Re: v$session_event questions

Richard Hansen <hansenrd_at_BITEME_SPAMMERS_cadvision.com> wrote in article <34441705.10032149_at_news.cadvision.com>...

<snip>

> Our database appears to be getting a large amount of waits for these
> events (event = 'db file scattered read' and 'db file sequential read'
> are also high).

db file sequential read is usually associated with a fetch by rowid or an index range scan.

A db file scattered read is usually a full table scan. Look at the explain for the process's sql - this usually gives some kind of idea what's going on.

> What problems could these events be symptomatic of?

The problem is when the wait time gets high. If a 1000 events each takes a millisecond it ok, however is the average wait time is 20 milliseconds then you have a problem. Not much you can do but to look at the explain plan to get an idea of what the query process is doing and then to also monitor physical i/o, fragmentation, cache hit ratios etc for problems other than a "bad" sql statement which may cause problems.

> Also, where can I get a detailed explanation of this view? I've
> looked though the manuals that accompany the server as well as Oracle
> Press' Tuning Oracle and Advanced Tuning ... - none really give a good
> explanation of this view (and please authors, forgive me if I'm
> wrong!).

True. I've asked Oracle. Their reply was that even inside Oracle it's difficult to get the gurus to release the exact definitions for some of the event and stats... :-(

regards,
Billy Received on Thu Oct 16 1997 - 00:00:00 CDT