How to prevent shared locks in SELECT statement?

Hi,
In SQL Server we can use (NOLOCK) to prevent shared locks on each row:
Select * from table (NOLOCK)
Do we have similar technique for oracle so it doesn’t consider a shared lock for each returned row?
Thank you,
Alan

Yes - it's called a query ;-)
Oracle was designed with a 'consistent read' mechanism that guarantees that a query will see the image of the data at the moment when the query started, regardless of the number of updates (including deletes) that have occurred since the query started. This is done using the rollback (aka undo) segment. Flip side - there is no such thing as a 'dirty read'.
Because of the implementation, a simple select or subselect without coersion (such as the 'FOR UPDATE' clause) will not block writers, nor will writers (updates/inserts/deletes) block readers.
In addition, an update in Oracle will only lock the rows affected by the update, there is no escalation of locks needed (or possible), and commits do not introduce any 'lock clearing' overhead.
The penalties for all of this
- the rollback segment must be sized appropriately or you end up with ORA-01555 errors;
- you should not commit in loops, especially not loops controlled by a cursor;
- code written to be efficient in SQL Server is often inefficient in Oracle, and vice versa.
Recommended reading is Tom Kyte's book at http://www.apress.com

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Timesten create a lock for select statement through sqldev

When use ttisql connect to TimesTen Release 7.0.6.15.0 at autocommit=1, there is no lock for select statement.
but when I use sql developer (driver is ttjdbc5.jar, regardless of version) to connect, even with autocommit=1, there will be locks for select statement.
Is it a bug? How can I achieve the same no locks for select statement through sql developer?Thanks.

-your update tells me that you are connected to a remote timesten data store using the client driver
-the ttXactAdmin output indicates that SqlNavigator has a shared lock on the database itself: this will not interfere with anybody else' read operations, and I believe that until such time as you actually attempt some kind of DML against the data store that th IX lock on the database lock will not interfere with any other DML either.
-a shared database lock will always be acquired for any transaction in TimesTen. You can test this for yourself from ttisql: set autocommit off, perform a simple update and do not commit the transaction. Then open a separate session and execute ttxactadmin - you will the IX database lock as well as the various locks on tables and indexes.
-I believe this pretty much proves my original thinking: that sqlDeveloper attaches to TimesTen in transaction mode. However, the IX lock on the database will not interfere with anybody else's work and should not be a problem.

How to call user fuction in select statement.

hi,
i am facing some problem.How to call user functions in select statement.please send me answer with example.
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Locations to Call User-Defined Functions
• Select list of a SELECT command
• Condition of the WHERE and HAVING clauses
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Restrictions on Calling Functions from SQL Expressions
To be callable from SQL expressions, a user-defined
function must:
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• Functions called from SQL expressions cannot
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jeneesh

How to put OR clause in SELECT statement

Hi
How to put OR clause in SELECT statement to return number_first/number_last to match records from another table's column.
<pre>
SELECT
a.id ,
flat_number ||' '|| a.number_first||' '||a.street_name||' '||a.suburb address1,
apt_no ||' '|| street_no||' '||b.street_name||' '||b.suburb address2
from
a ,
b
where b.street_name = a.street_name
AND b.SUBURB = a.SUBURB
AND b.STATE = a.STATE
</pre>
Thsi will return this as exact match.
ADDRESS 1
12 TAMAN TENANG A ORCHARD 3142
10 RAMA YISHUN 2095
ADDRESS2
12 TAMAN TENANG A ORCHARD 3142
10 RAMA YISHUN 2095
However this only matches number_first.
How can I get the query work that it will match both number_first and number_last (table b)in address 1 to match street_no in address2 ( table b).My oracle version is 10GR/2.

Hi, I have a hard time understanding your request, and below is what I thought you want:
SELECT
    a.id ,
       flat_number ||' '|| (decode(b.street_no, a.number_first, a.number_first, a.number_last, a.number_last)||' '||a.street_name||' '||a.suburb address1,
         apt_no ||' '|| street_no||' '||b.street_name||' '||b.suburb address2
      from
             a ,
             b
            where          b.street_name = a.street_name
             AND            b.SUBURB      = a.SUBURB
            AND            b.STATE       = a.STATE
            AND (B.street_no=a.number_first OR b.street_no=a.number_last);Not tested.
Also, since your B.street_no will be either a.number_first OR a.number_last, you could replace
(decode(b.street_no, a.number_first, a.number_first, a.number_last, a.number_last) with just b.street_no.
Edited by: PhoenixBai on Aug 26, 2010 11:33 AM

How to create shared lock

Hi,
Can any please tell me how create a shared lock in steps.
Thanks in advance
Priya

Hi Swati,
This may not be possible, because you have created shared lock for the four different views but the table is one.
So when one is editing then definitely if the other try to access the same entries then the object will be locked.
First understand how and which lock can do which type of action.
For your assistance read this and try to find the answer.
Exclusive lock
The locked data can be read or processed by one user only. A request for another exclusive lock or for a shared lock is rejected.
Shared lock
Several users can read the same data at the same time, but as soon as a user edits the data, a second user can no longer access this data. Requests for further shared locks are accepted, even if they are issued by different users, but exclusive locks are rejected.
Exclusive but not cumulative lock
Exclusive locks can be requested by the same transaction more than once and handled successively, but an exclusive but not cumulative lock can only be requested once by a given transaction. All other lock requests are rejected.
Cheers!!
VEnk@

How to avoid shared locks when validating foreign keys?

I have a table with a FK and I want to update a row in that table without being blocked by another transaction which is updating the parent row at the same time. Here is an example:
CREATE TABLE dbo.ParentTable
PARENT_ID int NOT NULL,
VALUE varchar(128) NULL,
CONSTRAINT PK_ParentTable PRIMARY KEY (PARENT_ID)
GO
CREATE TABLE dbo.ChildTable
CHILD_ID int NOT NULL,
PARENT_ID INT NULL,
VALUE varchar(128) NULL,
CONSTRAINT PK_ChildTable PRIMARY KEY (CHILD_ID),
CONSTRAINT FK_ChildTable__ParentTable FOREIGN KEY (PARENT_ID)
REFERENCES dbo.ParentTable (PARENT_ID)
GO
INSERT INTO ParentTable(PARENT_ID, VALUE)
VALUES (1, 'Some value');
INSERT INTO ChildTable(CHILD_ID, PARENT_ID, VALUE)
VALUES (1, 1, 'Some value');
GO
Now I have 2 transactions running at the same time:
The first transaction:
SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;BEGIN TRAN
UPDATE ParentTable
SET VALUE = 'Test'
WHERE PARENT_ID = 1;
The second transaction:
SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;BEGIN TRAN
UPDATE ChildTable
SET VALUE = 'Test',
PARENT_ID = 1
WHERE CHILD_ID = 1;
If 'UPDATE ParentTable' statement runs a bit earlier, then 'UPDATE ChildTable' statement is blocked untill the first transaction is committed or rollbacked. It happens because SQL Server acquires shared locks when validating foreign keys, even
if the transaction is using read uncommitted, read committed snapshot (read committed using row versioning) or snapshot isolation level. I cannot see why change in the ParentTable.VALUE should prevent me from updating ChildTable. Please note that ParentTable.PARENT_ID
is not changed by the first transaction, which means that from FK's point of view whatevere is set to the ParentTable.VALUE is never a problem for referential integrity. So, such blocking behavior seems to me not logical. Furthermore, it contradicts to the
MSDN:
Transactions running at the READ UNCOMMITTED level do not issue shared locks to prevent other transactions from modifying data read by the current transaction. READ UNCOMMITTED transactions are also not blocked by exclusive locks that would prevent the
current transaction from reading rows that have been modified but not committed by other transactions.
Does anybody know how to workaround the issue? In other words, are there any tricks to avoid shared locks when validating foreign keys? (Disabling FK is not an option.) Thank you.
Alexey

If you change the primary key of the parent table to be nonclustered, there is no blocking.
Indeed, when I update ParentTable.VALUE, then:
in case of PK_ParentTable is clustered, a particular row in the clustered index is locked (request_mode:X, resource_type: KEY)
in case of PK_ParentTable is non-clustered, a particular physical row in the heap is locked (request_mode:X, resource_type: RID).
and when I update ChildTable.PARENT_ID, then:
in case of PK_ParentTable is clustered, this index is used to verify referential integrity:
in case of PK_ParentTable is non-clustered, again this index is used to verify referential integrity, but this time it is not locked:
It is important to note that in both cases SQL Server acquires shared locks when validating foreign keys. The principal difference is that in case of clustered PK_ParentTable the request is blocked, while for non-clustered index it is granted.
Thank you, Erland for the idea and explanations.
The only thing that upsets me is that this solution cannot be applied, because I don't want to convert PK_ParentTable from clustered to non-clustered just to avoid blocking issues. It is a pity that SQL Server is not smart enough to realize that:
ParentTable.PARENT_ID is not changed and, as a result, should not be locked
ChildTable.PARENT_ID is not actually changed either (old value in my example is 1 and the new value is also 1) and, as a result, there is no need at all for validating the foreign key.
In fact, the problem I described is just a tip of the iceberg. The real challenge is that I have deadlocks because of the FK validation. In reality, the first transaction has an additional statement which updates ChildTable:
SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;
BEGIN TRAN
UPDATE ParentTable
SET VALUE = 'Test'
WHERE PARENT_ID = 1;
UPDATE ChildTable
SET VALUE = 'Test'
WHERE PARENT_ID = 1;
The result is famous message:
Msg 1205, Level 13, State 51, Line xx
Transaction (Process ID xx) was deadlocked on lock resources with another process and has been chosen as the deadlock victim. Rerun the transaction.
I know that if I change the order of the two statements, it will solve the deadlock issue. But let's imagine I cannot do it. What are the other options?
Alexey

How to Implement shared lock

Hi friends,
For a table I have created views. I want to create shared lock for that table.
How to achieve that.
can we create shared lock for views?
Thanks.

Hi Pagidala,
Go to Se11-> Select Lock object radiobutton->give some name starting with E for example EZDEMO_LOCK->click on Create ->give short description->clcik on Tables Tab->give the table name for which you want to implement shared lock example ZTABLE ->lock mode you select as Read Lock.After this save check and activate your lock object.
We have selected READ LOCK since it protects read access to an object. The read lock allows other transactions read access but not write access to the locked area of the table.
Check the below link for the complete information on Lock Concept.
http://help.sap.com/saphelp_nw04/helpdata/en/41/7af4c5a79e11d1950f0000e82de14a/content.htm
Cheers!!
VEnk@
Edited by: Venkat Reddy on Oct 29, 2008 11:54 AM

Delete adjacent duplicates how to use in the below select statement

hi i have a problem
i am suing the below select statement
SELECT    a~extno
          a~guid_lclic       " for next select
          e~ctsim
          e~ctsex
*revised spec 3rd
          f~guid_pobj
          f~amnt_flt
          f~amcur
          f~guid_mobj
          e~srvll     "pk
          e~ctsty     "PK
          e~lgreg "PK
INTO TABLE gt_sagmeld
FROM /SAPSLL/LCLIC as a
INNER JOIN /sapsll/tlegsv as e on elgreg = algreg
inner join /sapsll/legcon as f on fguid_lclic = aguid_lclic   " for ccngn1 selection
inner join /sapsll/corcts as g on gguid_pobj = fguid_pobj
                           where   a~extno in s_extno.
sort gt_sagmeld by guid_lclic lgreg ctsty srvll GUID_POBJ GUID_MOBJ.
delete adjacent duplicates from gt_sagmeld comparing guid_lclic lgreg ctsty srvll GUID_POBJ GUID_MOBJ .
now i am confused how to use delete adjacent dupliacate and on which fields
as first table /sal../lclic primary key is guid_lclic
and it is joined to table
legcon by guid_lclci ( not a primary key here)
legcon primary key is guid_legcon
and table 3 legsv by lgreg (pk here)
table 3 has tow more primary key srvll and ctsty also
NOW MY QUESTIO IS TAHT IS I USE ABOVE DELETE ADJACENT STATMENT IT FETCHES 20 LAKH RECORDS
I WANT TO REDUCE IS LET ME KNOW ON WHAT fields i need to use delete adjacen duplicates
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regards
Arora

hi sudha
if u see my select statement is contains four Primary keys
srvll
lgreg
ctsty
guid_lclic
but the next table connected to this table legcon is by guid_pobj and anothe table by guid_mobj
and if i take this gt_sagmeld to another temp table and i find abt 10 lakh uniques guid_pobj
similary 6 lakh guid_mobj so the next slect is hanpering because of this
not COMING TO OUR POINT IF I SORT ONLY BY OUR PRIMARY KEYS NOT TAKING INTO ACCOUNT TEH GUID_POBJ AND GUID_MOBJ
THE ENTRIES ARE VERY LESS BUT IF I TAKE INOT ACCCOUNT IN GT_SAGMELD THE ENTRIES ARE ABT 20 LAKH
SO I AM NOT SURE WHETHER TO TAKNE GUID_POBJ AND GUID_MOBJ INOT ACCOUNT FOR DELECTING ADJACENT DUPLICATES?
HENCE THE QUESTION OF ON WHICH FIRLD DELETE OR COMPARING ALL FIELDS I USE?

How user variable table names in select statement

Dear all,
I have three table gp1,gp2,g3. i want user variable table in sql query
for example at oracle forms have a list table showing table names gp1,gp2,gp3
at form i want user this query
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Forms_DDL is a one-way street: You can only pass DDL commands TO the database; you cannot get data back using Forms_DDL.
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The ref cursor method should work. You could also retrieve the data into a record group using populate_group_with_query -- it also enables dynamic data retrieval.
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How display number of row in select statement

How can I display number of row in select statement?
Table
data1 data2
xxx ccd
wss qwe
qws uij
I need get from SELECT statement:
1 xxx ccd
2 wss qwe
3 qws uij

user13734495 wrote:
Thank you from answer.
Statement
select rownum rn, data1, data2 from table
is good.
And what have I do went I use
select rownum rn, data1, data2 from table order by data1
and I get
3 qws uij
2 wss qwe
1 xxx ccd
I need
1 qws uij
2 wss qwe
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rownum,
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select
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Hi,
I have a function which inserts record on basis of some condition
INSERT INTO Case
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Closure_Date
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caseStatus,
Closure_Code,
Closure_Date,
FROM Case
WHERE Case_ID = caseID
Now i want new casestatus value in place of select statement caseStatus value. I have a variable m_caseStatus and i want to use the value of this variable in above select statement.
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thanks

Hi,
I have a function which inserts record on basis of some condition
INSERT INTO Case
Case_ID,
Case_Status,
Closure_Code,
Closure_Date
SELECT newCaseID,
caseStatus,
Closure_Code,
Closure_Date,
FROM Case
WHERE Case_ID = caseID
Now i want new casestatus value in place of select statement caseStatus value. I have a variable m_caseStatus and i want to use the value of this variable in above select statement.
how can i use this. Do not select Case_Status from inner select, so null will be inserted then after inserting it update the case status with m_caseStatus.
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How to avoid the below nested select statement

Please any one help me how this select statemet is working and      how to avoid the nesetd select statement .
if we avoid below nested , does it improve performace ?
select field1 field2
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           from ZTable as t
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           ( SELECT MAX( position_postdt ) FROM zTable
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Thanks in Advace.

Hi,
Instead of nested query go for two separate queries. I see you are querying on the same table...so better go by this approach
select field1 field2 POSITION_POSTDT
into table w_feeds
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where field2 in r_feedf1.
Remove the where condition on POSITION_POSTDT
Sort the table w_feeds by POSITION_POSTDT Descending; So you will get data pertaining to Max Position_Postdt.
Finally delete the other entries which are not Max.
This will enhance the performance over the nested query.
Regards
Shiva
Edited by: Shiva Kumar Tirumalasetty on Apr 27, 2010 7:00 PM
Edited by: Shiva Kumar Tirumalasetty on Apr 27, 2010 7:00 PM

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Hi,
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