Author Archive: Gail

A deadlock can appear to be a very obtuse error, as the only advice offered with the error message is an instruction to ‘rerun the transaction’, and there’s no apparent way to find the cause of the deadlock.

There are in fact several ways to get information on what caused the deadlock and on what resources the deadlock occurred. This information is generally referred to as the ‘deadlock graph’

Traceflag 1204

This is the oldest of the ways to get at the deadlock graph and it’s the main way used on SQL 2000. If traceflag 1204 is enabled server-wide, either by adding it as a startup parameter or by using the TraceOn command (DBCC TRACEON(1204,-1)), then anytime the SQL deadlock detector detects and resolves a deadlock, the information on that is written into the SQL Server error log. It looks something like this:

[source:XML] Deadlock encountered …. Printing deadlock information
Wait-for graph

Node:1

OBJECT: 12:629577281:0         CleanCnt:3 Mode:S Flags: 0x1
Grant List 2:
Owner:0x000000008673B900 Mode: S        Flg:0x40 Ref:2 Life:02000000 SPID:52 ECID:0 XactLockInfo: 0x0000000085F64ED0
SPID: 52 ECID: 0 Statement Type: UPDATE Line #: 11
Input Buf: Language Event: exec CauseDeadlock
Requested by:
ResType:LockOwner Stype:’OR’Xdes:0x0000000085F65740 Mode: IX SPID:53 BatchID:0 ECID:0 TaskProxy:(0x0000000085F5C538) Value:0x85b66a00 Cost:(0/0)

Node:2

OBJECT: 12:629577281:0         CleanCnt:3 Mode:S Flags: 0x1
Grant List 2:
Owner:0x00000000867FA180 Mode: S        Flg:0x40 Ref:2 Life:02000000 SPID:53 ECID:0 XactLockInfo: 0x0000000085F65780
SPID: 53 ECID: 0 Statement Type: UPDATE Line #: 11
Input Buf: Language Event: exec CauseDeadlock
Requested by:
ResType:LockOwner Stype:’OR’Xdes:0x0000000085F64E90 Mode: IX SPID:52 BatchID:0 ECID:0 TaskProxy:(0x00000000810B8538) Value:0x85b66a40 Cost:(0/0)

Victim Resource Owner:
ResType:LockOwner Stype:’OR’Xdes:0x0000000085F65740 Mode: IX SPID:53 BatchID:0 ECID:0 TaskProxy:(0x0000000085F5C538) Value:0x85b66a00 Cost:(0/0) [/source]

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Removing the time from a datetime is a task that comes up again and again and it sometimes seems like everyone’s got their own favorite way of doing it. I though I’d take a run through some of the ways I’ve seen and see how the compare in terms of performance.

The methods that I’ll be comparing are:

1. Cast to varchar and back to datetime
2. Cast to float, floor and cast back to datetime
3. Use dateadd and datediff to get rid of the time
4. Cast to date and back to datetime (SQL 2008 specific)

I ran each one 4 times and averaged the results

CREATE TABLE #DateTest (
ID INT IDENTITY(1,1) PRIMARY KEY CLUSTERED,
DateValue  DATETIME
)

INSERT INTO #DateTest (DateValue)
SELECT TOP 1000000
DATEADD(mi,RAND(s1.number*5000 + s2.number)*5000,'2000/01/01' )
FROM master..spt_values s1 CROSS JOIN master..spt_values s2
WHERE s1.[name] IS NULL AND s2.NAME IS null
GO

SET NOCOUNT ON
GO
SET STATISTICS TIME ON
GO

SELECT dateadd(dd, datediff(dd,0, DateValue),0)
FROM #DateTest
GO 4

SELECT convert(datetime,convert(varchar(10),DateValue,101))
FROM #DateTest
GO 4

SELECT CAST(FLOOR(CAST(DateValue AS FLOAT)) AS DATETIME)
FROM #DateTest
GO 4

SELECT CAST(CAST(DateValue AS DATE) AS DATETIME)
FROM #DateTest
GO 4

DROP TABLE #DateTest

And so, the winner of the date challenge:

1. Dateadd and datediff – CPU time 348ms, execution time 8092 ms
2. Cast to float and floor – CPU time 395ms, execution time 8270ms
3. Cast to varchar – CPU time 1450ms, execution time 9280ms
4. Cast to Date – CPU time 3063ms, execution time 7905ms

I was not expecing the cast to Date to take so much processing time. I think I’m going to take a look at the new date types in more detail, see what they perform like.

Someone asked this question on SQLServerCentral, I thought I’d post the test here for interest.

The question was on which would execute faster, creating a view, then creating a procedure that accepted a parameter and filtered the view, or creating a table valued function that took a parameter.

From testing, the answer is the procedure, but not by much. A inline table-valued-function comes a very close second and the multi-statement table-valued-function waddles in last. Not really surprising. (more…)