Earlier this year I wrote for a whole month on SQL Server Wait Stats and the series was one of the best reviewed I have ever written. The same series has been enhanced and compiled into a book as SQL Server Wait Stats [Amazon] | [Flipkart] | [Kindle]. The best part of this book is it is an evolving book. I am planning to expand this book at certain intervals.
Yesterday I came across a very interesting system, where the top most wait type was TRACEWRITE. The DBA of the system reached out to me asking what this wait types means and how it can be resolved. As I had not written about this in the book so far, this is the blog post dedicated to his question. It will definitely be included in future versions of the book. For the moment let us go over it quickly and see what we can learn about TRACEWRITE.
Personally I consider TRACEWRITE a harmless and innocent wait type and I recommend that you ignore it too. However, the DBA who ran the script mentioned in my very first blog still found this wait type on the top as I did not include this wait type in the exclusion list. I think it should be there and in future versions of the script I will include it.
Occurs when the SQL Trace rowset trace provider waits for either a free buffer or a buffer with events to process.
SQL Trace is a SQL Server database engine technology which monitors specific events generated when various actions occur in the database engine. When any event is fired it goes through various stages as well various routes. One of the routes is Trace I/O Provider, which sends data to its final destination either as file or rowset. This rowset provider does not provide any guarantees to data. It stores the data into its internal buffers. If the data from the internal buffer is not consumed quickly enough (20 seconds) the buffers start to drop the events to free itself up to handle future events. This is when it sends a special error messages to the profiler client. When more threads are waiting for free buffers the wait type TRACEWRITE is implemented. The higher this wait type, the higher the number of threads waiting for free buffer, degrading performance in most of the system.
It is not necessary to consider this wait type as bad or evil. In most systems it can be a perfectly normal wait type and you just need to ignore it. If you are convinced, you should stop reading this blog post here. However, if still want to reduce this wait type, here is something you can experiment with on your development server (never on production server).
Run the following query and see if it returns any value. This query will list all the trace running in your system.
In most of the systems I have come across I have noticed default trace enabled for the system. I personally like this to keep it on as it helps the DBA to diagnosis problems the first time they occur. Additionally, this helps Microsoft to diagnosis your system if you request their support. (One more reason to ignore this wait type and do not attempt to disable default trace). However, you can manually disable this trace by following script.
sp_configure 'show advanced options', 1;
sp_configure 'default trace enabled', 0;
Well, as this is not harmful wait type, I had not included it in my book or initial series. Anyway, now we have learned about this wait type so I will include it in future versions.
Read all the post in the Wait Types and Queue series.
Note: The information presented here is from my experience and there is no way that I claim it to be accurate. I suggest reading my book OnLine for further clarification. All the discussion of Wait Stats in this blog is generic and varies from system to system. It is recommended that you test this on a development server before implementing it to a production server.
Reference: Pinal Dave (http://blog.SQLAuthority.com)