As always Hotsos started off with a nice keynote, this time done by Tom Kyte. Tom Kyte was introduced by Hotsos president Gary Goodman after the HOTSOS 2010 opening. Tom’s keynote theme was “Should we be less smart some times”. Tom told about own experiences, that he in the past gave sometimes too fast an answer. It is very important to think about an answer before giving it… Why? Well some things applied in the past or for a specific version, and now they don’t anymore… this can be a problem, a real issue. Always make sure you talk about the same definitions, and agree on them. Make sure talking about the same version and of course about similar circumstances. When you start giving answers in general be sure to work with facts and not some assumptions which might be wrong. So you should always think about the information, about the circumstances and the assumptions you do, it means “Continuous Thinking”.
During the years I heard lots of stories about sizing the Oracle Database Buffer Cache. Oracle introduced in Oracle 8i (8.1.7) the view V$DB _CACHE_ADVICE. According the documentation this view shows IO’s that would be performed at various cache sizes from 10% to 200% of the current size. For example (GV$DB_CACHE_ADVISE):
The thing what is crossing my mind all the time is the question, will a system really react the way the advisor is predicting? This question is a very obvious question of course and in this post I like to place a nice little discussion in place.
As you know I have just started my own blog and I realized that sometimes pretty simple things can be really handy to know. Some time ago I found out by accident that Oracle 11G database has a nice feature to find out the available underscore parameters in the pfile/spfile (there are more underscore parameters, but these are really dangerous).
=================== DISCLAIMER ===================
The usage of underscore parameters is officially prohibited. Underscore parameters should only be used after having instructions from Oracle Support. The usage from underscore parameters without having these instructions can lead to an unsupported Oracle environment. Also instability, crashes or even corruptions can be caused by usage of these parameters. So please use the information in this post with care.
These parameters can be easily obtained by giving the following command on the sql prompt as shown here: