Select...for update and close()

I am seeing unexpected behaviour when working with select for update, and I hope to get some clarification about it. I have RTFM and checked out any online information I could find, but didn't see too much about row level locks. See below for the problem I am encountering
We have an application with lots of threads on multiple nodes that uses a combination of row level locking and status flags to mark a row as being processed.
We are locking the rows, and then after completing the select ... for update statement we are closing the JDBC statement.
On executing the statement.close() it appears as though the row level lock is lost. Can anyone confirm this behaviour, or tell me that I am misreading the behaviour that I am seeing.
Thanks in advance,
Robert Dawson

I'd expect this behavior regardless of whether autocommit was on. If a statement is closed, any locks held by that statement must be released. If they weren't, no other statement would have permission to remove the locks, so the rows would remain locked indefinitely.
Justin

Similar Messages

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

Difference in select for update of - in Oracle Database 10g and 11g

Hi, I found out that Oracle Database 10g and 11g treat the following PL/SQL block differently (I am using scott schema for convenience):
DECLARE
  v_ename bonus.ename%TYPE;
BEGIN
  SELECT b.ename
    INTO v_ename
    FROM bonus b
    JOIN emp e ON b.ename = e.ename
    JOIN dept d ON d.deptno = e.deptno
   WHERE b.ename = 'Scott'
     FOR UPDATE OF b.ename;
END;
/While in 10g (10.2) this code ends successfully (well NO_DATA_FOUND exception is raised but that is expected), in 11g (11.2) it raises exception "column ambiguously defined". And that is definitely not expected. It seems like it does not take into account table alias because I found out that when I change the column in FOR UPDATE OF e.empno (also does not work) to e.mgr (which is unique) it starts working. So is this some error in 11g? Any thoughts?
Edited by: Libor Nenadál on 29.4.2010 21:46
It seems that my question was answered here - http://stackoverflow.com/questions/2736426/difference-in-select-for-update-of-in-oracle-database-10g-and-11g

The behaviour seems like it really is a bug and can be avoided using non-ANSI syntax. (It makes me wonder why Oracle maintains two query languages while dumb me thinks that this is just a preprocessor matter and query engine could be the same).

Pros and cons of select for update clause

hi,
Can anybody explain what are the
pros and cons of select for update clause
11.2.0.1

As commented, there are no pros versus cons in this case.
What is important is to understand conceptually what this do and why it would be use.
Conceptually, a select for update reads and locks row(s). It is known as pessimistic locking.
Why would you want to do that? Well, you have a fat client (Delphi for example) and multiple users. When userA updates an invoice, you want that invoice row(s) locked and prevent others from making updates at the same time. Without locking, multiple users updating the same invoice will result in existing updated data being overwritten by old data that also has been updated. A situation called lost updates.
For web based clients that are stateless, pessimistic locking does not work - as the clients do not have state and pessimistic locking requires state. Which means an alternative method to select for update needs to be used to prevent lost updates. This method is called optimistic locking.
So it is not about pros versus cons. It is about understanding how the feature/technique/approach works and when to use it.. and when it is not suited to use it. All problems are not nails. All solutions are not the large hammer for driving in nails.

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You already have all the free updates that are pertinent to Snow Leopard. Software Update only finds and installs free updates to your Apple software — it doesn't do anything with upgrades that must be purchased, like Lion. If you were to purchase and install Lion, Software Update would then find and offer to install all the free updates that are applicable to Lion.

[Forms6]Select for update before update and commit

Hi,
In the KEY-COMMIT forms trigger
My code finds the primary keys of the rows to be updated,
then there is "select ...where "these keys".. for update nowait"
then there is a commit
(There also is a pragma exception init -54 "Resource Busy")
At runtime I get an error:
"Cannot insert rows here".
Maybe I should lock these rows before triggering the Key-commit?
--> message edited
Oops, I just reproduced the code in Forms 10,
I select for update from emp where empno=7839 then update King's sal then commit_form;
and everything works fine.
So I have to locate where this error message comes from.
--< End of edit
Many thanks for your help.
Edited by: JeanParis on Dec 23, 2009 10:31 PM

Hi,
The issue is solved on my Developer 2000 10 installed on Windows XP.
At work on Forms 6 I have hidden the warning with a :system.message_level.
What I'm searching now is a script to check the locks in the situation where
I don't have access to the catblock.sql script because I'm not DBA on the database. (but I can see DBA_LOCKS).
The problem starts because on the master block there is an item that can ben changed
from 'CREAT' to 'VALID', and in the When Validate Item trigger on that item I cannot issue a go_block( 'xxx' ).
I have to go to the 'xxx' block in order to start a first record - next loop to gather values and update a table accordingly.
Many thanks for your care.
JBM.

FF lets me access Facebook but I can't click or select any icons nor will it let me access Facebook games. IE will let me but its so slow. I've alread checked for updates and everything is fine.

FF lets me access Facebook but I can't click or select any icons nor will it let me access Facebook games. IE will let me but its so slow. I've alread checked for updates and everything is fine.

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"Remove the Cookies" from sites that cause problems: Tools > Options > Privacy > Cookies: "Show Cookies"<br />
Start Firefox in [[Safe Mode]] to check if one of your add-ons is causing your problem (switch to the DEFAULT theme: Tools > Add-ons > Themes).
See [[Troubleshooting extensions and themes]] and [[Troubleshooting plugins]]

JDBC SELECT FOR UPDATE

I'm trying to issue a SELECT ... FROM ... FOR UPDATE, and under specific verified conditions runs an UPDATE (where the current is positioned!).
The error code I get is:
ORA-01002: Fetch out of sequence.
Here you are my code:
/////////////////////START
import java.sql.*;
import oracle.jdbc.*;
import oracle.sql.*;
public class SelForUpdDin{
static{
     try{
          Class.forName("oracle.jdbc.driver.OracleDriver");
     catch(Exception e){e.printStackTrace();}
// Queries and cursor name
public static void main (java.lang.String[] args){
String cursorName = null;
int codice = 0;
String cognome = null;
String job = null;
int manager = 0;
java.sql.Date dataAss = null;
int salario = 0;
int commissioni = 0;
int reparto = 0;
String rowid = null;
String sqlSelect = "SELECT empno, ename, "+
"job, mgr, hiredate, sal, comm, deptno, ROWID "+
"FROM scott.emp FOR UPDATE";
String sqlUpdate = "UPDATE scott.emp SET comm = ? WHERE ROWID = ? ";
try {
Connection con = DriverManager.getConnection("jdbc:Oracle:oci8:@","system","manager");
// Esecuzione della SELECT e produzione del RESULT SET
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(sqlSelect);
PreparedStatement ps = con.prepareStatement(sqlUpdate);
while (rs.next()) {
codice = rs.getInt(1);
cognome = rs.getString(2);
job = rs.getString(3);
manager = rs.getInt(4);
dataAss = rs.getDate(5);
salario = rs.getInt(6);
commissioni = rs.getInt(7);
reparto = rs.getInt(8);
rowid = rs.getString(9);
// Applicazione della business logic
if (reparto == 30)
{ System.out.println (cognome + " in dept= "+ reparto +
" with salary=" + salario + " has a commission= " +
commissioni);
int newcomm = 5555;
ps.setInt(1,newcomm);
ps.setString(2,rowid);
ps.executeUpdate();
else
{ System.out.println (cognome + " in dept= "+ reparto +
" with salary=" + salario + " has a commission= " + commissioni);
} // if - else
} // end while
rs.close();
ps.close();
stmt.close();
catch(Exception e)
e.printStackTrace();
} // end main()
} // end class
//PS.
//Many thanks to Bachar and Elangovan that ansewerd me to my previous posting and addressed me towards the right solution

Hi
The documentation gives following explanation for the error :
ORA-01002 fetch out of sequence
Cause: In a host language program, a FETCH call was issued out of sequence. A successful parse-and-execute call must be issued before a fetch. This can occur if an attempt was made to FETCH from an active set after all records have been fetched. This may be caused by fetching from a SELECT FOR UPDATE cursor after a commit. A PL/SQL cursor loop implicitly does fetches and may also cause this error.
Action: Parse and execute a SQL statement before attempting to fetch the data.
In your program you should set auto commit to false as follows :
con.setAutoCommit(false);
Do this before executing the SELECT FOR UPDATE sql query.
At the end of program you can commit to save the updations as follows:
con.commit();
This should solve the problem.
Chandar

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

Select for update on stateless connections

i have read that using select for update for a web application will not work specially if the stateless connection are used , and the best way to make sure that the column you are reading was not changed is to use the time stamp approach and not select for update?? i am right

Not entirely correct.
A connection/session to Oracle has state. There is no such thing as a stateless Oracle connection.
The stateless connection is from the web browser to the web server. It makes a connection. Asks for a page (GET, PUT or POST typically). It gets a response from the web server. It closes that connection.
When the web server response, it opens a (stateful) connection to Oracle. Or it re-uses an existing (stateful) Oracle connection (now idle after having serviced another web browser/web server request).
The problem with pessimistic locking (e.g. SELECT FOR UPDATE) is that the very same (stateful) Oracle session will either
a) be closed when a response is send to the web browser
b) be used for another totally different web browser
Thus any locks made will either be lost (option a) or will get used by the wrong web browser (option b).
A method is therefore needed to make the lock spans different Oracle (stateful) sessions. Web browser selects rows to update using Oracle session 101 at Time 1. Web browser submits updated rows and a commit using Oracle session 142 at Time 2.
The "best way" to handle optimistic locking is likely using the Oracle System Change Number (SCN). This represents the "current version" of the rows.
So at Time 1, via Session 101, you give the web browser a 100 rows to update - together with the SCN that says the current version of the rows are v1.2.0.1.
At Time 2, using Session 142, the web browser submits its changes for those 100 rows. Together with the SCN v1.2.0.1.
The SQL UPDATE issues the update statement - but adds the SCN version criteria. If the UPDATE fails to update all 100 rows, it means that some of the rows no longer exist, or that some rows have a new version number (was changed in the meantime).
In this case, the UPDATE is rolled back and an exception raised to tell the web browser that some (or all) of those 100 rows have been changed in the meantime.
Refer to the [url http://download.oracle.com/docs/cd/B19306_01/server.102/b14200/pseudocolumns007.htm#BABFAFIC]Oracle® Database SQL Reference for details.

Error message: "playlists selected for updating no longer exist"

I tried to update my ipod nano and I guess I had deleted a playlist, but since then, I have not been able to update. Every time I try, I get the following message:
"Cannot be updated because all of the playlists selected for updating no longer exist."
I haven't been able to highlight which playlists are selected to begin with.
I read through the manual and thought that maybe rebooting the whole system might work. So I deleted Itunes from my computer and re-installed.
Then I tried re-setting my ipod. So now I have nothing on my ipod.
I also deleted everything from my library, thinking it might help to start from scratch. Nothing has worked.
How do I "select" and "unselect" playlists so I can get up and running again?

Here you go.
http://discussions.apple.com/thread.jspa?messageID=607312&#607312

Lost music on ipod because "playlists selected for updating no longer exist

Not sure what I've done. I recently downloaded newer version of itunes. Then when synching, I had too much music in my library for the ipod to handle so it told me about doing the smart playlist. I erased a couple of playlists on the itunes menu I no longer wanted and then when I went to synch, this error came up "songs on the ipod cannot be updated because all of the playlists selected for updating no longer exist."
Please help.....

Check this out.
iPod cannot sync because one or more playlist....

"All of the Playlists Selected for Updating No Longer Exist"

My family has 2 ipod shuffles. After purchasing a Nano recently, I inserted the cd that came with it. Apparently the existing iTunes software was removed and reinstalled. At any rate, the library still shows all the original songs, but when the Nano is plugged in, iTunes immediately gives a prompt stating "Songs on the iPod *** cannot be updated because all of the playlists selected for updating no longer exist." The library is there, the playlists that were there are there, and I can play the songs on my cpu. Is there anything I can do besides completely uninstalling everything and starting over?
iPod Nano Windows XP Pro

This user tip should help you sort out your missing playlist problem: Hudgie - iPod cannot sync because one or more playlists are missing

"Playlists selected for updating no longer exist"?!

everytime i plug my ipod mini into the computer, a pop up appears saying that the playlists selected for updating no longer exist!!! it's done this before, so i completely restored the setting and made a whole new library. now it's doing it again. i have all the playlists and songs on my computer in a folder. all the songs that were on my ipod, got deleted when i plugged it into the computer. so my ipod is blank, but i have the songs in my library still. they just wont upload. any help would be greatly appreciated....

Check this out.
iPod cannot sync because one or more playlist....

I accidently deleted the playlist selected for updating thing...

i was adding new songs to my ipod and i guess there were too many songs there so it asked me if i wanted it to choose some songs randomly...
so i chose "ok" but actually i didnt really want it to choose songs on its own so i deleted the list that was automatically created by itself and decided to delete some songs on my own...
after doin that, i tried to update it but now it says i cant do it because i deleted that list...
it says "songs on the ipod "stephanie kim" cannot be updated because all of the playlists selected for updating no longer exists"
i turned my computer off and tried it again several times but it wont work...
and all the songs in my ipod are gone now...
is there anything i can do?

http://support.apple.com/kb/PH10918
Best.

Select...for update and close()

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