Check VLF Counts
Today I stumbled across a database with 87,302 VLF's. Yes, that's right... 87 THOUSAND. Most of our databases have a few dozen VLF's, but this was an old database that had grown to 1.5 TB and had the default autogrowth settings left in tact. How did we discover this? During a routine reboot of the server, this database took 30 minutes to recover, but there were no error messages or status messages in the log.
Now, this blog post is not about VLF's or why you should keep the number of VLF's to a small, manageable number -- although I hear under 50 is a good rule of thumb. No, the purpose of this blog post is to share a little script I wrote to check the number of VLF's each database uses:
CREATE TABLE #stage( FileID INT , FileSize BIGINT , StartOffset BIGINT , FSeqNo BIGINT , [Status] BIGINT , Parity BIGINT , CreateLSN NUMERIC(38) ); CREATE TABLE #results( Database_Name sysname , VLF_count INT ); EXEC sp_msforeachdb N'Use ?; Insert Into #stage Exec sp_executeSQL N''DBCC LogInfo(?)''; Insert Into #results Select DB_Name(), Count(*) From #stage; Truncate Table #stage;' SELECT * FROM #results ORDER BY VLF_count DESC; DROP TABLE #stage; DROP TABLE #results;
This script is low-impact and is safe to run on large, production databases during business hours. However, just be aware that it's using some undocumented commands.
For more information on VLF's, check out these excellent articles:
Index Defrag Script, v4.0
In my blog post, "Index Defrag Script Updates - Beta Testers Needed", I stated "I'll hopefully have the new version online in just a few days." That was dated January 26th. I had every intention of following through with it, too, but something came up:

My daughter, Chloe Lynn, was born on February 10th. She's a happy, healthy baby girl who consumes all of my free time and already has both her parents wrapped around her adorable little finger. So while I apologize for the delay in posting the latest version, I hope you can understand and forgive me.
Alrighty, back to SQL stuff! This version of the script has been significantly overhauled from previous versions. Here's a full synopsis of the changes and enhancements:
- There's now a time limit option so you have more control over how long your defrags run. This time limit is checked *before* a defrag is begun, so it's still possible to have a defrag occur after the time limit is exceeded (i.e. a large index).
- I've added a static table for managing the index defrag scans. This way, you can start and stop the defrag process without the need to rescan. This is especially useful for VLDB's or any environment where you're unable to complete the defrags in one operation.
- Just in case you want to perform a rescan, even if there's still indexes left to defrag from your last rescan, there's a parameter to force it.
- There's now an option to sort by page count, range scan count, or fragmentation level. Range scan count is defaulted, as the indexes that have high amounts of range scans will benefit the most from having a defragged index. You can also specify whether you want to sort by ASC or DESC.
- There's now min and max parameters for page counts. This is useful for a) ignoring indexes with less than 1 extent (as recommended by Microsoft) and b) for scheduling index operations by size. For instance, you may want to defrag your small indexes during business hours but leave your big indexes for evening or weekend hours.
- There's now a parameterized option for sorting in TEMPDB. This may reduce execution time and will prevent unnecessary database file size inflation during defrags. NOTE: Make sure you have enough free space in TEMPDB prior to enabling this option.
- I moved the SQL statement output to display before execution so you can see what's currently executing.
- I've added a debug output of the parameters selected. I've added additional validation to the start of the script, so this will help show you if an invalid value was submitted and overwritten.
- I've added new columns to the log table to show what command is being executed and what error, if any, occurred when trying to execute.
- I've added try/catch logic to handle errors during execution; this way, a single error will not prevent the whole script from terminating.
- The script will now force a rebuild for indexes with allow_page_locks = off.
- For those who use partitioning, you can now exclude the right-most populated partition from the defrag operation. This won't be applicable for all partitioning schemes, but for sliding-window scenarios (one of the most common schemes), it'll reduce contention on the partition that's being actively written to.
- I've fixed a bug where tables with LOB indexes may have more than one record returned from sys.dm_db_index_physical_stats.
- For various reasons, I've removed the option to rebuild stats.
Also, if you have a previous version of the script installed, this version will rename those tables, since there have been some changes made to them.
FAQ:
I often receive the same questions about this script, so allow me to answer them here:
"I keep running the script, but my index is still fragmented. Why?"
This is most likely a very small index. Here's what Microsoft has to say:
"In general, fragmentation on small indexes is often not controllable. The pages of small indexes are stored on mixed extents. Mixed extents are shared by up to eight objects, so the fragmentation in a small index might not be reduced after reorganizing or rebuilding the index. For more information about mixed extents, see Understanding Pages and Extents."
"What database should I create it in?" or "Can I create this in the MASTER database?"
It's up to you where you create it. You could technically create it in the MASTER database, but I recommend creating a utility database for your DBA administrative tasks.
"Can I run this againt a SharePoint database?"
I've never tried personally, but I've been told it runs just fine.
"What are the minimum requirements to run this script?" or "Will this run on SQL Server 2000 instances?"
You need to be on SQL Server 2005 SP2 or higher.
Without further ado, here's the script:
/* Scroll down to the see notes, disclaimers, and licensing information */ DECLARE @indexDefragLog_rename VARCHAR(128) , @indexDefragExclusion_rename VARCHAR(128) , @indexDefragStatus_rename VARCHAR(128); SELECT @indexDefragLog_rename = 'dba_indexDefragLog_obsolete_' + CONVERT(VARCHAR(10), GETDATE(), 112) , @indexDefragExclusion_rename = 'dba_indexDefragExclusion_obsolete_' + CONVERT(VARCHAR(10), GETDATE(), 112) , @indexDefragStatus_rename = 'dba_indexDefragStatus_obsolete_' + CONVERT(VARCHAR(10), GETDATE(), 112); IF Exists(SELECT [OBJECT_ID] FROM sys.tables WHERE [name] = 'dba_indexDefragLog') EXECUTE SP_RENAME dba_indexDefragLog, @indexDefragLog_rename; IF Exists(SELECT [OBJECT_ID] FROM sys.tables WHERE [name] = 'dba_indexDefragExclusion') EXECUTE SP_RENAME dba_indexDefragExclusion, @indexDefragExclusion_rename; IF Exists(SELECT [OBJECT_ID] FROM sys.tables WHERE [name] = 'dba_indexDefragStatus') EXECUTE SP_RENAME dba_indexDefragStatus, @indexDefragStatus_rename; Go CREATE TABLE dbo.dba_indexDefragLog ( indexDefrag_id INT IDENTITY(1,1) Not Null , databaseID INT Not Null , databaseName NVARCHAR(128) Not Null , objectID INT Not Null , objectName NVARCHAR(128) Not Null , indexID INT Not Null , indexName NVARCHAR(128) Not Null , partitionNumber SMALLINT Not Null , fragmentation FLOAT Not Null , page_count INT Not Null , dateTimeStart DATETIME Not Null , dateTimeEnd DATETIME Null , durationSeconds INT Null , sqlStatement VARCHAR(4000) Null , errorMessage VARCHAR(1000) Null CONSTRAINT PK_indexDefragLog_v40 PRIMARY KEY CLUSTERED (indexDefrag_id) ); PRINT 'dba_indexDefragLog Table Created'; CREATE TABLE dbo.dba_indexDefragExclusion ( databaseID INT Not Null , databaseName NVARCHAR(128) Not Null , objectID INT Not Null , objectName NVARCHAR(128) Not Null , indexID INT Not Null , indexName NVARCHAR(128) Not Null , exclusionMask INT Not Null /* 1=Sunday, 2=Monday, 4=Tuesday, 8=Wednesday, 16=Thursday, 32=Friday, 64=Saturday */ CONSTRAINT PK_indexDefragExclusion_v40 PRIMARY KEY CLUSTERED (databaseID, objectID, indexID) ); PRINT 'dba_indexDefragExclusion Table Created'; CREATE TABLE dbo.dba_indexDefragStatus ( databaseID INT , databaseName NVARCHAR(128) , objectID INT , indexID INT , partitionNumber SMALLINT , fragmentation FLOAT , page_count INT , range_scan_count BIGINT , schemaName NVARCHAR(128) Null , objectName NVARCHAR(128) Null , indexName NVARCHAR(128) Null , scanDate DATETIME , defragDate DATETIME Null , printStatus BIT DEFAULT(0) , exclusionMask INT DEFAULT(0) CONSTRAINT PK_indexDefragStatus_v40 PRIMARY KEY CLUSTERED(databaseID, objectID, indexID, partitionNumber) ); PRINT 'dba_indexDefragStatus Table Created'; IF OBJECTPROPERTY(OBJECT_ID('dbo.dba_indexDefrag_sp'), N'IsProcedure') = 1 BEGIN DROP PROCEDURE dbo.dba_indexDefrag_sp; PRINT 'Procedure dba_indexDefrag_sp dropped'; END; Go CREATE PROCEDURE dbo.dba_indexDefrag_sp /* Declare Parameters */ @minFragmentation FLOAT = 10.0 /* in percent, will not defrag if fragmentation less than specified */ , @rebuildThreshold FLOAT = 30.0 /* in percent, greater than @rebuildThreshold will result in rebuild instead of reorg */ , @executeSQL BIT = 1 /* 1 = execute; 0 = print command only */ , @defragOrderColumn NVARCHAR(20) = 'range_scan_count' /* Valid options are: range_scan_count, fragmentation, page_count */ , @defragSortOrder NVARCHAR(4) = 'DESC' /* Valid options are: ASC, DESC */ , @timeLimit INT = 720 /* defaulted to 12 hours */ /* Optional time limitation; expressed in minutes */ , @DATABASE VARCHAR(128) = Null /* Option to specify a database name; null will return all */ , @tableName VARCHAR(4000) = Null -- databaseName.schema.tableName /* Option to specify a table name; null will return all */ , @forceRescan BIT = 0 /* Whether or not to force a rescan of indexes; 1 = force, 0 = use existing scan, if available */ , @scanMode VARCHAR(10) = N'LIMITED' /* Options are LIMITED, SAMPLED, and DETAILED */ , @minPageCount INT = 8 /* MS recommends > 1 extent (8 pages) */ , @maxPageCount INT = Null /* NULL = no limit */ , @excludeMaxPartition BIT = 0 /* 1 = exclude right-most populated partition; 0 = do not exclude; see notes for caveats */ , @onlineRebuild BIT = 1 /* 1 = online rebuild; 0 = offline rebuild; only in Enterprise */ , @sortInTempDB BIT = 1 /* 1 = perform sort operation in TempDB; 0 = perform sort operation in the index's database */ , @maxDopRestriction TINYINT = Null /* Option to restrict the number of processors for the operation; only in Enterprise */ , @printCommands BIT = 0 /* 1 = print commands; 0 = do not print commands */ , @printFragmentation BIT = 0 /* 1 = print fragmentation prior to defrag; 0 = do not print */ , @defragDelay CHAR(8) = '00:00:05' /* time to wait between defrag commands */ , @debugMode BIT = 0 /* display some useful comments to help determine if/where issues occur */ AS /********************************************************************************* Name: dba_indexDefrag_sp Author: Michelle Ufford, http://sqlfool.com Purpose: Defrags one or more indexes for one or more databases Notes: CAUTION: TRANSACTION LOG SIZE SHOULD BE MONITORED CLOSELY WHEN DEFRAGMENTING. DO NOT RUN UNATTENDED ON LARGE DATABASES DURING BUSINESS HOURS. @minFragmentation defaulted to 10%, will not defrag if fragmentation is less than that @rebuildThreshold defaulted to 30% as recommended by Microsoft in BOL; greater than 30% will result in rebuild instead @executeSQL 1 = execute the SQL generated by this proc; 0 = print command only @defragOrderColumn Defines how to prioritize the order of defrags. Only used if @executeSQL = 1. Valid options are: range_scan_count = count of range and table scans on the index; in general, this is what benefits the most from defragmentation fragmentation = amount of fragmentation in the index; the higher the number, the worse it is page_count = number of pages in the index; affects how long it takes to defrag an index @defragSortOrder The sort order of the ORDER BY clause. Valid options are ASC (ascending) or DESC (descending). @timeLimit Optional, limits how much time can be spent performing index defrags; expressed in minutes. NOTE: The time limit is checked BEFORE an index defrag is begun, thus a long index defrag can exceed the time limitation. @database Optional, specify specific database name to defrag; If not specified, all non-system databases will be defragged. @tableName Specify if you only want to defrag indexes for a specific table, format = databaseName.schema.tableName; if not specified, all tables will be defragged. @forceRescan Whether or not to force a rescan of indexes. If set to 0, a rescan will not occur until all indexes have been defragged. This can span multiple executions. 1 = force a rescan 0 = use previous scan, if there are indexes left to defrag @scanMode Specifies which scan mode to use to determine fragmentation levels. Options are: LIMITED - scans the parent level; quickest mode, recommended for most cases. SAMPLED - samples 1% of all data pages; if less than 10k pages, performs a DETAILED scan. DETAILED - scans all data pages. Use great care with this mode, as it can cause performance issues. @minPageCount Specifies how many pages must exist in an index in order to be considered for a defrag. Defaulted to 8 pages, as Microsoft recommends only defragging indexes with more than 1 extent (8 pages). NOTE: The @minPageCount will restrict the indexes that are stored in dba_indexDefragStatus table. @maxPageCount Specifies the maximum number of pages that can exist in an index and still be considered for a defrag. Useful for scheduling small indexes during business hours and large indexes for non-business hours. NOTE: The @maxPageCount will restrict the indexes that are defragged during the current operation; it will not prevent indexes from being stored in the dba_indexDefragStatus table. This way, a single scan can support multiple page count thresholds. @excludeMaxPartition If an index is partitioned, this option specifies whether to exclude the right-most populated partition. Typically, this is the partition that is currently being written to in a sliding-window scenario. Enabling this feature may reduce contention. This may not be applicable in other types of partitioning scenarios. Non-partitioned indexes are unaffected by this option. 1 = exclude right-most populated partition 0 = do not exclude @onlineRebuild 1 = online rebuild; 0 = offline rebuild @sortInTempDB Specifies whether to defrag the index in TEMPDB or in the database the index belongs to. Enabling this option may result in faster defrags and prevent database file size inflation. 1 = perform sort operation in TempDB 0 = perform sort operation in the index's database @maxDopRestriction Option to specify a processor limit for index rebuilds @printCommands 1 = print commands to screen; 0 = do not print commands @printFragmentation 1 = print fragmentation to screen; 0 = do not print fragmentation @defragDelay Time to wait between defrag commands; gives the server a little time to catch up @debugMode 1 = display debug comments; helps with troubleshooting 0 = do not display debug comments Called by: SQL Agent Job or DBA ---------------------------------------------------------------------------- DISCLAIMER: This code and information are provided "AS IS" without warranty of any kind, either expressed or implied, including but not limited to the implied warranties or merchantability and/or fitness for a particular purpose. ---------------------------------------------------------------------------- LICENSE: This index defrag script is free to download and use for personal, educational, and internal corporate purposes, provided that this header is preserved. Redistribution or sale of this index defrag script, in whole or in part, is prohibited without the author's express written consent. ---------------------------------------------------------------------------- Date Initials Version Description ---------------------------------------------------------------------------- 2007-12-18 MFU 1.0 Initial Release 2008-10-17 MFU 1.1 Added @defragDelay, CIX_temp_indexDefragList 2008-11-17 MFU 1.2 Added page_count to log table , added @printFragmentation option 2009-03-17 MFU 2.0 Provided support for centralized execution , consolidated Enterprise & Standard versions , added @debugMode, @maxDopRestriction , modified LOB and partition logic 2009-06-18 MFU 3.0 Fixed bug in LOB logic, added @scanMode option , added support for stat rebuilds (@rebuildStats) , support model and msdb defrag , added columns to the dba_indexDefragLog table , modified logging to show "in progress" defrags , added defrag exclusion list (scheduling) 2009-08-28 MFU 3.1 Fixed read_only bug for database lists 2010-04-20 MFU 4.0 Added time limit option , added static table with rescan logic , added parameters for page count & SORT_IN_TEMPDB , added try/catch logic and additional debug options , added options for defrag prioritization , fixed bug for indexes with allow_page_lock = off , added option to exclude right-most partition , removed @rebuildStats option , refer to http://sqlfool.com for full release notes ********************************************************************************* Example of how to call this script: Exec dbo.dba_indexDefrag_sp @executeSQL = 1 , @printCommands = 1 , @debugMode = 1 , @printFragmentation = 1 , @forceRescan = 1 , @maxDopRestriction = 1 , @minPageCount = 8 , @maxPageCount = Null , @minFragmentation = 1 , @rebuildThreshold = 30 , @defragDelay = '00:00:05' , @defragOrderColumn = 'page_count' , @defragSortOrder = 'DESC' , @excludeMaxPartition = 1 , @timeLimit = Null; *********************************************************************************/ SET NOCOUNT ON; SET XACT_Abort ON; SET Quoted_Identifier ON; BEGIN BEGIN Try /* Just a little validation... */ IF @minFragmentation IS Null Or @minFragmentation Not Between 0.00 And 100.0 SET @minFragmentation = 10.0; IF @rebuildThreshold IS Null Or @rebuildThreshold Not Between 0.00 And 100.0 SET @rebuildThreshold = 30.0; IF @defragDelay Not Like '00:[0-5][0-9]:[0-5][0-9]' SET @defragDelay = '00:00:05'; IF @defragOrderColumn IS Null Or @defragOrderColumn Not In ('range_scan_count', 'fragmentation', 'page_count') SET @defragOrderColumn = 'range_scan_count'; IF @defragSortOrder IS Null Or @defragSortOrder Not In ('ASC', 'DESC') SET @defragSortOrder = 'DESC'; IF @scanMode Not In ('LIMITED', 'SAMPLED', 'DETAILED') SET @scanMode = 'LIMITED'; IF @debugMode IS Null SET @debugMode = 0; IF @forceRescan IS Null SET @forceRescan = 0; IF @sortInTempDB IS Null SET @sortInTempDB = 1; IF @debugMode = 1 RAISERROR('Undusting the cogs and starting up...', 0, 42) WITH NoWait; /* Declare our variables */ DECLARE @objectID INT , @databaseID INT , @databaseName NVARCHAR(128) , @indexID INT , @partitionCount BIGINT , @schemaName NVARCHAR(128) , @objectName NVARCHAR(128) , @indexName NVARCHAR(128) , @partitionNumber SMALLINT , @fragmentation FLOAT , @pageCount INT , @sqlCommand NVARCHAR(4000) , @rebuildCommand NVARCHAR(200) , @dateTimeStart DATETIME , @dateTimeEnd DATETIME , @containsLOB BIT , @editionCheck BIT , @debugMessage NVARCHAR(4000) , @updateSQL NVARCHAR(4000) , @partitionSQL NVARCHAR(4000) , @partitionSQL_Param NVARCHAR(1000) , @LOB_SQL NVARCHAR(4000) , @LOB_SQL_Param NVARCHAR(1000) , @indexDefrag_id INT , @startDateTime DATETIME , @endDateTime DATETIME , @getIndexSQL NVARCHAR(4000) , @getIndexSQL_Param NVARCHAR(4000) , @allowPageLockSQL NVARCHAR(4000) , @allowPageLockSQL_Param NVARCHAR(4000) , @allowPageLocks INT , @excludeMaxPartitionSQL NVARCHAR(4000); /* Initialize our variables */ SELECT @startDateTime = GETDATE() , @endDateTime = DATEADD(MINUTE, @timeLimit, GETDATE()); /* Create our temporary tables */ CREATE TABLE #databaseList ( databaseID INT , databaseName VARCHAR(128) , scanStatus BIT ); CREATE TABLE #processor ( [INDEX] INT , Name VARCHAR(128) , Internal_Value INT , Character_Value INT ); CREATE TABLE #maxPartitionList ( databaseID INT , objectID INT , indexID INT , maxPartition INT ); IF @debugMode = 1 RAISERROR('Beginning validation...', 0, 42) WITH NoWait; /* Make sure we're not exceeding the number of processors we have available */ INSERT INTO #processor EXECUTE XP_MSVER 'ProcessorCount'; IF @maxDopRestriction IS Not Null And @maxDopRestriction > (SELECT Internal_Value FROM #processor) SELECT @maxDopRestriction = Internal_Value FROM #processor; /* Check our server version; 1804890536 = Enterprise, 610778273 = Enterprise Evaluation, -2117995310 = Developer */ IF (SELECT SERVERPROPERTY('EditionID')) In (1804890536, 610778273, -2117995310) SET @editionCheck = 1 -- supports online rebuilds ELSE SET @editionCheck = 0; -- does not support online rebuilds /* Output the parameters we're working with */ IF @debugMode = 1 BEGIN SELECT @debugMessage = 'Your selected parameters are... Defrag indexes with fragmentation greater than ' + CAST(@minFragmentation AS VARCHAR(10)) + '; Rebuild indexes with fragmentation greater than ' + CAST(@rebuildThreshold AS VARCHAR(10)) + '; You' + CASE WHEN @executeSQL = 1 THEN ' DO' ELSE ' DO NOT' END + ' want the commands to be executed automatically; You want to defrag indexes in ' + @defragSortOrder + ' order of the ' + UPPER(@defragOrderColumn) + ' value; You have' + CASE WHEN @timeLimit IS Null THEN ' not specified a time limit;' ELSE ' specified a time limit of ' + CAST(@timeLimit AS VARCHAR(10)) END + ' minutes; ' + CASE WHEN @DATABASE IS Null THEN 'ALL databases' ELSE 'The ' + @DATABASE + ' database' END + ' will be defragged; ' + CASE WHEN @tableName IS Null THEN 'ALL tables' ELSE 'The ' + @tableName + ' table' END + ' will be defragged; We' + CASE WHEN Exists(SELECT TOP 1 * FROM dbo.dba_indexDefragStatus WHERE defragDate IS Null) And @forceRescan <> 1 THEN ' WILL NOT' ELSE ' WILL' END + ' be rescanning indexes; The scan will be performed in ' + @scanMode + ' mode; You want to limit defrags to indexes with' + CASE WHEN @maxPageCount IS Null THEN ' more than ' + CAST(@minPageCount AS VARCHAR(10)) ELSE ' between ' + CAST(@minPageCount AS VARCHAR(10)) + ' and ' + CAST(@maxPageCount AS VARCHAR(10)) END + ' pages; Indexes will be defragged' + CASE WHEN @editionCheck = 0 Or @onlineRebuild = 0 THEN ' OFFLINE;' ELSE ' ONLINE;' END + ' Indexes will be sorted in' + CASE WHEN @sortInTempDB = 0 THEN ' the DATABASE' ELSE ' TEMPDB;' END + ' Defrag operations will utilize ' + CASE WHEN @editionCheck = 0 Or @maxDopRestriction IS Null THEN 'system defaults for processors;' ELSE CAST(@maxDopRestriction AS VARCHAR(2)) + ' processors;' END + ' You' + CASE WHEN @printCommands = 1 THEN ' DO' ELSE ' DO NOT' END + ' want to print the ALTER INDEX commands; You' + CASE WHEN @printFragmentation = 1 THEN ' DO' ELSE ' DO NOT' END + ' want to output fragmentation levels; You want to wait ' + @defragDelay + ' (hh:mm:ss) between defragging indexes; You want to run in' + CASE WHEN @debugMode = 1 THEN ' DEBUG' ELSE ' SILENT' END + ' mode.'; RAISERROR(@debugMessage, 0, 42) WITH NoWait; END; IF @debugMode = 1 RAISERROR('Grabbing a list of our databases...', 0, 42) WITH NoWait; /* Retrieve the list of databases to investigate */ INSERT INTO #databaseList SELECT database_id , name , 0 -- not scanned yet for fragmentation FROM sys.databases WHERE name = IsNull(@DATABASE, name) And [name] Not In ('master', 'tempdb')-- exclude system databases And [STATE] = 0 -- state must be ONLINE And is_read_only = 0; -- cannot be read_only /* Check to see if we have indexes in need of defrag; otherwise, re-scan the database(s) */ IF Not Exists(SELECT TOP 1 * FROM dbo.dba_indexDefragStatus WHERE defragDate IS Null) Or @forceRescan = 1 BEGIN /* Truncate our list of indexes to prepare for a new scan */ TRUNCATE TABLE dbo.dba_indexDefragStatus; IF @debugMode = 1 RAISERROR('Looping through our list of databases and checking for fragmentation...', 0, 42) WITH NoWait; /* Loop through our list of databases */ WHILE (SELECT COUNT(*) FROM #databaseList WHERE scanStatus = 0) > 0 BEGIN SELECT TOP 1 @databaseID = databaseID FROM #databaseList WHERE scanStatus = 0; SELECT @debugMessage = ' working on ' + DB_NAME(@databaseID) + '...'; IF @debugMode = 1 RAISERROR(@debugMessage, 0, 42) WITH NoWait; /* Determine which indexes to defrag using our user-defined parameters */ INSERT INTO dbo.dba_indexDefragStatus ( databaseID , databaseName , objectID , indexID , partitionNumber , fragmentation , page_count , range_scan_count , scanDate ) SELECT ps.database_id AS 'databaseID' , QUOTENAME(DB_NAME(ps.database_id)) AS 'databaseName' , ps.OBJECT_ID AS 'objectID' , ps.index_id AS 'indexID' , ps.partition_number AS 'partitionNumber' , SUM(ps.avg_fragmentation_in_percent) AS 'fragmentation' , SUM(ps.page_count) AS 'page_count' , os.range_scan_count , GETDATE() AS 'scanDate' FROM sys.dm_db_index_physical_stats(@databaseID, OBJECT_ID(@tableName), Null , Null, @scanMode) AS ps Join sys.dm_db_index_operational_stats(@databaseID, OBJECT_ID(@tableName), Null , Null) AS os ON ps.database_id = os.database_id And ps.OBJECT_ID = os.OBJECT_ID and ps.index_id = os.index_id And ps.partition_number = os.partition_number WHERE avg_fragmentation_in_percent >= @minFragmentation And ps.index_id > 0 -- ignore heaps And ps.page_count > @minPageCount And ps.index_level = 0 -- leaf-level nodes only, supports @scanMode GROUP BY ps.database_id , QUOTENAME(DB_NAME(ps.database_id)) , ps.OBJECT_ID , ps.index_id , ps.partition_number , os.range_scan_count OPTION (MaxDop 2); /* Do we want to exclude right-most populated partition of our partitioned indexes? */ IF @excludeMaxPartition = 1 BEGIN SET @excludeMaxPartitionSQL = ' Select ' + CAST(@databaseID AS VARCHAR(10)) + ' As [databaseID] , [object_id] , index_id , Max(partition_number) As [maxPartition] From ' + DB_NAME(@databaseID) + '.sys.partitions Where partition_number > 1 And [rows] > 0 Group By object_id , index_id;'; INSERT INTO #maxPartitionList EXECUTE SP_EXECUTESQL @excludeMaxPartitionSQL; END; /* Keep track of which databases have already been scanned */ UPDATE #databaseList SET scanStatus = 1 WHERE databaseID = @databaseID; END /* We don't want to defrag the right-most populated partition, so delete any records for partitioned indexes where partition = Max(partition) */ IF @excludeMaxPartition = 1 BEGIN DELETE ids FROM dbo.dba_indexDefragStatus AS ids Join #maxPartitionList AS mpl ON ids.databaseID = mpl.databaseID And ids.objectID = mpl.objectID And ids.indexID = mpl.indexID And ids.partitionNumber = mpl.maxPartition; END; /* Update our exclusion mask for any index that has a restriction on the days it can be defragged */ UPDATE ids SET ids.exclusionMask = ide.exclusionMask FROM dbo.dba_indexDefragStatus AS ids Join dbo.dba_indexDefragExclusion AS ide ON ids.databaseID = ide.databaseID And ids.objectID = ide.objectID And ids.indexID = ide.indexID; END SELECT @debugMessage = 'Looping through our list... there are ' + CAST(COUNT(*) AS VARCHAR(10)) + ' indexes to defrag!' FROM dbo.dba_indexDefragStatus WHERE defragDate IS Null And page_count Between @minPageCount And IsNull(@maxPageCount, page_count); IF @debugMode = 1 RAISERROR(@debugMessage, 0, 42) WITH NoWait; /* Begin our loop for defragging */ WHILE (SELECT COUNT(*) FROM dbo.dba_indexDefragStatus WHERE ( (@executeSQL = 1 And defragDate IS Null) Or (@executeSQL = 0 And defragDate IS Null And printStatus = 0) ) And exclusionMask & POWER(2, DATEPART(weekday, GETDATE())-1) = 0 And page_count Between @minPageCount And IsNull(@maxPageCount, page_count)) > 0 BEGIN /* Check to see if we need to exit our loop because of our time limit */ IF IsNull(@endDateTime, GETDATE()) < GETDATE() BEGIN RAISERROR('Our time limit has been exceeded!', 11, 42) WITH NoWait; END; IF @debugMode = 1 RAISERROR(' Picking an index to beat into shape...', 0, 42) WITH NoWait; /* Grab the index with the highest priority, based on the values submitted; Look at the exclusion mask to ensure it can be defragged today */ SET @getIndexSQL = N' Select Top 1 @objectID_Out = objectID , @indexID_Out = indexID , @databaseID_Out = databaseID , @databaseName_Out = databaseName , @fragmentation_Out = fragmentation , @partitionNumber_Out = partitionNumber , @pageCount_Out = page_count From dbo.dba_indexDefragStatus Where defragDate Is Null ' + CASE WHEN @executeSQL = 0 THEN 'And printStatus = 0' ELSE '' END + ' And exclusionMask & Power(2, DatePart(weekday, GetDate())-1) = 0 And page_count Between @p_minPageCount and IsNull(@p_maxPageCount, page_count) Order By + ' + @defragOrderColumn + ' ' + @defragSortOrder; SET @getIndexSQL_Param = N'@objectID_Out int OutPut , @indexID_Out int OutPut , @databaseID_Out int OutPut , @databaseName_Out nvarchar(128) OutPut , @fragmentation_Out int OutPut , @partitionNumber_Out int OutPut , @pageCount_Out int OutPut , @p_minPageCount int , @p_maxPageCount int'; EXECUTE SP_EXECUTESQL @getIndexSQL , @getIndexSQL_Param , @p_minPageCount = @minPageCount , @p_maxPageCount = @maxPageCount , @objectID_Out = @objectID OUTPUT , @indexID_Out = @indexID OUTPUT , @databaseID_Out = @databaseID OUTPUT , @databaseName_Out = @databaseName OUTPUT , @fragmentation_Out = @fragmentation OUTPUT , @partitionNumber_Out = @partitionNumber OUTPUT , @pageCount_Out = @pageCount OUTPUT; IF @debugMode = 1 RAISERROR(' Looking up the specifics for our index...', 0, 42) WITH NoWait; /* Look up index information */ SELECT @updateSQL = N'Update ids Set schemaName = QuoteName(s.name) , objectName = QuoteName(o.name) , indexName = QuoteName(i.name) From dbo.dba_indexDefragStatus As ids Inner Join ' + @databaseName + '.sys.objects As o On ids.objectID = o.object_id Inner Join ' + @databaseName + '.sys.indexes As i On o.object_id = i.object_id And ids.indexID = i.index_id Inner Join ' + @databaseName + '.sys.schemas As s On o.schema_id = s.schema_id Where o.object_id = ' + CAST(@objectID AS VARCHAR(10)) + ' And i.index_id = ' + CAST(@indexID AS VARCHAR(10)) + ' And i.type > 0 And ids.databaseID = ' + CAST(@databaseID AS VARCHAR(10)); EXECUTE SP_EXECUTESQL @updateSQL; /* Grab our object names */ SELECT @objectName = objectName , @schemaName = schemaName , @indexName = indexName FROM dbo.dba_indexDefragStatus WHERE objectID = @objectID And indexID = @indexID And databaseID = @databaseID; IF @debugMode = 1 RAISERROR(' Grabbing the partition count...', 0, 42) WITH NoWait; /* Determine if the index is partitioned */ SELECT @partitionSQL = 'Select @partitionCount_OUT = Count(*) From ' + @databaseName + '.sys.partitions Where object_id = ' + CAST(@objectID AS VARCHAR(10)) + ' And index_id = ' + CAST(@indexID AS VARCHAR(10)) + ';' , @partitionSQL_Param = '@partitionCount_OUT int OutPut'; EXECUTE SP_EXECUTESQL @partitionSQL, @partitionSQL_Param, @partitionCount_OUT = @partitionCount OUTPUT; IF @debugMode = 1 RAISERROR(' Seeing if there are any LOBs to be handled...', 0, 42) WITH NoWait; /* Determine if the table contains LOBs */ SELECT @LOB_SQL = ' Select @containsLOB_OUT = Count(*) From ' + @databaseName + '.sys.columns With (NoLock) Where [object_id] = ' + CAST(@objectID AS VARCHAR(10)) + ' And (system_type_id In (34, 35, 99) Or max_length = -1);' /* system_type_id --> 34 = image, 35 = text, 99 = ntext max_length = -1 --> varbinary(max), varchar(max), nvarchar(max), xml */ , @LOB_SQL_Param = '@containsLOB_OUT int OutPut'; EXECUTE SP_EXECUTESQL @LOB_SQL, @LOB_SQL_Param, @containsLOB_OUT = @containsLOB OUTPUT; IF @debugMode = 1 RAISERROR(' Checking for indexes that do not allow page locks...', 0, 42) WITH NoWait; /* Determine if page locks are allowed; for those indexes, we need to always rebuild */ SELECT @allowPageLockSQL = 'Select @allowPageLocks_OUT = Count(*) From ' + @databaseName + '.sys.indexes Where object_id = ' + CAST(@objectID AS VARCHAR(10)) + ' And index_id = ' + CAST(@indexID AS VARCHAR(10)) + ' And Allow_Page_Locks = 0;' , @allowPageLockSQL_Param = '@allowPageLocks_OUT int OutPut'; EXECUTE SP_EXECUTESQL @allowPageLockSQL, @allowPageLockSQL_Param, @allowPageLocks_OUT = @allowPageLocks OUTPUT; IF @debugMode = 1 RAISERROR(' Building our SQL statements...', 0, 42) WITH NoWait; /* If there's not a lot of fragmentation, or if we have a LOB, we should reorganize */ IF (@fragmentation < @rebuildThreshold Or @containsLOB >= 1 Or @partitionCount > 1) And @allowPageLocks = 0 BEGIN SET @sqlCommand = N'Alter Index ' + @indexName + N' On ' + @databaseName + N'.' + @schemaName + N'.' + @objectName + N' ReOrganize'; /* If our index is partitioned, we should always reorganize */ IF @partitionCount > 1 SET @sqlCommand = @sqlCommand + N' Partition = ' + CAST(@partitionNumber AS NVARCHAR(10)); END /* If the index is heavily fragmented and doesn't contain any partitions or LOB's, or if the index does not allow page locks, rebuild it */ ELSE IF (@fragmentation >= @rebuildThreshold Or @allowPageLocks <> 0) And IsNull(@containsLOB, 0) != 1 And @partitionCount <= 1 BEGIN /* Set online rebuild options; requires Enterprise Edition */ IF @onlineRebuild = 1 And @editionCheck = 1 SET @rebuildCommand = N' Rebuild With (Online = On'; ELSE SET @rebuildCommand = N' Rebuild With (Online = Off'; /* Set sort operation preferences */ IF @sortInTempDB = 1 SET @rebuildCommand = @rebuildCommand + N', Sort_In_TempDB = On'; ELSE SET @rebuildCommand = @rebuildCommand + N', Sort_In_TempDB = Off'; /* Set processor restriction options; requires Enterprise Edition */ IF @maxDopRestriction IS Not Null And @editionCheck = 1 SET @rebuildCommand = @rebuildCommand + N', MaxDop = ' + CAST(@maxDopRestriction AS VARCHAR(2)) + N')'; ELSE SET @rebuildCommand = @rebuildCommand + N')'; SET @sqlCommand = N'Alter Index ' + @indexName + N' On ' + @databaseName + N'.' + @schemaName + N'.' + @objectName + @rebuildCommand; END ELSE /* Print an error message if any indexes happen to not meet the criteria above */ IF @printCommands = 1 Or @debugMode = 1 RAISERROR('We are unable to defrag this index.', 0, 42) WITH NoWait; /* Are we executing the SQL? If so, do it */ IF @executeSQL = 1 BEGIN SET @debugMessage = 'Executing: ' + @sqlCommand; /* Print the commands we're executing if specified to do so */ IF @printCommands = 1 Or @debugMode = 1 RAISERROR(@debugMessage, 0, 42) WITH NoWait; /* Grab the time for logging purposes */ SET @dateTimeStart = GETDATE(); /* Log our actions */ INSERT INTO dbo.dba_indexDefragLog ( databaseID , databaseName , objectID , objectName , indexID , indexName , partitionNumber , fragmentation , page_count , dateTimeStart , sqlStatement ) SELECT @databaseID , @databaseName , @objectID , @objectName , @indexID , @indexName , @partitionNumber , @fragmentation , @pageCount , @dateTimeStart , @sqlCommand; SET @indexDefrag_id = SCOPE_IDENTITY(); /* Wrap our execution attempt in a try/catch and log any errors that occur */ BEGIN Try /* Execute our defrag! */ EXECUTE SP_EXECUTESQL @sqlCommand; SET @dateTimeEnd = GETDATE(); /* Update our log with our completion time */ UPDATE dbo.dba_indexDefragLog SET dateTimeEnd = @dateTimeEnd , durationSeconds = DATEDIFF(SECOND, @dateTimeStart, @dateTimeEnd) WHERE indexDefrag_id = @indexDefrag_id; END Try BEGIN Catch /* Update our log with our error message */ UPDATE dbo.dba_indexDefragLog SET dateTimeEnd = GETDATE() , durationSeconds = -1 , errorMessage = Error_Message() WHERE indexDefrag_id = @indexDefrag_id; IF @debugMode = 1 RAISERROR(' An error has occurred executing this command! Please review the dba_indexDefragLog table for details.' , 0, 42) WITH NoWait; END Catch /* Just a little breather for the server */ WAITFOR Delay @defragDelay; UPDATE dbo.dba_indexDefragStatus SET defragDate = GETDATE() , printStatus = 1 WHERE databaseID = @databaseID And objectID = @objectID And indexID = @indexID And partitionNumber = @partitionNumber; END ELSE /* Looks like we're not executing, just printing the commands */ BEGIN IF @debugMode = 1 RAISERROR(' Printing SQL statements...', 0, 42) WITH NoWait; IF @printCommands = 1 Or @debugMode = 1 PRINT IsNull(@sqlCommand, 'error!'); UPDATE dbo.dba_indexDefragStatus SET printStatus = 1 WHERE databaseID = @databaseID And objectID = @objectID And indexID = @indexID And partitionNumber = @partitionNumber; END END /* Do we want to output our fragmentation results? */ IF @printFragmentation = 1 BEGIN IF @debugMode = 1 RAISERROR(' Displaying a summary of our action...', 0, 42) WITH NoWait; SELECT databaseID , databaseName , objectID , objectName , indexID , indexName , partitionNumber , fragmentation , page_count , range_scan_count FROM dbo.dba_indexDefragStatus WHERE defragDate >= @startDateTime ORDER BY defragDate; END; END Try BEGIN Catch SET @debugMessage = Error_Message() + ' (Line Number: ' + CAST(Error_Line() AS VARCHAR(10)) + ')'; PRINT @debugMessage; END Catch; /* When everything is said and done, make sure to get rid of our temp table */ DROP TABLE #databaseList; DROP TABLE #processor; DROP TABLE #maxPartitionList; IF @debugMode = 1 RAISERROR('DONE! Thank you for taking care of your indexes! :)', 0, 42) WITH NoWait; SET NOCOUNT OFF; RETURN 0 END
You can also download it here: dba_indexDefrag_sp_v40_public.txt
I've had this latest version in production on terabyte-size databases running SQL Server 2005 and 2008 Enterprise editions for the last 3 months, where it runs nightly without issue. I've also had numerous beta testers report success in their environments, too. But to be safe, make sure to keep an eye on it the first time it runs to ensure you understand the impact on your server.
Enjoy!
Michelle
Filtered Indexes Work-Around
Recently, I needed to create a stored procedure that queried a rather large table. The table has a filtered index on a date column, and it covers the query. However, the Query Optimizer was not using the index, which was increasing the execution time (not to mention IO!) by at least 10x. This wasn't the first time I've had the Optimizer fail to use a filtered index. Normally when this happens, I use a table hint to force the filtered index -- after I verify that it is indeed faster, of course. However, since this was a stored procedure, I was receiving the following error message whenever I tried to execute the proc:
Query processor could not produce a query plan because of the hints defined in this query. Resubmit the query without specifying any hints and without using SET FORCEPLAN.
SQL Server would not allow me to execute the stored procedure using the filtered index hint. If I removed the hint, it executed, but it used a different, non-covering and far more expensive index. For those of you not familiar with this issue, allow me to illustrate the problem.
First, create a table to play with and populate it with some bogus data:
CREATE TABLE dbo.filteredIndexTest ( myID INT IDENTITY(1,3) , myDate SMALLDATETIME , myData CHAR(100) CONSTRAINT PK_filteredIndexTest PRIMARY KEY CLUSTERED(myID) ); SET NOCOUNT ON; DECLARE @DATE SMALLDATETIME = '2010-01-01'; WHILE @DATE < '2010-02-01' BEGIN INSERT INTO dbo.filteredIndexTest ( myDate , myData ) SELECT @DATE , 'Date: ' + CONVERT(VARCHAR(20), @DATE, 102); SET @DATE = DATEADD(MINUTE, 1, @DATE); END; SELECT COUNT(*) FROM dbo.filteredIndexTest;
It looks like this will generate 44,640 rows of test data... plenty enough for our purposes. Now, let's create our filtered index and write a query that will use it:
CREATE NONCLUSTERED INDEX IX_filteredIndexTest_1 ON dbo.filteredIndexTest(myDate) Include (myData) WHERE myDate >= '2010-01-27'; SELECT DISTINCT myData FROM dbo.filteredIndexTest WHERE myDate >= '2010-01-28';
If you look at the execution plan for this query, you'll notice that the Optimizer is using the filtered index. Perfect! Now let's parameterize it.
DECLARE @myDate1 SMALLDATETIME = '2010-01-28'; SELECT DISTINCT myData FROM dbo.filteredIndexTest WHERE myDate >= @myDate1;
Uh oh. Looking at the execution plan, we see that SQL Server is no longer using the filtered index. Instead, it's scanning the clustered index! Why is this? There's actually a good explanation for it. The reason is that I could, in theory, pass a date to my parameter that fell outside of the filtered date range. If that's the case, then SQL Server could not utilize the filtered index. Personally, I think it's a bug and SQL Server should identify whether or not a filtered index could be used based on the actual value submitted, but... that's a whole other blog post.
So what can we do? Well, dynamic SQL may be able to help us out in this case. Let's give it a go. First, let's try parameterized dynamic SQL.
DECLARE @mySQL1 NVARCHAR(2000) , @myParam NVARCHAR(2000) = '@p_myDate2 smalldatetime' , @myDate2 SMALLDATETIME = '2010-01-28'; SET @mySQL1 = 'Select Distinct myData From dbo.filteredIndexTest Where myDate >= @p_myDate2'; EXECUTE SP_EXECUTESQL @mySQL1, @myParam, @p_myDate2 = @myDate2;
Looking at the execution plan, we see we're still scanning on the clustered index. This is because the parameterized dynamic SQL resolves to be the exact same query as the one above it. Let's try unparameterized SQL instead:
DECLARE @mySQL2 NVARCHAR(2000) , @myDate3 SMALLDATETIME = '2010-01-28'; SET @mySQL2 = 'Select Distinct myData From dbo.filteredIndexTest Where myDate >= ''' + CAST(@myDate3 AS VARCHAR(20)) + ''''; EXECUTE SP_EXECUTESQL @mySQL2; -- Drop Table dbo.filteredIndexTest;
Voila! We have a seek on our filtered index. Why? Because the statement resolves to be identical to our first query, where we hard-coded the date value in the WHERE clause.
Now, I want to stress this fact: you should always, ALWAYS use parameterized dynamic SQL whenever possible. Not only is it safer, but it's also faster, because it can reuse cached plans. But sometimes you just cannot accomplish the same tasks with it. This is one of those times. If you do end up needing to use unparameterized dynamic SQL as a work-around, please make sure you're validating your input, especially if you're interfacing with any sort of external source.
There's an even easier work-around for this problem that Dave (http://www.crappycoding.com) shared with me: recompile.
Adding "Option (Recompile)" to the end of your statements will force the Optimizer to re-evaluate which index will best meet the needs of your query every time the statement is executed. More importantly, it evaluates the plan based on the actual values passed to the parameter... just like in our hard-coded and dynamic SQL examples. Let's see it in action:
DECLARE @myDate4 SMALLDATETIME = '2010-01-28'; SELECT DISTINCT myData FROM dbo.filteredIndexTest WHERE myDate >= @myDate4 OPTION (RECOMPILE); DECLARE @myDate5 SMALLDATETIME = '2010-01-20'; SELECT DISTINCT myData FROM dbo.filteredIndexTest WHERE myDate >= @myDate5 OPTION (RECOMPILE);
If we look at the execution plans for the 2 queries above, we see that the first query seeks on the filtered index, and the second query scans on the clustered index. This is because the second query cannot be satisfied with the filtered index because we initially limited our index to dates greater than or equal to 1/27/2010.
There are, of course, trade-offs associated with each approach, so use whichever one best meets your needs. Do you have another work-around for this issue? If so, please let me know.
Update:
Alex Kuznetsov (http://www.simple-talk.com/author/alex-kuznetsov/) shared this method too:
DECLARE @myDate1 SMALLDATETIME = '2010-01-28'; SELECT DISTINCT myData FROM dbo.filteredIndexTest WHERE myDate = @myDate1 AND myDate >= '2010-01-27';
Like the other examples, this will result in an index seek on the filtered index. Basically, by explicitly declaring the start date of your filter, you're letting the Optimizer know that the filtered index can satisfy the request, regardless of the parameter value passed. Thanks for the tip, Alex!
Index Defrag Script Updates – Beta Testers Needed
Update: Wow! I've received a ton of responses to my request for beta testers. Thank you all! The SQL Community is really amazing. I'll hopefully have the new version online in just a few days.
Over the last few months, I've received many great comments and suggestions regarding my Index Defrag Script v3.0. I've just recently had time to implement most of these suggestions, plus some other things that I thought would be useful.
Here's some of what you can look forward to shortly:
- Probably the single most requested feature, the new version of the script allows you to set a time limit for index defrags.
- There's now a static table for managing the status of index defrags. This way, when your time limit is reached, you can pick up where you left off the next day, without the need to rescan indexes.
- There's now an option to prioritize defrags by range scan counts, fragmentation level, or page counts.
- For those using partitioning, there is now an option to exclude the right-most populated partition from defrags (in theory, the one you're writing to in a sliding-window scenario).
- Options such as page count limits and SORT_IN_TEMPDB are now parameterized.
- I've enhanced error logging.
- ... and more!
Right now, I'm looking for a few folks who are willing to beta test the script. If you're interested, please send me an e-mail at michelle at sqlfool dot com with the editions of SQL Server you can test this on (i.e. 2005 Standard, 2008 Enterprise, etc.).
Thank you!
#PASSAwesomeness
Allen Kinsel on Twitter (@sqlinsaneo) recently started a new Twitter tag, #PASSAwesomeness, about all of the cool things about PASS Summit. I really like the tag, so I'm going to blatantly steal borrow it for this post.
First, and long overdue, I want to give a brief recap of the East Iowa SQL Saturday. On October 17th, our local PASS chapter, 380PASS, sponsored our first ever SQL Saturday at the University of Iowa in Iowa City. By all accounts, the event was a great success! We had 90 attendees, 11 speakers, and 21 sessions. We received numerous compliments on the quality of the speakers, the niceness of the facilities, and the abundance of food. Not too shabby for our first time hosting the event, if I do say so myself.
I'd like to thank all of our wonderful speakers, especially those who traveled from out of town and out of state, for making this event such a success. I'd also like to thank our amazing volunteers for helping put this all together. Lastly, but certainly not least, I'd like to thank our generous sponsors, without whom this event would not be possible. Because this event went so smoothly and was so well received in the community, we've already started planning our next big SQL event! In the meantime, don't forget to check out our monthly 380PASS meetings to tide you over.
I'd also like to take a moment to discuss the PASS Summit. Unless you're a DBA who's been living under a rock, you've probably heard of the PASS Summit. If you *have* been living under a rock -- and hey, I'm not poking fun, I used to live under a rock, too! -- then what you need to know is that the Summit is the largest SQL Server conference in the world. It's a gathering of Microsoft developers and SQL Server gurus; the rest of us show up to try to absorb as much from them as possible. Since I've recently moved to the Business Intelligence team, I'm extremely excited to delve into the amazing amount of BI content offered.
I'm also deeply honored to be presenting at the Summit this year on some of the performance tuning techniques I've used with great success in my production environments. The session is titled, Super Bowl, Super Load - A Look At Performance Tuning for VLDB's. If you're interested in performance tuning or VLDB (very large database) topics, consider stopping by to catch my session. From what I can tell, I'll be presenting on Tuesday from 10:15am - 11:30am in room(s?) 602-604.
If you read my blog, or if we've ever interacted in any way on the internet -- Twitter, LinkedIn, e-mails, blog comments, etc. -- please stop by and say "hi"! Aside from all of the awesome SQL Server content, I'm really looking forward to meeting as many new folks as possible.
And on that note...
Getting to meet all of the amazing SQL Server professionals out there who have inspired and encouraged me in so many ways #PASSAwesomeness
Partitioning Tricks
For those of you who are using partitioning, or who are considering using partitioning, allow me to share some tips with you.
Easy Partition Staging Tables
Switching partitions (or more specifically, hobts) in and out of a partitioned table requires the use of a staging table. The staging table has very specific requirements: it must be completely identical to the partitioned table, including indexing structures, and it must have a check constraint that limits data to the partitioning range. Thanks to my co-worker Jeff, I've recently started using the SQL Server Partition Management tool on CodePlex. I haven't used the automatic partition switching feature -- frankly, using any sort of data modification tool in a production environment makes me nervous -- but I've been using the scripting option to create staging tables in my development environment, which I then copy to production for use. It's nothing you can't do yourself, but it does make the whole process easy and painless, plus it saves you from annoying typos. But be careful when using this tool to just create the table and check constraints automatically, because you may need to...
Add Check Constraints After Loading Data
Most of the time, I add the check constraint when I create the staging table, then I load data and perform the partition switch. However, for some reason, I was receiving the following error:
.Net SqlClient Data Provider: Msg 4972, Level 16, State 1, Line 1
ALTER TABLE SWITCH statement failed. Check constraints or partition function of source table 'myStagingTable' allows values that are not allowed by check constraints or partition function on target table 'myDestinationTable'.
This drove me crazy. I confirmed my check constraints were correct, that I had the correct partition number, and that all schema and indexes matched identically. After about 30 minutes of this, I decided to drop and recreate the constraint. For some reason, it fixed the issue. Repeat tests produced the same results: the check constraint needed to be added *after* data was loaded. This error is occurring on a SQL Server 2008 SP1 box; to be honest, I'm not sure what's causing the error, so if you know, please leave me a comment. But I figured I'd share so that anyone else running into this issue can hopefully save some time and headache.
Replicating Into Partitioned and Non-Partitioned Tables
Recently, we needed to replicate a non-partitioned table to two different destinations. We wanted to use partitioning for Server A, which has 2008 Enterprise; Server B, which is on 2005 Standard, could not take advantage of partitioning. The solution was really easy: create a pre-snapshot and post-snapshot script for the publication, then modify to handle each server group differently. Using pseudo-code, it looked something like this:
/* Identify which servers get the partitioned version */ IF @@SERVERNAME In ('yourServerNameList') BEGIN /* Create your partitioning scheme if necessary */ IF Not Exists(SELECT * FROM sys.partition_schemes WHERE name = 'InsertPartitionScheme') CREATE PARTITION SCHEME InsertPartitionScheme AS PARTITION InsertPartitionFunction ALL TO ([PRIMARY]); /* Create your partitioning function if necessary */ IF Not Exists(SELECT * FROM sys.partition_functions WHERE name = 'InsertPartitionFunction') CREATE PARTITION FUNCTION InsertPartitionFunction (SMALLDATETIME) AS RANGE RIGHT FOR VALUES ('insertValues'); /* Create a partitioned version of your table */ CREATE TABLE [dbo].[yourTableName] ( [yourTableSchema] ) ON InsertPartitionScheme([partitioningKey]); END ELSE BEGIN /* Create a non-partitioned version of your table */ CREATE TABLE [dbo].[yourTableName] ( [yourTableSchema] ) ON [PRIMARY]; END
You could also use an edition check instead of a server name check, if you prefer. The post-snapshot script basically looked the same, except you create partitioned indexes instead.
Compress Old Partitions
Did you know you can set different compression levels for individual partitions? It's true! I've just completed doing this on our largest partitioned table. Here's how:
/* Apply compression to your partitioned table */ ALTER TABLE dbo.yourTableName Rebuild Partition = All WITH ( Data_Compression = Page ON Partitions(1 TO 9) , Data_Compression = ROW ON Partitions(10 TO 11) , Data_Compression = NONE ON Partitions(12) ); /* Apply compression to your partitioned index */ ALTER INDEX YourPartitionedIndex ON dbo.yourTableName Rebuild Partition = All WITH ( Data_Compression = Page ON Partitions(1 TO 9) , Data_Compression = ROW ON Partitions(10 TO 11) , Data_Compression = NONE ON Partitions(12) ); /* Apply compression to your unpartitioned index */ ALTER INDEX YourUnpartitionedIndex ON dbo.yourTableName Rebuild WITH (Data_Compression = ROW);
A couple of things to note. In all of our proof-of-concept testing, we found that compression significantly reduced query execution time, reads (IO), and storage. However, CPU was also increased significantly. The results were more dramatic, both good and bad, with page compression versus row compression. Still, for our older partitions, which aren't queried regularly, it made sense to turn on page compression. The newer partitions receive row compression, and the newest partitions, which are still queried very regularly by routine processes, were left completely uncompressed. This seems to strike a nice balance in our environment, but of course, results will vary depending on how you use your data.
Something to be aware of is that compressing your clustered index does *not* compress your non-clustered indexes; those are separate operations. Lastly, for those who are curious, it took us about 1 minute to apply row compression and about 7 minutes to apply page compression to partitions averaging 30 million rows.
Looking for more information on table partitioning? Check out my overview of partitioning, my example code, and my article on indexing on partitioned tables.
Monitoring Process for Performance Counters
Recently I needed to create a process to monitor performance counters over a short period of time. We were going to implement a change and we wanted to compare performance before and after to see if there was any impact.
To do this, I first created a couple of tables. One table is used to actually store the monitored values. The second table is used for configuration; you insert only the counters you want to monitor.
/* Create the table to store our logged perfmon counters */ CREATE TABLE dbo.dba_perfCounterMonitor ( capture_id INT IDENTITY(1,1) Not Null , captureDate SMALLDATETIME Not Null , objectName NVARCHAR(128) Not Null , counterName NVARCHAR(128) Not Null , instanceName NVARCHAR(128) Not Null , VALUE FLOAT(6) Not Null , valueType NVARCHAR(10) Not Null CONSTRAINT PK_dba_perfCounterMonitor PRIMARY KEY CLUSTERED(capture_id) ); /* Create the table that controls which counters we're going to monitor */ CREATE TABLE dbo.dba_perfCounterMonitorConfig ( objectName NVARCHAR(128) Not Null , counterName NVARCHAR(128) Not Null , instanceName NVARCHAR(128) Null );
If you leave the instanceName NULL in the config table, it'll monitor all instances. Now we're going to insert some sample performance counters into the config table. The counters you're interested in can, and likely will, vary.
/* Insert some perfmon counters to be monitored */ INSERT INTO dbo.dba_perfCounterMonitorConfig SELECT 'SQLServer:Buffer Manager', 'Page Life Expectancy', Null UNION All SELECT 'SQLServer:Locks', 'Lock Requests/sec', Null UNION All SELECT 'SQLServer:Locks', 'Lock Waits/sec', Null UNION All SELECT 'SQLServer:Locks', 'Lock Wait Time (ms)', Null UNION All SELECT 'SQLServer:Buffer Manager', 'Page reads/sec', Null UNION All SELECT 'SQLServer:Buffer Manager', 'Page writes/sec', Null UNION All SELECT 'SQLServer:Buffer Manager', 'Buffer cache hit ratio', Null UNION All SELECT 'SQLServer:Databases', 'Transactions/sec', 'AdventureWorks' UNION All SELECT 'SQLServer:General Statistics', 'Processes blocked', Null;
Now let's create our proc. This proc will run for a specified time period and will *average* the counters over that time. I personally take snapshots every 15 seconds for 4 minutes; I have a scheduled task that runs this every 5 minutes. It's not perfect, but it gives me a good idea of what's happening on the server.
CREATE PROCEDURE dbo.dba_perfCounterMonitor_sp /* Declare Parameters */ @samplePeriod INT = 240 /* how long to sample, in seconds */ , @sampleRate CHAR(8) = '00:00:15' /* how frequently to sample, in seconds */ , @displayResults BIT = 0 /* display the results when done */ AS /********************************************************************************* Name: dba_perfCounterMonitor_sp Author: Michelle Ufford, http://sqlfool.com Purpose: Monitors performance counters. Uses the dba_perfCounterMonitorConfig table to manage which perf counters to monitor. @samplePeriod - specifies how long the process will try to monitor performance counters; in seconds. @sampleRate - how long inbetween samples; in seconds. The average values over sample period is then logged to the dba_perfCounterMonitor table. Notes: There are 3 basic types of performance counter calculations: Value/Base: these calculations require 2 counters. The value counter (cntr_type = 537003264) has to be divided by the base counter (cntr_type = 1073939712). Per Second: these counters are store cumulative values; the value must be compared at 2 different times to calculate the difference (cntr_type = 537003264). Point In Time: these counters show what the value of the counter is at the current point-in-time (cntr_type = 65792). No calculation is necessary to derive the value. Called by: DBA Date User Description ---------------------------------------------------------------------------- 2009-09-04 MFU Initial Release ********************************************************************************* Exec dbo.dba_perfCounterMonitor_sp @samplePeriod = 60 , @sampleRate = '00:00:01' , @displayResults = 1; *********************************************************************************/ SET NOCOUNT ON; SET XACT_Abort ON; SET Ansi_Padding ON; SET Ansi_Warnings ON; SET ArithAbort ON; SET Concat_Null_Yields_Null ON; SET Numeric_RoundAbort OFF; BEGIN /* Declare Variables */ DECLARE @startTime DATETIME , @endTime DATETIME , @iteration INT; SELECT @startTime = GETDATE() , @iteration = 1; DECLARE @samples TABLE ( iteration INT Not Null , objectName NVARCHAR(128) Not Null , counterName NVARCHAR(128) Not Null , instanceName NVARCHAR(128) Not Null , cntr_value FLOAT Not Null , base_value FLOAT Null , cntr_type BIGINT Not Null ); BEGIN Try /* Start a new transaction */ BEGIN TRANSACTION; /* Grab all of our counters */ INSERT INTO @samples SELECT @iteration , RTRIM(dopc.OBJECT_NAME) , RTRIM(dopc.counter_name) , RTRIM(dopc.instance_name) , RTRIM(dopc.cntr_value) , (SELECT cntr_value FROM sys.dm_os_performance_counters AS dopc1 WHERE dopc1.OBJECT_NAME = pcml.objectName And dopc1.counter_name = pcml.counterName + ' base' And dopc1.instance_name = IsNull(pcml.instanceName, dopc.instance_name)) , dopc.cntr_type FROM sys.dm_os_performance_counters AS dopc Join dbo.dba_perfCounterMonitorConfig AS pcml ON dopc.OBJECT_NAME = pcml.objectName And dopc.counter_name = pcml.counterName And dopc.instance_name = IsNull(pcml.instanceName, dopc.instance_name); /* During our sample period, grab our counter values and store the results */ WHILE GETDATE() < DATEADD(SECOND, @samplePeriod, @startTime) BEGIN SET @iteration = @iteration + 1; INSERT INTO @samples SELECT @iteration , RTRIM(dopc.OBJECT_NAME) , RTRIM(dopc.counter_name) , RTRIM(dopc.instance_name) , dopc.cntr_value , (SELECT cntr_value FROM sys.dm_os_performance_counters AS dopc1 WHERE dopc1.OBJECT_NAME = pcml.objectName And dopc1.counter_name = pcml.counterName + ' base' And dopc1.instance_name = IsNull(pcml.instanceName, dopc.instance_name)) , dopc.cntr_type FROM sys.dm_os_performance_counters AS dopc Join dbo.dba_perfCounterMonitorConfig AS pcml ON dopc.OBJECT_NAME = pcml.objectName And dopc.counter_name = pcml.counterName And dopc.instance_name = IsNull(pcml.instanceName, dopc.instance_name); /* Wait for a small delay */ WAITFOR Delay @sampleRate; END; /* Grab our end time for calculations */ SET @endTime = GETDATE(); /* Store the average of our point-in-time counters */ INSERT INTO dbo.dba_perfCounterMonitor ( captureDate , objectName , counterName , instanceName , VALUE , valueType ) SELECT @startTime , objectName , counterName , instanceName , AVG(cntr_value) , 'value' FROM @samples WHERE cntr_type = 65792 GROUP BY objectName , counterName , instanceName; /* Store the average of the value vs the base for cntr_type = 537003264 */ INSERT INTO dbo.dba_perfCounterMonitor ( captureDate , objectName , counterName , instanceName , VALUE , valueType ) SELECT @startTime , objectName , counterName , instanceName , AVG(cntr_value)/AVG(IsNull(base_value, 1)) , 'percent' FROM @samples WHERE cntr_type = 537003264 GROUP BY objectName , counterName , instanceName; /* Compare the first and last values for our cumulative, per-second counters */ INSERT INTO dbo.dba_perfCounterMonitor ( captureDate , objectName , counterName , instanceName , VALUE , valueType ) SELECT @startTime , objectName , counterName , instanceName , (MAX(cntr_value) - MIN(cntr_value)) / DATEDIFF(SECOND, @startTime, @endTime) , 'value' FROM @samples WHERE cntr_type = 272696576 GROUP BY objectName , counterName , instanceName; /* Should we display the results of our most recent execution? */ IF @displayResults = 1 SELECT captureDate , objectName , counterName , instanceName , VALUE , valueType FROM dbo.dba_perfCounterMonitor WITH (NoLock) WHERE captureDate = CAST(@startTime AS SMALLDATETIME) ORDER BY objectName , counterName , instanceName; /* If you have an open transaction, commit it */ IF @@TRANCOUNT > 0 COMMIT TRANSACTION; END Try BEGIN Catch /* Whoops, there was an error... rollback! */ IF @@TRANCOUNT > 0 ROLLBACK TRANSACTION; /* Return an error message and log it */ EXECUTE dbo.dba_logError_sp; END Catch; SET NOCOUNT OFF; RETURN 0; END Go
Like I said, it's not perfect, but it gets the job done.
Getting an error about dba_logError_sp? Take a look at my error handling proc.
Bored this summer?
Bored this summer? Do you like to help others? Do you have too much free time? Do you find yourself thinking, "Man, I really should spend more time indoors." If you answered "yes" to all any of these questions, then have I got a proposition for you!
Sorry, guys, not that kind of proposition
What could be more fun than getting second-degree burns at the waterpark, you ask? Volunteering on the PASS Performance SIG! That's right, we're looking for a few good women and men to join our ranks as content contributors. Specifically, we're looking for people to write articles and/or host LiveMeeting events on performance-related topics. Not a performance expert? This can be a great way for you to learn more.
In case I scared you off in my opening paragraph, let me assure you that it really does not take that much time to be a volunteer. Just 3-4 hours a month can be a huge help. We're also looking for contributors of all experience levels, so if you're only comfortable writing intro-level articles, that's definitely okay.
Oh, and while I'm begging for volunteers, we're still looking for speakers for the SQL Saturday in East Iowa.
If you're interested in either, then please send me an e-mail at michelle at sqlfool dot com for more information.
Index Defrag Script, v3.0
UPDATE: This script has been significantly updated. Find the latest version here: Index Defrag Script, v4.0
I've just completed the latest version of my index defrag script! Here's a brief list of the updates:
- Fixed a bug with the LOB logic. In the previous version, after a LOB was encountered, all subsequent indexes would be reorganized.
- Added support for stat rebuilds after the index defrag is complete (@rebuildStats)
- Added an exclusion list table (dba_indexDefragExclusion) to support index scheduling
- Modified logging to show which defrags are "in progress"; added columns to dba_indexDefragLog
- Added support for the defrag of the model and msdb databases
- Added @scanMode as a configurable parameter
So what can this index defrag script do? Well, for starters, you can:
- 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
To use this last option, you need to add a record to the dba_indexDefragExclusion table. I think all of the columns are pretty self-explanatory except the [exclusionMask] column. The way this works is each day of the week is assigned a value:
1=Sunday, 2=Monday, 4=Tuesday, 8=Wednesday, 16=Thursday, 32=Friday, 64=Saturday
Take a SUM of the values for the days that you want excluded. So if you want an index to only be defragged on weekends, you would add up Monday through Friday (2+4+8+16+32) and use a value of 62 for the exclusionMask column. For a little more information on how this works, check out my blog post on Bitwise Operations.
Please note: if you don't insert any records into the dba_indexDefragExclusion table, by default all indexes will be defragged every run-time if they exceed the specified thresholds. This is normal behavior and may be perfectly fine in your environment. However, if the dba_indexDefragExclusion table does not exist, the script will fail.
I try to document each parameter within the code, so check the comments section in the script for a full list of parameters and what they do.
Special thanks to everyone who helped beta test this script!
Without further ado, the script:
/* Drop Table Scripts: Drop Table dbo.dba_indexDefragLog; Drop Table dbo.dba_indexDefragExclusion; */ IF Not Exists(SELECT [OBJECT_ID] FROM sys.tables WHERE [name] In (N'dba_indexDefragLog', 'dba_indexDefragExclusion')) BEGIN CREATE TABLE dbo.dba_indexDefragLog ( indexDefrag_id INT IDENTITY(1,1) Not Null , databaseID INT Not Null , databaseName NVARCHAR(128) Not Null , objectID INT Not Null , objectName NVARCHAR(128) Not Null , indexID INT Not Null , indexName NVARCHAR(128) Not Null , partitionNumber SMALLINT Not Null , fragmentation FLOAT Not Null , page_count INT Not Null , dateTimeStart DATETIME Not Null , dateTimeEnd DATETIME Null , durationSeconds INT Null CONSTRAINT PK_indexDefragLog PRIMARY KEY CLUSTERED (indexDefrag_id) ); PRINT 'dba_indexDefragLog Table Created'; CREATE TABLE dbo.dba_indexDefragExclusion ( databaseID INT Not Null , databaseName NVARCHAR(128) Not Null , objectID INT Not Null , objectName NVARCHAR(128) Not Null , indexID INT Not Null , indexName NVARCHAR(128) Not Null , exclusionMask INT Not Null /* 1=Sunday, 2=Monday, 4=Tuesday, 8=Wednesday, 16=Thursday, 32=Friday, 64=Saturday */ CONSTRAINT PK_indexDefragExclusion PRIMARY KEY CLUSTERED (databaseID, objectID, indexID) ); PRINT 'dba_indexDefragExclusion Table Created'; END ELSE RAISERROR('One or more tables already exist. Please drop or rename before proceeding.', 16, 0); IF OBJECTPROPERTY(OBJECT_ID('dbo.dba_indexDefrag_sp'), N'IsProcedure') = 1 BEGIN DROP PROCEDURE dbo.dba_indexDefrag_sp; PRINT 'Procedure dba_indexDefrag_sp dropped'; END; Go CREATE PROCEDURE dbo.dba_indexDefrag_sp /* Declare Parameters */ @minFragmentation FLOAT = 5.0 /* in percent, will not defrag if fragmentation less than specified */ , @rebuildThreshold FLOAT = 30.0 /* in percent, greater than @rebuildThreshold will result in rebuild instead of reorg */ , @executeSQL BIT = 1 /* 1 = execute; 0 = print command only */ , @DATABASE VARCHAR(128) = Null /* Option to specify a database name; null will return all */ , @tableName VARCHAR(4000) = Null -- databaseName.schema.tableName /* Option to specify a table name; null will return all */ , @scanMode VARCHAR(10) = N'LIMITED' /* Options are LIMITED, SAMPLED, and DETAILED */ , @onlineRebuild BIT = 1 /* 1 = online rebuild; 0 = offline rebuild; only in Enterprise */ , @maxDopRestriction TINYINT = Null /* Option to restrict the number of processors for the operation; only in Enterprise */ , @printCommands BIT = 0 /* 1 = print commands; 0 = do not print commands */ , @printFragmentation BIT = 0 /* 1 = print fragmentation prior to defrag; 0 = do not print */ , @defragDelay CHAR(8) = '00:00:05' /* time to wait between defrag commands */ , @debugMode BIT = 0 /* display some useful comments to help determine if/where issues occur */ , @rebuildStats BIT = 1 /* option to rebuild stats after completed index defrags */ AS /********************************************************************************* Name: dba_indexDefrag_sp Author: Michelle Ufford, http://sqlfool.com Purpose: Defrags all indexes for the current database Notes: CAUTION: TRANSACTION LOG SIZE SHOULD BE MONITORED CLOSELY WHEN DEFRAGMENTING. @minFragmentation defaulted to 10%, will not defrag if fragmentation is less than that @rebuildThreshold defaulted to 30% as recommended by Microsoft in BOL; greater than 30% will result in rebuild instead @executeSQL 1 = execute the SQL generated by this proc; 0 = print command only @database Optional, specify specific database name to defrag; If not specified, all non-system databases will be defragged. @tableName Specify if you only want to defrag indexes for a specific table, format = databaseName.schema.tableName; if not specified, all tables will be defragged. @scanMode Specifies which scan mode to use to determine fragmentation levels. Options are: LIMITED - scans the parent level; quickest mode, recommended for most cases. SAMPLED - samples 1% of all data pages; if less than 10k pages, performs a DETAILED scan. DETAILED - scans all data pages. Use great care with this mode, as it can cause performance issues. @onlineRebuild 1 = online rebuild; 0 = offline rebuild @maxDopRestriction Option to specify a processor limit for index rebuilds @printCommands 1 = print commands to screen; 0 = do not print commands @printFragmentation 1 = print fragmentation to screen; 0 = do not print fragmentation @defragDelay Time to wait between defrag commands; gives the server a little time to catch up @debugMode 1 = display debug comments; helps with troubleshooting 0 = do not display debug comments @rebuildStats Affects only statistics that need to be rebuilt 1 = rebuild stats 0 = do not rebuild stats Called by: SQL Agent Job or DBA Date Initials Version Description ---------------------------------------------------------------------------- 2007-12-18 MFU 1.0 Initial Release 2008-10-17 MFU 1.1 Added @defragDelay, CIX_temp_indexDefragList 2008-11-17 MFU 1.2 Added page_count to log table , added @printFragmentation option 2009-03-17 MFU 2.0 Provided support for centralized execution , consolidated Enterprise & Standard versions , added @debugMode, @maxDopRestriction , modified LOB and partition logic 2009-06-18 MFU 3.0 Fixed bug in LOB logic, added @scanMode option , added support for stat rebuilds (@rebuildStats) , support model and msdb defrag , added columns to the dba_indexDefragLog table , modified logging to show "in progress" defrags , added defrag exclusion list (scheduling) ********************************************************************************* Exec dbo.dba_indexDefrag_sp @executeSQL = 0 , @printCommands = 1 , @debugMode = 1 , @printFragmentation = 1; *********************************************************************************/ SET NOCOUNT ON; SET XACT_Abort ON; SET Ansi_Padding ON; SET Ansi_Warnings ON; SET ArithAbort ON; SET Concat_Null_Yields_Null ON; SET Numeric_RoundAbort OFF; SET Quoted_Identifier ON; BEGIN IF @debugMode = 1 RAISERROR('Undusting the cogs and starting up...', 0, 42) WITH NoWait; /* Declare our variables */ DECLARE @objectID INT , @databaseID INT , @databaseName NVARCHAR(128) , @indexID INT , @partitionCount BIGINT , @schemaName NVARCHAR(128) , @objectName NVARCHAR(128) , @indexName NVARCHAR(128) , @partitionNumber SMALLINT , @fragmentation FLOAT , @pageCount INT , @sqlCommand NVARCHAR(4000) , @rebuildCommand NVARCHAR(200) , @dateTimeStart DATETIME , @dateTimeEnd DATETIME , @containsLOB BIT , @editionCheck BIT , @debugMessage VARCHAR(128) , @updateSQL NVARCHAR(4000) , @partitionSQL NVARCHAR(4000) , @partitionSQL_Param NVARCHAR(1000) , @LOB_SQL NVARCHAR(4000) , @LOB_SQL_Param NVARCHAR(1000) , @rebuildStatsID INT , @rebuildStatsSQL NVARCHAR(1000) , @indexDefrag_id INT; /* Create our temporary tables */ CREATE TABLE #indexDefragList ( databaseID INT , databaseName NVARCHAR(128) , objectID INT , indexID INT , partitionNumber SMALLINT , fragmentation FLOAT , page_count INT , defragStatus BIT , schemaName NVARCHAR(128) Null , objectName NVARCHAR(128) Null , indexName NVARCHAR(128) Null ); CREATE TABLE #databaseList ( databaseID INT , databaseName VARCHAR(128) , scanStatus BIT , statsStatus BIT ); CREATE TABLE #processor ( [INDEX] INT , Name VARCHAR(128) , Internal_Value INT , Character_Value INT ); IF @debugMode = 1 RAISERROR('Beginning validation...', 0, 42) WITH NoWait; /* Just a little validation... */ IF @minFragmentation Not Between 0.00 And 100.0 SET @minFragmentation = 10.0; IF @rebuildThreshold Not Between 0.00 And 100.0 SET @rebuildThreshold = 30.0; IF @defragDelay Not Like '00:[0-5][0-9]:[0-5][0-9]' SET @defragDelay = '00:00:05'; IF @scanMode Not In ('LIMITED', 'SAMPLED', 'DETAILED') SET @scanMode = 'LIMITED'; /* Make sure we're not exceeding the number of processors we have available */ INSERT INTO #processor EXECUTE XP_MSVER 'ProcessorCount'; IF @maxDopRestriction IS Not Null And @maxDopRestriction > (SELECT Internal_Value FROM #processor) SELECT @maxDopRestriction = Internal_Value FROM #processor; /* Check our server version; 1804890536 = Enterprise, 610778273 = Enterprise Evaluation, -2117995310 = Developer */ IF (SELECT SERVERPROPERTY('EditionID')) In (1804890536, 610778273, -2117995310) SET @editionCheck = 1 -- supports online rebuilds ELSE SET @editionCheck = 0; -- does not support online rebuilds IF @debugMode = 1 RAISERROR('Grabbing a list of our databases...', 0, 42) WITH NoWait; /* Retrieve the list of databases to investigate */ INSERT INTO #databaseList SELECT database_id , name , 0 -- not scanned yet for fragmentation , 0 -- statistics not yet updated FROM sys.databases WHERE name = IsNull(@DATABASE, name) And [name] Not In ('master', 'tempdb')-- exclude system databases And [STATE] = 0; -- state must be ONLINE IF @debugMode = 1 RAISERROR('Looping through our list of databases and checking for fragmentation...', 0, 42) WITH NoWait; /* Loop through our list of databases */ WHILE (SELECT COUNT(*) FROM #databaseList WHERE scanStatus = 0) > 0 BEGIN SELECT TOP 1 @databaseID = databaseID FROM #databaseList WHERE scanStatus = 0; SELECT @debugMessage = ' working on ' + DB_NAME(@databaseID) + '...'; IF @debugMode = 1 RAISERROR(@debugMessage, 0, 42) WITH NoWait; /* Determine which indexes to defrag using our user-defined parameters */ INSERT INTO #indexDefragList SELECT database_id AS databaseID , QUOTENAME(DB_NAME(database_id)) AS 'databaseName' , [OBJECT_ID] AS objectID , index_id AS indexID , partition_number AS partitionNumber , avg_fragmentation_in_percent AS fragmentation , page_count , 0 AS 'defragStatus' /* 0 = unprocessed, 1 = processed */ , Null AS 'schemaName' , Null AS 'objectName' , Null AS 'indexName' FROM sys.dm_db_index_physical_stats (@databaseID, OBJECT_ID(@tableName), Null , Null, @scanMode) WHERE avg_fragmentation_in_percent >= @minFragmentation And index_id > 0 -- ignore heaps And page_count > 8 -- ignore objects with less than 1 extent And index_level = 0 -- leaf-level nodes only, supports @scanMode OPTION (MaxDop 2); /* Keep track of which databases have already been scanned */ UPDATE #databaseList SET scanStatus = 1 WHERE databaseID = @databaseID; END CREATE CLUSTERED INDEX CIX_temp_indexDefragList ON #indexDefragList(databaseID, objectID, indexID, partitionNumber); /* Delete any indexes from our to-do that are also in our exclusion list for today */ DELETE idl FROM #indexDefragList AS idl Join dbo.dba_indexDefragExclusion AS ide ON idl.databaseID = ide.databaseID And idl.objectID = ide.objectID And idl.indexID = ide.indexID WHERE exclusionMask & POWER(2, DATEPART(weekday, GETDATE())-1) > 0; SELECT @debugMessage = 'Looping through our list... there''s ' + CAST(COUNT(*) AS VARCHAR(10)) + ' indexes to defrag!' FROM #indexDefragList; IF @debugMode = 1 RAISERROR(@debugMessage, 0, 42) WITH NoWait; /* Begin our loop for defragging */ WHILE (SELECT COUNT(*) FROM #indexDefragList WHERE defragStatus = 0) > 0 BEGIN IF @debugMode = 1 RAISERROR(' Picking an index to beat into shape...', 0, 42) WITH NoWait; /* Grab the most fragmented index first to defrag */ SELECT TOP 1 @objectID = objectID , @indexID = indexID , @databaseID = databaseID , @databaseName = databaseName , @fragmentation = fragmentation , @partitionNumber = partitionNumber , @pageCount = page_count FROM #indexDefragList WHERE defragStatus = 0 ORDER BY fragmentation DESC; IF @debugMode = 1 RAISERROR(' Looking up the specifics for our index...', 0, 42) WITH NoWait; /* Look up index information */ SELECT @updateSQL = N'Update idl Set schemaName = QuoteName(s.name) , objectName = QuoteName(o.name) , indexName = QuoteName(i.name) From #indexDefragList As idl Inner Join ' + @databaseName + '.sys.objects As o On idl.objectID = o.object_id Inner Join ' + @databaseName + '.sys.indexes As i On o.object_id = i.object_id Inner Join ' + @databaseName + '.sys.schemas As s On o.schema_id = s.schema_id Where o.object_id = ' + CAST(@objectID AS VARCHAR(10)) + ' And i.index_id = ' + CAST(@indexID AS VARCHAR(10)) + ' And i.type > 0 And idl.databaseID = ' + CAST(@databaseID AS VARCHAR(10)); EXECUTE SP_EXECUTESQL @updateSQL; /* Grab our object names */ SELECT @objectName = objectName , @schemaName = schemaName , @indexName = indexName FROM #indexDefragList WHERE objectID = @objectID And indexID = @indexID And databaseID = @databaseID; IF @debugMode = 1 RAISERROR(' Grabbing the partition count...', 0, 42) WITH NoWait; /* Determine if the index is partitioned */ SELECT @partitionSQL = 'Select @partitionCount_OUT = Count(*) From ' + @databaseName + '.sys.partitions Where object_id = ' + CAST(@objectID AS VARCHAR(10)) + ' And index_id = ' + CAST(@indexID AS VARCHAR(10)) + ';' , @partitionSQL_Param = '@partitionCount_OUT int OutPut'; EXECUTE SP_EXECUTESQL @partitionSQL, @partitionSQL_Param, @partitionCount_OUT = @partitionCount OUTPUT; IF @debugMode = 1 RAISERROR(' Seeing if there''s any LOBs to be handled...', 0, 42) WITH NoWait; /* Determine if the table contains LOBs */ SELECT @LOB_SQL = ' Select @containsLOB_OUT = Count(*) From ' + @databaseName + '.sys.columns With (NoLock) Where [object_id] = ' + CAST(@objectID AS VARCHAR(10)) + ' And (system_type_id In (34, 35, 99) Or max_length = -1);' /* system_type_id --> 34 = image, 35 = text, 99 = ntext max_length = -1 --> varbinary(max), varchar(max), nvarchar(max), xml */ , @LOB_SQL_Param = '@containsLOB_OUT int OutPut'; EXECUTE SP_EXECUTESQL @LOB_SQL, @LOB_SQL_Param, @containsLOB_OUT = @containsLOB OUTPUT; IF @debugMode = 1 RAISERROR(' Building our SQL statements...', 0, 42) WITH NoWait; /* If there's not a lot of fragmentation, or if we have a LOB, we should reorganize */ IF @fragmentation < @rebuildThreshold Or @containsLOB >= 1 Or @partitionCount > 1 BEGIN SET @sqlCommand = N'Alter Index ' + @indexName + N' On ' + @databaseName + N'.' + @schemaName + N'.' + @objectName + N' ReOrganize'; /* If our index is partitioned, we should always reorganize */ IF @partitionCount > 1 SET @sqlCommand = @sqlCommand + N' Partition = ' + CAST(@partitionNumber AS NVARCHAR(10)); END; /* If the index is heavily fragmented and doesn't contain any partitions or LOB's, rebuild it */ IF @fragmentation >= @rebuildThreshold And IsNull(@containsLOB, 0) != 1 And @partitionCount <= 1 BEGIN /* Set online rebuild options; requires Enterprise Edition */ IF @onlineRebuild = 1 And @editionCheck = 1 SET @rebuildCommand = N' Rebuild With (Online = On'; ELSE SET @rebuildCommand = N' Rebuild With (Online = Off'; /* Set processor restriction options; requires Enterprise Edition */ IF @maxDopRestriction IS Not Null And @editionCheck = 1 SET @rebuildCommand = @rebuildCommand + N', MaxDop = ' + CAST(@maxDopRestriction AS VARCHAR(2)) + N')'; ELSE SET @rebuildCommand = @rebuildCommand + N')'; SET @sqlCommand = N'Alter Index ' + @indexName + N' On ' + @databaseName + N'.' + @schemaName + N'.' + @objectName + @rebuildCommand; END; /* Are we executing the SQL? If so, do it */ IF @executeSQL = 1 BEGIN IF @debugMode = 1 RAISERROR(' Executing SQL statements...', 0, 42) WITH NoWait; /* Grab the time for logging purposes */ SET @dateTimeStart = GETDATE(); /* Log our actions */ INSERT INTO dbo.dba_indexDefragLog ( databaseID , databaseName , objectID , objectName , indexID , indexName , partitionNumber , fragmentation , page_count , dateTimeStart ) SELECT @databaseID , @databaseName , @objectID , @objectName , @indexID , @indexName , @partitionNumber , @fragmentation , @pageCount , @dateTimeStart; SET @indexDefrag_id = SCOPE_IDENTITY(); /* Execute our defrag! */ EXECUTE SP_EXECUTESQL @sqlCommand; SET @dateTimeEnd = GETDATE(); /* Update our log with our completion time */ UPDATE dbo.dba_indexDefragLog SET dateTimeEnd = @dateTimeEnd , durationSeconds = DATEDIFF(SECOND, @dateTimeStart, @dateTimeEnd) WHERE indexDefrag_id = @indexDefrag_id; /* Just a little breather for the server */ WAITFOR Delay @defragDelay; /* Print if specified to do so */ IF @printCommands = 1 PRINT N'Executed: ' + @sqlCommand; END ELSE /* Looks like we're not executing, just printing the commands */ BEGIN IF @debugMode = 1 RAISERROR(' Printing SQL statements...', 0, 42) WITH NoWait; IF @printCommands = 1 PRINT IsNull(@sqlCommand, 'error!'); END IF @debugMode = 1 RAISERROR(' Updating our index defrag status...', 0, 42) WITH NoWait; /* Update our index defrag list so we know we've finished with that index */ UPDATE #indexDefragList SET defragStatus = 1 WHERE databaseID = @databaseID And objectID = @objectID And indexID = @indexID And partitionNumber = @partitionNumber; END /* Do we want to output our fragmentation results? */ IF @printFragmentation = 1 BEGIN IF @debugMode = 1 RAISERROR(' Displaying fragmentation results...', 0, 42) WITH NoWait; SELECT databaseID , databaseName , objectID , objectName , indexID , indexName , fragmentation , page_count FROM #indexDefragList; END; /* Do we want to rebuild stats? */ IF @rebuildStats = 1 BEGIN WHILE Exists(SELECT TOP 1 * FROM #databaseList WHERE statsStatus = 0) BEGIN /* Build our SQL statement to update stats */ SELECT TOP 1 @rebuildStatsSQL = 'Use [' + databaseName + ']; ' + 'Execute sp_updatestats;' , @rebuildStatsID = databaseID FROM #databaseList WHERE statsStatus = 0; SET @debugMessage = 'Rebuilding Statistics: ' + @rebuildStatsSQL; IF @debugMode = 1 RAISERROR(@debugMessage, 0, 42) WITH NoWait; /* Execute our stats update! */ EXECUTE SP_EXECUTESQL @rebuildStatsSQL; /* Keep track of which databases have been updated */ UPDATE #databaseList SET statsStatus = 1 WHERE databaseID = @rebuildStatsID; END; END; /* When everything is said and done, make sure to get rid of our temp table */ DROP TABLE #indexDefragList; DROP TABLE #databaseList; DROP TABLE #processor; IF @debugMode = 1 RAISERROR('DONE! Thank you for taking care of your indexes! :)', 0, 42) WITH NoWait; SET NOCOUNT OFF; RETURN 0 END Go SET Quoted_Identifier OFF SET ANSI_Nulls ON Go
PASS Summit 2009
My abstract for PASS Summit 2009 was accepted! Woot! You may not be able to see it from where you're sitting, but I'm doing the happy dance.
In case you missed my original post on my abstract submission, here's what I'll be presenting on:
Super Bowl, Super Load - A Look at Performance Tuning for VLDB’s
Few DBA’s have the opportunity to experience a real-life load test in their production environment. Michelle Ufford works for GoDaddy.com, a company that has experienced phenomenal success with its Super Bowl ads. These ads are designed to drive traffic to the company’s websites, which puts the database servers under high load. In her presentation, Michelle will explore the performance tuning techniques that have resulted in an 80% reduction in server response times and allowed her VLDB’s to reach rates of 27k transactions per second. Topics will include vertical and horizontal partitioning, bulk operations, table design, and indexing.
Do you read my blog? Do I read yours? Do we exchange weird messages on Twitter? Do you have free cookies? If you're going to to the PASS Summit and answered "yes" to any of these questions, then I want to meet you! Make sure to say "hi" to me in Seattle.

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