Solved

Simple Query Hangs

Posted on 2007-11-14
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Last Modified: 2010-04-21
SQL Server 2005..
I have a database procedure that has always worked quickly, recently it is hanging.   I narrowed it down to one query with multiple joins, then dissected it to a single table and a simple where clause.

When entered directly into SQL Management Studio, this query hangs...

 select * from myTable where Fkey = 123

Yet this query returns immediately..
 
  select * from myTable

The column "Fkey" is a foreign key to a parent table.    There is a foreign key constraint defined on it.

The database is in use, after a reboot, I can fetch from the table OK for a few minutes, then it just hangs.     My last run (which I let go on and on) took 11 minutes to complete.   There are only 100 records in this table !


After 11 minutes, this message was returned..

[Macromedia][SQLServer JDBC Driver][SQLServer]Transaction (Process ID 60) was deadlocked on lock resources with another process and has been chosen as the deadlock victim. Rerun the transaction.

So if its a deadlock and all I'm doing is a select.. how do I figure out why its deadlocking and how do I keep it from happening?  

Thanks!
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Question by:gdemaria
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12 Comments
 
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Expert Comment

by:James Murrell
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Author Comment

by:gdemaria
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Thanks cs.  But I have tried "with (NOLOCK)" and it doesn't help.

Any idea how I can track down the code that is involved in the lock?
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James Murrell earned 250 total points
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mmmmm found this

Listing 1: Procedure That Finds the Head of a Chain of Blockers
USE master
SET QUOTED_IDENTIFIER OFF
GO

IF EXISTS (SELECT * FROM sysobjects WHERE name='sp_leadblocker' AND type='P')
   DROP PROC sp_leadblocker
GO

CREATE PROCEDURE sp_leadblocker
AS
IF EXISTS
    (SELECT * FROM master.dbo.sysprocesses
    WHERE spid IN (SELECT blocked FROM master.dbo.sysprocesses))
    SELECT
        spid, status, loginame=substring(loginame, 1, 12),
        hostname=substring(hostname, 1, 12),
            blk=CONVERT(char(3), blocked),
            open_tran,
        dbname=substring(db_name(dbid),1,10),cmd,
            waittype, waittime, last_batch
        FROM master.dbo.sysprocesses
        WHERE spid IN (SELECT blocked FROM master.dbo.sysprocesses)
            AND blocked=0
ELSE
SELECT "No blocking processes found!"
GO
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Expert Comment

by:Wizilling
Comment Utility
start a sql profiler and you will be able to capture rpc starting and sql starting and rpc completed and sql st completed and deadlock and lock... (analyse the trace and u can find out which transaction were blocking and deadlocked)

Also doing a sp_who2 or trying the procedure above will help too.

also have u a index on the Fkey column of your table. Have they been rebuilt lately. This will speed up your query.
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Author Comment

by:gdemaria
Comment Utility
surprisingly, the script doesn't indicate any deadlocks.

I know I had deadlocks sometimes when run, other times the query just goes on for 4+ minutes.  I used to run this query along with dozens of others in db procedures in less then 4 seconds, now this one query takes 4 minutes with very small tables (less than a couple hundred records in most).    So its hard to see if its temporary deadlock or what..  

I will try to get sql profiler installed, thanks for that wiz..
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Assisted Solution

by:Wizilling
Wizilling earned 250 total points
Comment Utility
it would be worthwhile have the following statement in your sql statement /procedure) to avoid any locks. (if you are only interested in uncommitted data)

SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED
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by:gdemaria
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Wiz, could you explain what that would do ?

Would I place it at the top of each procedure that I run?

thanks!
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Expert Comment

by:ScottPletcher
Comment Utility
Run a check on the table, just to be sure there isn't some corruption that is causing this problem.

USE yourDbName
DBCC CHECKTABLE ('tableName')

Also, a full scan won't use an index, the = single value should.  So rebuild the indexes on the table.

CREATE [ UNIQUE ] [ CLUSTERED | NONCLUSTERED ] INDEX index_name
    ON tableName ( column1, ...)
WITH DROP_EXISTING

NOTE: Dropping and recreating the index(es) will make the table unavailable during that time.
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Expert Comment

by:Wizilling
Comment Utility
From BooksOnLine
READ UNCOMMITTED.

Specifies that statements can read rows that have been modified by other transactions but not yet committed.

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. When this option is set, it is possible to read uncommitted modifications, which are called dirty reads. Values in the data can be changed and rows can appear or disappear in the data set before the end of the transaction. This option has the same effect as setting NOLOCK on all tables in all SELECT statements in a transaction. This is the least restrictive of the isolation levels.

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Author Closing Comment

by:gdemaria
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Thanks for your help.  We had to put the project on hold because of this issue.  Sorry to have disappeared.  Your help was greatly appreciated!  Although the issue still exists and is still a mystery.  I will post new questions though..
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Expert Comment

by:aleto1
Comment Utility
hi, author, did you solve the problem ?, I have the same problem with a sql7  database, allways worked but since a few days ago, the same select, simply does not work,
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Author Comment

by:gdemaria
Comment Utility

My problem may be different from yours, this resolution was rather unique..

Our dual nic cards where not correctly set to auto detect causing packets to be dropped and the queries to get deadlocked or hung.   Other symptoms of the network card issue were slow copy times between folders on networked computers.

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