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I have been doing some more looking at SQL Server indexes lately and came across a great script that may be of use to others as well.

So what can this index defrag script do?

• Schedule it to run with the default settings; it works “right out of the box” with no additional configuration necessary
• Run this one script from a centralized database for all databases on a server
• Run this script for a specific database or table
• Configure custom threshold limits and the point at which a rebuild should be performed (instead of a reorganize)
• Defrag individual partitions
• Log its actions and the duration of the defrag
• Run in “commands only” mode (@executeSQL = 0, @printCommands = 1)
• Customize performance parameters such as @maxDopRestriction and @defragDelay to minimize impact on the server
• Schedule specific indexes to only be defragged on weekends, or every other day

The script source code (very well documented) and author (Michelle Ufford) can be found at http://sqlfool.com/2009/06/index-defrag-script-v30/

declare @dt datetime
set @dt = getdate()
 
print 'Now'
print @dt
print ''


print 'Today - no time'
print dateadd(D, 0, datediff(D, 0, @dt))
print ''

print 'Today – 23:59:59.997'
print dateadd(ms,-3, dateadd(D, datediff(D, 0, @dt),1))
print ''


print 'Start of this week - Starts on MONDAY'
print dateadd(wk,datediff(wk,0, @dt),0) 
print ''


print 'End of this week - Starts on MONDAY 23:59:59.997'
print dateadd(ms,-3, dateadd(wk,datediff(wk,0,@dt),7))
print ''

print 'Start of this week - Starts on SUNDAY'
print dateadd(wk,datediff(wk,0,getdate()),-1) 
print ''


print 'End of this week - Starts on SUNDAY 23:59:59.997'
print dateadd(ms,-3,dateadd(wk,datediff(wk,0,@dt),5)) 
print ''


print 'Start of Month'
print dateadd(mm,datediff(mm,0,@dt),0) 
print ''


print 'Last day of current Month - 23:59:59.997'
print dateadd(ms,-3, dateadd(mm,datediff(mm,0,@dt)+1,0))
print ''
 

Here is a simple break down to how these snippets actually work

print 'Today - no time'
print dateadd(D, 0, datediff(D, 0, @dt))
print ''

First off we return the number of days between the date/time passed and 0 so we get the number of whole days (we have lost the time)

Today is July 14, 2009 (as an example) which using this code

print datediff(D, 0, '2009-07-14 03:34:21')

This will return 40006

We then add 40006 days to 0 and this returns the date 2009-07-14.

print dateadd(D, 0, 40006)

Jul 14 2009 12:00AM

So adding it together we get

print dateadd(D, 0, datediff(D, 0, @dt))

You will notice that some of the functions have a –3 as part of the code, this is because we want to return the last actual time that SQL Server can reference on a particular day. SQL Server can store the maximum time as 23:59:59.997. That is because SQL Server is only accurate to 3 milliseconds. If we used 23:59:59.999 it would actually roll over to the next day.

So if we were wanting to return the last time for today’s date/time we can use the following

print DATEADD(ms, - 3, DATEADD(D, DATEDIFF(D, 0, GETDATE()), 1))