How To Prevent Table-locking With Multiple Queue Readers

Apr 26, 2007



In a situation where messages are coming in faster than they can be processed, at what point will service broker start up another queue_reader? Also, how do you prevent table locking if part of the processing of that message involves inserting or updating data in a table? We are experiencing this problem because of the high number of messages coming through, and I'm not sure what the best solution is - does service broker have some built-in support for preventing contention on a table when multiple readers are running? Or maybe a pattern that can be used to get around it?

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Clarifications On Queue Service And Queue Readers

Jan 11, 2006

Hello,
This is info that I am still not certain about and I just need to make sure, my gut feeling is correct:

A.
When a procedure is triggered upon reception of a message in a queue, what happens when the procedure fails and rolls back?
1. Message is left on the Queue.
2. is the worker procedure triggered again for the same message by the queue?
3. I am hoping the Queue keeps on triggering workers until it is empty.

My scenario is that my queue reader procedure only reads one message at a time, thus I do not loop to receive many messages.

B.
For my scenario messages are independent and ordering does not matter.
Thus I want to ensure my Queue reader procedures execute simultaneously. Is reading the Top message in one reader somehow blocking the queue for any other reader procedures? I.e. if I have BEGIN TRANSACTION when reading messages of the Queue, is that effectively going prevent many reader procedures working simultaneously. Again, I want to ensure that Service broker is effectively spawning procedures that work simultaneously.

Thank you very much for the time,

Lubomir

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Row Level Locking For Queue Table To Get Rid Of Concurrency Problem

Apr 7, 2004

Hi all

We are writing a web-based multi-user call centre application application.

we are getting concurrency problems as you would expect with a multiuser application.

the application is made for callers who will bring up a different contact to call based on some predefined priority. now because the algorithm that prioritises the contacts takes a good 2 seconds to run, if 2 different caller request for the next prioritised contact, they will retrieve the same contact.

The only way that we think can resolve this problem is by building a queue. The queue would be implemented as a table, the particular implementation of this queue would be, when ever someone retrieves an entry from the queue, a background process will go on and generate a new queued item, i.e. in a FIFO manner. So that's how we think we should implement the queue.

Now come the question how to implement it. My idea is to have row level locking and a trigger to remove queue items from the queue. so that once one caller have looked at one of the item in the queue, another user can't look at the same item.

Any suggestions as to how i might be able to avoid concurrency problems?

What do you all think of my idea of implementing the FIFO queue?/
Is it possible to do row level locking in such a way that other users won't even be able to read the locked entry??



James :)

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May 2, 2008

Hi,

I found out that executing the procedure SP_INDEXOPTION and setting 'AllowRowLocks' to false i can prevent the sql server from locking rows in a table and 'AllowPageLocks' prevents from pages being locked. I need to preform same operation
in case of tables. I need to perform insertion operations concurrently and acquire required locks manually. Is there a way to stop sqlserver from acquiring locks on the table. I need to disable all the locks (row, page and table).

Thank you in advance.

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May 26, 2008

Hello All,
Greetings!!!

Due to certain constraints on my Table, I am not able to place unique Key constraint on it.
So I have take care about the uniqueness in my T-SQL code. I don't want to use the serializable transaction isolation level as it will result in frequent deadlocks.
I want some means by which one select will block other select.
Can this be done in SQL Server. I tried using TablockX along with holdlock as Table hint, but still the Selects does not block other select.
Will appreciate if you can resolve this issue

Thanks in Advance,
Mitesh Shah
MCTS- SQL Server 2005

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Jul 20, 2005

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Queue Processing Using Updlock, Readpast Locking Hints

Apr 25, 2008

This article instructed me on how to process rows from a table used as a data queue for multiple processes.

http://www.mssqltips.com/tip.asp?tip=1257

I tested this against the AdventureWorks DB (SQL 2005) and multiple SQL connections inside of Sql Mgmt. Studio).

Connection1:


BEGIN TRANSACTION


SELECT TOP 1 * FROM Production.WorkOrder WITH (updlock, readpast) --skips over locked rows
--COMMIT TRANSACTION

Connection2:


BEGIN TRANSACTION


SELECT TOP 1 * FROM Production.WorkOrder WITH (updlock, readpast) --skips over locked rows

COMMIT TRANSACTION



This works like I want where connection 2 skips over the locked row from connection 1 and gets the next available record from the table / queue. However, when I add ORDER BY tsql to each sql statement, connection 2 is now blocked waiting for Connection 1 to commit. (This is not what I want)

Connection1:


BEGIN TRANSACTION


SELECT TOP 1 * FROM Production.WorkOrder WITH (updlock, readpast) order by DueDate

--COMMIT TRANSACTION

Connection2:


BEGIN TRANSACTION


SELECT TOP 1 * FROM Production.WorkOrder WITH (updlock, readpast) order by DueDate --is blocked until connection 1 commits transaction

COMMIT TRANSACTION




How do I prevent blocking when using these locking hints with ORDER BY?


thanks

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Multiple Services On Same Queue Or Not ?

Oct 11, 2006

Hi There

I am guessing defining multiple services on the same queue is basically for providing different services to outside sources while using 1 queue, obviously as long as the contracts and activated sp logic applies to all services defined on that queue.

I am defining a queue per service, is this right or wrong or irrelevant ? It just works better for me in terms of manageability.

I just want to make sure there is no "best practice" reason for doing either or ? Is it just a matter of preference?

Any comments?

Thanx

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Many thanks for advice.

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Aug 14, 2007

Hi,

I am using distributed transactions where in I start a TransactionScope in BLL and receive data from service broker queue in DAL, perform various actions in BLL and DAL and if everything is ok call TransactionScope.Commit().

I have a problem where in if i run multiple instances of the same app ( each app creates one thread ), the threads pop out the same message and I get a deadlock upon commit.

My dequeue SP is as follows:

CREATE PROC [dbo].[queue_dequeue]
@entryId int OUTPUT
AS
BEGIN
DECLARE @conversationHandle UNIQUEIDENTIFIER;
DECLARE @messageTypeName SYSNAME;
DECLARE @conversationGroupId UNIQUEIDENTIFIER;

GET CONVERSATION GROUP @conversationGroupId FROM ProcessingQueue;
if (@conversationGroupId is not null)
BEGIN
RECEIVE TOP(1) @entryId = CONVERT(INT, [message_body]), @conversationHandle = [conversation_handle], @messageTypeName = [message_type_name] FROM ProcessingQueue WHERE conversation_group_id=@conversationGroupId
END

if @messageTypeName in
(
'http://schemas.microsoft.com/SQL/ServiceBroker/EndDialog',
'http://schemas.microsoft.com/SQL/ServiceBroker/Error'
)
begin
end conversation @conversationHandle;
end
END

Can anyone explain to me why the threads are able to pop the same message ? I thought service broker made sure this cannot happen?

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Readers Not Queued?

Jan 9, 2007

When multiple readers are waiting on a message from the same queue, I would expect that the reader that has been waiting the longest would be the first to pick up a message. However, I'm shocked to discover that the opposite seems to be true; in my tests I'm showing that the reader that has been waiting the least time picks up a message first! This seems totally counter-intuitive, and I'd like to know why it's working this way. This implementation will cause a lot more reader timeouts to occur than a properly queued method. For instance, assume that I have two readers, each using a one minute timeout. Reader #1 starts waiting, and reader #2 is busy for another 20 seconds before it starts waiting. 39 seconds later a message comes in and reader #2 will pick it up, leaving reader #1 to time out one second later! I would much rather have reader #1 pick up the message and reader #2 continue to wait for 20 more seconds.

I'm considering filing a bug on Connect about this, but I thought I'd post here first and see if I can get an answer...

Following is the script I'm using to test:

---Setup / Window #1---

--------------------------------------
CREATE DATABASE SimpleSSB
GO

USE SimpleSSB
GO

--Create a database master key
CREATE MASTER KEY
ENCRYPTION BY PASSWORD = 'onteuhoeu'
GO

--Create a message type
CREATE MESSAGE TYPE Simple_Msg
VALIDATION = EMPTY
GO

--Create a contract based on the message type
CREATE CONTRACT Simple_Contract
(Simple_Msg SENT BY INITIATOR)
GO

--create a queue
CREATE QUEUE Simple_Queue
GO

--Create a service
CREATE SERVICE Simple_Service
ON QUEUE Simple_Queue
(Simple_Contract)
GO
--------------------------------------

---Go start the other windows now---

---Readers: Windows #2-n ---

--------------------------------------
USE SimpleSSB
GO

WAITFOR
(
RECEIVE *
FROM Simple_Queue
), TIMEOUT 300000

--------------------------------------


---Start at least two readers, then do---
--------------------------------------

--send a message...
DECLARE @h UNIQUEIDENTIFIER

BEGIN DIALOG CONVERSATION @h
FROM SERVICE Simple_Service
TO SERVICE 'Simple_Service'
ON CONTRACT Simple_Contract
WITH ENCRYPTION=OFF;

SEND ON CONVERSATION @h
MESSAGE TYPE Simple_Msg
GO

--------------------------------------


... the last reader you've started will pick up the message first. Note I'm testing on 9.0.3033, in case that matters.

Thanks!

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Nov 22, 2002

I have a table that I want to act as a queue.

It has no indexes and no key. Just one column.

Basically I want a stored procedure that will pull / return the first record off the queue (table) and delete it. I'd rather not use MSMQ for this.

There will be about 10 users trying to do this at the same time and will be trying to pull of about 15 times every second.

How can I do this and ensure that no two requests pull off the same row?

Thanks,

Kevin

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I know we are not allowed to benchmark SQL Server but..... It would be nice to have material to present which demonstrates the performance gains using a queue compared to insert/delete in a SQL table.



Logically it seems faster to use a queue due to the conversation grouping locking and the service broker itself. But there seems to be some overhead involved just to manage these queues that the service broker has to perform.

I am sure we are not unique with the choice to figure out if we will get a boost in performance using SQL a queue between services rather than a table to queue data. What is available to help understand the performance gains of using a queue?

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Here is a sample of some data:

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Is there a simpler way to prevent duplicate entries in a table using sql?

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DECLARe
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[code]...

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Feb 14, 2007

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I'm using SQL Server 2008 R2.

From Management Studio I execute:

begin transaction
<my query>
exec sp_lock
rollback transaction

In the output I see interesting information about which locks are acquired, but:

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I logged the registry by a tool and alas there was it. So the thing is to set the registry entry by our own setup after installing the SSMS.

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Feb 7, 2002

Gurus,

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(
@Dept char(8),
@DDept char(8)

)
As
Set NoCOUNt On

Begin
Select '@DDept'
update phodept set fo_dept = @Ddept
where fo_dept = @Dept
update phone set fo_dept = @Ddept where fo_dept = @Dept
End
GO

The table/database is being used by others, generally in a read only mode.
via a VB 5.0 FE program.

The Stored procedure, when it is invoked, just hangs like it is waiting for exclusive use of the table.

Is there a way around it, without doing major surgery on the VB code?

Thanks.

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May 24, 2002

Hello,
I am working on the implementation of a database for my company and I have
a simple (I hope) question to ask.
I have the following stored procedure that will be running when I want
(actually when I want to delete a customer).
Do not mind if you do not understand what this procedure does... ;-)
Actually the Level8View is a VIEW of a nested table
(CustomerData->CustomerData).

CREATE Procedure DeleteCustomer
@ClientID INT
AS
UPDATE Level8View
SET UpCode = Level2, Level1=Level2, Level2=Level3, Level3=Level4, Level4=Level5, Level5=Level6, Level6=Level7, Level7=Level8
WHERE Level1=@ClientID
UPDATE Level8View
SET Level2=Level3, Level3=Level4, Level4=Level5, Level5=Level6, Level6=Level7, Level7=Level8
WHERE Level2=@ClientID
UPDATE Level8View
SET Level3=Level4, Level4=Level5, Level5=Level6, Level6=Level7, Level7=Level8
WHERE Level3=@ClientID
UPDATE Level8View
SET Level4=Level5, Level5=Level6, Level6=Level7, Level7=Level8
WHERE Level4=@ClientID
UPDATE Level8View
SET Level5=Level6, Level6=Level7, Level7=Level8
WHERE Level5=@ClientID
UPDATE Level8View
SET Level6=Level7, Level7=Level8
WHERE Level6=@ClientID
UPDATE Level8View
SET Level7=Level8
WHERE Level7=@ClientID
DELETE FROM Customers
WHERE ClientID=@ClientID
GO

I checked this procedure and works perfectly.
What I want to do is to somehow lock the WHOLE TABLE (CustomerData) or the
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delete statements.
I do not want to do a Row by Row lock, or Page by Page lock since the updates
in this table occur in the whole table and during that operation I do not
want other threads to issue SELECT, INSERT or UPDATE statements.

Can someone answer me how I can lock and unlock the whole view or table
please?

I will appreciate it for your answer. Thanks.

Yours, sincerely
Efthymios Kalyviotis
ekalyviotis@comerclub.gr

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Nov 11, 2005

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*Critical Section
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*End Critical Section
-Insert into order lines table, address table, etc.
commit

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Presumably, I'd use something like this:

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Apr 30, 2004

hi

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May 6, 2008

hi,
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my query is like :

insert into testdb.dbo.tabletest

select * from
livedb.dbo.tablex
inner join liveb.dbo.table1 on tablex.id=table1.xid


It seems to be locking the table and blocking other users from accessing the table.

suppose my question is why is the select locking the table ?

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I've tried applying the code below, but it doesn't work.
 Any help appreciated.
BEGIN TRAN
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