Oracle select update nowait error

oracle select update nowait error

The SELECT FOR UPDATE statement allows you to lock the records in the cursor result set. You are not required to make changes to the records in order to use. The nowait method is formulated for retrieval, so when it is found that the data is locked by another session, it will quickly return an ORA-00054 error, and. NOWAIT. A locking read that uses NOWAIT never waits to acquire a row lock. The query executes immediately, failing with an error if a requested row is locked. oracle select update nowait error

Oracle select update nowait error - consider

for update nowait tips

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The difference between ORACLE for update and for update nowait

1. The difference between for update and for update nowait.
        First of all, if it is just select, Oracle will not add any locks, that is, Oracle will not have any restrictions on the data read by select, although there may be another process at this time The data in the table is being modified, and the result of the modification may affect the result of your current select statement, but because there is no lock, the result of the select is the state recorded in the current time table.
        If for update is added, once Oracle finds that this batch of data (that meets the query conditions) is being modified, it will not issue the select statement query until the data is modified (committed), and the select statement will be automatically executed immediately.
        Similarly, if someone needs to modify this batch of data (one or more of them) after the query statement is issued, it must wait until the query is over (commit) before it can be modified.
        Both for update nowait and for update will lock the result set that is queried. The difference is that if another thread is modifying the data in the result set, for update nowait will not wait for resources, as long as some data in the result set is found to be Lock it, and immediately return "ORA-00054 error, the content is that the resource is busy, but the NOWAIT method is specified to obtain the resource".
        For update and for update nowait add a row-level lock, that is, only data that meets the where condition is locked. If you only use the update statement to change the data, you may wait unresponsively and inexplicably because it cannot be locked. However, if the for update NOWAIT statement tentatively locks the data to be changed before that, you can pass immediately The error message returned and understand the reason, maybe this is the meaning of For Update and NOWAIT.
        After testing, query and lock in for update or for update nowait mode. In the result set of select, as long as any record is locked, the entire result set is waiting for system resources (if it is nowait, the corresponding abnormal)


2. The purpose of for update nowait and for update is to
        lock all rows of the table and exclude other write operations for this table. Ensure that only the current transaction writes to the specified table.
        The difference between for update nowait and for update: When
        other transactions want to write to this table, do they wait for a period of time or are rejected by the database system immediately and return. The nowait method is formulated for retrieval, so when it is found that the data is locked by another session, it will quickly return an ORA-00054 error, and the content is that the resource is busy. So in the program, we can use the nowait method to quickly determine whether the current data is locked, and if it is locked, we must take corresponding business measures for processing. 

        Examples:

        Open a PL/SQL, execute update deployop.tt t set ta ='X' where ta = '1';
View Image

        Open another PL/SQL, execute select * from tt t where ta in ('1','2') for update nowait; returns RA-00054 error, the content is that the resource is busy. View Image
           If execute select * from tt t where ta in ('1','2') for update in the above window, the result is just blocking and no error is returned, as shown below:
View Image
 

3. SELECT...FOR UPDATE statement syntax 
SELECT ... FOR UPDATE [OF column_list][WAIT n

The difference between oracle-select for update nowait and select for update



Oracle--select for update nowait is different from select for update
. The meaning of nowait is misunderstood by many people as "do not wait, execute immediately." But in fact, the meaning of this keyword is "no need to wait, return immediately."
If the currently requested resource is locked by another session, blocking will occur, nowait can avoid this blocking, because

If another user is in the process of modifying that row, we will get an ORA‐00054 Resource Busy error. We are blocked and must wait for the other user to finish with it.

Can experiment, I use pl/sql developer to lock the table game
SQL> select * from game where game_id =1;
return a record

SQL> select * from game where game_id=1 for update nowait; select * from game where game_id=1 for update nowait

             *
ERROR at line 1:
ORA-00054: resource is busy, requires you to specify NOWAIT
use NOWAIT keyword, will report ORA-00054 error
how to see what resources caused by this situation? And how to solve it?
View locked objects, users and sessions

SQL> select lo.oracle_username,do.object_name,s.logon_time,lo.process,s.sid as s ession_id 2 from v$locked_object lo,v$session s,dba_objects do 3 where lo.session_id = s.sid and do.object_id = lo.OBJECT_ID 4/ ORACLE_USERNAME ------------------------------ OBJECT_NAME -------------------------------------------- LOGON_TIME PROCESS SESSION_ID ------------------- ------------ ---------- NBA---User Name GAME-the object of operation 2009-08-04 10:55:15---Login time 840:5176 10


Use as sysdba
to view specific SQL statements based on sid

selectsql_textfromv$session a,v$sqltext_with_newlines b whereDECODE(a.sql_hash_value,0, prev_hash_value, sql_hash_value)=b.hash_value anda.sid=10; begin :id := sys.dbms_transaction.local_transaction_id; end; kill session SQL> select sid,serial# from v$session where sid =10; SID SERIAL# ---------- ---------- 10 23 SQL> alter system kill session '10,23';


The system has been changed.
select * from game where game_id=1 for update nowait;
data returned
when two users simultaneously update the same record is used select for update, the performer, will be blocked, use is thrown select for update nowait :ORA-00054 resource busy and acquire with NOWAIT specified exception, inform the user that this line is locked.
Original source: http://www.blogjava.net/parable-myth/archive/2010/11/05/337350.html?opt=admin

oracle – When should I use for update nowait in cursors?

Using will cause the rows to be busy and acquires a lock until a commit or rollback is executed.
Any other session that tries to acquire a lock will get an Oracle error message like instead of waiting the lock to release.

Session1:

Here the rows are locked until the cursor is closed or a commit/rollback gets executed. If, meanwhile, another user from session 2 tries to access the same records then this will throw an error as shown below:

Session2:

This user cannot even update or delete the same records that have been locked by the first session.

Usage:
Now if you want to do some manipulation on certain sets of records and you dont want another user from another session to override your data then you must first lock the records(using ) and then do your manipulation. After youre done with your manipulation, close the cursor and commit.

EDIT
Suppose there are 10 rows in temp and I execute the following script in my session 1 :

In session 2, I execute the following while the script in session 1 is still running

If I execute the same script, in session 2, while the script in session 1 is still running

Then I get

oracle – When should I use for update nowait in cursors?

Terms of Use

The difference between oracle-select for update nowait and select for update



Oracle--select for update nowait is different from select for update
. The meaning of nowait is misunderstood by many people as "do not wait, execute immediately." But in fact, the meaning of this keyword is "no need to wait, return immediately."
If the currently requested resource is locked by another session, blocking will occur, oracle select update nowait error, nowait can avoid this blocking, because

If another user is in the process of modifying that row, we will get an ORA‐00054 Resource Busy error. We are blocked and must wait for the other user to finish with it.

Can experiment, I use pl/sql developer to lock the table game
SQL> select * from game where game_id =1;
return a record

SQL> select * from game where game_id=1 for update nowait; select * from game where game_id=1 for update nowait

             *
ERROR at line 1:
ORA-00054: resource is busy, requires you to specify NOWAIT
use NOWAIT oracle select update nowait error, will report ORA-00054 error
how to see what resources caused by this situation? And how to solve it?
View locked objects, users and sessions

SQL> select lo.oracle_username,do.object_name,s.logon_time,lo.process,s.sid as s ession_id 2 from v$locked_object lo,v$session s,dba_objects do 3 where lo.session_id = s.sid and do.object_id = lo.OBJECT_ID 4/ ORACLE_USERNAME ------------------------------ OBJECT_NAME -------------------------------------------- LOGON_TIME PROCESS SESSION_ID ------------------- ------------ ---------- NBA---User Name GAME-the object of operation 2009-08-04 10:55:15---Login time 840:5176 10


Use as sysdba
to view specific SQL statements based on sid

selectsql_textfromv$session a,v$sqltext_with_newlines b whereDECODE(a.sql_hash_value,0, prev_hash_value, sql_hash_value)=b.hash_value anda.sid=10; begin :id := sys.dbms_transaction.local_transaction_id; end; kill session SQL> select sid,serial# from v$session where sid =10; SID SERIAL# ---------- ---------- 10 23 SQL> alter system kill session '10,23';


The system has been changed.
select * from game where game_id=1 for update nowait;
data returned
when two users simultaneously update the same record is used select for update, the performer, will be blocked, use is thrown select for update nowait :ORA-00054 resource busy and acquire with NOWAIT specified exception, inform the user that this line is locked.
Original source: http://www.blogjava.net/parable-myth/archive/2010/11/05/337350.html?opt=admin
NOWAIT][SKIP LOCKED];
        Among them: 
        OF clause is used to specify the column to be updated, that is, the lock on the mail for exchange error 15006 Specific column.
        The WAIT clause specifies the number of seconds to wait for other users to release the lock to prevent waiting indefinitely. 
The advantages of "using FOR UPDATE WAIT" clause are as follows:
        1. Prevents waiting for locked rows indefinitely;
        2. Allows more control over lock waiting time in the
        application 3. Very useful for interactive applications, Because these users cannot wait for uncertainty
       . 4. If skip locked is used, the locked row can be skipped, and the "resource busy" exception report caused by wait n will not be reported.

        Examples:

Open two sql windows in plsql develope and
run the following sql
         select * from t where a='1' for update; 
in window 1; run sql1
        sql1: select * from t where a='1' for update  in window 2 ; this point there is no problem, because row-level locks do not affect pure select statements
run SQL2
        SQL2: select * from t the WHERE a = '1' for Update; the sql in the implementation of this sentence, always in a wait state, oracle select update nowait error, unless the window 1 sql was submitted or rolled back.
How can I make sql2 not wait or wait for the specified time? We then run sql3
        sql3:select * from t where a='1' for update nowait; Then when this sql is executed, it will directly report the resource busy oki 5900 error.ru.
If you execute select * from t where a='1' for update wait 6;, after waiting 6 seconds, the resource busy exception will be reported.
If we execute sql4
        sql4:select * from t where a='1' for update nowait skip Locked; when executing sql, neither wait nor report resource busy exception, skip locked rows, and only display unlocked rows

        example:

        Window 1:
View Image
        Window 2: Skip the locked a=1 rows and only display the unlocked a=2 rows
View Image

 

Four.select for update of

        This of clause has a greater effect when involving multiple tables. If you do not use of to specify the columns of the locked table, oracle select update nowait error, all relevant rows of the table are locked. If the columns to be modified are specified in of, then Only the rows of the table related to these columns will be locked.

Example 1:

        select * from tt,tt2 where tt.a = tt2.a2 for update; Both tables are locked
View Image
         select * from tt2 for update wait 3; Attempt to lock the tt2 table and throw "ORA -30006: Resource has been occupied; "WAIT timeout" error occurred during operation

View Image
 

Example 2:

        select * from tt,tt2 where tt.a = tt2.a2 for update of a; only lock the tt table, not lock the tt2 table
View Image

        select * from tt2 for update wait 3; successfully locked the tt2 table

View Image
        select * from tt for update wait 3; Attempt to lock the tt table, after 3 seconds it throws the error "ORA-30006: resource has been occupied; WAIT timeout occurred while performing the operation"
View Image
        can be concluded, for update of columns When used in multi-table connection locking, you can specify which tables to lock, and if the column in the table does not appear after the for update of, it means that the table is not actually locked, and other users can Update the data of these tables. This situation often occurs when users operate on views with connected queries. The user only locks the data of the related table, and other users can still operate on the data of other original tables in the view. 

       Summary:
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