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  SQL Server Tips by Robin Schumacher

The Impact of Speed

One might look at this performance model and think, “Well, speed doesn’t seem to matter much at all in this model.” This simply is not true. If there is a database server with accessibility nearly always ensured and with resource availability at peak levels around the clock, does that mean peak efficiency is not at risk? No, of course not. Speed becomes the all-important component of the performance model when and only when availability is under control. After availability is assured, speed becomes king.

The phone call most DBAs hate is the one that starts off with the complaint “Gee, the database sure seems to be running slow!” Of course, the network, application, and various other stress points could not be the problem. It always has to be the database, right? For the moment, remove all other mitigating factors and consider a situation where there actually is something going on at the database level.

What does slow mean? Slow could mean results from a SELECT statement are not coming back in reasonable amount of time, the heavy-duty procedure that is doing some serious number crunching is not completing within historical timeframes, or a process just seems to hang. The first two symptoms generally fall into the area of speed, while the last problem is typically one of resource availability.

Speed’s impact on the overall peak efficiency model will seldom reduce the overall measure to zero or near zero, but low speed ratings in the performance model can certainly make life miserable for users. How can the overall impact of speed be measured? First, availability has no such dependencies tied to speed.

It is important to understand that speed, as it is defined in the performance model, does not come into play with issues like how fast an incident of lock contention is resolved or the quickness at which a database’s free space is restored. Speed is comprised of how quickly and effectively data is accessed, the efficiency of a database’s code line, and the success of the physical database design.

As with availability, the various components and building blocks of speed cannot be weighted in some static nature. Some will count more than others, depending on the particular personality of the database and the total work being done at the moment. For example, nearly every SQL Server professional has watched database performance suffer at the hands of a user who has executed a massive procedure or runaway query.

Such a situation could signal problems in either the access or code efficiency components of the performance model. More than likely, it is a code imbalance in the system, which would fall under the code efficiency portion of the model. While the problem procedure or query would temporarily depress measures like a cache hit ratio or other memory statistics, the root cause of overall speed degradation is a piece of code out of balance with the normal work being conducted on a system.


The above book excerpt is from:

High-Performance SQL Server DBA
Tuning & Optimization Secrets

ISBN: 0-9761573-6-5
Robin Schumacher

 http://www.rampant-books.com/book_2005_2_sql_server_dba.htm  

 

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