DBA technoid questions

Last night at our local user group we had a speaker who came from
mainframe and other backgrounds with extensive DBA experience. He spoke
about some of the stuff in iNav that blows away stuff he's seen on these
other platforms (like Visual Explain), or if it was available on other
platforms, cost extra. His presentation was good but my constructive
criticism dealt with what in this stuff should we be looking for and what
actions should we take on them?

One example was that VE showed a table scan. Most of the attendees did
not know that a table scan was bad (for other than a small test table) and
why. But he showed how he used that to generate an index and chopped a
query that took several seconds down to milliseconds. Then he ran VE
again and was able to see that it no longer did a table scan but hit the
index, the table and then got the result. He chopped the remaining time
into a third by adding some of the columns in the table to the index that
were not even used for sorting or selection. This allowed the query to
never touch the table.

But remaining questions I have include stuff like:
- if I run this query
SELECT SYSTEM_TABLE_SCHEMA, SYSTEM_TABLE_NAME, LOGICAL_READS,
PHYSICAL_READS
FROM systablestat
WHERE system_table_schema='ERPLXF'
ORDER BY PHYSICAL_READS DESC
Why should I care?

Are there particular statistics that people pay attention to and what
actions do you perform based on them?



Rob Berendt