Data Compression– a unique feature of SQL Server TIP #91

A part from performance many times we faced challenges related to space  of our database. Sometimes our database is actually taking huge space and sometimes it our mistake due to which it took space.

It is worst condition when you are on a dedicated hosting or cloud hosting with limited space. In such case “Compression” is one of the best option.

This feature introduce in SQL SERVER 2008 onwards with Enterprise & Developer Edition.

By the name it is clear that it compress the data and provide more space on disk.

There are 2 options available in Data compression

Row level compression:-

 Row level compression primarily turns fixed-length data-types into variable data-types, thereby saving space. It also ignores zero and null values saving additional space. Because of this, more number of rows can be accommodated in a single data page.

Page level compression:-

Page level compression initially performs Row Level compression and adds two additional compression features – Prefix and Dictionary Compression. Page level compression offers better space saving than row level compression. Although the page level compression produce more space but obvious the CPU utilization is higher in page level compression. Overall we can say the page level compression is highly CPU consuming operation means it involves lot of  CPU efforts for compress & de compression. So choosing this option requires a high CPU & RAM configuration machine. Due to this feature it mostly used in data warehouse database where repeated values occurs. using this option with a table where lots of write operation occurs in day to day activity will be a bad idea.

Now we aware of data compression and its two options. Now lets discussed some of the major points before using this valuable feature

1) Data compression is SQL SERVER feature so we don’t need to do any tweak or rewrite our application code which is a good thing.

2) Compression is real time so again you don’t need to re run a maintenance job each time to compress the data.

3) As mention earlier you have to pay bit CPU cost for compression.

4) with Compression data files MDF files, ldf files and buffer cache size can be improve.

5) Compression not compress FILESTREAM data object which is obvious.

6) Although maintenance of compressed index is higher.

In next post I will show simple steps for implementing this best feature.

Enjoy !!!

Thanks

RJ!!!

How to replace a specific string from a large string with Write feature ? TIP #72

 

This is very interesting feature and I recently come to know this awesome feature.

Lets understand this by an example below

Suppose we have a student table with following structure  as shown in below image

 

We have a detail column with VARCHAR(MAX) .

Now as it is VARCHAR(MAX) column it may content a large amount of data currently it has following data as shown in below figure

Suppose we want to replace a specific string from this large column value like we want to replace “interested in” with “Always”  of  studentId = 1 then

we can use write function easily.

With the help of Write we can update a specific text/string  of a large column.

syntax of Write is as shown below

UPDATE TABLENAME

SET COLUMNNAME.WRITE (ReplacedWithString, startPosition, length)

WHERE clause

Now lets understand this by above student example where we want to replace “Interested in” which is doubled by mistake with “always”

So when you run above query you will get following result when you run select command.

great we have replaced the string which we want.

The main benefit of this the entire column value is not logged. suppose you have 2 GB data in your column then instead of logging 2 GB data at the time update only few KB will be logged.

I hope this might helpful to you somewhere.

Thanks !!!

RJ!!!

Oh! I forgot When I took last Database Backup ? How to determine this? TIP # 66

 

In last few tips TIP #64 & TIP #65  we get information  how to take backup & How to ensure it can be restore? Now lets me share some more information related to backup.

Problem:-   Sometimes , we are interested to know when last backup is taken for particular database ?

Solution:  The first thing I want to share here that  you should have proper maintenance plan to take backup of database and by job History you are able to know when last backup is taken but if this is not the case then not to worry SQL Server maintain itself information related to backup. to determine this you need to write a simple query as shown below

SELECT 
   CONVERT(CHAR(100), SERVERPROPERTY('Servername')) AS Server,
   msdb.dbo.backupset.database_name, 
   msdb.dbo.backupset.backup_start_date, 
   msdb.dbo.backupset.backup_finish_date,
   msdb.dbo.backupset.expiration_date,
   CASE msdb..backupset.type 
       WHEN 'D' THEN 'Database' 
       WHEN 'L' THEN 'Log' 
   END AS backup_type, 
   msdb.dbo.backupset.backup_size, 
   msdb.dbo.backupmediafamily.logical_device_name, 
   msdb.dbo.backupmediafamily.physical_device_name,  
   msdb.dbo.backupset.name AS backupset_name,
   msdb.dbo.backupset.description
FROM   msdb.dbo.backupmediafamily 
   INNER JOIN msdb.dbo.backupset ON msdb.dbo.backupmediafamily.media_set_id = msdb.dbo.backupset.media_set_id

ORDER BY 
   msdb.dbo.backupset.database_name,
   msdb.dbo.backupset.backup_finish_date

  When I run above command I get information related backup like databasename, backup start date, Backup finish date, expiry date(if any) , backup type like whether it is database backup or Log backup , size of backup , path where database is taken, name of backup set.

see below snap for detail

I hope this tip might help you somewhere.

Thanks !!

Rj!!

A hidden feature sp_MSforeachdb TIP #52

 

As we discussed yesterday a hidden feature tip #51 which is sp_MSForeachtable . sp_MsForeachtable is useful to run command on each table of selected database. Now what if we want to run command on each database also ? then in that case we need to take help of sp_MsForeachDB.

Sp_MsForEachDB  by the name it is clear that it will run provided command to each database.

The syntax of sp_MsForEachDB  is very simple almost like sp_MsForEachTable.

Lets understand this by an example

Suppose we want name of each database  of our SQL server for this we will run following command

Execute sp_MSforeachdb " SELECT  '?' AS Name"

Now  when we execute it we will get following result as shown in below figure.

This two stored procedures are not documented but it help a lot in maintenance task and other tasks.

I will share some maintenance query  with sp_MsForEachDB & sp_MsForEachtable  soon.

I hope this will help you somewhere.

Enjoy !!!

RJ!!!

How to determine when Last backup taken of a database n SQL Server? TIP #15

Sometime we require to know when we have taken last backup.
So let me share here all the backup, log shipping related detail you can find in the MSDB database which is system database.
SQL server maintain all the backup related detail in the MSDB database table
As Show in the figure

Now we can run the following command to determine the database backups
GO
SELECT Name,
       database_creation_date,
       backup_start_date ,
       backup_finish_date,
       database_name,
      bmf.physical_device_name
FROM MSDB.dbo.backupset bs
INNER JOIN msdb.dbo.backupmediafamily bmf  ON bmf.media_set_id = bs.media_set_id
WHERE database_name='DBayDB'

GO
WHERE DBAY is database name when you run this command you will get all the backup taken for this database.

Enjoy !!!

How to find what is currently running on your SQL SERVER? TIP # 12

When we are keen to know that what is currently running on SQL SERVER for analysis purpose then with the help of below SQL statement we can easily find those statements, Stored procedure, status etc.

Go
SELECT [Spid] = session_Id
, ecid
, [Database] = DB_NAME(sp.dbid)
, [User] = nt_username
, [Status] = er.status
, [Wait] = wait_type
, [Individual Query] = SUBSTRING (qt.text,
er.statement_start_offset/2,
(CASE WHEN er.statement_end_offset = -1
THEN LEN(CONVERT(NVARCHAR(MAX), qt.text)) * 2
ELSE er.statement_end_offset END -
er.statement_start_offset)/2)
,[Parent Query] = qt.text
, Program = program_name
, Hostname
, nt_domain
, start_time
FROM sys.dm_exec_requests er
INNER JOIN sys.sysprocesses sp ON er.session_id = sp.spid
CROSS APPLY sys.dm_exec_sql_text(er.sql_handle)as qt
WHERE session_Id > 50 — Ignore system spids.
AND session_Id NOT IN (@@SPID) — Ignore this current statement.
ORDER BY 1, 2
Go

Enjoy !!!

GET all columns of a table–TIP #4

 

To Get all columns information of a table we can use following command

GO

SELECT st.name, sc.name,sc.is_identity AS IdentityColumn,
sc.is_nullable AS NullableColumn,
sc.max_length as colmaxlength,
sty.name as columnType
FROM sys.columns sc
INNER JOIN sys.tables st ON st.object_id  = sc.object_id
INNER JOIN systypes sty on sty.xtype = sc.system_type_id
ORDER By st.name,sc.name
GO

Or we can use following statement

SELECT TABLE_NAME,COLUMN_NAME,DATA_TYPE,
CHARACTER_MAXIMUM_LENGTH,
IS_NULLABLE
FROM [INFORMATION_SCHEMA].[COLUMNS]

Enjoy !!!

sp_help a way to know detail tip #2

To determine table detail like column name & data types for each individual table ,Index, primary key, foreign keys etc,  sp_help is one of the best way.

Syntax of sp_help is very simple as shown below

sp_help tableName

GO

Instead of writing  sp_help tablename you can get same information by highlighting table and press ALT+ F1

Note: if you just right sp_help and run it then all the objects of database will be listed down as a result.

Enjoy !!!

SP_SPACEUSED–Determine size (Space) - SQL Server TIP #1

 

To determine size of table in a database or size of database, we have simple syntax in SQL Server which is SP_SPACEUSED.

Syntax is simple enough as shown below

1) If we want to determine size of the database then we have to write below statement and execute

Use DatabaseName

GO

SP_SPACEUSED

GO

2) Now to determine size of particular table  we need to write following syntax

GO

SP_SPACEUSED TABLENAME

GO

3) Now to determine size of each table in a database we need to write following syntax

GO

SP_MSFOREACHTABLE ‘SP_SPACEUSED [1]’

GO

4) When we are running sp_spaceused it may possible the size is not updated so to make sure size is updated we need to write following command

GO

SP_SPACEUSED @updateUsage =N’True’

GO

In the output of each statements we are seeing reserved, data,Index_Size & unused columns.

so

1) reserved column shows total space reserved by object.

2) data column shows total space used by the data.

3) index_Size shows total space used by index in object.

4)unused shows total space reserved by object but not yet used.

For more information you can visit following link

http://msdn.microsoft.com/en-us/library/ms188776.aspx

Enjoy.