Search Results for: dynamic management view

Dynamic Management Views Put to Work on Blocking

This is my first pass at a modern (2005/2008) blocking monitoring script. I think it's a decent blocking script to capture information about blocks as they are occurring. Filters can be applied and it wouldn't be hard at all to add on other information such as execution plans, plan hash, etc. SELECT  tl.request_session_id AS WaitingSessionID        ,wt.blocking_session_id AS BlockingSessionID        ,wt.resource_description        ,wt.wait_type        ,wt.wait_duration_ms        ,DB_NAME(tl.resource_database_id) AS DatabaseName        ,tl.resource_associated_entity_id AS WaitingAssociatedEntity        ,tl.resource_type AS WaitingResourceType        ,tl.request_type AS WaitingRequestType        ,wrt.[text] AS WaitingTSql        ,btl.request_type BlockingRequestType        ,brt.[text] AS BlockingTsql FROM    sys.dm_tran_locks tl         JOIN sys.dm_os_waiting_tasks wt         ON tl.lock_owner_address = wt.resource_address         JOIN sys.dm_exec_requests wr         ON wr.session_id = tl.request_session_id         CROSS APPLY sys.dm_exec_sql_text(wr.sql_handle) AS wrt         LEFT JOIN sys.dm_exec_requests br         ON br.session_id = wt.blocking_session_id         OUTER APPLY…
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More Dynamic Management Views: sys.dm_tran_locks

I'm working on the chapter on blocking in the new book. Explaining blocking of course means explaining locks. Prior to 2005, to understand locks, you went to sp_lock. Not anymore. Now you can query sys.dm_tran_locks. It's so much more sophisticated than the old system procedure.  Best of all, the information within it is simply a view into the internal locking infrastructure, so you're not placing extra load or extra processing on the system to marshal this data. A simple query to get basic locking information would look like this:   SELECT tl.request_session_id             ,tl.resource_database_id             ,tl.resource_associated_entity_id             ,tl.resource_type             ,tl.resource_description             ,tl.request_mode             ,tl.request_status   FROM sys.dm_tran_locks tl That just outputs roughly the same information as sp_lock. Lots more detail, not available in sp_lock, is available if you need it. Things…
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Procedure Cache and Dynamic Management Views

I'm just going through the chapter on the procedure cache in the new book and I'm having a blast playing with the dynamic management views and functions that let you access the procedure cache. It's just too much fun and way too easy to get detailed information about the queries in the system, not like the old days. First, you can access the cache itself with the DMV, sys.dm_exec_cached_plans. This shows some of the data describing the plan in cache, but most importantly it provides the plan_handle. You need this for other joins later. You can also use sys.dm_exec_query_stats to get aggregated performance statistics about the plan. It also has the plan_handle and two things new to SQL Server 2008, the query_hash and the query_plan_hash, also known as query fingerprints.…
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Measuring Query Execution Time: What Is Most Accurate

Probably the single most important factor when deciding which query to tune, or actively tuning a query, is how you go about measuring query execution time. SQL Server provides a number of different mechanisms (really, maybe too many) to get this done. However, all measures are not created equally. In fact, they frequently disagree with one another. Let's take a look at this odd phenomenon. Measuring Query Execution Time Before we get into all the choices and compare them, let's baseline on methodology and a query to use. Not sure why, but many people give me blow back when I say "on average, this query runs in X amount of time." The feedback goes "You can't say that. What if it was just blocking or resources or..." I get it.…
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Query Optimizer and Data Definition Language Queries

Data Definition Language queries don't go through the optimizer, right? While normally, my short answer to this question in the past would have been, yes. However, with testing comes knowledge and I want to be sure about the statement. I'm working with a team of people to completely rewrite the SQL Server Execution Plans book. We'll probably be published in April or May. It's going to be amazing. The structure will be completely different and the book will represent five years of additional knowledge in how execution plans work and how to read and interpret them since the last book was written. However, enough on that. Let's answer the question about Data Definition Language. First of all, we need to quickly define our terms. Data Definition Language (DDL) represents the syntax for queries that build…
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Monitor Query Performance

Blog post #7 in support of Tim Ford’s (b|t) #iwanttohelp, #entrylevel. Read about it here. Sooner or later when you're working with SQL Server, someone is going to complain that the server is slow. I already pointed out the first place you should look when this comes up. But what if they're more precise? What if, you know, or at least suspect, you have a problem with a query? How do you get information about how queries are behaving in SQL Server? Choices For Query Metrics It's not enough to know that you have a slow query or queries. You need to know exactly how slow they are. You must measure. You need to know how long they take to run and you need to know how many resources are…
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Why Is The Server Slow?

This is blog post #2 in support of Tim Ford's (b|t) #iwanttohelp, #entrylevel. If you haven't been working in SQL Server for very long, you may not have got this phone call yet, but you will: Hi, yeah, the server is slow. Thanks. Bye. Let's pretend for a moment that you know which server they're referring to (because just finding out that piece of information can be a challenge). Now what? The list of tools and mechanisms within SQL Server for gathering metrics is extremely long: Performance Monitor Dynamic Management Views & Functions System Views Extended Events Trace Events Activity Monitor Data Collector Execution Plans 3rd Party Tools I'm leaving out lots of stuff in that list. So where do you start when you get this phone call? Where is the server slow?…
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Query Performance Tuning in SQL Server

I have a pre-con coming up at the PASS Summit. You can read about it here. I named it "Query Performance Tuning in SQL Server 2014" because it seemed like a good idea to bring out the aspects of 2014, and we will. But, I need to tell you, this is primarily a session about query performance tuning in SQL Server, full stop. I'm going to cover information that's applicable all the way back to SQL Server 2000 and 2005. The majority of the information will be applicable to 2008 and up. I'm going to go over the things you can do with dynamic management views to pull information about queries to tune right out of the cache. That's applicable to more than 2014. We're also going to go over…
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More Azure Goodies

Microsoft keeps sneaking little things under the door for Windows Azure SQL Database. This time it's a couple of new views, a system view and a Dynamic Management View (DMV); sys.resource_stats and sys.dm_operation_stats. But, I also learned another fun fact, not all this stuff rolls out at the same speed. For example, if I run sys.resource_stats on a database on a server located in the North Central US data center, the output looks like this: But, if I run the same query against the same view with a database in a data center in East Asia (I experiment with where I put things), it looks like this (click on it to expand it, probably want to do that into a second tab or window so you can refer to it…
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New DMO in Azure SQL Database: sys.dm_db_wait_stats

I just did a series of Boogle searches and when that didn't find anything I tried Ging. Neither listed sys.dm_db_wait_stats. Nothing in a search directly against MSDN either. So, let me introduce you to a new DMO, sys.dm_db_wait_stats. It's a dynamic management view since it doesn't require any input. The output is about what you would expect if you thought about it for a second:   In short, what we have is the sys.dm_os_wait_stats moved internally into your SQL Database so, even though you cannot get at any of the OS counters from with an a SQL Database normally. In short, thanks Microsoft. Now we can see the wait statistics on our Azure SQL Database in order to better understand where things are problematic. Without documentation I don't know for…
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