How to reduce physical reads - very interesting issue

Question

HI,
Every week i generate a statspack report which will give me top20 buffer gets queries and top 20 physical reads query.When i start reducing physical reads by placing the heavy accessed table in buffer i will get the same query in top 20 higher buffer gets list in the next week.If i want to reduce buffer gets i have to remove the heavy accessed table from buffer which will cause higer physical reads.How can i solve this problem.I am trying to tune query as much as possible.
Your help is appreciated..
Thanks and Regards
Anand

Answer 1

I think that you are labouring under a misapprehension. Buffer gets and physical reads are basically the same thing. In order to satisfy your query, Oracle needsto read X number of blocks to find all of the data. Admittedly, it is generally faster to read those blocks from memory (buffer gets) than from disk (physical reads), but the blocks have to be read (this is called logical I/O). The only way to reduce I/O is to re-write the query to be more efficient. This may or may not be possible.
As Kamal said, if the query is fast enough, then you are done. If it is too slow, then you need to look at ways of reducing I/O. It is unlikely that any database parameters will have a significant impact on the I/O. You need to look at the statisitics on the table and the actual sql statement.
John