What does cntr_type mean?

Have you ever wondered if the cntr_type column value in the sys.sysperfinfo or sys.dm_os_performance_counters output has a significant meaning or not. Well since the column value is there, it obviously has a meaning. Additionally, if the raw values represented by the output of some of the counter types is considered at face value, then your performance base lining can take a severe beating.

Each cntr_type value meaning can be found from the WMI Performance Counter Type or Windows Server Performance Counter Type documentation on MSDN. 

The common counter types in SQL Server are:
PERF_COUNTER_RAWCOUNT | Decimal | 65536
Raw counter value that does not require calculations, and represents one sample.

PERF_COUNTER_LARGE_RAWCOUNT | Decimal | 65792
Same as PERF_COUNTER_RAWCOUNT, but a 64-bit representation for larger values.

PERF_COUNTER_COUNTER | Decimal | 272696320
Average number of operations completed during each second of the sample interval. NOTE: For "per-second counters", this value is cumulative. The rate value must be calculated by sampling the value at discrete time intervals. The difference between any two successive sample values is equal to the rate for the time interval used. For example, batch requests/sec is a per-second counter, it would show cumulative values.

PERF_COUNTER_BULK_COUNT | Decimal | 272696576
Average number of operations completed during each second of the sample interval. This counter type is the same as the PERF_COUNTER_COUNTER type, but it uses larger fields to accommodate larger values.

PERF_AVERAGE_BULK | Decimal | 1073874176 | Decimal | 537003264
Number of items processed, on average, during an operation. This counter type displays a ratio of the items processed (such as bytes sent) to the number of operations completed, and requires a base property with PERF_AVERAGE_BASE as the counter type.

PERF_LARGE_RAW_BASE | Decimal | 1073939712
Base value found in the calculation of PERF_RAW_FRACTION, 64 bits.

Example:
If you had the following values:
SQLServer:Plan Cache | Cache Hit Ratio | Temporary Tables & Table Variables | 381
SQLServer:Plan Cache | Cache Hit Ratio Base | Temporary Tables & Table Variables | 386
Then the Temp Table/Variable cache hit ratio percentage would be: 98.7% (approx.)

You can use the query below to get the comments for each counter type as discussed above:

select object_name,counter_name,instance_name,cntr_value,
case cntr_type 
	when 65792 then 'Absolute Meaning' 
	when 65536 then 'Absolute Meaning' 
	when 272696576 then 'Per Second counter and is Cumulative in Nature'
	when 1073874176 then 'Bulk Counter. To get correct value, this value needs to be divided by Base Counter value'
	when 537003264 then 'Bulk Counter. To get correct value, this value needs to be divided by Base Counter value' 
end as counter_comments
from sys.dm_os_performance_counters
where cntr_type not in (1073939712)

 

Documentation on MSDN:

WMI Performance Counter Types

http://msdn.microsoft.com/en-us/library/aa394569(VS.85).aspx

SQL Server 2005 BOL Topic

sys.dm_os_performance_counters (Transact-SQL) 

The broad classes of counters are as follows:

Non-computational Counter Types

http://msdn.microsoft.com/en-us/library/aa392713(VS.85).aspx

Basic Algorithm Counter Types

http://msdn.microsoft.com/en-us/library/aa384813(VS.85).aspx

Counter Algorithm Counter Types

http://msdn.microsoft.com/en-us/library/aa389384(VS.85).aspx

Timer Algorithm Counter Types

http://msdn.microsoft.com/en-us/library/aa393909(VS.85).aspx

Precision Timer Algorithm Counter Types

http://msdn.microsoft.com/en-us/library/aa392755(VS.85).aspx

Queue-length Algorithm Counter Types

http://msdn.microsoft.com/en-us/library/aa392905(VS.85).aspx

Base Counter Types

http://msdn.microsoft.com/en-us/library/aa384811(VS.85).aspx

Statistical Counter Types

http://msdn.microsoft.com/en-us/library/aa393663(VS.85).aspx

What can you tell me Default Trace

The default trace functionality introduced in SQL Server 2005 is still a much under appreciated feature of the product. This is somewhat like a black box trace which is analogous to a airline black box can help you in certain post-mortem analysis as a DBA. I am sure a lot of you have a host of in-house scripts that you have in-place or some monitoring/auditing tool that reports some inadvertent/unscrupulous activity on the databases that you administer. Nonetheless, it is always a good idea to be aware of the out-of-the-box features that are available that can make your job a wee bit easier.

Deepak Rangarajan (Blog), a Microsoft MVP, had blogged about the set of events which are captured by this default trace. So, I shall not attempt to duplicate his efforts here but collate a set of issues that CSS has been able to resolve using Default Traces in the past and will continue to do so in the future.

Dude: Where’s my database?
Not really a question that you want to be pondering on if you do not have any monitoring/auditing tools in place. And nor do you want to BING that search term. (Ok, if you prefer even Google it!) The default trace captures the following events: Object:Created, Object:Altered and Object:Deleted which will help you track down inadvertent deletion of databases. SQL Server Management Studio has a standard report called “Schema Changes History” report which can help you track such changes on a SQL instance in the form of a report.

Memory pressure: Where, When?
Ideally this can be tracked by Perfmon data collection and most of the SQL monitoring tools available in the market today track the Target and Total Server Memory counters for SQL instances. When you monitor the delta changes for these counters, you can track the amount of fluctuations that are occurring. The default trace tracks these changes using the Server Memory Change profiler event which will help you decide if there is a large fluctuation in Max Server Memory configuration for the SQL instance. This event gets raised when SQL Server memory usage has increased or decreased by either 1 megabyte (MB) or 5 percent of the maximum server memory (Buffer Pool only), whichever is greater. This is quite useful when tracking memory pressure being experienced for a SQL instance due to factors external to the SQL instance.

Mirrored Database: When did your state change?
All database mirroring state changes for all your mirrored databases are also monitored using the Default Trace using the event: Database mirroring status change. This helps track all database mirroring state changes without having to parse the SQL Errorlogs for the same.

OMG: Someone’s mucking around with my database security?
We have handled multiple issues in the past where we needed to identify various security related audit activity on a SQL instance like new Logins/Users being added, mostly for post-mortem analysis. The default trace “Security Audit” event classes show their usefulness by letting you trace such kind of activity using the default trace.

Full-Text: What are you upto?
The default traces also help trace Full-Text crawl activity which at times have been known to cause performance degradation when very large FT catalogs are involved.

Database: Did you just grow or shrink?
SQL Server databases enabled for Autogrow help prevent the database from going down if the file becomes full but at the same time Autogrow events can cause performance issues like blocking. Additionally, database auto shrink (both log and data files) operations can severely impact database performance. With the help of the default traces, you can can all Auto Grow/Shrink operations for your databases on the instance.

SQL Performance: Now how can I use the default trace for this?
Well the answer is not a definitive one but the default trace can give you an indication if you have a baseline established. The default trace traces the following events: Hash Warning, Missing Column Statistics, Missing Join Predicate and Sort Warning. These events can be used to find out if there is an excessive amount of sorting or hashing that is occurring on your SQL instance (without a baseline, this data is moot point though). You can also identify if a number of your queries are suffering from missing statistics and missing join predicates.

One thing to note here is that the default traces rollover which means that if the default traces are not copied over to an alternate location, they will be overwritten and valuable information required for post-mortem information will be lost.

Sleeping session ID: Where art thou?

This has been an age old confusion ever since the Dynamic Management Views changed the way SQL Performance monitoring was done.

A SPID/Session ID will show up as Sleeping/Awaiting Command when it has no active work request that it needs to execute on the Database Engine. Consider the following scenario:

1. You connect to a SQL instance using Management Studio

2. You execute: SELECT @@SPID

3. You then open another SSMS query window and try and lookup the Session ID returned by the output of Step #2 using the DMV: sys.dm_exec_requests.

If you didn’t know of this behavior, then you will be in for a surprise! This is because the Session ID associated with the query in Step #2 has no active work to perform which is why the DMV didn’t report a row for that particular session. However, when you look up this session id using sys.dm_exec_connections or sys.sysprocesses. The reason sys.sysprocesses reports this SPID is because it doesn’t differentiate between a session with/without an active work request. It will report all SPIDs currently connected to the database engine.

The above behavior is expected and by-design.

Bob Dorr has mentioned about this in his post on the CSS SQL Escalation blog and also talks about how this can affect concurrency if such a session has open transactions:

How It Works: What is a Sleeping / Awaiting Command Session