Auto Update Statistics & Auto Create Statistics

The ability to create and update statistics is a crucial liberty for the query optimizer. The optimizer needs to know how it is going to query underlying tables, and when the statistics do not match the data, it is very probable that it will choose a non-efficient method for querying. I’ve seen and heard a lot of debate from DBA’s who think they should turn this off. Of all those DBA’s I think there is one who was correct, and he ended up convincing me of his scenario so I’m not as closed minded as I was before. His server was so bottle-necked during peak time, that he updated the stats off hours. I’m very weary of those who blindly say “it’s better to turn it off” without any factual statistics to back them up. Most of the DBA’s that think they should turn it off are stuck in the SQL Server 7.0 days. At that time, turning this feature off was acceptable because they interfered with the currently running queries. Example Case in point, we had a DBA who did turn this feature off in an environment that mirrored production. I overheard the developers complaining how their queries took twice as long on this box. Looking at perfmon, I saw no physical bottlenecks. Since this was the case, I turned to statistics and found both auto update and auto create turned off. After turning it back on, the box was just as fast as production. Long story short, these […]

Continue reading ...