Tài liệu SQL Server MVP Deep Dives- P17 pptx

594 CHAPTER 47 How to use Dynamic Management Views queries that are relatively inexpensive for individual executions but are called very frequently (which makes them expensive in aggregate), or you may have individual queries that are more expensive CPU-wise, but are not called as often Looking at total worker time is a reliable method for finding the most expensive queries from an overall CPU perspective Another similar DMV query, shown in listing 6, sorts by average worker time This will let you find expensive CPU queries that may be easier to improve at the database level with standard database tuning techniques Listing Finding expensive stored procedures, sorted by average worker time Get Top 20 executed SP's ordered by Avg worker time (CPU pressure) SELECT TOP 20 qt.text AS 'SP Name', qs.total_worker_time/qs.execution_count AS 'AvgWorkerTime', qs.total_worker_time AS 'TotalWorkerTime', qs.execution_count AS 'Execution Count', ISNULL(qs.execution_count/ DATEDIFF(Second, qs.creation_time, GetDate()), 0) AS 'Calls/Second', ISNULL(qs.total_elapsed_time/qs.execution_count, 0) AS 'AvgElapsedTime', qs.max_logical_reads, qs.max_logical_writes, DATEDIFF(Minute, qs.creation_time, GetDate()) AS 'Age in Cache' FROM sys.dm_exec_query_stats AS qs CROSS APPLY sys.dm_exec_sql_text(qs.sql_handle) AS qt WHERE qt.dbid = db_id() Filter by current database ORDER BY qs.total_worker_time/qs.execution_count DESC Finding I/O pressure in SQL Server Most large-scale SQL Server 2005/2008 deployments sooner or later run into I/O bottlenecks This happens for several reasons First, systems engineers often just think about CPU and RAM when sizing “big” database servers, and neglect the I/O subsystem Second, many DBAs are unable to completely tune the SQL Server workload to minimize excessive I/O requirements Finally, there are often budgetary issues that prevent the acquisition of enough I/O capacity to support a large workload Whatever your situation, it helps if you know how recognize and measure signs of I/O pressure on SQL Server 2005/2008 One thing you can to help reduce I/O pressure in general is to make sure you’re not under memory pressure, which will cause added I/O pressure We’ll look at how to detect memory pressure a little later For large SQL Server 2005/2008 deployments, you should make sure you’re running a 64-bit edition of SQL Server (so you can better use the RAM that you have), and you should try to get as much RAM as you can afford or will fit into the database server Having sufficient RAM installed will reduce I/O pressure for reads, and will allow SQL Server to issue checkpoints less frequently (which will tend to minimize write I/O pressure) Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark Licensed to Kerri Ross Finding I/O pressure in SQL Server 595 The DMV queries in listings through 11 are useful for measuring signs of I/O pressure You’ll want to run the query in listing multiple times, because the results will rapidly change on a busy system Don’t get too excited by a single high number If you see consistently high numbers over time, then you have evidence of I/O pressure Listing Checking for I/O pressure Check for Pending I/O (lower is better) SELECT pending_disk_io_count FROM sys.dm_os_schedulers The query in listing can help you identify which data and log files are causing the highest I/O waits For example, perhaps you have a transaction log file on a slower RAID array or LUN (which isn’t a good idea) This query will help prove that the log file is causing user waits Listing Identifying the highest I/O waits Avg I/O Stalls (Lower is better) SELECT database_id, file_id , io_stall_read_ms, num_of_reads, CAST(io_stall_read_ms/(1.0 + num_of_reads) AS NUMERIC(10,1)) AS 'avg_read_stall_ms', io_stall_write_ms, num_of_writes, CAST(io_stall_write_ms/(1.0 + num_of_writes) AS NUMERIC(10,1)) AS 'avg_write_stall_ms', io_stall_read_ms + io_stall_write_ms AS io_stalls, num_of_reads + num_of_writes AS total_io, CAST((io_stall_read_ms + io_stall_write_ms) /(1.0 + num_of_reads + num_of_writes) AS NUMERIC(10,1)) AS 'avg_io_stall_ms' FROM sys.dm_io_virtual_file_stats(null,null) This can be filtered by database and file id ORDER BY avg_io_stall_ms DESC The query in listing lets you focus on the read/write activity for each file in a particular database It shows you the percentage of reads and writes, both in number of reads and writes and in actual bytes read and written This can help you analyze and size your disk I/O subsystem Listing Checking I/O statistics for a database I/O Statistics for a single database SELECT file_id , num_of_reads , num_of_writes , (num_of_reads + num_of_writes) AS 'Writes + Reads' , num_of_bytes_read , num_of_bytes_written , CAST(100 * num_of_reads/(num_of_reads + num_of_writes) AS DECIMAL(10,4)) AS '# Reads Pct' Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark Licensed to Kerri Ross 596 CHAPTER 47 How to use Dynamic Management Views , CAST(100 * num_of_writes/(num_of_reads + num_of_writes) AS DECIMAL(10,4)) AS '# Write Pct' , CAST(100 * num_of_bytes_read /(num_of_bytes_read + num_of_bytes_written) AS DECIMAL(10,4)) AS 'Read Bytes Pct' , CAST(100 * num_of_bytes_written /(num_of_bytes_read + num_of_bytes_written) AS DECIMAL(10,4)) AS 'Written Bytes Pct' FROM sys.dm_io_virtual_file_stats(DB_ID(N'yourdatabasename'), NULL); The query in listing 10 will help you find the stored procedures that are causing the most physical read I/O pressure (which means that the data has to be read from your disk subsystem instead of being found in memory) Obviously, adding more RAM to the server will help here, but standard query and index tuning can make a big difference also Listing 10 Locating physical read I/O pressure Get Top 20 executed SP's ordered by physical reads (read I/O pressure) SELECT TOP 20 qt.text AS 'SP Name', qs.total_physical_reads, ➥qs.total_physical_reads/qs.execution_count AS 'Avg Physical Reads', qs.execution_count AS 'Execution Count', qs.execution_count/DATEDIFF(Second, qs.creation_time, GetDate()) AS ➥'Calls/Second', qs.total_worker_time/qs.execution_count AS 'AvgWorkerTime', qs.total_worker_time AS 'TotalWorkerTime', qs.total_elapsed_time/qs.execution_count AS 'AvgElapsedTime', qs.max_logical_reads, qs.max_logical_writes, DATEDIFF(Minute, qs.creation_time, GetDate()) AS 'Age in Cache' FROM sys.dm_exec_query_stats AS qs CROSS APPLY sys.dm_exec_sql_text(qs.sql_handle) AS qt WHERE qt.dbid = db_id() Filter by current database ORDER BY qs.total_physical_reads DESC The query in listing 11 will help you find the stored procedures that are causing the most write activity Query and index tuning can help here You can also talk to your developers about middle-tier write caching or other application changes to reduce writes if possible Listing 11 Finding stored procedures with the most write activity Get Top 20 executed SP's ordered by logical writes/minute (write I/O ➥pressure) SELECT TOP 20 qt.text AS 'SP Name', qs.total_logical_writes, ➥qs.total_logical_writes/qs.execution_count AS 'AvgLogicalWrites', qs.total_logical_writes/DATEDIFF(Minute, qs.creation_time, GetDate()) ➥AS 'Logical Writes/Min', qs.execution_count AS 'Execution Count', qs.execution_count/DATEDIFF(Second, qs.creation_time, GetDate()) AS ➥'Calls/Second', qs.total_worker_time/qs.execution_count AS 'AvgWorkerTime', qs.total_worker_time AS 'TotalWorkerTime', qs.total_elapsed_time/qs.execution_count AS 'AvgElapsedTime', Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark Licensed to Kerri Ross SQL Server memory pressure 597 qs.max_logical_reads, qs.max_logical_writes, qs.total_physical_reads, DATEDIFF(Minute, qs.creation_time, GetDate()) AS 'Age in Cache', qs.total_physical_reads/qs.execution_count AS 'Avg Physical Reads' FROM sys.dm_exec_query_stats AS qs CROSS APPLY sys.dm_exec_sql_text(qs.sql_handle) AS qt WHERE qt.dbid = db_id() Filter by current database ORDER BY qs.total_logical_writes DESC SQL Server memory pressure SQL Server 2005/2008 loves memory, the more the better If you’re running on a 64- bit version of Windows Server 2003 or newer, with a 64-bit Enterprise Edition version of SQL Server 2005/2008, you can and should take advantage of as much memory as will fit in your server In the commodity-level server space, the sweet spot for installed memory has moved up from 32 GB to 64 GB to 128 GB over the past several years, which makes it even more important to make sure you’re running a 64-bit version of SQL Server Once you’ve loaded up your 64-bit database server with as much memory as possible, it’s important that you two things to make sure that SQL Server 2005/2008 will play nicely with all of the available memory First, you should grant the Lock Pages in Memory Windows right (using gpedit.msc) to the SQL Server Service account Second, you should set the Max Server Memory setting in SQL Server to a value that will leave sufficient available memory for the operating system (and anything else that’s running on the server) while SQL Server is under a load This is typically anywhere from about GB to GB available, depending on how much RAM you have installed and what else is running on the server After you have SQL Server properly configured for memory, you’ll want to monitor how SQL Server is handling the memory that it has to work with With Performance Monitor, I like to keep track of these three counters: ƒ SQL Server\Memory Manager\Memory Grants Pending (lower is better) ƒ SQL Server\Buffer Manager\Buffer Cache Hit Ratio (higher is better) ƒ SQL Server\Buffer Manager\Page Life Expectancy (higher is better) The trend for these values is more important than their absolute value at any given time If the average Page Life Expectancy is dropping over time, that’s significant (and not in a good way) Still, people typically want to know what values are “good” and what values are “bad” for these counters, so here’s what I look for: ƒ Memory Grants Pending above is bad ƒ Buffer Cache Hit Ratio below 95 percent is bad ƒ Page Life Expectancy below 300 is bad There are many good DMV queries that give you much more detail about how SQL Server 2005/2008 is using memory We’ll cover some of the more useful ones Listing 12 lists the top 10 memory consumers in your buffer pool Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark Licensed to Kerri Ross 598 CHAPTER 47 Listing 12 How to use Dynamic Management Views Top 10 consumers of memory from buffer pool SELECT TOP (10) type, SUM(single_pages_kb) AS [SPA Mem, KB] FROM sys.dm_os_memory_clerks GROUP BY type ORDER BY SUM(single_pages_kb) DESC Here are some of the common types you’ll see when you run the query in listing 12: ƒ CACHESTORE_SQLCP—SQL plans (dynamic or prepared SQL) ƒ CACHESTORE_OBJCP—Object plans (stored procedures, functions, and triggers) ƒ CACHESTORE_PHDR—Bound Trees ƒ USERSTORE_TOKENPERM—The User and Token permissions cache that caused so many performance issues with early builds of SQL Server 2005 In listing 13, we’ll obtain the use counts for each query plan Listing 13 Getting query mix and use counts for each plan SELECT usecounts, cacheobjtype, objtype, bucketid FROM sys.dm_exec_cached_plans AS cp WHERE cacheobjtype = 'Compiled Plan' ORDER BY objtype, usecounts DESC You want to see plans with high use counts Avoiding ad hoc queries with concatenated WHERE clauses can help here You can also take advantage of table valued parameters in SQL Server 2008 Using the new Optimize for Ad Hoc Workloads instance setting in SQL Server 2008 is also beneficial here The query in listing 14 will tell you which tables and indexes are taking up the most buffer space Listing 14 Finding indexes and tables that use the most buffer space Breaks down buffers by object (table, index) in the buffer cache SELECT OBJECT_NAME(p.object_id) AS 'ObjectName', p.object_id, p.index_id, COUNT(*)/128 AS 'buffer size(MB)', COUNT(*) AS 'buffer_count' FROM sys.allocation_units AS a INNER JOIN sys.dm_os_buffer_descriptors AS b ON a.allocation_unit_id = b.allocation_unit_id INNER JOIN sys.partitions AS p ON a.container_id = p.hobt_id WHERE b.database_id = db_id() GROUP BY p.object_id, p.index_id ORDER BY buffer_count DESC In listing 15, we’ll find the largest ad hoc queries sitting in the plan cache Listing 15 Finding ad hoc queries that are bloating the plan cache SELECT TOP(100) [text], size_in_bytes FROM sys.dm_Exec_cached_plans CROSS APPLY sys.dm_exec_sql_text(plan_handle) Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark Licensed to Kerri Ross SQL Server memory pressure 599 WHERE cacheobjtype = 'Compiled Plan' AND objtype = 'Adhoc' AND usecounts = ORDER BY size_in_bytes DESC Again, using the new Optimize for Ad Hoc Workloads instance setting in SQL Server 2008 can really help if you have problems here The query in listing 16 will show you your 25 most expensive queries from a logical reads perspective (which equates to memory pressure) Listing 16 Finding your 25 most expensive queries Get Top 25 executed SP's ordered by logical reads (memory pressure) SELECT TOP 25 qt.text AS 'SP Name', total_logical_reads, qs.execution_count AS 'Execution Count', ➥total_logical_reads/qs.execution_count AS 'AvgLogicalReads', ➥qs.execution_count/DATEDIFF(Second, qs.creation_time, GetDate()) AS ➥'Calls/Second', qs.total_worker_time/qs.execution_count AS 'AvgWorkerTime', qs.total_worker_time AS 'TotalWorkerTime', qs.total_elapsed_time/qs.execution_count AS 'AvgElapsedTime', qs.total_logical_writes, qs.max_logical_reads, qs.max_logical_writes, qs.total_physical_reads, DATEDIFF(Minute, qs.creation_time, GetDate()) AS 'Age in Cache' FROM sys.dm_exec_query_stats AS qs CROSS APPLY sys.dm_exec_sql_text(qs.sql_handle) AS qt WHERE qt.dbid = db_id() Filter by current database ORDER BY total_logical_reads DESC The query in listing 17 will help you find tables with the most reads (User scans are much more expensive than user seeks or lookups.) Listing 17 Finding tables with the most reads SELECT object_name(s.object_id) AS 'Tablename', SUM(user_seeks) AS 'User Seeks', SUM(user_scans) AS 'User Scans', SUM(user_lookups)AS 'User Lookups', SUM(user_seeks + user_scans + user_lookups)AS 'Total Reads', SUM(user_updates) AS 'Total Writes' FROM sys.dm_db_index_usage_stats AS s INNER JOIN sys.indexes AS i ON s.object_id = i.object_id AND i.index_id = s.index_id WHERE objectproperty(s.object_id,'IsUserTable') = AND s.database_id = db_id() GROUP BY object_name(s.object_id) ORDER BY 'Total Reads' DESC The query in listing 18 will help you find tables with the most writes Listing 18 Finding tables with the most writes SELECT object_name(s.object_id) AS 'Tablename', SUM(user_updates) AS 'Total Writes', SUM(user_seeks) AS 'User Seeks', SUM(user_scans) AS 'User Scans', Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark Licensed to Kerri Ross 600 CHAPTER 47 How to use Dynamic Management Views SUM(user_lookups)AS 'User Lookups', SUM(user_seeks + user_scans + user_lookups)AS 'Total Reads' FROM sys.dm_db_index_usage_stats AS s INNER JOIN sys.indexes AS i ON s.object_id = i.object_id AND i.index_id = s.index_id WHERE objectproperty(s.object_id,'IsUserTable') = AND s.database_id = db_id() GROUP BY object_name(s.object_id) ORDER BY 'Total Writes' DESC SQL Server index usage As you’re probably aware, having proper indexes in place to support your workload is critical with SQL Server 2005/2008 (as with any relational database) Generally speaking, you’ll want more indexes with a reporting or DSS workload, and fewer indexes with an OLTP workload Regardless of your workload type, you should be aware of whether your indexes are being used and whether you’re missing any indexes that would be useful for SQL Server In the dark ages before SQL Server 2005, it was difficult to discover this critical information, but with DMV queries, you can easily discover what’s going on with your indexes You can find indexes that aren’t being used and you can find missing indexes As Microsoft’s Rico Mariani says, “If you aren’t measuring, you’re not engineering.” The DMV queries that you see in this section will tell you this information If you see an index that has millions of writes, with zero or very few reads, then that means that you’re getting little to no benefit from maintaining the index, and you should strongly consider dropping that index As the number of reads goes up, it becomes more of a judgment call That’s why being familiar with your workload is important One caveat with the “missing index” query is that it can return results based on ad hoc queries or maintenance job–related work that can make it harder to interpret You always want to look at the last_user_seek and the user_seeks columns to see the last time and how often SQL Server thinks it wants the index that it thinks is “missing.” If you see a row with a high index advantage with a last_user_seek from a few seconds or minutes ago, it’s probably from your regular workload, so you probably want to seriously consider adding that index You should also be aware that this query won’t recommend adding any clustered indexes One feature I’ve discovered over time is that if you add a new index of any sort to a table, or if you delete an index, it will clear out all of the missing index stats for that table This may lead you to believe that there are no more missing indexes on the table, which is probably not true Wait a little while, and then run the missing index query again to confirm whether there are any more missing indexes for the table The DMV queries in listings 19 through 21 will show bad indexes and missing indexes, and then let you concentrate on an individual table to determine whether you should make any index changes for that table based on your workload Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark Licensed to Kerri Ross SQL Server index usage Listing 19 601 Finding bad indexes Possible Bad Indexes (writes > reads) SELECT object_name(s.object_id) AS 'Table Name', i.name AS 'Index Name', i.index_id, user_updates AS 'Total Writes', user_seeks + user_scans + user_lookups AS 'Total Reads', user_updates - (user_seeks + user_scans + user_lookups) AS 'Difference' FROM sys.dm_db_index_usage_stats AS s INNER JOIN sys.indexes AS i ON s.object_id = i.object_id AND i.index_id = s.index_id WHERE objectproperty(s.object_id,'IsUserTable') = AND s.database_id = db_id() Filter for current database AND user_updates > (user_seeks + user_scans + user_lookups ) ORDER BY 'Difference' DESC, 'Total Writes' DESC, 'Total Reads' ASC; Indexes that have many more writes than reads are possible candidates for elimination You should be aware that user scans are much more expensive than user seeks or user lookups If you see lots of user scans, you may be missing some important indexes or you could be doing lots of aggregate queries or have small tables Listing 20 Looking at Index Advantage to find missing indexes Missing Indexes by Index Advantage (make sure to also look at last user ➥seek time) SELECT user_seeks * avg_total_user_cost * (avg_user_impact * 0.01) AS ➥index_advantage, migs.last_user_seek, mid.statement AS 'Database.Schema.Table', mid.equality_columns, mid.inequality_columns, mid.included_columns, migs.unique_compiles, migs.user_seeks, migs.avg_total_user_cost, ➥migs.avg_user_impact FROM sys.dm_db_missing_index_group_stats AS migs WITH (NOLOCK) INNER JOIN sys.dm_db_missing_index_groups AS mig WITH (NOLOCK) ON migs.group_handle = mig.index_group_handle INNER JOIN sys.dm_db_missing_index_details AS mid WITH (NOLOCK) ON mig.index_handle = mid.index_handle ORDER BY index_advantage DESC; Listing 21 Looking at Last User Seek to find missing indexes Missing Indexes by Last User Seek SELECT user_seeks * avg_total_user_cost * (avg_user_impact * 0.01) AS ➥index_advantage, migs.last_user_seek, mid.statement AS 'Database.Schema.Table', mid.equality_columns, mid.inequality_columns, mid.included_columns, migs.unique_compiles, migs.user_seeks, migs.avg_total_user_cost, ➥migs.avg_user_impact FROM sys.dm_db_missing_index_group_stats AS migs WITH (NOLOCK) INNER JOIN sys.dm_db_missing_index_groups AS mig WITH (NOLOCK) ON migs.group_handle = mig.index_group_handle INNER JOIN sys.dm_db_missing_index_details AS mid WITH (NOLOCK) ON mig.index_handle = mid.index_handle ORDER BY migs.last_user_seek DESC; Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark Licensed to Kerri Ross 602 CHAPTER 47 How to use Dynamic Management Views After running the DMV queries in listings 20 and 21, you may see the same table showing up with multiple missing indexes If I see this, I start to examine that table more closely Once you’ve narrowed your focus to a particular table, you can gather more specific index information about that table with the queries in listings 22 and 23 Listing 22 Getting statistics for a table Index Read/Write stats for a single table SELECT object_name(s.object_id) AS 'TableName', i.name AS 'IndexName', i.index_id, SUM(user_seeks) AS 'User Seeks', SUM(user_scans) AS 'User Scans', SUM(user_lookups)AS 'User Lookups', SUM(user_seeks + user_scans + user_lookups)AS 'Total Reads', SUM(user_updates) AS 'Total Writes' FROM sys.dm_db_index_usage_stats AS s INNER JOIN sys.indexes AS i ON s.object_id = i.object_id AND i.index_id = s.index_id WHERE objectproperty(s.object_id,'IsUserTable') = AND s.database_id = db_id() AND object_name(s.object_id) = 'YourTableName' GROUP BY object_name(s.object_id), i.name, i.index_id ORDER BY 'Total Writes' DESC, 'Total Reads' DESC; Listing 23 Missing indexes for a single table SELECT user_seeks * avg_total_user_cost * (avg_user_impact * 0.01) AS ➥index_advantage, migs.last_user_seek, mid.statement AS 'Database.Schema.Table', mid.equality_columns, mid.inequality_columns, mid.included_columns, migs.unique_compiles, migs.user_seeks, migs.avg_total_user_cost, ➥migs.avg_user_impact FROM sys.dm_db_missing_index_group_stats AS migs WITH (NOLOCK) INNER JOIN sys.dm_db_missing_index_groups AS mig WITH (NOLOCK) ON migs.group_handle = mig.index_group_handle INNER JOIN sys.dm_db_missing_index_details AS mid WITH (NOLOCK) ON mig.index_handle = mid.index_handle WHERE statement = '[databasename].[dbo].[yourtablename]' Specify one ➥table ORDER BY index_advantage DESC; Show existing indexes for this table (does not show included columns) EXEC sp_HelpIndex 'yourtablename'; As you consider making index changes to a large, busy table, you need to consider your workload characteristics You should be more reluctant to add additional indexes if you have an OLTP workload You should take advantage of online index operations whenever possible if you’re running Enterprise Edition in order to avoid locking and blocking issues during index builds You also should consider using the MAXDOP option during index builds to prevent SQL Server from using all of the CPU cores for an index build This may mean that the index takes longer to build, but the rest of your workload won’t be starved for CPU during the index-creation process Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark Licensed to Kerri Ross Detecting blocking in SQL Server 603 Detecting blocking in SQL Server Especially with OLTP workloads, you may run into blocking issues with SQL Server Listing 24 shows one quick DMV query that’s a good, indirect early warning signal of blocking Listing 24 Checking SQL Server schedulers to see if you may have blocking SELECT scheduler_id, current_tasks_count, runnable_tasks_count FROM sys.dm_os_schedulers WHERE scheduler_id < 255 If you see the current_tasks_count above 10 for a sustained period, it’s likely that you have blocking When you have severe blocking, the current_tasks_count for each scheduler tends to go up quickly The two DMV queries in listings 25 and 26 will give you more direct confirmation of blocking Listing 25 Detecting blocking SELECT blocked_query.session_id AS blocked_session_id, blocking_query.session_id AS blocking_session_id, sql_text.text AS blocked_text, sql_btext.text AS blocking_text, waits.wait_type AS blocking_resource FROM sys.dm_exec_requests AS blocked_query INNER JOIN sys.dm_exec_requests AS blocking_query ON blocked_query.blocking_session_id = blocking_query.session_id CROSS APPLY (SELECT * FROM sys.dm_exec_sql_text(blocking_query.sql_handle)) AS sql_btext CROSS APPLY (SELECT * FROM sys.dm_exec_sql_text(blocked_query.sql_handle)) AS sql_text INNER JOIN sys.dm_os_waiting_tasks AS waits ON waits.session_id = blocking_query.session_id Listing 26 Detecting blocking (a more accurate and complete version) SELECT t1.resource_type AS 'lock type',db_name(resource_database_id) AS ➥'database', t1.resource_associated_entity_id AS 'blk object',t1.request_mode AS 'lock - lock requested ➥req', t1.request_session_id AS 'waiter sid', t2.wait_duration_ms AS 'wait time', (SELECT [text] FROM sys.dm_exec_requests AS r CROSS APPLY sys.dm_exec_sql_text(r.sql_handle) WHERE r.session_id = t1.request_session_id) AS 'waiter_batch', (SELECT substring(qt.text,r.statement_start_offset/2, (CASE WHEN r.statement_end_offset = -1 THEN LEN(CONVERT(nvarchar(max), qt.text)) * ELSE r.statement_end_offset END - r.statement_start_offset)/2) FROM sys.dm_exec_requests AS r CROSS APPLY sys.dm_exec_sql_text(r.sql_handle) AS qt WHERE r.session_id = t1.request_session_id) AS 'waiter_stmt', t2.blocking_session_id AS 'blocker sid', (SELECT [text] FROM sys.sysprocesses AS p Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark Licensed to Kerri Ross ... it is common to see SQL Server read-ahead reads posting I/O requests that are greater than 128 KB in size SQL Server 2005 and SQL Server 2008 are more aggressive than SQL Server 2000 when they... found that the sizes of read-ahead requests issued by SQL Server 2005 and SQL Server 2008 are often larger than those by SQL Server 2000 When SQL Server decides to use a table scan or an index scan... Detecting blocking in SQL Server 603 Detecting blocking in SQL Server Especially with OLTP workloads, you may run into blocking issues with SQL Server Listing 24 shows one quick DMV