In SQL Server 2008 I have tried to reproduce the results from the experiments on clustered index on sequential vs. non-sequential GUID keys seen here http://sqlblog.com/blogs/denis_gobo/archive/2009/02/05/11743.aspx but I do not experience the significant speedup for insertions that I would expect (and the author experiences). The page utilization is clearly improved with the sequential GUID, but for some reasons, inserting 10,000 rows is only around 100 ms faster (out of 10,300 ms).
I use the following code:
CREATE TABLE TestGuid1 (Id UNIQUEIDENTIFIER not null DEFAULT newid(),
SomeDate DATETIME, batchNumber BIGINT)
CREATE TABLE TestGuid2 (Id UNIQUEIDENTIFIER not null DEFAULT newsequentialid(),
SomeDate DATETIME, batchNumber BIGINT)
CREATE CLUSTERED INDEX ix_id1 ON TestGuid1(id)
CREATE CLUSTERED INDEX ix_id2 ON TestGuid2(id)
go
SET NOCOUNT ON
INSERT TestGuid1 (SomeDate,batchNumber) VALUES (GETDATE(),3)
go 10000
SET NOCOUNT ON
INSERT TestGuid2 (SomeDate,batchNumber) VALUES (GETDATE(),3)
go 10000
DBCC showcontig ('TestGuid1') WITH tableresults
DBCC showcontig ('TestGuid2') WITH tableresults
SELECT batchNumber,DATEDIFF(ms,MIN(SomeDate),MAX(SomeDate))
FROM TestGuid1
GROUP BY batchNumber
SELECT batchNumber,DATEDIFF(ms,MIN(SomeDate),MAX(SomeDate))
FROM TestGuid2
GROUP BY batchNumber
Can anyone explain why I do not experience a more significant speedup for insertions on TestGuid2?
Follow-up: As requested in the thread below, I have expanded the test: the test results tend to vary significantly over time, so now the experiments are repeated N times, and the total and average time usage reported. I have also added a third test, namely for primary keys on sequential integer columns. This should be the fastest and most compact of all three methods as the integer type is smaller and IDENTITY(1,1) is (or at least should be) fast. At least by my intuition. The average execution time is now to the benefit of the sequential GUID, but surprisingly insertions in the third experiment (with sequential integer keys) is slower than sequential GUIDs. I have no explanation of this. Here is the code for the new experiments:
SET NOCOUNT ON
CREATE TABLE TestGuid1 (Id UNIQUEIDENTIFIER NOT NULL DEFAULT NEWID() PRIMARY KEY,
SomeDate DATETIME, batchNumber BIGINT, FILLER CHAR(100))
CREATE TABLE TestGuid2 (Id UNIQUEIDENTIFIER NOT NULL DEFAULT NEWSEQUENTIALID() PRIMARY KEY,
SomeDate DATETIME, batchNumber BIGINT, FILLER CHAR(100))
CREATE TABLE TestInt (Id Int NOT NULL identity(1,1) PRIMARY KEY,
SomeDate DATETIME, batchNumber BIGINT, FILLER CHAR(100))
DECLARE @BatchCounter INT = 1
DECLARE @Numrows INT = 100000
WHILE (@BatchCounter <= 20)
BEGIN
BEGIN TRAN
DECLARE @LocalCounter INT = 0
WHILE (@LocalCounter <= @NumRows)
BEGIN
INSERT TestGuid1 (SomeDate,batchNumber) VALUES (GETDATE(),@BatchCounter)
SET @LocalCounter +=1
END
SET @LocalCounter = 0
WHILE (@LocalCounter <= @NumRows)
BEGIN
INSERT TestGuid2 (SomeDate,batchNumber) VALUES (GETDATE(),@BatchCounter)
SET @LocalCounter +=1
END
SET @LocalCounter = 0
WHILE (@LocalCounter <= @NumRows)
BEGIN
INSERT TestInt (SomeDate,batchNumber) VALUES (GETDATE(),@BatchCounter)
SET @LocalCounter +=1
END
SET @BatchCounter +=1
COMMIT
END
DBCC showcontig ('TestGuid1') WITH tableresults
DBCC showcontig ('TestGuid2') WITH tableresults
DBCC showcontig ('TestInt') WITH tableresults
SELECT batchNumber,DATEDIFF(ms,MIN(SomeDate),MAX(SomeDate)) AS [NEWID()]
FROM TestGuid1
GROUP BY batchNumber
SELECT batchNumber,DATEDIFF(ms,MIN(SomeDate),MAX(SomeDate)) AS [NEWSEQUENTIALID()]
FROM TestGuid2
GROUP BY batchNumber
SELECT batchNumber,DATEDIFF(ms,MIN(SomeDate),MAX(SomeDate)) AS [IDENTITY()]
FROM TestInt
GROUP BY batchNumber
DROP TABLE TestGuid1
DROP TABLE TestGuid2
DROP TABLE TestInt
And the average execution times:
NEWID() 3064
NEWSEQUENTIALID() 1977
IDENTITY() 2223
The page usage is as follows:
Table Pages AveragePageDensity
----------------------------------------
TestGuid1 50871 68,4
TestGuid2 35089 99,2
TestInt 32259 98,7
I fail to see, why these page statistics (which are best for TestInt) doesn't imply that experiment three is fastest.
Can you try this modified script and post your results?
SET NOCOUNT ON
CREATE TABLE TestGuid1 (Id UNIQUEIDENTIFIER NOT NULL DEFAULT NEWID() PRIMARY KEY,
SomeDate DATETIME, batchNumber BIGINT, FILLER CHAR(100))
CREATE TABLE TestGuid2 (Id UNIQUEIDENTIFIER NOT NULL DEFAULT NEWSEQUENTIALID() PRIMARY KEY,
SomeDate DATETIME, batchNumber BIGINT, FILLER CHAR(100))
DECLARE @BatchCounter INT = 1
WHILE (@BatchCounter <= 20)
BEGIN
BEGIN TRAN
DECLARE @LocalCounter INT = 0
WHILE (@LocalCounter <= 100000)
BEGIN
INSERT TestGuid1 (SomeDate,batchNumber) VALUES (GETDATE(),@BatchCounter)
SET @LocalCounter +=1
END
SET @LocalCounter = 0
WHILE (@LocalCounter <= 100000)
BEGIN
INSERT TestGuid2 (SomeDate,batchNumber) VALUES (GETDATE(),@BatchCounter)
SET @LocalCounter +=1
END
SET @BatchCounter +=1
COMMIT
END
DBCC showcontig ('TestGuid1') WITH tableresults
DBCC showcontig ('TestGuid2') WITH tableresults
SELECT batchNumber,DATEDIFF(ms,MIN(SomeDate),MAX(SomeDate)) AS [NEWID()]
FROM TestGuid1
GROUP BY batchNumber
SELECT batchNumber,DATEDIFF(ms,MIN(SomeDate),MAX(SomeDate)) AS [NEWSEQUENTIALID()]
FROM TestGuid2
GROUP BY batchNumber
DROP TABLE TestGuid1
DROP TABLE TestGuid2
I see quite wildly varying results between individual runs (on my laptop not a server!) but a definite trend for sequential to be faster.
NEWID() Average 5168.9
batchNumber NEWID()
-------------------- -----------
1 4270
2 2480
3 2706
4 3333
5 7480
6 5346
7 4306
8 7713
9 7313
10 4760
11 4680
12 4113
13 3433
14 2686
15 4963
16 8040
17 5313
18 8160
19 9533
20 2750
NEWSEQUENTIALID() Average 3000.85
batchNumber NEWSEQUENTIALID()
-------------------- -----------------
1 2016
2 1820
3 1886
4 1870
5 4873
6 3473
7 3730
8 3690
9 1983
10 2020
11 1906
12 5596
13 2100
14 1950
15 2096
16 1876
17 5196
18 2110
19 2113
20 7713