Logical I/O

Hi,
is logical I/O a bad thing in an oracle database, specifically 10gR2 10.2.0.4
I have one database that we monitor and it appears that logical I/O is very high. As I understand it however if logical IO is being done then it is better than physical IO
I view logical I/O from gv$segment_statistics
thanks

bi_nary wrote:
and then this would I hope lead to less logical I/O as the index is more efficient.As sb92075 said: The premise that less logical I/O is better, is wrong. What is better is less I/O. Period. Does not matter that is logical or physical.
Lots of logical I/O is however indicative of cached rows being used and re-used and used again... Which begs the question why?
Why use multiple passes through the same set of rows? Surely a single pass through a data set is significantly faster and will generate a a lot less I/O.
And this is the typical cause for high logical I/O. Multiple passes through the same data set. This can be PL/SQL based. For example, a stored proc has a bunch of IF conditions, where each condition requires rows in a specific table to be updated. The structure looks something as follows:
if confition-1 then
  update foo_tab
    set ..
  where ... //updates 100 of a 1000 rows
end if;
if confition-2 then
  update foo_tab
    set ..
  where ... //updates 500 of a 1000 rows
end if;
.. etc..
if confition-n then
  update foo_tab
    set ..
  where ... //updates 300 of a 1000 rows
end if;So this code hits the same rows again and again with updates - instead of using a single update and adding the logic of which rows to update with what, in the SQL statement.
Multiple passes can also result from poorly designed and written SQL statements. For example, the following SQL requires 2 selects on table 2, with a single select required for for every row processed in table 1:
update table1
  set some_column = (select bcol from table2 where table2.key = table1.key )
where key in (select key from table2)This is a problem as 2 SQLs are used against table 2. In such a case, tables 1 and 2 can be joined instead, and an "+updatable view+" created and used. This will result in a single select against table 2 for updating the rows in table 1.
Bottom line is that messing around with indexes, counting "+leave depths+", thinking "+unbalanced indexes+", contemplating index rebuilds and the like.. well, that is all silly bugger stuff. It has nothing to do with the actual problem.
There is a reason for that I/O. That reason resides in the design of the data model and the nature of the code using that data model. That is what you need to look at and evaluate.

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