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Decreasing disk_reads

The Disk_Reads for a particular update statement is 3071090. This has slowed down my activity. What are the solutions to decrease the Disk_Reads?

This is a large amount of disk reads for your UPDATE statement. When you issue an update statement you can include a WHERE clause, similar to the following:

UPDATE emp SET sal=3000 WHERE empid=1001;
Tuning this statement is similar to tuning a similar SELECT statement like:
SELECT * FROM emp WHERE empid=1001;
The most common cause of a high number of disk reads is by the statement performing a full table scan (FTS). A FTS means that the SQL statement has to read every single block in the table. Indexes typically reduce the number of reads (but not always), so you might want to investigate employing an index. In my case, I'd create an index on the EMPID column of the EMP table.

Statement tuning is quite a lengthy topic. There is lots to learn and many resources out there. The Oracle documentss touch on this subject. And Guy Harrison has a nice Oracle SQL performance tuning book on the market as well.

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This was last published in August 2003

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