Posts Tagged ‘maintenance’

Ola Hallengren’s Maintenance Solution Command Log Analysis

October 23rd, 2015

Yeah yeah yeah, it’s been a while since I blogged last. Spent a glorious two years in New York City, but am very happily back in Jacksonville now. That whole story is a blog post in itself, so won’t get into it here. Suffice to say, it’s nice to be back home…full of renewed energy and raring to go. This is me…
To say that a large number of shops use Ola Hallengren’s maintenance solution is probably the understatement of the decade. It has proven itself over the years to be as thorough, easy-to-use, and flexible as any free, custom, or paid backup/index maintenance solution out there…and there are MANY out there, so that’s saying a lot. The balance of this post is assuming you’re familiar with it’s workings, capabilities, & output. While there’s a lot of verbage out there in blogland about how to use and set up the routines, there isn’t a lot to be found on how one might want to analyze the output. Thusly, I’ve put together over the years a few scripts I’d love to share.

Within Ola’s scripts, there exists the ability to log all activity to a table called “CommandLog”. I highly recommend one turns this option on for every part of the solution you employ. This means the same table will contain rows for each backup (full, t-log, or diff) taken, each index maintained (rebuilt or reorganized), each statistic updated, as well as for each time you use the scripts to perform DBCC integrity checks. The table of metadata is extremely valuable in analyzing exactly what took place the night before, the last month, etc. For the most part, turning on the logging is simply a matter of including a “@LogToTable = ‘Y'” parameter in the procedure call. Easy peazy.

One thing I really like to know is how many index maintenance operations were performed. It may be the case that normal business processes (combined with less-than-stellar schema) fragment our indexes on a regular basis and you don’t have any control over it. This might be so for instance when you do a lot of writes against a clustering key that places these new rows in one of the middle extents, and not at the end. This will cause page splits and natural fragmentation. As DBA’s, it’s our job to limit fragmentation as much as possible. Maybe we alter the cluster key. Maybe we alter the fill factor. Maybe we change the INSERT process to place new rows at the end. Whatever methodology you employ, you’d like to see some sort of reduction in the number of rebuilds and then eventually, reorgs as well. This is what I use to track them…

FROM commandlog c
WHERE c.command like '%reorganize%'
  AND NOT EXISTS (SELECT 1 FROM IndexExceptions WHERE IndexName = c.IndexName)
GROUP BY CONVERT (DATE, c.starttime)

FROM commandlog c
WHERE c.command like '%rebuild%'
  AND NOT EXISTS (SELECT 1 FROM IndexExceptions WHERE IndexName = c.IndexName)
GROUP BY CONVERT (DATE, c.starttime)

The “IndexExceptions” table reference you see in the 4th row of each SELECT, refers to a small table I keep to exclude any indexes from my counts that I know for 100% sure that I’m going to leave be, and I don’t want them in my report. It’s simple schema is…

CREATE TABLE [dbo].[IndexExceptions](
  [IndexExceptionID] [int] IDENTITY(1,1) NOT NULL,
  [IndexName] [varchar](200) NOT NULL,
  [Reason] [varchar](max) NULL

When I want to analyze exactly how long my index maintenance operations are taking, I use the following…

SELECT commandtype Activity,
  CAST(CONVERT(CHAR(11), starttime, 113) AS DATETIME) Work_Date,
  COUNT(*) How_Many,
  AVG(DATEDIFF(ms,starttime,endtime)) Avg_ms,
  AVG(DATEDIFF(s,starttime,endtime)) Avg_Secs,
  AVG(DATEDIFF(mi,starttime,endtime)) Avg_Mins
FROM commandlog
WHERE commandtype NOT IN ('xp_create_subdir','xp_delete_file','RESTORE_VERIFYONLY','BACKUP_DATABASE')
GROUP BY commandtype
  ,CAST(CONVERT(CHAR(11), starttime, 113) AS DATETIME)
ORDER BY CommandType, CAST(CONVERT(CHAR(11), starttime, 113) AS DATETIME) DESC

…use the WHERE clause to change what you see and what you don’t.

This snippet will tell you how many times individual indexes where rebuilt/reorg’d in a specific period. Adjust both parts of the WHERE clause as necessary…

SELECT DatabaseName, ObjectName, IndexName, COUNT(*) CommandCount
FROM dbo.CommandLog
WHERE commandtype = 'ALTER_INDEX'
  AND DATEDIFF(d,starttime,GETDATE()) < 14
GROUP BY DatabaseName, ObjectName, IndexName
ORDER BY CommandCount DESC

And this SELECT tells us important information about a single index; including it’s current fill factor (in case you want to change it to a lower amount and in theory, reduce splits and fragmentation), the current fragmentation percentage, as well as the size of the index. Again, change the WHERE clause as neccessary…

SELECT starttime,
  objectname [table],
  CAST(CAST(extendedinfo as XML).query('data(/ExtendedInfo/Fragmentation)') as VARCHAR(10)) as fragmentation,
  CAST(CAST(extendedinfo as XML).query('data(/ExtendedInfo/PageCount)') as VARCHAR(10)) as [pagecount],
FROM commandlog c
JOIN sys.indexes i ON = c.indexname
WHERE indexname = 'IndexNameHere'
 AND CommandType like '%alter%'
ORDER by databasename, objectname, c.starttime DESC

These are just some of the things you can do with the CommandLog table and the plethora of useful information it contains. Of course, feel free to use these scripts, adjust them, and let me know how it works for you.

Thanks and have a grateful day…Troy

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Posted in Backups, Index Tuning, SSMS, T-SQL | Comments (0)

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