Statistics update job
SQL Server statistics are extremely important for good query performance since they provide invaluable guidelines that allow the query optimizer to pick an optimal plan. Out-of-date or non-existent statistics objects can cause excessive I/O, poor memory utilization, and spills to tempdb, which eventually result in poor client performance.
By default, SQL Server automatically manages statistics objects by updating them on-the-fly when it detects a statistically significant portion of the data in the affected table has been modified. For many databases, this functionality works wonders, however for larger tables where the number of modifications doesn’t trigger the automatic stats updates, you may want to manage stats updates pro-actively. This post provides some T-SQL code and a SQL Server Agent job that can be used to maintain statistics.
I use a stored procedure that is marked as a system-object to enable it to be called from the context of any user database. The stored procedure code:
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USE master; IF EXISTS ( SELECT 1 FROM sys.schemas s INNER JOIN sys.objects o ON s.schema_id = o.schema_id WHERE s.name = 'dbo' AND o.name = 'dba_update_all_stats' ) BEGIN DROP PROCEDURE dbo.dba_update_all_stats; END GO CREATE PROCEDURE dbo.dba_update_all_stats ( @min_hours_since_last_update int = 0 , @show_cmd bit = 1 , @debug_only bit = 0 ) AS BEGIN /* Updates statistics for all objects in the current database. Date: 2019-04-16 By: Hannah Vernon NOTE: Stored Proc must be created in the [master] database, and must be marked as a "system procedure" to enable proper functionality. EXEC sys.sp_MS_marksystemobject dbo.dba_update_all_stats; Version History: 1.0 Initial Version 1.1 Reduced noise messages 1.2 Excluded columnstore indexes */ SET NOCOUNT ON; SET ANSI_WARNINGS ON; DECLARE @cmd nvarchar(MAX); DECLARE @ObjectID int; DECLARE @StatsID int; DECLARE @SchemaName sysname; DECLARE @ObjectName sysname; DECLARE @StatsName sysname; DECLARE @StatsDate datetime; DECLARE @StartTime datetime; DECLARE @EndTime datetime; DECLARE @Rows int; DECLARE @RowsSampled int; DECLARE @ModificationCounter int; DECLARE @DatabaseName sysname; DECLARE @Action varchar(50); SET @DatabaseName = DB_NAME(); SET @cmd = ''; DECLARE cur CURSOR LOCAL FORWARD_ONLY READ_ONLY FOR WITH StatsDetails AS ( SELECT ObjectID = o.object_id , SchemaName = sch.name , ObjectName = o.name , StatsName = st.name , StatsID = st.stats_id , StatsDate = dsp.last_updated , Rows = dsp.rows , RowsSampled = dsp.rows_sampled , ModificationCounter = dsp.modification_counter /* number of modifications to the stat's leading column that have been modified since the last stats update */ , UpdateStatement = 'UPDATE STATISTICS ' + quotename(sch.name) + '.' + quotename(o.name) + '(' + quotename(st.name) + ') WITH FULLSCAN' + CASE WHEN st.no_recompute = 1 THEN ', NORECOMPUTE' ELSE '' END + ';' FROM sys.schemas sch INNER JOIN sys.objects o ON sch.schema_id = o.schema_id INNER JOIN sys.stats st ON o.object_id = st.object_id OUTER APPLY sys.dm_db_stats_properties(o.object_id, st.stats_id) dsp WHERE o.is_ms_shipped = 0 AND NOT EXISTS ( --exclude columnstore indexes since they cannot have stats updates SELECT 1 FROM sys.indexes i WHERE i.object_id = st.object_id AND i.index_id = st.stats_id AND ( i.type_desc = N'CLUSTERED COLUMNSTORE' OR i.type_desc = N'NONCLUSTERED COLUMNSTORE' ) ) ) SELECT sd.ObjectID , sd.StatsID , sd.SchemaName , sd.ObjectName , sd.StatsName , sd.UpdateStatement , sd.StatsDate , sd.Rows , sd.RowsSampled , sd.ModificationCounter FROM StatsDetails sd ORDER BY sd.SchemaName , sd.ObjectName , sd.StatsID; OPEN cur; FETCH NEXT FROM cur INTO @ObjectID , @StatsID , @SchemaName , @ObjectName , @StatsName , @cmd , @StatsDate , @Rows , @RowsSampled , @ModificationCounter; WHILE @@FETCH_STATUS = 0 BEGIN IF @show_cmd = 1 BEGIN PRINT ('Processing Stats: ' + @SchemaName + '.' + @ObjectName + '.' + @StatsName); END SET @Action = ''; IF COALESCE(@Rows, 0) = 0 BEGIN /* sys.dm_db_stats_properties may return NULL values if the stats have never been updated. Get the current row count for the object. */ SET ANSI_WARNINGS OFF; SELECT @Rows = SUM(ips.record_count) FROM ( SELECT record_count = ips.record_count FROM sys.dm_db_index_physical_stats(DB_ID(), @ObjectID, NULL, NULL, 'SAMPLED') ips UNION ALL SELECT 0 /* ensure NULL is never returned to @Rows */ ) ips SET ANSI_WARNINGS ON; END IF COALESCE(@Rows, 0) > 0 AND ((@StatsDate IS NULL) OR DATEDIFF(HOUR, @StatsDate, GETDATE()) > @min_hours_since_last_update) BEGIN SET @StartTime = GETDATE(); /* only update the statistics if rows have been modified. @ModificationCounter will be NULL if the statistics object has never been updated via UPDATE STATISTICS */ IF @show_cmd = 1 AND COALESCE(@ModificationCounter, 1) > 0 BEGIN PRINT (CHAR(9) + 'Last updated ' + CASE WHEN @StatsDate IS NULL THEN '(never)' ELSE CONVERT(VARCHAR(50), @StatsDate, 120) END + '.'); PRINT (CHAR(9) + 'Modifications since last stats update: ' + CONVERT(VARCHAR(50), @ModificationCounter)); PRINT (CHAR(9) + 'Will update stats using:'); PRINT (CHAR(9) + @cmd); END IF COALESCE(@ModificationCounter, 1) = 0 BEGIN SET @Action = 'ZeroModificationsSinceLastUpdate'; IF @show_cmd = 1 BEGIN PRINT (CHAR(9) + 'Zero modifications since last update on ' + CASE WHEN @StatsDate IS NULL THEN '(never)' ELSE CONVERT(VARCHAR(50), @StatsDate, 120) END + '.'); END END IF @debug_only = 0 AND COALESCE(@ModificationCounter, 1) > 0 BEGIN EXEC sp_executesql @cmd; SET @Action = 'Updated'; END SET @EndTime = GETDATE(); IF @debug_only = 0 BEGIN SELECT @StatsDate = COALESCE(dsp.last_updated, GETDATE()) , @Rows = COALESCE(dsp.rows, 0) , @RowsSampled = COALESCE(dsp.rows_sampled, 0) /* Leave this out since it will be zero at this point. The value from prior to executing UPDATE STATISTICS shows the number of rows modified since the last time stats were updated, and is useful to save in the dbo.StatsHistory table; the below code clobbers that value. , @ModificationCounter = COALESCE(dsp.modification_counter, 0) */ FROM sys.schemas sch INNER JOIN sys.objects o ON sch.schema_id = o.schema_id INNER JOIN sys.stats st ON o.object_id = st.object_id OUTER APPLY sys.dm_db_stats_properties(o.object_id, st.stats_id) dsp WHERE sch.name = @SchemaName AND o.name = @ObjectName AND st.name = @StatsName; INSERT INTO master.dbo.StatsHistory (DatabaseName, SchemaName, ObjectName, StatsName, UpdateDate, UpdateDurationMs, Rows, RowsSampled, ModificationCounter, Action) VALUES (@DatabaseName, @SchemaName, @ObjectName, @StatsName, @StatsDate, DATEDIFF(MILLISECOND, @StartTime, @EndTime), @Rows, @RowsSampled, @ModificationCounter, @Action); END ELSE BEGIN SET @Action = 'DebugMode'; INSERT INTO master.dbo.StatsHistory (DatabaseName, SchemaName, ObjectName, StatsName, UpdateDate, UpdateDurationMs, Rows, RowsSampled, ModificationCounter, Action) VALUES (@DatabaseName, @SchemaName, @ObjectName, @StatsName, @StatsDate, DATEDIFF(MILLISECOND, @StartTime, @EndTime), @Rows, @RowsSampled, @ModificationCounter, @Action); END END ELSE BEGIN IF COALESCE(@Rows, 0) = 0 BEGIN IF @show_cmd = 1 BEGIN PRINT (CHAR(9) + 'Contains zero rows. Stats will not be updated.'); END SET @Action = 'ContainsZeroRows'; INSERT INTO master.dbo.StatsHistory (DatabaseName, SchemaName, ObjectName, StatsName, UpdateDate, UpdateDurationMs, Rows, RowsSampled, ModificationCounter, Action) VALUES (@DatabaseName, @SchemaName, @ObjectName, @StatsName, @StatsDate, DATEDIFF(MILLISECOND, @StartTime, @EndTime), @Rows, @RowsSampled, @ModificationCounter, @Action); END ELSE BEGIN IF @show_cmd = 1 BEGIN PRINT (CHAR(9) + 'Last updated ' + CASE WHEN @StatsDate IS NULL THEN '(never)' ELSE CONVERT(VARCHAR(50), @StatsDate, 120) END + '.'); PRINT (CHAR(9) + 'SKIPPING'); END SET @Action = 'UpdatedTooRecently'; INSERT INTO master.dbo.StatsHistory (DatabaseName, SchemaName, ObjectName, StatsName, UpdateDate, UpdateDurationMs, Rows, RowsSampled, ModificationCounter, Action) VALUES (@DatabaseName, @SchemaName, @ObjectName, @StatsName, @StatsDate, DATEDIFF(MILLISECOND, @StartTime, @EndTime), @Rows, @RowsSampled, @ModificationCounter, @Action); END END IF @show_cmd = 1 BEGIN PRINT (''); /* add a blank line between output rows */ END FETCH NEXT FROM cur INTO @ObjectID , @StatsID , @SchemaName , @ObjectName , @StatsName , @cmd , @StatsDate , @Rows , @RowsSampled , @ModificationCounter; END CLOSE cur; DEALLOCATE cur; END GO EXEC sys.sp_MS_marksystemobject @objname = 'dbo.dba_update_all_stats', @namespace = NULL; GO |
The procedure above stores statistics history in a table named dbo.StatsHistory. That table is defined as:
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CREATE TABLE dbo.StatsHistory ( StatsHistoryID int NOT NULL CONSTRAINT StatsHistory_X1_pkc PRIMARY KEY CLUSTERED IDENTITY(1,1) , StatsHistoryDate datetime NOT NULL CONSTRAINT StatsHistory_StatsHistoryDate_DC DEFAULT (GETDATE()) , DatabaseName sysname NOT NULL , SchemaName sysname NOT NULL , ObjectName sysname NOT NULL , StatsName sysname NOT NULL , UpdateDate datetime NULL , UpdateDurationMs int NULL , Rows int NOT NULL , RowsSampled int NULL , ModificationCounter int NULL , Action varchar(50) NOT NULL ) WITH (COMPRESSION = PAGE) ON [PRIMARY]; |
This code will create a SQL Server Agent job to run the stats update job:
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USE [msdb] BEGIN TRANSACTION; DECLARE @ReturnCode int; SET @ReturnCode = 0; IF NOT EXISTS ( SELECT name FROM msdb.dbo.syscategories WHERE name = N'Database Maintenance' AND category_class=1 ) BEGIN EXEC @ReturnCode = msdb.dbo.sp_add_category @class=N'JOB', @type=N'LOCAL', @name=N'Database Maintenance'; IF (@@ERROR <> 0 OR @ReturnCode <> 0) GOTO QuitWithRollback; END DECLARE @jobId binary(16); EXEC @ReturnCode = msdb.dbo.sp_add_job @job_name = N'Update Stats' , @enabled = 1 , @notify_level_eventlog = 3 , @notify_level_email = 2 , @notify_level_netsend = 0 , @notify_level_page = 0 , @delete_level = 0 , @description = N'No description available.' , @category_name = N'Database Maintenance' , @owner_login_name = N'sa' , @notify_email_operator_name = N'DBA' , @job_id = @jobId OUTPUT; IF (@@ERROR <> 0 OR @ReturnCode <> 0) GOTO QuitWithRollback; EXEC @ReturnCode = msdb.dbo.sp_add_jobstep @job_id = @jobId , @step_name = N'Run UPDATE STATISTICS' , @step_id = 1 , @cmdexec_success_code = 0 , @on_success_action = 3 , @on_success_step_id = 0 , @on_fail_action = 2 , @on_fail_step_id = 0 , @retry_attempts = 0 , @retry_interval = 0 , @os_run_priority = 0 , @subsystem = N'TSQL' , @command = N'EXEC dbo.dba_update_all_stats;' , @database_name = N'<database_name_here>' --modify this to point to your database , @flags = 0; IF (@@ERROR <> 0 OR @ReturnCode <> 0) GOTO QuitWithRollback; EXEC @ReturnCode = msdb.dbo.sp_update_job @job_id = @jobId , @start_step_id = 1; IF (@@ERROR <> 0 OR @ReturnCode <> 0) GOTO QuitWithRollback; EXEC @ReturnCode = msdb.dbo.sp_add_jobserver @job_id = @jobId, @server_name = N'(local)' IF (@@ERROR <> 0 OR @ReturnCode <> 0) GOTO QuitWithRollback COMMIT TRANSACTION GOTO EndSave QuitWithRollback: IF (@@TRANCOUNT > 0) ROLLBACK TRANSACTION; EndSave: GO </database_name_here> The job has no schedule attached - you probably want to schedule this to run every day or every week during some period of low or no user activity. |
[…] probably want to update your stats objects on a regular basis to ensure good performance. See my previous post for details about how to do […]
Be advised that SQL Server does a sample of random pages, but gets all rows in the sampled pages. This is very different from a true random row sample, which however, is much more expensive to do.
To compensate for sampling issuing on a specific column, SQL Server first looks to see if there is an index in which the column of interest is not the lead key. If not, too bad for you.
The important point is that for indexes in which the lead key is not unique, statistics should be updated with full scan. Otherwise rows estimates will be high, and if compounded in multi-table joins, can lead to serious problems
see my statistics update script
http://www.qdpma.com/SQL/sp_updatestats2.html
http://www.qdpma.com/CBO/Statistics.html
[…] if you do decide you need to rebuild indexes on an ongoing basis, and have determined that automating statistics updates isn’t cutting it, you might consider using this script. The script only updates row-store […]