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Also Extensions Created Because of SQL Plan Directives Can Invalidate Packages – Take Two

In a previous post I described a situation where the creation of an extension, independently of whether it’s carried out manually by a person or automatically by the database engine, can lead to the invalidation of PL/SQL objects. In this second post on that subject, I describe, with the help of an example (I love examples!) based on the extension_invalidate_pkg_remote.sql script, what can happen when the table on which the extension is created is stored in a remote database.

Let’s start by creating the required objects. Notice that all objects are local but, because the package body references the table through a database link that points to the very same schema owning all other objects, the database engine considers it a remote table.

Also Extensions Created Because of SQL Plan Directives Can Invalidate Packages

UPDATE 2015-12-18: As metioned by Bryn Llewellyn in this tweet, the invalidation I describe below is caused by bug 19450314. A patch for it is available here for several releases (e.g. it is available for, or, but not for I successfully tested it on

The fact that an extension explicitly created by a user through DBMS_STATS can invalidate objects like packages is not new in 12c. It has been like that since the introduction of extensions in 11g. In my opinion, since such an invalidation takes place only when a developer or DBA triggers it, I do not consider it a major problem.

Auto SGA Management Impacts the Default Value of DB_FILE_MULTIBLOCK_READ_COUNT

The database engine determines the maximum disk I/O size used during multiblock reads (for example, full table scans or index fast full scans) by multiplying the values of the db_block_size and db_file_multiblock_read_count initialization parameters. The db_file_multiblock_read_count initialization parameter can be set explicitly, or, as of version 10.2, it’s also possible to instruct the database engine to automatically configure it. For the latter, simply don’t set it.

About the value which is automatically determined by the database engine the Oracle Database 12c Reference Guide gives us the following information:

Foreign Keys and Library Cache Locks

In this post I would like to describe a behavior of Oracle Database that, at least for me, isn’t obvious at all. Actually, it’s something that I can’t explain why it works in that way.

Let’s start by setting the scene by describing the schema I’m using for the following tests. As you can see from the image, there are three tables: one table (PARENT) that is referenced by two other tables (CHILD1 and CHILD2). Schema used for the tests In my case every table is owned by a different schema (P, C1 and C2 respectively). But, the behavior I describe is independent from that fact (i.e. it works in the same way if all tables are owned by the same schema). If you are interested, here is the SQL*Plus script I used to create them.

Extension Bypassed Because of Missing Histogram

Today, while tuning a fairly complex query experiencing wrong cardinality estimates, I noticed something I was not aware of. Hence, I thought to write this short post to illustrate how to reproduce the problem I experienced…

The Broken Statistics: "parse count (total)" and "session cursor cache hits"

The values provided by the “parse count (total)” and “session cursor cache hits” statistics are subject to several bugs. And, what’s worse, for years Oracle didn’t care to fix it. This is my impression, at least.

Then, when few weeks ago I read in the Oracle Support note 13837105.8 (Bug 13837105 – statistics “parse count (total)” and “session cursor cache hits” miscounted) that the bug introduced in was fixed, I hoped that others bugs in this area were fixed as well.

Unfortunately, it’s not the case. What a disappointment!

Even though several posts were already wrote about this topic (e.g. here and here; check the comments as well…), I thought it could be useful to summarize what the current status is.

ITL Deadlocks (script)

A reader of this blog, VijayS, asked me to share the script I use to demo ITL deadlocks that I mentioned in this comment. Since other readers might be interested, here is the script.

Event 10046 – Full List of Levels

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.

Display System Activity without Enterprise Manager

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:


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: