA using eclipselink and java.sql: when connect to DB

Question

I explain better my question since from the title it could be not very clear, but I didn't find a way to summarize the problem in few work. Basically I have a web application whose DB have 5 tables. 3 of these are managed using JPA and eclipselink implementation. The other 2 tables are manager directly with SQL using the package java.sql. When I say "managed" I mean just that query, insertion, deletion and updates are performed in two different way. Now the problem is that I have to monitor the response time of each call to the DB. In order to do this I have a library that use aspects and at runtime I can monitor the execution time of any code snippet. Now the question is, if I want to monitor the response time of a DB request (let's suppose the DB in remote, so the response time will include also network latency, but actually this is fine), what are in the two distinct case described above the instructions whose execution time has to be considered. I make an example in order to be more clear. Suppose tha case of using JPA and execute a DB update. I have the following code:

EntityManagerFactory emf = Persistence.createEntityManagerFactory(persistenceUnit);
EntityManager em=emf.createEntityManager();
EntityToPersist e=new EntityToPersist();
em.persist(e);

Actually it is correct to suppose that only the em.persist(e) instruction connects and make a request to the DB? The same for what concern using java.sql:

Connection c=dataSource.getConnection();
Statement statement = c.createStatement();
statement.executeUpdate(stm);
statement.close();
c.close();

In this case it is correct to suppose that only the statement.executeUpdate(stm) connect and make a request to the DB? If it could be useful to know, actually the remote DBMS is mysql.

I try to search on the web, but it is a particular problem and I'm not sure about what to look for in order to find a solution without reading the JPA or java.sql full specification. Please if you have any question or if there is something that is not clear from my description, don't hesitate to ask me. Thank you a lot in advance.

V G · Accepted Answer · 2015-03-16 09:23:23Z

In JPA (so also in EcliplseLink) you have to differentiate from SELECT queries (that do not need any transaction) and queries that change the data (DELETE, CREATE, UPDATE: all these need a transacion). When you select data, then it is enough the measure the time of Query.getResultList() (and calls alike). For the other operations (EntityManager.persist() or merge() or remove()) there is a mechanism of flushing, which basically forces the queue of queries (or a single query) from the cache to hit the database. The question is when is the EntityManager flushed: usually on transaction commit or when you call EntityManager.flush(). And here again another question: when is the transaction commit: and the answer is: it depends on your connection setup (if autocommit is true or not), but a very correct setup is with autocommit=false and when you begin and commit your transactions in your code.

When working with statement.executeUpdate(stm) it is enough to measure only such calls.

PS: usually you do not connect directly to any database, as that is done by a pool (even if you work with a DataSource), which simply gives you a already established connection, but that again depends on your setup.

PS2: for EclipseLink probably the most correct way would be to take a look in the source code in order to find when the internal flush is made and to measure that part.

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