"joel garry" <joel-garry_at_home.com> wrote in message
news:1162417597.219001.165100_at_e64g2000cwd.googlegroups.com...
>
> Ben wrote:
>> 9.2.0.5 Ent Ed AIX5L
>>
>> I've got a few long running processes that are all performing full
>> table scans and they are waiting on db file % reads. When a file read
>> is performed, is it reading the blocks into the buffer and then on to
>> the user or does it just dump them straight out to the user? What I'm
>> getting at is, Could these table scans be aging each other's blocks out
>> of the buffer and thus causing more file reads?
>> I guess if I could do away with the table scans in general that would
>> solve my problem though...
>>
>> I hope that wasn't too confusing.
>
> It reads the blocks to the buffer, but puts them on the least recently
> used end of the LRU list, so they get aged out first.
> http://download-west.oracle.com/docs/cd/B10501_01/server.920/a96524/c08memor.htm#8550
>
> You do run into aging each other's blocks out when you do lots of
> indexed reads. That's when it helps to use another buffer pool.
>
> You can look at what segments are in the buffer with v$bh.
> http://download-west.oracle.com/docs/cd/B10501_01/server.920/a96533/memory.htm#33797
>
> Table scans aren't necessarily bad. If you really do need most of the
> table, for example. Poke about in asktom.oracle.com for more info.
> You could make things worse going from full table scans to thrashing
> your buffers.
>
> jg
> --
> @home.com is bogus.
> http://www.signonsandiego.com/news/nation/20061101-1133-paypal-halloween-explosion.html
>
Received on Thu Nov 02 2006 - 02:06:20 CST
