Hello Thomas,
Thank you very much for looking at this issue.
The problem, however, is that my connection is exactly this :
jdbc:h2:/tmp/prod/
h2cache;TRACE_LEVEL_FILE=3;CACHE_SIZE=1048576;LOCK_MODE=3;MVCC=TRUE;MULTI_THREADED=0
But I am opening and using several Sessions, concurrently, from
different threads .
I know that you are using, I think, a synchonized(database){ } for
MVCC=FALSE;MULTI_THREADED=0 mode ; but I have the feeling that even
with MVCC=TRUE;MULTI_THREADED=0, the situation might occur, since , I
believe, for MVCC=TRUE, you are synchronizing in sessions, not
database ( I need to look into the h2 source code again , to check
this )
Can you, please, check, that there is really no way this situation
desccribed earlier, can happen in MVCC=FALSE;MULTI_THREADED=0 mode ?
Thank you,
Ionut
On Sep 10, 3:45 am, "Thomas Mueller" <[EMAIL PROTECTED]>
wrote:
> Hi,
>
> You are right, if two threads concurrently update the same table when
> using multi-version concurrency, things could break. However by
> default this can not happend because only one thread can concurrently
> update: MULTI_THREADED is disabled by default.
>
> I wrote a test case that enables MULTI_THREADED and MVCC, and I can
> reproduce the problem. In the next release I will make sure the
> features can not be used at the same time:
>
> "Multi-Version Concurrency (MVCC) may no longer be used when using
> the multi-threaded kernel feature (MULTI_THREADED). An exception is
> thrown when trying to connect with both settings. Additional
> synchronization is required before those features can be used
> together."
>
> Regards,
> Thomas
>
> On Wed, Sep 3, 2008 at 4:22 PM, ivrusuboca <[EMAIL PROTECTED]> wrote:
>
> > Hello Thomas,
>
> > Thank you for the reply. I had a look at release notes and I think the
> > changes below are unrelated to my problem.
>
> > On the other hand, I had a look at the source code and I would kindly
> > ask you if the scenario below can happen; because, if it happens, then
> > I think we have an issue :
>
> > Source code snippets ( from h2 version 1.0.69 ) :
>
> > TableData.java ( line 275 ) :
>
> > 275 public void removeRow(Session session, Row row) throws
> > SQLException {
> > 276 lastModificationId = database.getNextModificationDataId();
> > 277 if (database.isMultiVersion()) {
> > 278 if (row.getDeleted()) {
> > 279 throw
> > Message.getSQLException(ErrorCode.CONCURRENT_UPDATE_1, getName());
> > 280 }
> > 281 int old = row.getSessionId();
> > 282 int newId = session.getId();
> > 283 if (old == 0) {
> > 284 row.setSessionId(newId);
> > 285 } else if (old != newId) {
> > 286 throw
> > Message.getSQLException(ErrorCode.CONCURRENT_UPDATE_1, getName());
> > 287 }
> > 288 }
> > ................
>
> > Record.java ( line 65 onwards ) :
>
> > 65 public void setSessionId(int sessionId) {
> > 66 this.sessionId = sessionId;
> > 67 }
> > 68
> > 69 public int getSessionId() {
> > 70 return sessionId;
> > 71 }
> > 72
> > 73 /**
> > 74 * This record has been committed. The session id is reset.
> > 75 */
> > 76 public void commit() {
> > 77 this.sessionId = 0;
> > 78 }
> > ......
>
> > Scenario :
>
> > Suppose there are two threads, T1 and T2, which read and update
> > 'value' in a table, for a certain row with key = 123
>
> > Let's assume that initially value = 0 ( zero )
>
> > T1 :
> > T1.1 begin tran
> > T1.2 select value from my_table where key = 123
> > T1.3 newValue = value + 5
> > T1.4 update my_table set value = newValue where key = 123
> > T1.5 commit
>
> > T2 :
> > T2.1 begin tran
> > T2.2 select value from my_table where key = 123
> > T2.3 newValue = value + 8
> > T2.4 update my_table set value = newValue where key = 123
> > T2.5 commit
>
> > Now, if MVCC = true and both threads T1 & T2 are running, we should
> > have a final result of 13, as either 0 + 5 + 8 or 0 + 8 + 5.
>
> > However, I think, we might end up having either 5 or 8 , in the
> > following situation :
>
> > step 1 : Thread T1 executes T1.1 & T1.2 , and so it reads value = 0
> > step 2 : Thread T2 executes T2.1 & T2.2 , and so it also reads value =
> > 0
> > step 3 : Thread T1 executes T1.3 and calculates newValue = value + 5 =
> > 5
> > step 4 : Thread T2 executes T2.3 and calculates newValue = value + 8 =
> > 8
> > step 5 : Thread T1 executes T1. 4 and updates row with newValue = 5
> > step 6 : Thread T1 executes T1.5 and so it commits the transaction; in
> > this moment, row.sessionId becomes 0 ( zero ) ( Record.java line 77 )
> > step 7 : Thread T2 executes T2.4 & T2.5 and so it updates the row with
> > newValue = 8 because, somehow, the code below _might_ work this way :
>
> > 275 public void removeRow(Session session, Row row) throws
> > SQLException { <=== 'this' is T2
> > 276 lastModificationId = database.getNextModificationDataId();
> > 277 if (database.isMultiVersion()) { <=== yes, returns true
> > 278 if (row.getDeleted()) { <=== returns false; the row is
> > not deleted
> > 279 throw
> > Message.getSQLException(ErrorCode.CONCURRENT_UPDATE_1, getName());
> > 280 }
> > 281 int old = row.getSessionId(); <=== returns '0' ( zero )
> > because T1 committed ( at step 6 above )
> > 282 int newId = session.getId(); <=== returns some non-zero
> > Id ( '1122334455' )
> > 283 if (old == 0) { <== returns true , as per the line 281
> > result
> > 284 row.setSessionId(newId); <== so this line executes
> > and row gets assigned T2's session Id
> > 285 } else if (old != newId) { <=== _but_ this else branch
> > is not executed, so the old != newId check is skipped
> > 286 throw
> > Message.getSQLException(ErrorCode.CONCURRENT_UPDATE_1, getName()); <==
> > so this does not happen
> > 287 }
> > 288 }
> > 289 <=== so T2 continues here and eventually commits the row
> > with an updated newValue = 8
>
> > Can you, please, confirm if this is a problem or it is I who got
> > something wrong here ? ( I hope I do .... )
>
> > Thank you very much, indeed.
>
> > Ionut
>
> > On Aug 20, 4:24 am, "Thomas Mueller" <[EMAIL PROTECTED]>
> > wrote:
> >> Hi,
>
> >> Maybe the problem is solved in a newer version of H2 - could you try
> >> 1.0.77 (2008-08-16)? Two problems related with MVCC have been solved
> >> (CREATE TABLE AS SELECT did not work correctly in the multi-version
> >> concurrency mode., Multi version concurrency (MVCC): when a row was
> >> updated or deleted, but this change was rolled back, the row was not
> >> visible by other sessions if no index was used to access it.) see
> >> alsohttp://www.h2database.com/html/changelog.html
>
> >> If this doesn't help, could you send me or post the .trace.db file?
>
> >> Regards,
> >> Thomas
>
> >> On Fri, Aug 15, 2008 at 6:23 AM,ivrusuboca<[EMAIL PROTECTED]> wrote:
>
> >> > Thanks guys, for your replies.
>
> >> > Thotheolh : unfortunately I cannot post the entire stuff 'cause it
> >> > contains corporate information ... etc ... None the less I will try to
> >> > get the most out of the h2 data and post it back.
>
> >> > Thomas : here are the connection details :
>
> >> > jdbc:h2:${DATASTORE_DIR}/${env}/
> >> > xstabcache;TRACE_LEVEL_FILE=3;CACHE_SIZE=$
> >> > {CACHE_SIZE};LOCK_MODE=3;MVCC=true;MULTI_THREADED=0
>
> >> > Regards,
> >> > Ionut
>
> >> > On Aug 8, 9:04 pm,ivrusuboca<[EMAIL PROTECTED]> wrote:
> >> >> Hi guys,
>
> >> >> I am having thrown the following exception ( layers are : H2,
> >> >> Hibernate & my app ) :
>
> >> >> org.h2.jdbc.JdbcSQLException: Concurrent update in table
> >> >> X_ACK_MESSAGE: another transaction has updated or deleted the same row
> >> >> [90131-74]
> >> >> at org.h2.message.Message.getSQLException(Message.java:103)
> >> >> at org.h2.message.Message.getSQLException(Message.java:114)
> >> >> at org.h2.message.Message.getSQLException(Message.java:77)
> >> >> at org.h2.table.TableData.removeRow(TableData.java:287)
> >> >> at org.h2.table.Table.updateRows(Table.java:356)
> >> >> at org.h2.command.dml.Update.update(Update.java:131)
> >> >> at
> >> >> org.h2.command.CommandContainer.update(CommandContainer.java:69)
> >> >> at org.h2.command.Command.executeUpdate(Command.java:203)
> >> >> at
> >> >> org.h2.jdbc.JdbcPreparedStatement.executeUpdateInternal(JdbcPreparedStatement.java:
> >> >> 137)
> >> >> at
> >> >> org.h2.jdbc.JdbcPreparedStatement.executeBatch(JdbcPreparedStatement.java:
> >> >> 1049)
> >> >> at
> >> >> com.mchange.v2.c3p0.impl.NewProxyPreparedStatement.executeBatch(NewProxyPreparedStatement.java:
> >> >> 1723)
> >> >> at
> >> >> org.hibernate.jdbc.BatchingBatcher.doExecuteBatch(BatchingBatcher.java:
> >> >> 48)
> >> >> at
> >> >> org.hibernate.jdbc.BatchingBatcher.addToBatch(BatchingBatcher.java:34)
> >> >> at
> >> >> org.hibernate.persister.entity.AbstractEntityPersister.update(AbstractEntityPersister.java:
> >> >> 2408)
> >> >> at
> >> >> org.hibernate.persister.entity.AbstractEntityPersister.updateOrInsert(AbstractEntityPersister.java:
> >> >> 2312)
> >> >> at
> >> >> org.hibernate.persister.entity.AbstractEntityPersister.update(AbstractEntityPersister.java:
> >> >> 2612)
> >> >> at
> >> >> org.hibernate.action.EntityUpdateAction.execute(EntityUpdateAction.java:
> >> >> 96)
> >> >> at org.hibernate.engine.ActionQueue.execute(ActionQueue.java:
> >> >> 279)
> >> >> at
> >> >> org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:263)
> >> >> at
> >> >> org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:168)
> >> >> at
> >> >> org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:
> >> >> 298)
> >> >> at
> >> >> org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:
> >> >> 27)
> >> >> at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1000)
> >> >> at
> >> >> org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:338)
> >> >> at
> >> >> org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:
> >> >> 106)
> >> >> <my app here>
>
> >> >> So the message suggests that another transaction has updated or
> >> >> deleted the same row I am trying to update here. But, unfortunatley, I
> >> >> am unable to trace ( via <myh2>.trace.db file ) any such transaction,
> >> >> although I have the tracelog on level 3 therefore I see all SQLs
> >> >> printed out.
>
> >> >> Do you have any suggestion as how to find the other transaction that
> >> >> it is interfering with this one above ?
>
> >> >> Thank you very much, indeed.
> >> >> -ivrusuboca-
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