Thursday, December 08, 2005

Keep Your Statistics Up To Date

I had a scheduled job that runs every hour and took about a minute to complete. Somehow for no good reason this job suddenly takes hours and hours to finish. There was nothing done to the server, no service packs or patches. I checked fragmentation with DBCC SHOWCONTIG and it looked fine. I checked for blocking by running sp_who2 and there was no blocking going on. Now I was puzzled, what could have caused this? The table is not huge, about 50000 rows. Then I decided to update the statistics by running UPDATE STATISTICS and the problem went away immediately. The strange part is that there was such a huge difference in excution time, if it was double or triple I would understand but this was hunderds times slower. I don't have auto update statistics enabled because I have huge tables and can not have SQL server running sp_updatestats in the middle of the day. I have added this one table to the statistics job that I currently have and will monitor if the stats are up to date

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