Lock Cascade With Select for UPDATE

If I had a employee table and a phone table with a parent/child relationship and a primary key constraint on the employee table-will issuing a select for update on the employee also lock the corresponding child rows on the phone table ?
If not how can I bring this about ?

You only need two sessions:
First session: Issue the 'select for update'
statements for the row(s) in both tables, don't
rollback or commit
Second session: try to update a row that you tried to
lock in the first session (with NOWAIT).
Thanks. I can try this definitely. A basic question.
You are asking me to do a join on both the tables right ?
Not two individual SQL statements ?
Updating the primary key is known as a Bad Idea (tm).
The key should never be touched because it should be
meaningless. When you have a column that holds 'real'
information it is no candidate for a primary key.
Rgds,
GuidoYes I am aware of that. I was just wondering what is the meaning behind this statement from this link ?
http://www.akadia.com/services/ora_locks_survival_guide.html
And the exact phrase from that link under the section Referential Integrity Locks (RI Locks)
"RI constraints are validated by the database via a simple SELECT from the dependent (parent) table in question-very simple, very straightforward. If a row is deleted or a primary key is modified within the parent table, all associated child tables need to be scanned to make sure no orphaned records will result. "
Thanks again.

Similar Messages

LOCK TABLE vs select for update

Hello All,
if the requirement is to lock an entire huge table to prevent any users from performing any update statement, which statement has more performance gain and why: LOCK TABLE or select fro update nowait?
is there any overhead of using LOCK TABLE statement?
Thanks,

The reason I said to revoke update privilege is because I do not understand the requirement. Why do you want to prevent users from updating the table? I am assuming that users should never be allowed to update the table. In that case locking the table and select for update would be no good. If you want to stop users from updating while some one else is updating, why? All the lock table or select for update will do is cause their session to wait (hang) until the locking process commits or rolls back. This could generate a few (sic) complaints that the user application is slow/freezing.
If you can state the business problem, perhaps we can offer a solution.

Trigger with SELECT-FOR-UPDATE

There is a trigger on a table, which updates a particular column with SYSDATE BEFORE an INSERT OR UPDATE in the table.
CREATE OR REPLACE TRIGGER my_schema.trg_Order
BEFORE INSERT OR UPDATE
ON my_schema.ORDER
REFERENCING NEW AS NEW OLD AS OLD
FOR EACH ROW
BEGIN
:NEW.LAST_UPDATE_DATE := SYSDATE;
END;
If I update the record using PL/SQL with SELECT-FOR-UPDATE & then UPDATE, the column LAST_UPDATE_DATE is not updated with the SYSDATE.
But if it is done by using the UPDATE Statement, then the column LAST_UPDATE_DATE is correctly updated with the SYSDATE.
Why? How can I ensure that for SELECT-FOR-UPDATE & then UPDATE will also update the LAST_UPDATE_DATE with SYSDATE.

The Table Order has a BLOB column.

Inconsistent Locking with Select for Update

Hi,
I seem to be having some issues in using SELECT FOR UPDATE and was hoping to get some insight from the Oralce Guru's out there.
I have a J2EE application, running in WebLogic 8.1.4 using Oralce 9.2.0.1.0.
The application contains code that requires locking to be done on a specific table with multiple transactions (tx) requesting the same lock. Eg:
Tx 1: Select * from Zone where Zoneid = 'Zone1' for update (Obtains lock)
Tx 2: Select * from Zone where Zoneid = 'Zone1' for update (waits)
Tx 100: Select * from Zone where Zoneid = 'Zone1' for update
Tx1 commits.
It appears that the following transactions, i.e. Tx2 - Tx100 do not seem to execute in the order the lock was requested. That is Tx 100 always appears to be the second last transaction to execute, after which some arbitrary transaction between Tx2 - Tx99 will execute after Tx100 has committed.
This seems to tell me that the lock is not being handed in a FIFO manner and is causing us great pain as our data is not longer consistent.
Does anyone know how i might be able to trace which transaction is being awarded the lock? Also if anyone has any suggestion on how to troubleshoot/solve this issue, greatly appreciated.
TIA
Prem

Oracle does not have a lock queue/manager at all. The locked status of a record is essentially an attribute of the record itself. It is stored on the datablock header. When a transaction requests a lock and can't get it, and is willing to wait (SELECT FOR UPDATE without NOWAIT), it first spins while waiting for the lock (four times as I recall), then sleeps waiting for the lock. The the more times it sleeps before getting the lock, the longer it will sleep before trying again.
What is likely happening here is that transaction 100 is still spinning when transaction 1 commits, so checks back more frequently and gets the lock first. The rest get the lock whenever they wake up and noone else has taken the lock.
If you need the transaction to occur in order, then I do not think you can use Oracle's native locking mechanism. Depending on what exactly you are trying to do, you may want to look at Advanced Queueing, or possibly the built-in package DBMS_LOCK.
HTH
John

When does select for update release locks

Hello all,
Does anyone know when Oracle realeases the row locks when a
select for update is issued?
Does Oracle realase the row lock at the time when an actual update statement is
issued for the locked row, or does it wait until a commit statment is executed?
So for example, can I lock several rows with a select for update clause, and then
issue update statements as many times as I want on each locked row without
having to worry about the lock being released until I issue a commit statement.
Thanks,
David

yes.
The lock is released only when your transaction ends. A transaction can end because of:
1). Commit.
2). Rollback.
3). client disconnects.
etc. etc...

Is SELECT FOR UPDATE lock ever released?

Hi,
Does any one know whether the lock acquired by SELECT FOR UPDATE will ever be released if user session ends without commit or rollback(e.g. crashed)? If it does, is there a default parameter to control the maximum wait time for Oracle to release the lock automatically?
Thanks,
JM

Your select statement won't be committed if the db crashes. That is a DML (data manipulation language)statement. In your scenario everything is rolled back upto the last commit or savepoint. For DDL (data definition Language) for the same situation you would get an implicit commit.
Hope this helps.

Disallow select for update

Hi,
I am making a read only user, with select rights on all of the tables in another scheme. How do I dissalow this user to lock the production table with select for update?
Regards
Nico

Good idea in principle, but there may be more efficient solutions than DISTINCT. Any operation which prevents view merging appears to work (or rather not work) e.g.
CREATE OR REPLACE VIEW view_name
AS
   SELECT /*+ NO_MERGE */ column_name
   FROM   table_name;...is sufficient to raise ORA-02014: cannot select FOR UPDATE from view with DISTINCT, GROUP BY, etc. when attempting SELECT ... FOR UPDATE.
It is important to note though that /*+ NO_MERGE */ could theoretically be ignored by the optimizer - another cheap alternative you might consider would be to reference ROWNUM in the view definition, e.g.
CREATE OR REPLACE VIEW view_name
AS
   SELECT column_name
   FROM   table_name
   WHERE ROWNUM >= 1;

Memory Leak - select for update

Hi All.
Doing an application using OCI 8.1.7 I faced with a memory leak. (or it seems to). The leak is caused by OCIStmtExecute with SELECT FOR UPDATE statement when the iters parameter of that function is 0. In all other cases it works Ok. Below you can find a code causes a leak:
const char* sqlStatement = "select integercol from test_types for update";
OCIStmt* ociStatementHandle = 0;
OCIHandleAlloc(ociEnvHandle,(dvoid **)&ociStatementHandle,
OCI_HTYPE_STMT, (size_t) 0, (dvoid **) 0));
OCIStmtPrepare(ociStatementHandle, ociErrorHandle,
(text*)sqlStatement, strlen(sqlStatement), OCI_NTV_SYNTAX, OCI_DEFAULT));
int int_test;
OCIDefine* ociDefineHandle = 0;
OCIDefineByPos(ociStatementHandle, &ociDefineHandle, ociErrorHandle,
1, (dvoid *)&int_test, (sword) sizeof(int), SQLT_INT, (dvoid *) 0, (ub2 *)0,
(ub2 *)0, OCI_DEFAULT));
ub4 iters = 0; // (0 causes a leak)
for( int i=0; i < 100000; i++ )
OCIStmtExecute(ociServiceHandle, ociStatementHandle, ociErrorHandle, iters, (ub4) 0, (CONST OCISnapshot *) NULL, (OCISnapshot *) NULL, OCI_DEFAULT));
If I change iter to 1 the leak disappears, but it is not suitable of course. Oracle documentation says following:
iters (IN)
For non-SELECT statements, the number of times this statement is executed is equal to iters - rowoff.
For SELECT statements, if iters is non-zero, then defines must have been done for the statement handle. The execution fetches iters rows into these predefined buffers and prefetches more rows depending upon the prefetch row count. If you do not know how many rows the SELECT statement will retrieve, set iters to zero.
This function returns an error if iters=0 for non-SELECT statements.
Did somebody face the problem? Do you know how to fix it?
null

<BLOCKQUOTE><font size="1" face="Verdana, Arial, Helvetica">quote:</font><HR>Originally posted by Bjorn Engsig ([email protected]):
Are you saying, that the memory leak disappears if you don't do 'for update' in the query?
Also, is the memory leak on the client or server side?<HR></BLOCKQUOTE>
Yes, the leak appeares ONLY for 'select ... for update' statements.
It is a client side leak, the client is Win2000.
null

SELECT FOR UPDATE with the SKIP LOCK clause

Hi,
I have a query regarding the SELECT FOR UPDATE with the SKIP LOCK clause.
Whether this will be really good for parallel processing.
Also if we are selecting a set of records in a cursor whether the lock will be done at the records level once we fetch the records?
Also do we have any known issues with this one?
We are trying to figure out whether this will fit for business requirement, we are trying to do a implement a threading kind of thing for our stored procedure invocation in background using shell script.
Any suggestion or feedback on this will be helpful for us.
Thanks a lot for the support given....
Regards,
Basil Abraham.

http://www.oracle.com/technology/oramag/oracle/08-mar/o28plsql.html
Please read the above thread for few information...Thanks!

Oracle select for update: not releasing lock

My JDBC code uses "select for update" to modify record in Oracle database. I tried to simulate network connection down situation.
After my JDBC code locked on a record using "select for update", I unplugged the network cable. I then tried to run the same code on another computer, but it could not accquire the lock, because the previous lock was not released. I tried sqlplus to lock the record, but failed also. The lock has been there for at least an hour now. I guess it may finally be released, but is there a way for oracle to release the lock as soon as the connection is down? Not know if it is a JDBC setting or oracle setting.

Dear Friend,
What you are trying to do is not correct way of checking the concurrency and transaction.
The reason is as listed below.
01.Always remember http is a stateless protocol and removing the connection or just closing the browser will never be informed to the database or to the application server thus the transaction monitor (TM)or processor will never release the lock as it will deem that the actor is manipulating the data.
02.As per locking goes every database is having a �TM� and the default isolation level setting is different like oracle uses serializable DB2udb 7.0 or db2/As400 uses repeatable read. You can change this setting by editing the default setting in the database but be very sure before touching it.
03. You can also transpose this with your Application server setting for that piece of code or Globally but again be very sure about it as it will change the entire gamete.
04. For releasing lock you have to manually do it or you can change the settings of App server or the Database to release the connection after some wait time.
Regards,
Ruchir

DBMS_LOCK vs Select for update locking

Hi,
In one of our database packages, we are using the dbms_lock (that package is used to generate unique numbers) instead of select for update locking.
I want to ask what is more suitable here. Our application is oracle forms and oracle db on oracle app server.
Are there any limitations to select for update locking?
What are the conditions favourable to use DBMS_LOCK?
Regards,

DBMS_LOCK is extremely efficient. Try it. Put a call to obtain/free a lock in a loop and see how long it takes to loop a few thousand times (don't SLEEP in the loop, just obtain and free the lock). If you are having performance issues with DBMS_LOCK or your select it is probably because whatever it is that gets the lock (whichever way you get it) is taking a certain amount of time to finish.
I too, am curious as to what "issues" you had. In either case, a lock for consistent read will be different than a lock for update (as it should be) in terms of how it impacts other users.

Updatable View issues: cannot select FOR UPDATE from view with DI

Hi All,
I have a simple view XY and an instead of trigger on that to insert data into one table which is used in the my view. When I do insert statement on view XY it is working fine from sql but when i used same thing with page process of " Process Row of XY Automatic Row Processing (DML) " i am getting following error. I am using APEX 3.0 . Please help me.
ORA-20001: Error in DML: p_rowid=xxxx, p_alt_rowid=abc, p_rowid2=, p_alt_rowid2=. ORA-02014: cannot select FOR UPDATE from view with DISTINCT, GROUP BY, etc.
Thanks

James,
are you already on 3.0.1.00.07 or 3.0.1.00.08? Have a look at the release notes, it says something about a bug fix for some occurrences of ORA-02014.
Also have a look at the new substitution value/item FSP_DML_LOCK_ROW which turns locking off if you set it to FALSE. See http://www.oracle.com/technology/products/database/application_express/html/3.0.1_readme.html#CHDIDIAF and also http://download-west.oracle.com/docs/cd/B32472_01/doc/appdev.300/b32471/advnc.htm#BCGFDAIJ
Patrick
My APEX Blog: http://inside-apex.blogspot.com
The ApexLib Framework: http://apexlib.sourceforge.net
The APEX Builder Plugin: http://apexplugin.sourceforge.net/ New!

How to SELECT FOR UPDATE with CMP (Oracle)

The most common database (Oracle) by default uses a scheme that does not fit into any of those isolation levels. A SELECT statement selects data at the start of the transactions, whereas a SELECT ... FOR UPDATE does something quite different. It is essential to do SELECT FOR UPDATEs before updating the row as SELECT does no lock. It's a hack that works well in practice.
1. Which isolation level is this?
2. More fundamentally, how an earth is it possible to use this scheme with CMP?! You would have to distinguish load() from loadForUpdate()! Is CMP inconsistent with Oracle?
This is a pretty big whole in the CMP spec!

No. thats no goes well.
Transaction serializable in Oracle uses a optimistic
concurrency system. And for update is a
pessimistic concurrency.
With optimistic: the system is faster but it can fail
With pessimistic: if doesnt fail (usually;)
You can solve the proble with many differents systems:
1. Edit the .xml descriptor files ans change the sql sentences.
And my prefer one.
2. Make a new jdbc driver that inherits from the original
oracledriver.
The new driver give u in "getConnection()" a new connection class that inherits from the original connection.
The executestatement and preparestatement adds the
string "for update" if the stattement was starting by select.
Configure your container to use the new driver.

Select for update returns no rows even though there is no locking thread

I'm using Ibatis library over oracle sql for my query. The select for update statement returns no rows. This happens intermittently. When this was happening last time, I executed the select statement on sqldeveloper (but without the 'for update') and got rows. This situation is not easily reproducible so I've not yet been able to ascertain whether rows are returned on sqldeveloper with the 'for update' clause. But I know for sure that there was no other thread locking the rows. How could this be happening?

The select for update statement returns no rowsWhy do you think that a select for update will always return rows?
the for update clause if there not to garantee the presence of rows but to lock the row when it is present
sql> select * from t;
         A          B C
         1          1 step1
         2          2 step2
         3          3 step3Then session 1 issues the following select
SELECT     *
      FROM t
     WHERE a = 1
FOR UPDATE NOWAIT;If session 2 issues the same select before session 1 commits or rolls back
SELECT     *
      FROM t
     WHERE a = 1
FOR UPDATE NOWAIT;It will get the following error
ERROR at line 1:
ORA-00054: resource busy and acquire with NOWAIT specifiedBut if session 2 issue such a kind of select
sql> SELECT     *
2        FROM t
3       WHERE a = 99
4 FOR UPDATE NOWAIT;
no rows selectedYou see then that a select for update can return no rows
Best Regards
Mohamed Houri

Database select for update locks ADF

Hi,
When a user has initiated an update session in an adf application and locking is optimistic it will acquire a lock on table row using select for update no wait; . But when the user closes a tab the session would not be terminated. Now i know as HTTP is a stateless protocol, we can wait for the timeout and then the lock will be released using a session listener implementation. But if the user instead tries to log in again in a new tab and tries to edit the same record he will receive a message stating that another user already holds a lock on the record which is correct, but is misleading.
So can we rely on javascript for these scenarios that as soon as the user closes the tab the session should be terminated.
Here's a snippet
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/dojo/1.4/dojo/dojo.xd.js" ></script>
<script type="text/javascript">
var unLoad = function() {
    dojo.io.script.get({
    url:'http://127.0.0.1:7101/myapp/adfAuthentication?logout=true',
    timeout:15000,
dojo.addOnWindowUnload(unLoad);
</script>I know this might not work always as it depends on the fact that request might / might not be processed by the server.
Are there any alternate solutions and also reducing the session timeout is ruled out in my scenario.

Ramandeep,
So are there other alternatives or solutionsAlternatives or solutions to what, exactly? As Jobinesh has told you, as long as you use optimistic locking, ADF doesn't acquire database locks except in the context of a transaction that is going to be completed in the current HTTP request. You could obviously force ADF to deviate from this if you called "postChanges" during an HTTP request and leave the transaction hanging, but that would just be wrong in an optimistic locking scenario - the solution would be "don't do that."
John

Lock Cascade With Select for UPDATE

Similar Messages

Maybe you are looking for