January 18, 2011 at 9:54 am
I would like to know what are the general baselines for read/writes. Lets say i am updating a table and if it is doing 27 million reads and 5000 writes is that normal? I would assume it is using a bad index. And i would expect reads to be more in select statements and writes to more in update/delete. Any suggestions?
January 18, 2011 at 10:03 am
sqldba_icon (1/18/2011)
I would like to know what are the general baselines for read/writes. Lets say i am updating a table and if it is doing 27 million reads and 5000 writes is that normal? I would assume it is using a bad index. And i would expect reads to be more in select statements and writes to more in update/delete. Any suggestions?
Baselines on read/writes are a 'breathing' statistic. Start breathing faster or slower, and you want to know why, but every system is different for the baseline.
As to your update, it depends. Is there a lot of joining in the FROM clause? That can spike reads if you're scanning a cluster somewhere. Are you scanning the base of a large table instead of seeking a clustered WHERE well? That'll spike your reads.
You need to know the data itself, the schema and index ddl, and the update execution plan to decide if this is normal.
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January 18, 2011 at 10:08 am
Is there any specific reason for your duplicate post (here's the other one)?
Based on your visit count I think you've been around long enough to know better...
January 18, 2011 at 10:21 am
sqldba_icon (1/18/2011)
I would like to know what are the general baselines for read/writes.
Fewer is better and if it changes without reason there's a problem
Lets say i am updating a table and if it is doing 27 million reads and 5000 writes is that normal?
It depends. Again, absolutely no way to say if that's normal, odd or a problem. The kind of statistics that you've been asking about are (like many in SQL) system-dependant. It's bad if they're way off from normal. Not normal for everyone, normal for that database and that application.
That query may need tuning. It may be as optimal as it can. No way to say without doing significant investigations into the query, how it behaves and what it does.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability
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