This is a short post about a strange behavior I discovered today… The fact is that it is not really possible to use the named notation with the SEM_MATCH table function. In fact, even though the parameter’s names can be specified, the order of the parameters overrides the specification done with...

The patch set 11.2.0.3 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...

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...

Most execution plans can be interpreted by following few basic rules (in TOP, Chapter 6, I provide such a list of rules). Nevertheless, there are some special cases. One of them is when an index scan, in addition to the access predicate, has a filter predicate applying a subquery. The following execution...

Challenges and Chances of the 11g Query Optimizer is the name of a presentation I gave at several events (e.g. Trivadis Performance Days, Oracle OpenWorld, DOAG Konferenz, UKOUG Conference) throughout 2011. Its abstract is the following: With every new release, the query optimizer is enhanced. Oracle...

Since the introduction of 11.2 I receive on a regular basis questions related to “strange” workload system statistics. The last email on that topic was sent to me yesterday. So, instead to send, again, a private reply, I decided to write this short post. What’s wrong with 11.2 and workload system statistics...

As of 11.2.0.2 a new package, DBMS_AUTO_SQLTUNE, is available for accessing and configuring Automatic SQL Tuning. The package provides three features: Execution of the Automatic SQL Tuning task (EXECUTE_AUTO_TUNING_TASK) Generation of a report showing the output generated by the Automatic SQL Tuning...

When I started writing the series of posts about Exadata Storage Server and the query optimizer, I didn’t expect to write more than three posts (part 1, part 2, part 3). Of course, things change. Hence, here is part 4 to cover a couple of things that I learned in the next couple of months. In [...]

The aim of this post is to describe a strange (buggy) situation that I observed recently. But before doing that, I shortly summarize what a parent cursor and a child cursor are as well as when they can be shared. By the way, I borrowed this description from the pages 20/21 of my book. Hence, [...]

According to the documentation the GET_COMPRESSION_RATIO procedure of the DBMS_COMPRESSION package can be used to assess the impact of different compression options for a given table. In other words, it allows us to find out the expected compression ratio for a given set of data without having to really...

Today’s post is dedicated to the Metalink SR identified by the number 6468252.994. I know, this number says noting to you. For me, however, it’s a very well known number. The reason is quite simple… Even if I open this SR almost two years ago (to be precise, September 5, 2007), it was closed few...

As you can read in the documentation, the columns MAX_TEMPSEG_SIZE and LAST_TEMPSEG_SIZE in the dynamic performance view V$SQL_WORKAREA provide information about the size of the temporary segment used for a specific workarea. The values are given in bytes. Let’s perform a test to check this information…...