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  • An XEvent a Day (11 of 31) – Targets Week – Using Multiple Targets to Debug Orphaned Transactions

    - by Jonathan Kehayias
    Yesterday’s blog post Targets Week – etw_classic_sync_target covered the ETW integration that is built into Extended Events and how the etw_classic_sync_target can be used in conjunction with other ETW traces to provide troubleshooting at a level previously not possible with SQL Server. In today’s post we’ll look at how to use multiple targets to simplify analysis of Event collection. Why Multiple Targets? You might ask why you would want to use multiple Targets in an Event Session with Extended...(read more)

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  • Session memory – who’s this guy named Max and what’s he doing with my memory?

    - by extended_events
    SQL Server MVP Jonathan Kehayias (blog) emailed me a question last week when he noticed that the total memory used by the buffers for an event session was larger than the value he specified for the MAX_MEMORY option in the CREATE EVENT SESSION DDL. The answer here seems like an excellent subject for me to kick-off my new “401 – Internals” tag that identifies posts where I pull back the curtains a bit and let you peek into what’s going on inside the extended events engine. In a previous post (Option Trading: Getting the most out of the event session options) I explained that we use a set of buffers to store the event data before  we write the event data to asynchronous targets. The MAX_MEMORY along with the MEMORY_PARTITION_MODE defines how big each buffer will be. Theoretically, that means that I can predict the size of each buffer using the following formula: max memory / # of buffers = buffer size If it was that simple I wouldn’t be writing this post. I’ll take “boundary” for 64K Alex For a number of reasons that are beyond the scope of this blog, we create event buffers in 64K chunks. The result of this is that the buffer size indicated by the formula above is rounded up to the next 64K boundary and that is the size used to create the buffers. If you think visually, this means that the graph of your max_memory option compared to the actual buffer size that results will look like a set of stairs rather than a smooth line. You can see this behavior by looking at the output of dm_xe_sessions, specifically the fields related to the buffer sizes, over a range of different memory inputs: Note: This test was run on a 2 core machine using per_cpu partitioning which results in 5 buffers. (Seem my previous post referenced above for the math behind buffer count.) input_memory_kb total_regular_buffers regular_buffer_size total_buffer_size 637 5 130867 654335 638 5 130867 654335 639 5 130867 654335 640 5 196403 982015 641 5 196403 982015 642 5 196403 982015 This is just a segment of the results that shows one of the “jumps” between the buffer boundary at 639 KB and 640 KB. You can verify the size boundary by doing the math on the regular_buffer_size field, which is returned in bytes: 196403 – 130867 = 65536 bytes 65536 / 1024 = 64 KB The relationship between the input for max_memory and when the regular_buffer_size is going to jump from one 64K boundary to the next is going to change based on the number of buffers being created. The number of buffers is dependent on the partition mode you choose. If you choose any partition mode other than NONE, the number of buffers will depend on your hardware configuration. (Again, see the earlier post referenced above.) With the default partition mode of none, you always get three buffers, regardless of machine configuration, so I generated a “range table” for max_memory settings between 1 KB and 4096 KB as an example. start_memory_range_kb end_memory_range_kb total_regular_buffers regular_buffer_size total_buffer_size 1 191 NULL NULL NULL 192 383 3 130867 392601 384 575 3 196403 589209 576 767 3 261939 785817 768 959 3 327475 982425 960 1151 3 393011 1179033 1152 1343 3 458547 1375641 1344 1535 3 524083 1572249 1536 1727 3 589619 1768857 1728 1919 3 655155 1965465 1920 2111 3 720691 2162073 2112 2303 3 786227 2358681 2304 2495 3 851763 2555289 2496 2687 3 917299 2751897 2688 2879 3 982835 2948505 2880 3071 3 1048371 3145113 3072 3263 3 1113907 3341721 3264 3455 3 1179443 3538329 3456 3647 3 1244979 3734937 3648 3839 3 1310515 3931545 3840 4031 3 1376051 4128153 4032 4096 3 1441587 4324761 As you can see, there are 21 “steps” within this range and max_memory values below 192 KB fall below the 64K per buffer limit so they generate an error when you attempt to specify them. Max approximates True as memory approaches 64K The upshot of this is that the max_memory option does not imply a contract for the maximum memory that will be used for the session buffers (Those of you who read Take it to the Max (and beyond) know that max_memory is really only referring to the event session buffer memory.) but is more of an estimate of total buffer size to the nearest higher multiple of 64K times the number of buffers you have. The maximum delta between your initial max_memory setting and the true total buffer size occurs right after you break through a 64K boundary, for example if you set max_memory = 576 KB (see the green line in the table), your actual buffer size will be closer to 767 KB in a non-partitioned event session. You get “stepped up” for every 191 KB block of initial max_memory which isn’t likely to cause a problem for most machines. Things get more interesting when you consider a partitioned event session on a computer that has a large number of logical CPUs or NUMA nodes. Since each buffer gets “stepped up” when you break a boundary, the delta can get much larger because it’s multiplied by the number of buffers. For example, a machine with 64 logical CPUs will have 160 buffers using per_cpu partitioning or if you have 8 NUMA nodes configured on that machine you would have 24 buffers when using per_node. If you’ve just broken through a 64K boundary and get “stepped up” to the next buffer size you’ll end up with total buffer size approximately 10240 KB and 1536 KB respectively (64K * # of buffers) larger than max_memory value you might think you’re getting. Using per_cpu partitioning on large machine has the most impact because of the large number of buffers created. If the amount of memory being used by your system within these ranges is important to you then this is something worth paying attention to and considering when you configure your event sessions. The DMV dm_xe_sessions is the tool to use to identify the exact buffer size for your sessions. In addition to the regular buffers (read: event session buffers) you’ll also see the details for large buffers if you have configured MAX_EVENT_SIZE. The “buffer steps” for any given hardware configuration should be static within each partition mode so if you want to have a handy reference available when you configure your event sessions you can use the following code to generate a range table similar to the one above that is applicable for your specific machine and chosen partition mode. DECLARE @buf_size_output table (input_memory_kb bigint, total_regular_buffers bigint, regular_buffer_size bigint, total_buffer_size bigint) DECLARE @buf_size int, @part_mode varchar(8) SET @buf_size = 1 -- Set to the begining of your max_memory range (KB) SET @part_mode = 'per_cpu' -- Set to the partition mode for the table you want to generate WHILE @buf_size <= 4096 -- Set to the end of your max_memory range (KB) BEGIN     BEGIN TRY         IF EXISTS (SELECT * from sys.server_event_sessions WHERE name = 'buffer_size_test')             DROP EVENT SESSION buffer_size_test ON SERVER         DECLARE @session nvarchar(max)         SET @session = 'create event session buffer_size_test on server                         add event sql_statement_completed                         add target ring_buffer                         with (max_memory = ' + CAST(@buf_size as nvarchar(4)) + ' KB, memory_partition_mode = ' + @part_mode + ')'         EXEC sp_executesql @session         SET @session = 'alter event session buffer_size_test on server                         state = start'         EXEC sp_executesql @session         INSERT @buf_size_output (input_memory_kb, total_regular_buffers, regular_buffer_size, total_buffer_size)             SELECT @buf_size, total_regular_buffers, regular_buffer_size, total_buffer_size FROM sys.dm_xe_sessions WHERE name = 'buffer_size_test'     END TRY     BEGIN CATCH         INSERT @buf_size_output (input_memory_kb)             SELECT @buf_size     END CATCH     SET @buf_size = @buf_size + 1 END DROP EVENT SESSION buffer_size_test ON SERVER SELECT MIN(input_memory_kb) start_memory_range_kb, MAX(input_memory_kb) end_memory_range_kb, total_regular_buffers, regular_buffer_size, total_buffer_size from @buf_size_output group by total_regular_buffers, regular_buffer_size, total_buffer_size Thanks to Jonathan for an interesting question and a chance to explore some of the details of Extended Event internals. - Mike

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  • An XEvent a Day (18 of 31) – A Look at Backup Internals and How to Track Backup and Restore Throughput (Part 2)

    - by Jonathan Kehayias
    In yesterday’s blog post A Look at Backup Internals and How to Track Backup and Restore Throughput (Part 1) , we looked at what happens when we Backup a database in SQL Server.  Today, we are going to use the information we captured to perform some analysis of the Backup information in an attempt to find ways to decrease the time it takes to backup a database.  When I began reviewing the data from the Backup in yesterdays post, I realized that I had made a mistake in the process and left...(read more)

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  • An XEvent a Day (3 of 31) – Managing Event Sessions

    - by Jonathan Kehayias
    Yesterdays post, Querying the Extended Events Metadata , showed how to discover the objects available for use in Extended Events.  In todays post, we’ll take a look at the DDL Commands that are used to create and manage Event Sessions based on the objects available in the system.  Like other objects inside of SQL Server, there are three DDL commands that are used with Extended Events; CREATE EVENT SESSION , ALTER EVENT SESSION , and DROP EVENT SESSION .  The command names are self...(read more)

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  • An XEvent a Day (13 of 31) – The system_health Session

    - by Jonathan Kehayias
    Today’s post was originally planned for this coming weekend, but seems I’ve caught whatever bug my kids had over the weekend so I am changing up today’s blog post with one that is easier to cover and shorter.  If you’ve been running some of the queries from the posts in this series, you have no doubt come across an Event Session running on your server with the name of system_health.  In today’s post I’ll go over this session and provide links to references related to it. When Extended Events...(read more)

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  • An XEvent a Day (14 of 31) – A Closer Look at Predicates

    - by Jonathan Kehayias
    When working with SQL Trace, one of my biggest frustrations has been the limitations that exist in filtering.  Using sp_trace_setfilter to establish the filter criteria is a non-trivial task, and it falls short of being able to deliver complex filtering that is sometimes needed to simplify analysis.  Filtering of trace data was performed globally and applied to the trace affecting all of the events being collected.  Extended Events introduces a much better system of filtering using...(read more)

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  • An XEvent a Day (15 of 31) – Tracking Ghost Cleanup

    - by Jonathan Kehayias
    If you don’t know anything about Ghost Cleanup, I recommend highly that you go read Paul Randal’s blog posts Inside the Storage Engine: Ghost cleanup in depth , Ghost cleanup redux , and Turning off the ghost cleanup task for a performance gain .  To my knowledge Paul’s posts are the only things that cover Ghost Cleanup at any level online. In this post we’ll look at how you can use Extended Events to track the activity of Ghost Cleanup inside of your SQL Server.  To do this, we’ll first...(read more)

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  • An XEvent a Day (5 of 31) - Targets Week – ring_buffer

    - by Jonathan Kehayias
    Yesterday’s post, Querying the Session Definition and Active Session DMV’s , showed how to find information about the Event Sessions that exist inside a SQL Server and how to find information about the Active Event Sessions that are running inside a SQL Server using the Session Definition and Active Session DMV’s.  With the background information now out of the way, and since this post falls on the start of a new week I’ve decided to make this Targets Week, where each day we’ll look at a different...(read more)

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  • An XEvent a Day (17 of 31) – A Look at Backup Internals and How to Track Backup and Restore Throughput (Part 1)

    - by Jonathan Kehayias
    Today’s post is a continuation of yesterday’s post How Many Checkpoints are Issued During a Full Backup? and the investigation of Database Engine Internals with Extended Events.  In today’s post we’ll look at how Backup’s work inside of SQL Server and how to track the throughput of Backup and Restore operations.  This post is not going to cover Backups in SQL Server as a topic; if that is what you are looking for see Paul Randal’s TechNet Article Understanding SQL Server Backups . Yesterday...(read more)

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  • Trace Flag 610 – When should you use it?

    - by simonsabin
    Thanks to Marcel van der Holst for providing this great information on the use of Trace Flag 610. This trace flag can be used to have minimal logging into a b tree (i.e. clustered table or an index on a heap) that already has data. It is a trace flag because in testing they found some scenarios where it didn’t perform as well. Marcel explains why below. “ TF610 can be used to get minimal logging in a non-empty B-Tree. The idea is that when you insert a large amount of data, you don't want to...(read more)

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  • An XEvent a Day (4 of 31) – Querying the Session Definition and Active Session DMV’s

    - by Jonathan Kehayias
    Yesterdays post, Managing Event Sessions , showed how to manage Event Sessions in Extended Events Sessions inside the Extended Events framework in SQL Server. In today's post, we’ll take a look at how to find information about the defined Event Sessions that already exist inside a SQL Server using the Session Definition DMV’s and how to find information about the Active Event Sessions that exist using the Active Session DMV’s. Session Definition DMV’s The Session Definition DMV’s provide information...(read more)

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  • Find a Hash Collision, Win $100

    - by Mike C
    Margarity Kerns recently published a very nice article at SQL Server Central on using hash functions to detect changes in rows during the data warehouse load ETL process. On the discussion page for the article I noticed a lot of the same old arguments against using hash functions to detect change. After having this same discussion several times over the past several months in public and private forums, I've decided to see if we can't put this argument to rest for a while. To that end I'm going to...(read more)

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  • SSAS DMVs: useful links

    - by Davide Mauri
    From time to time happens that I need to extract metadata informations from Analysis Services DMVS in order to quickly get an overview of the entire situation and/or drill down to detail level. As a memo I post the link I use most when need to get documentation on SSAS Objects Data DMVs: SSAS: Using DMV Queries to get Cube Metadata http://bennyaustin.wordpress.com/2011/03/01/ssas-dmv-queries-cube-metadata/ SSAS DMV (Dynamic Management View) http://dwbi1.wordpress.com/2010/01/01/ssas-dmv-dynamic-management-view/ Use Dynamic Management Views (DMVs) to Monitor Analysis Services http://msdn.microsoft.com/en-us/library/hh230820.aspx

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  • An XEvent a Day (6 of 31) – Targets Week – asynchronous_file_target

    - by Jonathan Kehayias
    Yesterday’s post, Targets Week - ring_buffer , looked at the ring_buffer Target in Extended Events and how it outputs the raw Event data in an XML document.  Today I’m going to go over the details of the other Target in Extended Events that captures raw Event data, the asynchronous_file_target. What is the asynchronous_file_target? The asynchronous_file_target holds the raw format Event data in a proprietary binary file format that persists beyond server restarts and can be provided to another...(read more)

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  • An XEvent a Day (2 of 31) – Querying the Extended Events Metadata

    - by Jonathan Kehayias
    In yesterdays post, An Overview of Extended Events , I provided some of the necessary background for Extended Events that you need to understand to begin working with Extended Events in SQL Server. After receiving some feedback by email (thanks Aaron I appreciate it), I have changed the post naming convention associated with the post to reflect “2 of 31” instead of 2/31, which apparently caused some confusion in Paul Randal’s and Glenn Berry’s series which were mentioned in the round up post for...(read more)

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  • An XEvent a Day (8 of 31) – Targets Week – synchronous_event_counter

    - by Jonathan Kehayias
    Yesterday’s post, Targets Week - Bucketizers , looked at the bucketizer Targets in Extended Events and how they can be used to simplify analysis and perform more targeted analysis based on their output.  Today’s post will be fairly short, by comparison to the previous posts, while we look at the synchronous_event_counter target, which can be used to test the impact of an Event Session without actually incurring the cost of Event collection. What is the synchronous_event_counter? The synchronous_event_count...(read more)

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  • An XEvent a Day (7 of 31) – Targets Week – bucketizers

    - by Jonathan Kehayias
    Yesterday’s post, Targets Week - asynchronous_file_target , looked at the asynchronous_file_target Target in Extended Events and how it outputs the raw Event data in an XML document. Continuing with Targets week today, we’ll look at the bucketizer targets in Extended Events which can be used to group Events based on the Event data that is being returned. What is the bucketizer? The bucketizer performs grouping of Events as they are processed by the target into buckets based on the Event data and...(read more)

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  • SYS2 Scripts Updated – Scripts to monitor database backup, database space usage and memory grants now available

    - by Davide Mauri
    I’ve just released three new scripts of my “sys2” script collection that can be found on CodePlex: Project Page: http://sys2dmvs.codeplex.com/ Source Code Download: http://sys2dmvs.codeplex.com/SourceControl/changeset/view/57732 The three new scripts are the following sys2.database_backup_info.sql sys2.query_memory_grants.sql sys2.stp_get_databases_space_used_info.sql Here’s some more details: database_backup_info This script has been made to quickly check if and when backup was done. It will report the last full, differential and log backup date and time for each database. Along with these information you’ll also get some additional metadata that shows if a database is a read-only database and its recovery model: By default it will check only the last seven days, but you can change this value just specifying how many days back you want to check. To analyze the last seven days, and list only the database with FULL recovery model without a log backup select * from sys2.databases_backup_info(default) where recovery_model = 3 and log_backup = 0 To analyze the last fifteen days, and list only the database with FULL recovery model with a differential backup select * from sys2.databases_backup_info(15) where recovery_model = 3 and diff_backup = 1 I just love this script, I use it every time I need to check that backups are not too old and that t-log backup are correctly scheduled. query_memory_grants This is just a wrapper around sys.dm_exec_query_memory_grants that enriches the default result set with the text of the query for which memory has been granted or is waiting for a memory grant and, optionally, its execution plan stp_get_databases_space_used_info This is a stored procedure that list all the available databases and for each one the overall size, the used space within that size, the maximum size it may reach and the auto grow options. This is another script I use every day in order to be able to monitor, track and forecast database space usage. As usual feedbacks and suggestions are more than welcome!

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  • An XEvent a Day (9 of 31) – Targets Week – pair_matching

    - by Jonathan Kehayias
    Yesterday’s post, Targets Week – synchronous_event_counter , looked at the counter Target in Extended Events and how it could be used to determine the number of Events a Event Session will generate without actually incurring the cost to collect and store the Events.  Today’s post is coming late, I know, but sometimes that’s just how the ball rolls.  My original planned demo’s for today’s post turned out to only work based on a fluke, though they were very consistent at working as expected,...(read more)

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  • ASP.Net performance counters

    - by nikolaosk
    I was involved in designing and implementing an ASP.Net application some time ago. After we deployed the application we wanted to monitor various aspects of the application. We can use the Performance Monitor. In my windows Server 2008 machine, I go to Start-Run and type " perfmon " and the Performance monitor window pops up. There are thousands of counters in there and it is impossible for anyone to know them all. Most people I know use the Performance Monitor to add counters to monitor SQL Server...(read more)

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  • SQL Server Certification - a database platform primer for your career path

    - by ssqa.net
    When you need to upgrade your knowledge then training is required, at the same time certifications will help you to keep up on what you have learned! There is a big debate on the web about whether certifications are important in your career or not, the bottomline is if you do not know the stuff or unable to answer few basic technical questions, it does'nt matter how many certifications you have then you will not get the job, well I'm not starting the same discussion here. But in the recent...(read more)

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  • T-SQL Tuesday #006: Tiger/Line Spatial Data

    - by Mike C
    This month’s T-SQL Tuesday post is about LOB data http://sqlblog.com/blogs/michael_coles/archive/2010/05/03/t-sql-tuesday-006-what-about-blob.aspx . For this one I decided to post a sample Tiger/Line SQL database I use all the time in live demos. For those who aren't familiar with it, Tiger/Line data is a dataset published by the U.S. Census Bureau . Tiger/Line has a lot of nice detailed geospatial data down to a very detailed level. It actually goes from the U.S. state level all the way down to...(read more)

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  • SQL Server v.Next (Denali) : OS compatibility & upgrade support

    - by AaronBertrand
    Microsoft's Manageability PPM Dan Jones has asked for our feedback on their proposed list of supported operating systems and upgrade paths for the next version of SQL Server. (See the original post ). This has generated all kinds of spirited debates on twitter, in protected mailing lists, and in private e-mail. If you're going to be involved in moving to Denali, you should be aware of these proposals and stay on top of the discussion until the results are in. (The media are starting to pick up on...(read more)

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  • An XEvent a Day (31 of 31) – Event Session DDL Events

    - by Jonathan Kehayias
    To close out this month’s series on Extended Events we’ll look at the DDL Events for the Event Session DDL operations, and how those can be used to track changes to Event Sessions and determine all of the possible outputs that could exist from an Extended Event Session.  One of my least favorite quirks about Extended Events is that there is no way to determine the Events and Actions that may exist inside a Target, except to parse all of the the captured data.  Information about the Event...(read more)

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  • Restricting logons during certain hours for certain users

    - by simonsabin
    Following a an email in a DL I decided to look at implementing a logon restriction system to prevent users from logging on at certain ties of the day. The poster had a solution but wanted to add auditing. I immediately thought of the My post on logging messages during a transaction because I new that part of the logon trigger functionality is that you rollback the connection. I therefore assumed you had to do the logging like I talk about in that post (otherwise the logging wouldn’t persist beyond...(read more)

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