XA and SERIALIZABLE isolation level

Hi,
I'm using JDBC with oracle DB 8.1.6. When I get the physical connection and set transaction isolation level to TRANSACTION_SERIALIZABLE then issue start() on the XAResource instance it gives me error number 24776 "cannot start a new transaction". Without setting isolation level, the transaction would go smoothly. Note that this is the only transaction I have in my small test program. You can test it with the example given in oracle documentation.

Similar Messages

Pls tel me what is the diffrence between snapshot isolation level of mssql and oracels isolation level

Hi,
In mssql i am using following things.
I have two database D1 and D2, i am using snapshot isolation (ALTER DATABASE MyDatabase
SET ALLOW_SNAPSHOT_ISOLATION ON) in both database.
Following is the situation.
1) There is one SP sp1 ( it can be in any database d1 or d2), it updates d2 from d1.
2) d2 is used for reading by web, execept above SP sp1
3) d1 gets updation from web in readcommite isolation.
4) both database will be on same instence of mssql.
Q1) wanted to know how to implement the same thing in oracle 11x express edition.
Q2) is there any diffrence between snapshot isolation level of mssql and oracel.
any link would be help full.
yours sincerely

>Q1) should i set the option to OFF after the process(ts) is complete
No keep it on.
>Q2) ALLOW_SNAPSHOT_ISOLATION ON , will affect other isolation level's transactions
No it will not affect any other transaction isolation level.
>Q3) is my choice of isolation level for process(ts) is correct or there can be any other solution.
Seems fine, although there are probably many other solutions.
David
David http://blogs.msdn.com/b/dbrowne/

Bug in Oracle's handling of transaction isolation levels?

Hello,
I think there is a bug in Oracle 9i database related to serializable transaction isolation level.
Here is the information about the server:
Operating System:     Microsoft Windows 2000 Server Version 5.0.2195 Service Pack 2 Build 2195
System type:          Single CPU x86 Family 6 Model 8 Stepping 10 GenuineIntel ~866 MHz
BIOS-Version:          Award Medallion BIOS v6.0
Locale:               German
Here is my information about the client computer:
Operaing system:     Microsoft Windows XP
System type:          IBM ThinkPad
Language for DB access: Java
Database information:
Oracle9i Enterprise Edition Release 9.2.0.1.0 - Production
With the Partitioning, OLAP and Oracle Data Mining options
JServer Release 9.2.0.1.0 - Production
The database has been set up using the default settings and nothing has been changed.
To reproduce the bug, follow these steps:
1. Create a user in 9i database called 'kaon' with password 'kaon'
2. Using SQL Worksheet create the following table:
CREATE TABLE OIModel (
modelID int NOT NULL,
logicalURI varchar (255) NOT NULL,
CONSTRAINT pk_OIModel PRIMARY KEY (modelID),
CONSTRAINT logicalURI_OIModel UNIQUE (logicalURI)
3. Run the following program:
package test;
import java.sql.*;
public class Test {
public static void main(String[] args) throws Exception {
java.util.Locale.setDefault(java.util.Locale.US);
Class.forName("oracle.jdbc.OracleDriver");
Connection connection=DriverManager.getConnection("jdbc:oracle:thin:@schlange:1521:ORCL","kaon","kaon");
DatabaseMetaData dmd=connection.getMetaData();
System.out.println("Product version:");
System.out.println(dmd.getDatabaseProductVersion());
System.out.println();
connection.setAutoCommit(false);
connection.setTransactionIsolation(Connection.TRANSACTION_SERIALIZABLE);
int batches=0;
int counter=2000;
for (int outer=0;outer<50;outer++) {
for (int i=0;i<200;i++) {
executeUpdate(connection,"INSERT INTO OIModel (modelID,logicalURI) VALUES ("+counter+",'start"+counter+"')");
executeUpdate(connection,"UPDATE OIModel SET logicalURI='next"+counter+"' WHERE modelID="+counter);
counter++;
connection.commit();
System.out.println("Batch "+batches+" done");
batches++;
protected static void executeUpdate(Connection conn,String sql) throws Exception {
Statement s=conn.createStatement();
try {
int result=s.executeUpdate(sql);
if (result!=1)
throw new Exception("Should update one row, but updated "+result+" rows, query is "+sql);
finally {
s.close();
The program prints the following output:
Product version:
Oracle9i Enterprise Edition Release 9.2.0.1.0 - Production
With the Partitioning, OLAP and Oracle Data Mining options
JServer Release 9.2.0.1.0 - Production
Batch 0 done
Batch 1 done
java.lang.Exception: Should update one row, but updated 0 rows, query is UPDATE OIModel SET logicalURI='next2571' WHERE modelID=2571
     at test.Test.executeUpdate(Test.java:35)
     at test.Test.main(Test.java:22)
That is, after several iterations, the executeUpdate() method returns 0, rather than 1. This is clearly an error.
4. Leave the database as is. Replace the line
int counter=2000;
with line
int counter=4000;
and restart the program. The following output is generated:
Product version:
Oracle9i Enterprise Edition Release 9.2.0.1.0 - Production
With the Partitioning, OLAP and Oracle Data Mining options
JServer Release 9.2.0.1.0 - Production
Batch 0 done
Batch 1 done
java.sql.SQLException: ORA-08177: can't serialize access for this transaction
     at oracle.jdbc.dbaccess.DBError.throwSqlException(DBError.java:134)
     at oracle.jdbc.ttc7.TTIoer.processError(TTIoer.java:289)
     at oracle.jdbc.ttc7.Oall7.receive(Oall7.java:573)
     at oracle.jdbc.ttc7.TTC7Protocol.doOall7(TTC7Protocol.java:1891)
     at oracle.jdbc.ttc7.TTC7Protocol.parseExecuteFetch(TTC7Protocol.java:1093)
     at oracle.jdbc.driver.OracleStatement.executeNonQuery(OracleStatement.java:2047)
     at oracle.jdbc.driver.OracleStatement.doExecuteOther(OracleStatement.java:1940)
     at oracle.jdbc.driver.OracleStatement.doExecuteWithTimeout(OracleStatement.java:2709)
     at oracle.jdbc.driver.OracleStatement.executeUpdate(OracleStatement.java:796)
     at test.Test.executeUpdate(Test.java:33)
     at test.Test.main(Test.java:22)
This is clearly an error - only one transaction is being active at the time, so there is no need for serialization of transactions.
5. You can restart the program as many times you wish (by chaging the initial counter value first). The same error (can't serialize access for this transaction) will be generated.
6. The error doesn't occur if the transaction isolation level isn't changed.
7. The error doesn't occur if the UPDATE statement is commented out.
Sincerely yours
     Boris Motik

I have a similar problem
I'm using Oracle and serializable isolation level.
Transaction inserts 4000 objects and then updates about 1000 of these objects.
Transactions sees inserted objects but cant update them (row not found or can't serialize access for this transaction are thrown).
On 3 tries for this transaction 1 succeds and 2 fails with one of above errors.
No other transactions run concurently.
In read commited isolation error doesn't arise.
I'm using plain JDBC.
Similar or even much bigger serializable transaction works perfectly on the same database as plsql procedure.
I've tried oci and thin (Oracle) drivers and oranxo demo (i-net) driver.
And this problems arises on all of this drivers.
This problem confused me so much :(.
Maby one of Oracle users, developers nows cause of this strange behaviour.
Thanx for all answers.

Transaction Isolation Levels

Hi Everyboody.
Oracle docs. say that Oracle supports three isolation levels and the isolation level should be set before the transaction begins with the SET TRANSACTION ISOLATION LEVEL .....
Resource: http://otn.oracle.com/docs/products/oracle9i/doc_library/release2/server.920/a96524/c21cnsis.htm#2641
But I find that Oracle 9i supports only two isolation levels, viz. Read Committed and Serializable.
SQL> SET TRANSACTION ISOLATION LEVEL READ ONLY
2 ;
SET TRANSACTION ISOLATION LEVEL READ ONLY
ERROR at line 1:
ORA-02179: valid options: ISOLATION LEVEL { SERIALIZABLE | READ COMMITTED }
Is READ ONLY isolatin level avalilable in Oracle 9i or is there any problem with my SET instruction?
Please help me at the earliest.
Have a nice day!
Kishore

Thanks Dmitry.
It works.
Continuing on the same thread, I would like to know what is the difference between READ COMMITTED and SERIALIZABLE isolation levels?
Thank you for your reply.
Kishore.

Changing Isolation Level Mid-Transaction

Hi,
I have a SS bean which, within a single container managed transaction, makes numerous
database accesses. Under high load, we start having serious contention issues
on our MS SQL server database. In order to reduce these issues, I would like
to reduce my isolation requirements in some of the steps of the transaction.
To my knowledge, there are two ways to achieve this: a) specify isolation at the
connection level, or b) use locking hints such as NOLOCK or ROWLOCK in the SQL
statements. My questions are:
1) If all db access is done within a single tx, can the isolation level be changed
back and forth?
2) Is it best to set the isolation level at the JDBC level or to use the MS SQL
locking hints?
Is there any other solution I'm missing?
Thanks,
Sebastien

Galen Boyer wrote:
On Sun, 28 Mar 2004, [email protected] wrote:
Galen Boyer wrote:
On Wed, 24 Mar 2004, [email protected] wrote:
Oracle's serializable isolation level doesn't offer what most
customers I've seen expect it to offer. They typically expect
that a serializable transaction will block any read-data from
being altered during the transaction, and oracle doesn't do
that.I haven't implemented WEB systems that employ anything but
the default concurrency control, because a web transaction is
usually very long running and therefore holding a connection
open during its life is unscalable. But, your statement did
make me curious. I tried a quick test case. IN ONE SQLPLUS
SESSION: SQL> alter session set isolation_level =
serializable; SQL> select * from t1; ID FL ---------- -- 1 AA
2 BB 3 CC NOW, IN ANOTHER SQLPLUS SESSION: SQL> update t1 set
fld = 'YY' where id = 1; 1 row updated. SQL> commit; Commit
complete. Now, back to the previous session. SQL> select *
from t1; ID FL ---------- -- 1 AA 2 BB 3 CC So, your
statement is incorrect.Hi, and thank you for the diligence to explore. No, actually
you proved my point. If you did that with SQLServer or Sybase,
your second session's update would have blocked until you
committed your first session's transaction. Yes, but this doesn't have anything to do with serializable.
This is the weak behaviour of those systems that say writers can
block readers.Weak or strong, depending on the customer point of view. It does guarantee
that the locking tx can continue, and read the real data, and eventually change
it, if necessary without fear of blockage by another tx etc.
In your example, you were able to change and commit the real
data out from under the first, serializable transaction. The
reason why your first transaction is still able to 'see the old
value' after the second tx committed, is not because it's
really the truth (else why did oracle allow you to commit the
other session?). What you're seeing in the first transaction's
repeat read is an obsolete copy of the data that the DBMS
made when you first read it. Yes, this is true.
Oracle copied that data at that time into the per-table,
statically defined space that Tom spoke about. Until you commit
that first transaction, some other session could drop the whole
table and you'd never know it.This is incorrect.Thanks. Point taken. It is true that you could have done a complete delete
of all rows in the table though..., correct?
That's the fast-and-loose way oracle implements
repeatable-read! My point is that almost everyone trying to
serialize transactions wants the real data not to
change. Okay, then you have to lock whatever you read, completely.
SELECT FOR UPDATE will do this for your customers, but
serializable won't. Is this the standard definition of
serializable of just customer expectation of it? AFAIU,
serializable protects you from overriding already committed
data.The definition of serializable is loose enough to allow
oracle's implementation, but non-changing relevant data is
a typically understood hope for serializable. Serializable
transactions typically involve reading and writing *only
already committed data*. Only DIRTY_READ allows any access to
pre-committed data. The point is that people assume that a
serializable transaction will not have any of it's data re
committed, ie: altered by some other tx, during the serializable
tx.
Oracle's rationale for allowing your example is the semantic
arguement that in spite of the fact that your first transaction
started first, and could continue indefinitely assuming it was
still reading AA, BB, CC from that table, because even though
the second transaction started later, the two transactions *so
far*, could have been serialized. I believe they rationalize it by saying that the state of the
data at the time the transaction started is the state throughout
the transaction.Yes, but the customer assumes that the data is the data. The customer
typically has no interest in a copy of the data staying the same
throughout the transaction.
Ie: If the second tx had started after your first had
committed, everything would have been the same. This is true!
However, depending on what your first tx goes on to do,
depending on what assumptions it makes about the supposedly
still current contents of that table, it may ether be wrong, or
eventually do something that makes the two transactions
inconsistent so they couldn't have been serialized. It is only
at this later point that the first long-running transaction
will be told "Oooops. This tx could not be serialized. Please
start all over again". Other DBMSes will completely prevent
that from happening. Their value is that when you say 'commit',
there is almost no possibility of the commit failing. But this isn't the argument against Oracle. The unable to
serialize doesn't happen at commit, it happens at write of
already changed data. You don't have to wait until issuing
commit, you just have to wait until you update the row already
changed. But, yes, that can be longer than you might wish it to
be. True. Unfortunately the typical application writer logic may
do stuff which never changes the read data directly, but makes
changes that are implicitly valid only when the read data is
as it was read. Sometimes the logic is conditional so it may never
write anything, but may depend on that read data staying the same.
The issue is that some logic wants truely serialized transactions,
which block each other on entry to the transaction, and with
lots of DBMSes, the serializable isolation level allows the
serialization to start with a read. Oracle provides "FOR UPDATE"
which can supply this. It is just that most people don't know
they need it.
With Oracle and serializable, 'you pay your money and take your
chances'. You don't lose your money, but you may lose a lot of
time because of the deferred checking of serializable
guarantees.
Other than that, the clunky way that oracle saves temporary
transaction-bookkeeping data in statically- defined per-table
space causes odd problems we have to explain, such as when a
complicated query requires more of this memory than has been
alloted to the table(s) the DBMS will throw an exception
saying it can't serialize the transaction. This can occur even
if there is only one user logged into the DBMS.This one I thought was probably solved by database settings,
so I did a quick search, and Tom Kyte was the first link I
clicked and he seems to have dealt with this issue before.
http://tinyurl.com/3xcb7 HE WRITES: serializable will give you
repeatable read. Make sure you test lots with this, playing
with the initrans on the objects to avoid the "cannot
serialize access" errors you will get otherwise (in other
databases, you will get "deadlocks", in Oracle "cannot
serialize access") I would bet working with some DBAs, you
could have gotten past the issues your client was having as
you described above.Oh, yes, the workaround every time this occurs with another
customer is to have them bump up the amount of that
statically-defined memory. Yes, this is what I'm saying.
This could be avoided if oracle implemented a dynamically
self-adjusting DBMS-wide pool of short-term memory, or used
more complex actual transaction logging. ? I think you are discounting just how complex their logging
is. Well, it's not the logging that is too complicated, but rather
too simple. The logging is just an alternative source of memory
to use for intra-transaction bookkeeping. I'm just criticising
the too-simpleminded fixed-per-table scratch memory for stale-
read-data-fake-repeatable-read stuff. Clearly they could grow and
release memory as needed for this.
This issue is more just a weakness in oracle, rather than a
deception, except that the error message becomes
laughable/puzzling that the DBMS "cannot serialize a
transaction" when there are no other transactions going on.Okay, the error message isn't all that great for this situation.
I'm sure there are all sorts of cases where other DBMS's have
laughable error messages. Have you submitted a TAR?Yes. Long ago! No one was interested in splitting the current
message into two alternative messages:
"This transaction has just become unserializable because
of data changes we allowed some other transaction to do"
or
"We ran out of a fixed amount of scratch memory we associated
with table XYZ during your transaction. There were no other
related transactions (or maybe even users of the DBMS) at this
time, so all you need to do to succeed in future is to have
your DBA reconfigure this scratch memory to accomodate as much
as we may need for this or any future transaction."
I am definitely not an Oracle expert. If you can describe for
me any application design that would benefit from Oracle's
implementation of serializable isolation level, I'd be
grateful. There may well be such.As I've said, I've been doing web apps for awhile now, and
I'm not sure these lend themselves to that isolation level.
Most web "transactions" involve client think-time which would
mean holding a database connection, which would be the death
of a web app.Oh absolutely. No transaction, even at default isolation,
should involve human time if you want a generically scaleable
system. But even with a to-think-time transaction, there is
definitely cases where read-data are required to stay as-is for
the duration. Typically DBMSes ensure this during
repeatable-read and serializable isolation levels. For those
demanding in-the-know customers, oracle provided the select
"FOR UPDATE" workaround.Yep. I concur here. I just think you are singing the praises of
other DBMS's, because of the way they implement serializable,
when their implementations are really based on something that the
Oracle corp believes is a fundamental weakness in their
architecture, "Writers block readers". In Oracle, this never
happens, and is probably one of the biggest reasons it is as
world-class as it is, but then its behaviour on serializable
makes you resort to SELECT FOR UPDATE. For me, the trade-off is
easily accepted.Well, yes and no. Other DBMSes certainly have their share of faults.
I am not critical only of oracle. If one starts with Oracle, and
works from the start with their performance arcthitecture, you can
certainly do well. I am only commenting on the common assumptions
of migrators to oracle from many other DBMSes, who typically share
assumptions of transactional integrity of read-data, and are surprised.
If you know Oracle, you can (mostly) do everything, and well. It is
not fundamentally worse, just different than most others. I have had
major beefs about the oracle approach. For years, there was TAR about
oracle's serializable isolation level *silently allowing partial
transactions to commit*. This had to do with tx's that inserted a row,
then updated it, all in the one tx. If you were just lucky enough
to have the insert cause a page split in the index, the DBMS would
use the old pre-split page to find the newly-inserted row for the
update, and needless to say, wouldn't find it, so the update merrily
updated zero rows! The support guy I talked to once said the developers
wouldn't fix it "because it'd be hard". The bug request was marked
internally as "must fix next release" and oracle updated this record
for 4 successive releases to set the "next release" field to the next
release! They then 'fixed' it to throw the 'cannot serialize' exception.
They have finally really fixed it.( bug #440317 ) in case you can
access the history. Back in 2000, Tom Kyte reproduced it in 7.3.4,
8.0.3, 8.0.6 and 8.1.5.
Now my beef is with their implementation of XA and what data they
lock for in-doubt transactions (those that have done the prepare, but
have not yet gotten a commit). Oracle's over-simple logging/locking is
currently locking pages instead of rows! This is almost like Sybase's
fatal failure of page-level locking. There can be logically unrelated data
on those pages, that is blocked indefinitely from other equally
unrelated transactions until the in-doubt tx is resolved. Our TAR has
gotten a "We would have to completely rewrite our locking/logging to
fix this, so it's your fault" response. They insist that the customer
should know to configure their tables so there is only one datarow per
page.
So for historical and current reasons, I believe Oracle is absolutely
the dominant DBMS, and a winner in the market, but got there by being first,
sold well, and by being good enough. I wish there were more real market
competition, and user pressure. Then oracle and other DBMS vendors would
be quicker to make the product better.
Joe

Multiple submits and Transaction setting and isolation level ????

From a Struts JSP,
I submit the form n times.
I have a session facade in place. The corresponding function has trnsaction attribute as "Required" and the isolation level as "serializable"
As a business rule the record cannot be inserted more than once.
But it is......
The Facade calls the Controller which in turn calls the VOA which calls DAO.
There is a find method which looks for that unique id if it exists it throws an Validation exception.
There are two scenes:
-----If I open two IE and submit the form it throws validation exception
-----If I click on submit more than once from the same IE it inserts as many records.
Can any one please put some light????
But the inserts is happening

Could you make the picture more clear, probably with some code snippets where the actual database handshake is taking place?
Also whether the business rule is a part of database constraints or is it done at the application level. From your description it seems that it is being done at the application level. Check if the find method check is getting executed each time, or is it being bypassed under certain conditions.

Problems in using isolation level serializable

Dear everyone:
This is the problem I met while using isolation level
serializable in ORALCE 8.0.3 for Netware:
Program 1 Program2
Insert record 1 into table 1
select record 1 from table1
commit
select record1 from table1
insert record 2 into table1
select record2 from table1
commit
select record2 from table1
update record2 from table1
commit
delete record2 from table1
commit
update record1 from table1
*ORA-8177 cannot serialize
access for this transaction
According to my understanding to the serialization isolation
level, it should not occurs.
Anyone can give me some ideas?
Regards!
null

Dear everyone:
This is the problem I met while using isolation level
serializable in ORALCE 8.0.3 for Netware:
Program 1 Program2
Insert record 1 into table 1
select record 1 from table1
commit
select record1 from table1
insert record 2 into table1
select record2 from table1
commit
select record2 from table1
update record2 from table1
commit
delete record2 from table1
commit
update record1 from table1
*ORA-8177 cannot serialize
access for this transaction
According to my understanding to the serialization isolation
level, it should not occurs.
Anyone can give me some ideas?
Regards!
null

Setting transaction isolation level in Weblogic 5.1

          Hi,
          I'm using Weblogic server5.1 and i'm trying to set the isolation level on one
          of my session bean. Below is the code :
          <weblogic-ejb-jar>
          <weblogic-enterprise-bean>
          <ejb-name>chargeMgr</ejb-name>
          <jndi-name>chargeMgr</jndi-name>
          <transaction-isolation>
          <isolation-level>Serializable</isolation-level>
          <method>
          <ejb-name>chargeMgr</ejb-name>
          <method-intf>Remote</method-intf>
          <method-name>*</method-name>
          </method>
          </transaction-isolation>
          </weblogic-enterprise-bean>
          </weblogic-ejb-jar>
          I have checked the syntax against the weblogic documentation.
          However, when i try to jar the beans up into the jar file (weblogic.ejbc), it
          give me the following error :
          org.xml.sax.SAXParseException: Element "weblogic-enterprise-bean" allows no further
          input; "transaction-isolation" is not allowed.
          Can anyone help?
          Regards.


yes, only in weblogic-ejb-jar.xml , and you can see that from the DTD
          source.
          thanks
          Yu
          "cw lee" <[email protected]> wrote in message
          news:[email protected]...
          >
          > thanks for ur advice.
          >
          > one thing i forgot to mention is that the isolation-level was specified in
          weblogic-ejb-jar.xml.
          > Do u mean that it must be placed in weblogic-cmp-rdbms-jar.xml and not
          weblogic-ejb-jar.xml
          > ?
          >
          > Are the codes u suggested to be in weblogic-ejb-jar.xml or
          weblogic-cmp-rdbms-jar.xml
          > ?
          >
          > Regards.
          >
          >
          >
          > "Yu Tian" <[email protected]> wrote:
          > >the right name for Seriealizable should be: TRANSACTION_SERIALIZABLE.
          > >so the
          > >DD looks like:
          > >
          > ><?xml version="1.0"?>
          > >
          > ><!DOCTYPE weblogic-ejb-jar PUBLIC '-//BEA Systems, Inc.//DTD WebLogic
          > >5.1.0
          > >EJB//EN' 'http://www.bea.com/servers/wls510/dtd/weblogic-ejb-jar.dtd'>
          > >
          > ><weblogic-ejb-jar>
          > > <weblogic-enterprise-bean>
          > > <ejb-name>containerManaged</ejb-name>
          > > <caching-descriptor>
          > > <max-beans-in-cache>1000</max-beans-in-cache>
          > > </caching-descriptor>
          > > <persistence-descriptor>
          > > <persistence-type>
          > > <type-identifier>WebLogic_CMP_RDBMS</type-identifier>
          > > <type-version>5.1.0</type-version>
          > > <type-storage>META-INF/weblogic-cmp-rdbms-jar.xml</type-storage>
          > > </persistence-type>
          > > <persistence-use>
          > > <type-identifier>WebLogic_CMP_RDBMS</type-identifier>
          > > <type-version>5.1.0</type-version>
          > > </persistence-use>
          > > </persistence-descriptor>
          > > <jndi-name>containerManaged.AccountHome</jndi-name>
          > > <transaction-isolation>
          > > <isolation-level>TRANSACTION_SERIALIZABLE</isolation-level>
          > > <method>
          > > <ejb-name>containerManaged</ejb-name>
          > > <method-name>*</method-name>
          > > </method>
          > > </transaction-isolation>
          > > </weblogic-enterprise-bean>
          > > </weblogic-ejb-jar>
          > >
          > >Thanks
          > >
          > >Yu
          > >
          > >
          > >"cw lee" <[email protected]> wrote in message
          > >news:[email protected]...
          > >>
          > >> Hi,
          > >>
          > >> I'm using Weblogic server5.1 and i'm trying to set the isolation level
          > >on
          > >one
          > >> of my session bean. Below is the code :
          > >>
          > >> <weblogic-ejb-jar>
          > >> <weblogic-enterprise-bean>
          > >> <ejb-name>chargeMgr</ejb-name>
          > >> <jndi-name>chargeMgr</jndi-name>
          > >> <transaction-isolation>
          > >> <isolation-level>Serializable</isolation-level>
          > >> <method>
          > >> <ejb-name>chargeMgr</ejb-name>
          > >> <method-intf>Remote</method-intf>
          > >> <method-name>*</method-name>
          > >> </method>
          > >> </transaction-isolation>
          > >> </weblogic-enterprise-bean>
          > >> </weblogic-ejb-jar>
          > >>
          > >> I have checked the syntax against the weblogic documentation.
          > >> However, when i try to jar the beans up into the jar file
          (weblogic.ejbc),
          > >it
          > >> give me the following error :
          > >>
          > >> org.xml.sax.SAXParseException: Element "weblogic-enterprise-bean"
          allows
          > >no further
          > >> input; "transaction-isolation" is not allowed.
          > >>
          > >> Can anyone help?
          > >>
          > >> Regards.
          > >>
          > >
          > >
          >

Isolation level when using UserTransaction

          What isolation level does WLS assign to JDBC connection objects when used within
          a user-controlled JTA transaction?
          e.g. when using the following code within a servlet:
          UserTransaction ut = (UserTransaction) ictx.lookup("java:comp/Usertransaction");
          ut.begin();
          DataSource ds = ictx.lookup("java:comp/env/jdbc/datasource");
          Connection conn = ds.getConnection();
          ResultSet rs = ps.executeQuery("....");
          conn.commit();
          Does weblogic force a specific isolation level, or will it fall back to the default
          of the database?
          We are using WLS 8.1 SP1 and Oracle 9.
          /Johan


          johan Eltes wrote:
          > What isolation level does WLS assign to JDBC connection objects when used within
          > a user-controlled JTA transaction?
          > e.g. when using the following code within a servlet:
          >
          > UserTransaction ut = (UserTransaction) ictx.lookup("java:comp/Usertransaction");
          > ut.begin();
          > DataSource ds = ictx.lookup("java:comp/env/jdbc/datasource");
          > Connection conn = ds.getConnection();
          > ...
          > ResultSet rs = ps.executeQuery("....");
          > ...
          > conn.commit();
          >
          > Does weblogic force a specific isolation level, or will it fall back to the default
          > of the database?
          > We are using WLS 8.1 SP1 and Oracle 9.
          The Spec says that the connection should be in the DBMS's default isolation level
          until set differently. For Oracle you will be in READ-COMMITTED. That's what you want
          because Oracle's SERIALIZABLE isolation level is problematic, not doing what most
          folks assume...
          Joe
          > /Johan

How to set the isolation level on Entity EJBs

I am using 10.1.3.3 of the OC4J app server.
I am creating an application that uses EJB 2.1.
I am trying to set the isolation levels on the EJBs to either serializable or repeatable read.
When i deploy the EAR file from the OC4J admin console, i can set the isolation level property on the EJB's however when i inspect the orion-ejb-jar.xml file I do not see the isolation level being set. Furthermore, i tried to manually change the isolation setting by editing the orion-ejb-jar.xml and adding the isolation="serialiable" attribute on the entity bean descriptor. I then stopped and restarted the server. I noticed that my change was no longer in the file.
Can someone please let me know how to solve this problem and set the isolation level on Entity EJBs . Thanks

I find it at ejb.pdf from BEA.
          The transaction-isolation stanza can contain the elements shown here:
          <transaction-isolation>
          <isolation-level>Serializable</isolation-level>
          <method>
          <description>...</description>
          <ejb-name>...</ejb-name>
          <method-intf>...</method-intf>
          <method-name>...</method-name>
          <method-params>...</method-params>
          </method>
          </transaction-isolation>
          "Hyun Min" <[email protected]> wrote in message
          news:3c4e7a83$[email protected]..
          > Hi!
          >
          > I have a question.
          > How to set the transaction isolation level using CMT in descriptor?
          >
          > The Isolation level not supported in CMT?
          >
          > Thanks.
          > Hyun Min
          >
          >

OCJ4's EJB transaction isolation level

Hello, all
Does OC4J supports various transaction isolation level?
I am using JDeveloper to create and deploy
EJBs and all I can find is transaction attributes,
and not isolation level. The book I am currently reading
suggests that there's tx isolation setting in BEA
WebLogic.
If anybody has found a way to do this in OC4J + Jdeveloer,
or if it is ever required, let me know.
Thanks

Hi
You can specify the isolation level using the "isolation" attribute of the "entity-deployment" tag.
Ex:
<entity-deployment name="MyEJB" isolation="serializable">
Go through the DTD for details :
http://xmlns.oracle.com/ias/dtds/orion-ejb-jar.dtd
--Shrini

Isolation Level vs. Locking

Hello,
I am still wrestlling a bit with the issues involved in setting an isolation
level. I am using WL 5.1, Oracle, and CMP.
I do now understand the issues involved between Oracle's
SERIALIZABLE and READ-COMMITTED isolation levels, etc.
But I also note that weblogic uses a pessimistic locking
approach for serializing access to entity ejb's. Doesn't this
locking supercede anything but an isolation level of
SERIALIZABLE? What happens with an isolation level
of READ-COMMITTED, even though the access to an
entity within any transaction will be serialized anyway?
Are there issues related to persistence issues outside of
ejb's, such as using JMS persistent messages within the
same system (same connection pool, etc.).
Also, I note that the ejb 2.0 spec in weblogic will allow
a more optimistic locking model. In this case, how will
multiple commits behave, will they behave according
to the isolation level chosen (READ-COMMITTED
or SERIALIZABLE?).
It's all confusing. What is the point, in ejb 1.1, for allowing
the bean developer to specify an isolation level, if all
access to entities will be done with exclusive locks?
What happens with multiple result finder methods? Does
this place exclusive locks on each entity found, within
a transaction?
Should I spend more time worrying about locking
models or isolation levels.
Am I just going around in circles?
Jason
Jason Rosenberg
SquareTrade
(remove 'nospam' from my return address)

Well, for now, I am designing for Oracle. What do you mean
by hazy?
Kirk Wylie <[email protected]> wrote in message news:[email protected]...
Probably not something you can count on guaranteeing no blocking. The
database could very well block here, particularly if your'e using
anything other than Oracle on the back-end, and Oracle can be a bit,
ahem, hazy in its acceptance of its own semantics here.
Kirk Wylie
Jason Rosenberg wrote:
Well, if the database table is set up to use READ-COMMITTED,
then it shouldn't block on the database, correct?
Jason
Cameron Purdy <[email protected]> wrote in message news:[email protected]...
... which means it could block on the database, correct?
Cameron Purdy
"Rob Woollen" <[email protected]> wrote in message
news:[email protected]...
A finder will never block on a container lock. For instance, imagine
that primary keys 3 and 4 are currently participating in a transaction
and are locked in server A. If a finder is called in server A which
returns these keys, the finder will run independently of the EJB server
locks. (Of course the database isolation will still apply.)
-- Rob
Jason Rosenberg wrote:
Ah, clustering saves the day!
I'm wondering though, since we don't have control over which
server in a cluster a given ejb may run on at any given time,
the concurrent behavior may be different to control. Some
times you can have concurrent access based on
READ-COMMITTED on the db level, and some times weblogic
will force a SERIALIZABLE behavior if 2 conflicting
ejb's get instantiated in the same container.
This is what I want. I would like complex finder methods
to be able to return a collection of primary keys over a
table, based on a READ-COMMITTED basis. This
needs to happen often, and shouldn't block (it's ok
if it misses out on uncommitted data in process, or
if it returns keys that may be in the process of being
deleted). But I don't ever want it to block because
another component has uncomitted changes in process.
Ideas? Wait for ejb2.0?
Jason
Rob Woollen <[email protected]> wrote in message
news:[email protected]...
It matters if you are in a cluster, or if othercomponents/applications
are accessing the same data.
It will also matter if your db does not have row-level locking.
-- Rob
Jason Rosenberg wrote:
I've excerpted below some of the text from the weblogic
documentation.
What this says to me is that, indeed, if an ejb entity is in anywayinvolved
in a transaction, all other transactions will be blocked frominstantiating
and using the bean instance until the transaction is over.
This is a de-facto SERIALIZABLE isolation level, is it not, with allthe
plusses and minuses. The plus is that data integrity is maintained,the
minus is that concurrent access is negatively effected.
What am I missing. Given this mechanism, what difference does it
make whether I use of a transaction isolation level ofREAD-COMMITTED
or SERIALIZABLE?
It looks like the story does change for ejb2.0.....
From the weblogic online documentation at:
http://www.weblogic.com/docs51/classdocs/API_ejb/EJB_environment.html#108796
7
Locking Model for Entity EJBs
The EJB 1.1 container in WebLogic Server Version 5.1 uses apessimistic locking mechanism for entity EJB instances. As clients
enlist an EJB or EJB method in a transaction, WebLogic Server placesan exclusive lock on the EJB instance or method for the
duration of the transaction. Other clients requesting the same EJBor method block until the current transaction completes.
This method of locking provides reliable access to EJB data, andavoids unnecessary calls to ejbLoad() to refresh the EJB
instance's
persistent fields. However, in certain circumstances pessimistic
locking may not provide the best model for concurrent access to
the
EJB's data. Once a client has locked an EJB instance, other clients
are blocked from the EJB's data even if they intend only to
read
the persistent fields.
To improve concurrent access for entity EJB's, the WebLogic Server
EJB 2.0 container enables you to defer locking services to
the
underlying database. In most cases, the underlying data store can
provide finer granularity for locking EJB data, and improve
throughput for concurrent access to the bean's data. See EJB 2.0 forBEA WebLogic Server Overview for more information.
Cameron Purdy <[email protected]> wrote in message
news:[email protected]...
I believe the "locking" refers to an internal WL implementationthat
prevents multiple threads from accessing an EJB instance.
Cameron Purdy, LiveWater
"Jason Rosenberg" <[email protected]> wrote in message
news:[email protected]...
Hello,
I am still wrestlling a bit with the issues involved in setting
an
isolation
level. I am using WL 5.1, Oracle, and CMP.
I do now understand the issues involved between Oracle's
SERIALIZABLE and READ-COMMITTED isolation levels, etc.
But I also note that weblogic uses a pessimistic locking
approach for serializing access to entity ejb's. Doesn't this
locking supercede anything but an isolation level of
SERIALIZABLE? What happens with an isolation level
of READ-COMMITTED, even though the access to an
entity within any transaction will be serialized anyway?
Are there issues related to persistence issues outside of
ejb's, such as using JMS persistent messages within the
same system (same connection pool, etc.).
Also, I note that the ejb 2.0 spec in weblogic will allow
a more optimistic locking model. In this case, how will
multiple commits behave, will they behave according
to the isolation level chosen (READ-COMMITTED
or SERIALIZABLE?).
It's all confusing. What is the point, in ejb 1.1, for allowing
the bean developer to specify an isolation level, if all
access to entities will be done with exclusive locks?
What happens with multiple result finder methods? Does
this place exclusive locks on each entity found, within
a transaction?
Should I spend more time worrying about locking
models or isolation levels.
Am I just going around in circles?
Jason
Jason Rosenberg
SquareTrade
(remove 'nospam' from my return address)
Kirk Wylie | mailto:[email protected] | http://www.radik.com

Read committed isolation level must not produce nonrepeatable read

Hi,
I am sql server DBA. But i am trying to improve myself in oracle too.
I read isolation levels in oracle. And it says, In read committed isolation level , oracle guarantees the result set that contains committed records at the beginning of reading operation.
İf it is guaranteed , how does nonrepeatable read can occur? It must not occur then.
I think , I misunderstood something .
can you explain me?
Thanks

>
I read isolation levels in oracle. And it says, In read committed isolation level , oracle guarantees the result set that contains committed records at the beginning of reading operation.
İf it is guaranteed , how does nonrepeatable read can occur? It must not occur then.
>
See the 'Multiversion Concurrency Control' section in the database concepts doc. It discusses this and has a simple diagram (can't post it) that shows it.
http://docs.oracle.com/cd/B28359_01/server.111/b28318/consist.htm
>
As a query enters the execution stage, the current system change number (SCN) is determined. In Figure 13-1, this system change number is 10023. As data blocks are read on behalf of the query, only blocks written with the observed SCN are used. Blocks with changed data (more recent SCNs) are reconstructed from data in the rollback segments, and the reconstructed data is returned for the query. Therefore, each query returns all committed data with respect to the SCN recorded at the time that query execution began. Changes of other transactions that occur during a query's execution are not observed, guaranteeing that consistent data is returned for each query.
Statement-Level Read Consistency
Oracle Database always enforces statement-level read consistency. This guarantees that all the data returned by a single query comes from a single point in time—the time that the query began. Therefore, a query never sees dirty data or any of the changes made by transactions that commit during query execution. As query execution proceeds, only data committed before the query began is visible to the query. The query does not see changes committed after statement execution begins.
>
The first sentence is the key:
>
As a query enters the execution stage, the current system change number (SCN) is determined.
>
Oracle will only query data AS OF that SCN that was determined.
If you now rerun the query Oracle repeats the process: it determines the SCN again which could be newer if other users have committed changes.
That second execution of the query may find that some rows have been modified or even deleted and that new rows have been inserted: nonrepeatable read.
If you use the SERIALIZABLE isolation level then that second query will use the SCN that was determined at the very START of the transaction. For the simple example above it means the second query would use the SAME SCN that the first query used: so the same data would be returned.
Table 13-2 in that doc (a few pages down) lists the isolation levels
>
Read committed
This is the default transaction isolation level. Each query executed by a transaction sees only data that was committed before the query (not the transaction) began. An Oracle Database query never reads dirty (uncommitted) data.
Because Oracle Database does not prevent other transactions from modifying the data read by a query, that data can be changed by other transactions between two executions of the query. Thus, a transaction that runs a given query twice can experience both nonrepeatable read and phantoms.

Transaction Isolation Level to Read UnCommited in Non OLTP Database

HI,
We are having a database which for NOT OLTP process. That is OLAP DB. Operation on that DB is only Select and (Incremental Insert - FOR DWH ) not Update/Delete and we are performing ROLAP operations in that DB.
By Default SQL Server DB isolation Level is READ COMMITTED.AS Our DB IS OLAP SQL Server DB we need to change the isolation level toRead Uncommited. We google it down but We can achive in
Transaction level only by SET isoaltion Level TO Read UNCOMMITED
or ALLOW_SNAPSHOT_ISOLATION ON or READ_COMMITTED_SNAPSHOT
Is there any other way if we can Change the Database isolation level to READ uncommitedfor Entire Database?, insteads of achiving in Transaction Level or With out enabling SET ALLOW_SNAPSHOT_ISOLATION ON or READ_COMMITTED_SNAPSHOT
Please use Marked as Answer if my post solved your problem and use Vote As Helpful if a post was useful.
Please use Marked as Answer if my post solved your problem and use Vote As Helpful if a post was useful.

Hi,
My first question would be why do you want to change Isolation level to read uncommitted, are you aware about the repercussions you will get dirty data, a wrong data.
Isolation level is basically associated with the connection so is define in connection.
>> Transaction level only by SET isoaltion Level TO Read UNCOMMITED or ALLOW_SNAPSHOT_ISOLATION ON or READ_COMMITTED_SNAPSHOT
Be cautious Read UNCOMMITED and Snapshot isolation level are not same.The former is pessimistic Isolation level and later is Optimistic.Snapshot isolation levels are totally different from read uncommitted as snapshot Isolation level
uses row versioning.I guess you wont require snapshot isolation level in O:AP DB.
Please read below blog about setting Isolation level Server wide
http://blogs.msdn.com/b/ialonso/archive/2012/11/26/how-to-set-the-default-transaction-isolation-level-server-wide.aspx
Please mark this reply as the answer or vote as helpful, as appropriate, to make it useful for other readers
My TechNet Wiki Articles

Isolation Level in Distributed Transaction

Hi All,
I setup a distributed transaction with a Serializable isolation level.
When the OracleConnection enlists the distributed transaction I have read-commited isolation on Oracle allowing the transaction to perform inconsistent reads.
Is the Oracle Provider ignoring the distributed transaction isolation level?
How can I make the provider set the appropriate isolation level?
Thanks a lot,
BMoscao

Hi,
i've got the same problem.
Could you solve it?
thanks

XA and SERIALIZABLE isolation level

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