RSS

Category Archives: Administration

Improve SQL Server Performance with Compression

Improve SQL Server Performance with Compression

SQL Server data compression is now available in all editions of SQL Server, starting with 2016 SP1.

In this Article, you will not only know how data compression will save space, you’ll also find out how compression can sometimes improve performance as well.

Space Savings vs. Performance

When I first heard about compression back in 2008, my first thought is that it would have a big performance penalty. Compression would save disk space, but it would probably decrease performance as the data was compressed and decompressed. It turns out that compression can improve performance instead. Because compressed data fits in a smaller number of data pages, there are decreased I/O requirements. Since I/O is generally the bottleneck in SQL Server, this can improve performance. Compressed data also has a decreased memory requirement. When querying compressed data, a smaller number of pages will be copied to the buffer pool. The one area that is impacted is CPU. You do need to have some CPU headroom because compression will require some additional CPU resources.

a1

The good thing is that if the workload is reasonably tuned, many SQL Server instances have more CPU resources than they need. One note of caution here. Don’t look to compression as the solution to solving major performance issues. You need to look at physical resources, configuration, indexing, and query tuning. The point I’m trying to make is that decreased I/O and better memory utilization will benefit the workload in many cases.

Availability

Compression has been available in SQL Server for all versions from 2008 to 2016 SQL server, but only for Enterprise Edition. Beginning with SQL Server 2016 SP1, it’s now available in Enterprise, Standard, and Express. I’m excited about this because now compression is within the reach of any organization.

Compression Types

There are two types of compression that you can use to compress a table, index, or even a partition:

  • Row Level:

  • Row level compression works by storing fixed-width data types as variable length data types. Nulls and zeroes do not take any space. For example, in an uncompressed table, an integer column takes 4 bytes per row, even for those rows that have a small number such as 1 or 10, or even null. Once row compression is implemented on the table, each value will be stored with the smallest possible number of bytes. So outside of the metadata, storing a 1 in an integer column will take 1 byte, storing a null or 0 will take 0 bytes.

 a2

  • Starting with SQL Server 2012, Unicode compression is implemented when you use row compression. This applies to Unicode columns in varchar and in char. In an uncompressed table, each character takes up 2 bytes in a Unicode column, even if a small character set is used. In those cases, compressing the table will store the Unicode characters in 1 byte instead.

a3

  • In the technical article, Data Compression: Strategy, Capacity Planning, and Best Practices, Microsoft recommends using row compression on all data, as long as you have 10% extra CPU capacity, and, of course, as long as you achieve some space savings.
  • It costs Low CPU penalty.
  • Page Level:

  • When you implement page level compression, the rows are automatically row-compressed first.
  • Page level compression also removes repeated data within a page by two mechanisms, prefix and dictionary compression.
  • Page level compression can compress a table to a smaller size than row compression, but it is recommended for tables that are mostly inserted, but not updated that often.
  • It does have a higher CPU penalty.

Neither of these compression types will work on row-overflow data. This is data from a row that exceeds 8K. For example, you can create a table that has two varchar 8000 columns. If a row exceeds 8060 bytes, then SQL Server will move one or more of those columns to another page so that the row fits. One way to get around this issue is the new COMPRESS function.

COMPRESS Function

  • You can use this function to compress individual values, which includes row-overflow data.
  • It uses a GZIP algorithm to compress the values. There is a downside to this, however. The COMPRESS function must be applied each time a value is inserted or updated, and a DECOMPRESS function must then be used to read the value. This means that there would be changes to the application or stored procedure.

Performance Metrics

In this demo, we’ll do some performance comparisons. We’ll take a close look at I/O and memory impact. We’ll see how compression affects both reads and writes to the data.

  • Select comparison

I created two tables; one with page compression called “bigTransactionHistoryPAGE” and one with row compression called “bigTransactionHistoryROW”. I also created a table with no compression called “bigTransactionHistory” that I’ll use during this demonstration as well. And finally, I populated the two compressed tables with around 31 million records.

Let’s take a look at the number of pages in each table or index:

SELECT OBJECT_NAME(i.[object_id]) AS TableName,

       i.name AS IndexName, SUM(s.used_page_count) IndexPages,

       FORMAT(1 - SUM(s.used_page_count) * 1.0/CASE WHEN i.name LIKE 'IX%' THEN 131819 ELSE 143645 END, 'P') AS PercentSaved

FROM sys.dm_db_partition_stats  AS s

JOIN sys.indexes AS i

ON s.[object_id] = i.[object_id] AND s.index_id = i.index_id

WHERE OBJECT_NAME(i.[object_id]) LIKE 'bigTransactionHistory%'

       AND OBJECT_NAME(i.[object_id]) <> 'bigTransactionHistoryTEST'

GROUP BY i.[object_id],i.name

ORDER BY IndexPages Desc;

a4

The uncompressed table from is the largest. The non-clustered index compressed with row compression saved about 30% of the space, and the clustered index saved about 37%. The page compressed table is really interesting. The clustered index is much smaller than the original table, while the non-clustered index is about 39% smaller.

I’m going to turn on STATISTICS IO to compare the number of pages touched when I query each table:

SET STATISTICS IO ON;

GO

SELECT SUM(Quantity) AS ItemsPurchased

FROM bigTransactionHistory;




SELECT SUM(Quantity) AS ItemsPurchased

FROM bigTransactionHistoryROW;




SELECT SUM(Quantity) AS ItemsPurchased

FROM bigTransactionHistoryPAGE;

a5

You see here that less I/O is needed for the compressed table. That’s actually obvious since the clustered and non-clustered indexes are smaller when compressed.

The next query shows how many pages are in the buffer for each index:

SELECT COUNT(*)AS cached_pages_count

,name ,index_id

FROM sys.dm_os_buffer_descriptors AS bd

INNER JOIN

(

SELECT object_name(object_id) AS name

,index_id ,allocation_unit_id

FROM sys.allocation_units AS au

INNER JOIN sys.partitions AS p

ON au.container_id = p.hobt_id

AND (au.type = 1 OR au.type = 3)

UNION ALL

SELECT object_name(object_id) AS name

,index_id, allocation_unit_id

FROM sys.allocation_units AS au

INNER JOIN sys.partitions AS p

ON au.container_id = p.partition_id

AND au.type = 2

) AS obj

ON bd.allocation_unit_id = obj.allocation_unit_id

WHERE database_id = DB_ID()  AND name LIKE 'bigTransactionHistory%'

GROUP BY name, index_id

ORDER BY cached_pages_count DESC;

a6

Again, when the index resides on fewer pages, the data takes less space and memory. Notice that the clustered index was used for the page-compressed table. We saw that the page-compressed clustered index is much smaller than the non-clustered index.

On this Azure VM, I have seen inconsistent results in the time to run the queries. For example, if I use DBCC DROPCLEANBUFFERS, or even restart SQL Server to ensure the data must be loaded from disk, one of these queries could run anywhere from 1 second to even a minute. I suspect that the VM is sharing resources with other VMs, and that is causing my discrepancies. I decided to run the queries each in a loop to better see the difference. Inside the loop, I use DBCC DROPCLEANBUFFERS to make sure that the data was loaded from disk, and not cached data.

DECLARE @Count INT = 0;

WHILE @Count < 100 BEGIN

       DBCC DROPCLEANBUFFERS;    

       SELECT SUM(Quantity) AS ItemsPurchased

       FROM bigTransactionHistory;

       SET @Count += 1;

END;

The loop against the uncompressed table took 3 minutes and 31 seconds. The row-compressed table took 3 minutes and 4 seconds and the page compressed table took 3 minutes and 18 seconds. So in this case, the row-compressed query performed the best, with the page-compressed query next.

  • Insert comparison

Let’s take a look at inserting data. In this script, I populated an uncompressed table and our two compressed tables with a loop of 1000 inserts of 1000 rows each. To make things fair, I ran DROPCLEANBUFFERS before each loop.

DBCC DROPCLEANBUFFERS;

GO

--2:40

DECLARE @Count INT = 0;

WHILE @Count < 1000 BEGIN

INSERT INTO dbo.bigTransactionHistoryTEST

SELECT *

FROM bigTransactionHistory

WHERE TransactionID BETWEEN @Count * 1000 + 1 AND (@Count + 1) * 1000;

SET @Count = @Count + 1;

END;

The uncompressed inserts took 2 minutes and 40 seconds. The row-compressed inserts completed a bit faster at 2 minutes and 23 seconds, and the page-compressed inserts completed in 2 minutes and 14 seconds. The page-compressed inserts were actually fastest, and I suspect that it might be due to less I/O.

  • Update comparison

Let’s take a look at updates.

DBCC DROPCLEANBUFFERS;

GO

–1:48

DECLARE @Count INT = 0;

WHILE @Count < 1000 BEGIN

UPDATE dbo.bigTransactionHistoryTEST

SET Quantity = Quantity + 1

WHERE TransactionID BETWEEN @Count * 1000 + 1 AND (@Count + 1) * 1000;

SET @Count = @Count + 1;

END;

Again, I ran loops. In this case, it’s 1000 updates of 1000 rows Updating the uncompressed table took 1 minute and 48 seconds. Updating the row-compressed table took 1 minute and 36 seconds. The page-compressed table was much slower at 2 minutes and 21 seconds. During the slides, I mentioned that Microsoft recommends page compression for workloads that have few updates, and you can see that the updates are slower for page compression.

To summarize, I saw decent space savings, especially with page compression. The compressed tables performed better for both selects and inserts. Updates, however, performed noticeably worse with page compression.

a7

Summary:

This Article is an overview of data compression. Compression is now available in all editions of SQL Server, starting with 2016 SP1. You can implement row and page level compression, and also use the new COMPRESS function. Compression can improve performance because of decreased I/O and memory pressure. I hope this article has been informative for you.

Useful Links:

 

Tags: , , , ,

sys.foreign_keys does not have matching row in sys.indexes

Running DBCC CHECKDB you are getting following error message:

Check Catalog Msg 3853, State 1: Attribute (referenced_object_id=194099732,key_index_id=7) of row (object_id=2040565179) in sys.foreign_keys does not have a matching row (object_id=194099732,index_id=7) in sys.indexes

This error means, that Unique key constraint (index_id 7) in the primary table (object_id 194099732) is missing, which was referenced by child table’s FK constraint (FK object_id 2040565179).  This should not happen, SQL Server will not allow you to drop a constraint that is referenced by FK.  If attempted should get following error message:

Msg 3723, Level 16, State 6, Line 1
An explicit DROP INDEX is not allowed on index ‘dbo.a.NonClusteredIndex-20151119-085219’. It is being used for FOREIGN KEY constraint enforcement.

So if we are suppose to get errors? Why do we have corruption; simple answer, someone be making updates to system tables directly, which is not allowed or supported!

Actually we are not able to update system tables in SQL Server 2005+ (ref), however in SQL 2000 days, we had setting called allow updates in sp_configure options.  Also supported by the KB2787112.

So question is how do you fix it?

First, identify the child table name from sys.foreign_keys:

SELECT object_name(parent_object_id) AS TableName
  FROM sys.foreign_keys
WHERE name = ‘FK_b_a’

Second, script our constraint definition:

  1. Find the table, we got in SQL Statement above.
  2. Go to Keys.
  3. Right click on FK constraint name.
  4. Script Key As.
  5. Create To.
  6. New Query Window.

Third, drop the FK constraint:

ALTER TABLE [schema].[tablename] DROP CONSTRAINT [fk_constraint_name]

Fourth, Re-create the constraint, with script generated in Step 2.

If it was issue of someone playing around in system tables, this should resolve it.  However, if you get error similar to below:

Msg 1776, Level 16, State 0, Line 1
There are no primary or candidate keys in the referenced table ‘dbo.a’ that match the referencing column list in the foreign key ‘FK_b_a’.

This means, that the key is missing in parent table and appropriate index needs be created before FK constraint can be created.  Since SQL doesn’t allow the index to be dropped there most likely are other corruption issues that have gone unnoticed.  If that is an issue, you will have to rely on your backups for recovery.

This post is cross posted on my SQLCAN Blog, MSDN Blog, and SQL server Consultation blog.

 
Leave a comment

Posted by on November 20, 2015 in Administration

 

Tags: , , , , ,

Change DB Owner on all Databases one time

this one of wonderful scripts and very important 

—Change DB Owner on All Databases
EXEC sp_MSforeachdb ‘IF ”?” NOT IN (”Master”,”tempDB”,”model”,”msdb”)
BEGIN
EXEC [?]..sp_changedbowner ”User Name”
END

To know More about new feature in SQL Server 2016 you can check it from HERE

Follow Us :

LinkedIn Slideshare ,Youtube Channel.MSDN POSTS ,Facebook WHO WE ARE

 
Leave a comment

Posted by on November 16, 2015 in Administration

 

Tags: , ,

Check and Enable Automatic Statistic Update on Database Level

AS SQL Server Best Practices: Auto-Create and Auto-Update Statistics Should Be On – Most of the Time in general they are a very good thing for performance. You could try to figure out which columns need statistics, but it’s often better to let SQL Server do that for you.You can turn on the AUTO_CREATE_STATISTICS database option and SQL Server will automatically determine when it needs the Statistics and create them for you.

Check And Enable Automatic Statistic Update on all databases have this option is disable

Select ‘ALTER DATABASE [‘+Name+’] SET AUTO_CREATE_STATISTICS ON;
GO
ALTER DATABASE [‘+Name+’] SET AUTO_UPDATE_STATISTICS ON;
GO
‘ from Sys.Databases where is_auto_update_stats_on = 0 or is_auto_create_stats_on = 0

Take the Result and Execute it in another session

Update Statistics

To check all my posts you godirect to my personal website or you can download this Excel sheet My Technical POSTS

View all my tips , LinkedIn Slideshare ,Youtube Channel.My posts in MSDN

 

Tags: , , ,

How to build , Manage and monitor your SQL Server replication

Hello my friends this my small post in SQL Server replication it is not everything about replication but at least it is the what any DBA should know it 11 Posts in SQL Server replication technology english and arabic posts

  • What is SQL Replication?
  • Types of SQL Replication
  • Replication Overview
  •  How to create Transaction Replication
  • How to Add New Publisher Server to the Distributor Server
  •  Disable Publishing and Distribution Servers
  • Publication Status
  • Subscription Status
  • Replication information for the Complete setup
  • Find publication article
  • How we can Check Distributor agent status
  • How we can Check log reader agent status

downloadreplica

All this previous point you can know it easily from the below Posts :

  1. Replication in SQL Server Part 1
  2. Replication in SQL Server Part 2
  3. Replication in SQL Server Part 3
  4. Replication in SQL Server Part 4
  5. SQL Server DMV Replication Monitoring Part 1
  6. SQL Server DMV Replication Monitoring Part 2
  7. SQL Server DMV Replication Monitoring Part 3
  8. SQL Server DMV Replication Monitoring Part 4
  9. الأكواد الديناميكية لمراقبة ومتابعة حلول تزامن البيانات 1/ 3
  10. الأكواد الديناميكية لمراقبة ومتابعة حلول تزامن البيانات 2/ 3
  11. الأكواد الديناميكية لمراقبة ومتابعة حلول تزامن البيانات 3/ 3

Follow me because i will do one online session in replication and i will enhance all this posts by adding lot of other information in replication .

To check all my posts you can direct to my personal website or you can download this Excel sheet My Technical POSTS

View all my tips , LinkedIn Website Slideshare ,Youtube Channel.

 
Leave a comment

Posted by on April 14, 2015 in Administration

 

Tags: , , , , ,

Where is index location on Database?

Where is index location on Database?

Where is index location on Database? 

Hi guys today I will show smoothing is easy but more important to know about it {Where is the index live} by the below DMV we can return all the index with table name and with File group hosted on it , another thing you can use this DMV to know the heap tables , Clustered index , non-Clustered index

Index Location:

WITH C AS
(

SELECT ps.data_space_id
, f.name
, d.physical_name
FROM sys.filegroups f
JOIN sys.database_files d ON d.data_space_id = f.data_space_id
JOIN sys.destination_data_spaces dds ON dds.data_space_id = f.data_space_id
JOIN sys.partition_schemes ps ON ps.data_space_id = dds.partition_scheme_id

UNION

SELECT f.data_space_id
, f.name
, d.physical_name
FROM sys.filegroups f
JOIN sys.database_files d ON d.data_space_id = f.data_space_id
)
–SELECT * FROM c
SELECT [ObjectName] = OBJECT_NAME(i.[object_id])
, [IndexID] = i.[index_id]
, [IndexName] = i.[name]
, [IndexType] = i.[type_desc]
, [Partitioned] = CASE WHEN ps.data_space_id IS NULL THEN ‘No’
ELSE ‘Yes’
END
, [StorageName] = ISNULL(ps.name, f.name)
, [FileGroupPaths] = CAST(( SELECT name AS “FileGroup”
, physical_name AS “DatabaseFile”
FROM C

WHERE i.data_space_id = c.data_space_id
FOR
XML PATH(”)
) AS XML)
FROM [sys].[indexes] i
LEFT JOIN sys.partition_schemes ps ON ps.data_space_id = i.data_space_id
LEFT JOIN sys.filegroups f ON f.data_space_id = i.data_space_id
WHERE OBJECTPROPERTY(i.[object_id], ‘IsUserTable’) = 1
ORDER BY [ObjectName], [IndexName]

index

Follow me because next post I will explain everything about the index and How you can build you index model How you can Enhance your expensive query by index more Secrets in the index …ETC

 

 
Leave a comment

Posted by on January 22, 2015 in Administration

 

Tags: , , ,

How to Grant Show Plan Privilege

How to Grant Show Plan Privilege

Showplan Privilege it’s granted for any one need to see the execution plane for SQL Server query to check the performance of the index or doing index analysis.

Grant Showplan for one user in one database  :

GRANT Showplan TO [DominName\username]

Grant Showplan for one user in All databases in one SQL instance:

 EXEC sp_MSforeachdb N’IF EXISTS
(
SELECT 1 FROM sys.databases WHERE name = ”?”
AND Is_read_only <> 1
)
BEGIN
print ”Use [?]; GRANT Showplan TO [DominName\username]”
END’;

after the execution take the Print scripts and run it in another session.

 
1 Comment

Posted by on November 16, 2014 in Administration

 

Tags: , ,