Multi tool use

Hibernate Delayed Write

I am wondering if there is a possibility of hibernate delaying its writes to the DB. I have hibernate configured for mysql. Scenarios I hope to support are 80% reads and 20% writes. So I do not want to optimize my writes, I rather have the client wait until the DB has been written to, than to return a bit earlier. My tests currently have 100 client in parallel, the cpu does sometimes max out. I need this flush method to write to DB immediately and return only when the data is written.

80%

20%

On my client side, I send a write request and then a read request, but the read request sometimes returns null. I suspect hibernate is not writing to db immediately.

public final ThreadLocal session = new ThreadLocal();

public Session currentSession() {
Session s = (Session) session.get();
// Open a new Session, if this thread has none yet
if (s == null || !s.isOpen()) {
s = sessionFactory.openSession();
// Store it in the ThreadLocal variable
session.set(s);
}
return s;
}
public synchronized void flush(Object dataStore) throws DidNotSaveRequestSomeRandomError {
Transaction txD;
Session session;
session = currentSession();
txD = session.beginTransaction();
session.save(dataStore);
try {
txD.commit();
} catch (ConstraintViolationException e) {
e.printStackTrace();
throw new DidNotSaveRequestSomeRandomError(dataStore, feedbackManager);
} catch (TransactionException e) {
log.debug("txD state isActive" + txD.isActive() + " txD is participating" + txD.isParticipating());
log.debug(e);
} finally {
// session.flush();
txD = null;
session.close();
}
// mySession.clear();
}


2 Answers
2

@Siddharth Hibernate does not really delay in writing the response , and your code also does not speaks the same. I have also faced similar issue earlier and doubt you might be facing the same that is , when there a numerous request for write into hibernate are there many threads share same instance of your db and even having consecutive commits by hibernate you really dont see any changes .
You may also catch this by simple looking at you MySQL logs during the transaction and see what exactly went wrong !

Thanks for your hint. Took me some time to debug. Mysql logs are amazing.
This is what I run to check the time stamp on my inserts and mysql writes. mysql logs all db operations in a binlog. To read it we need to use the tool called mysqlbinlog. my.cnf too needs to be http://publib.boulder.ibm.com/infocenter/tpfhelp/current/index.jsp?topic=%2Fcom.ibm.ztpf-ztpfdf.doc_put.cur%2Fgtpm7%2Fm7enablelogs.html

http://publib.boulder.ibm.com/infocenter/tpfhelp/current/index.jsp?topic=%2Fcom.ibm.ztpf-ztpfdf.doc_put.cur%2Fgtpm7%2Fm7enablelogs.html

I check which is the lastest mysql bin log file, and run this to grep for 1 line above the log, to get the time stamp. Then in java, I call Calendar.getInstance().getTimeInMilli() to compare with the time stamp.
sudo mysqlbinlog mysql/mysql-bin.000004 | grep "mystring" -1

So I debugged my problem. It was a delayed write problem. So I implemented a sync write too instead of all async. In other words the server call wont return until db is flushed for this object.

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