Premature optimization, (probably) because of Donald Knuth’s famous line “premature optimization is the root of all evil,” (see Structured Programming with go to Statements) is, at the very least, a controversial topic. The misconception based on that particular quote is that a programmer, while writing code, should ignore optimization altogether. In my opinion this is wrong. To put the quote in context, let’s have a look to at the text that precedes and follows it:
There is no doubt that the grail of efficiency leads to abuse. Programmers waste enormous amounts of time thinking about, or worrying about, the (more...)
The 11th and 12th of December and, therefore, the CBO Days in Zurich are approaching. Given the high quality of the speakers that accepted my invitation and the number of people that decided to attend the event, in my opinion it will be a blast! By the way, if you are interested in attending the event, do not wait any longer. In fact, from the 80 available seats, 75 are taken.
Here is a preview of the agenda:
Tuesday 11th December
- 09:00 – 09:10: Welcome and Introduction, Christian Antognini
- 09:10 – 10:30: The History of the Oracle Optimizer, Maria Colgan
In the last post I discussed a test case generating lot of child cursors. Today I wanted to show you, for the very same test case, that in 11.2 the parse time might increases linearly with the number of child cursors per parent cursor. This is the expected behavior. In fact, to check whether an already available child cursor can be reused, the list of child cursors must be scanned. And, in case no one of the already available child cursors is compatible, every entry needs to be probed.
Note that to generate the previous chart I simply run, (more...)
The patch set 126.96.36.199 includes a fix for bug# 10187168 which, in reality, is an enhancement request. Its purpose is to artificially limit the number of child cursors that a parent cursor can have. The concept is quite easy: when a parent cursor reaches _cursor_obsolete_threshold (default value is 100) child cursors the parent cursor is obsoleted and, as a result, a new one is created.
So, as of 188.8.131.52 (or with some PSUs and bundle patches), the answer to the question is: 100.
But how many child cursors are supported in previous 11.2 (more...)
The company I work for, Trivadis, is very pleased to organize, the 11th and 12th of December, an outstanding seminar with top guest speakers in Zurich. This year’s focus will be on the Oracle query optimizer, also known as a cost-based optimizer (CBO).
The query optimizer is not only one of the most complex pieces of software that constitutes the Oracle kernel; it is also one of the most unappreciated. Why? To make the best and most efficient use of the query optimizer, you definitely need to understand how it works. This is exactly what we are aiming for at (more...)
Extended SQL trace (a.k.a. debugging event 10046 at a level higher than 1) is one of the key features provided by Oracle to troubleshoot applications using Oracle Database. For many years the available levels were always the same (4, 8 and 12). In fact, since I wrote my first paper about it in May 2000 and the release of 11g nothing changed.
With 11g, as I described in this post, new levels (16 and 32) were introduced.
This is just a short post to point out that the company I work for, Trivadis, is organizing 3 classes with Cary Millsap. The topic, as the title suggests, is Cary’s 1-day class entitled “Mastering Oracle Trace Data”.
The following dates and locations are planned:
- September 11, 2012 – Münich (DE)
- September 13, 2012 – Zürich (CH)
- September 18, 2012 – Vienna (AT)
For detailed information have a look to the flyer. Note that the early bird registration period, that entitles you a 15% discount, ends on August 1.
I regularly use the system-level activity chart available in Enterprise Manager. In my opinion it is a simple and effective way to know how much a specific database is loaded at a specific time. This is for example an interesting way for observing how a specific load is processed (see this post for an example).
Unfortunately it also happens that this possibility is not available. The main reasons I faced in the past are the following:
- Standard Edition is used
- Enterprise Edition is used but Diagnostic Pack is not licensed
- Enterprise Manager is not available
- GUI is not available
Recently I used the COMMIT_WAIT and COMMIT_LOGGING parameters for solving (or, better, working around) a problem I faced while optimizing a specific task for one of my customers. Since it was the first time I used them in a production system, I thought to write this post not only to shortly explain the purpose of the these two parameters, but also to show a case where it is sensible to use them.
The purpose of the two parameters is the following:
- Simply put this parameter specifies whether a server process that issues a commit waits for the log writer (more...)