RE: db file scattered read
- From: "Justin Cave" <justin@xxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 6 Aug 2004 19:42:52 -0600
You have to collect statistics yourself prior to 10g, which defaults to
automatic collection.
There are two broad schools of thought on statistics collection. One
school, to which I believe folks like Tom Kyte subscribes, is that you
should have Oracle regularly gather statistics, since that will generally
lead the optimizer to choose the best execution plan. This school of though
carried the argument in 10g with automatic statistics collection.
The other school of though, to which most of the folks on this list tend to
subscribe, is that the only reason you would want to gather statistics is if
you want an execution plan to change and the only time you want an execution
plan to change is when a performance problem is identified. When you gather
statistics automatically, you run the risk that the CBO will identify a new,
poorly performing plan for one of your SQL statements, leading to frantic
calls to the DBA about substantial performance problems. The risk here is
that plans may grow slowly worse over time as data volumes and distributions
change.
Justin Cave
Distributed Database Consulting, Inc.
http://www.ddbcinc.com/askDDBC
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]
On Behalf Of Lyndon Tiu
Sent: Friday, August 06, 2004 6:31 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: Re: db file scattered read
On Fri, 6 Aug 2004 19:24:26 -0400 oracle-l@xxxxxxxxxxxxx wrote:
> It means that you have databases to tune before you sleep.
> You'll do so by paying particular attention to the most expensive SQL,
> and look for the full table scans. Something is doing full table scan.
I found the problem, I needed to do a "analyze" on the table.
I always thought oracle will do statistics automatically. I guess I was
wrong.
I have to analyze manually all the time?
--
Lyndon Tiu
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