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Oracle 12.2 wait event ‘PGA memory operation’

When sifting through a sql_trace file from Oracle version 12.2, I noticed a new wait event: ‘PGA memory operation’:

WAIT #0x7ff225353470: nam='PGA memory operation' ela= 16 p1=131072 p2=0 p3=0 obj#=484 tim=15648003957

The current documentation has no description for it. Let’s see what V$EVENT_NAME says:

SQL> select event#, name, parameter1, parameter2, parameter3, wait_class 
  2  from v$event_name where name = 'PGA memory operation';

EVENT# NAME                                  PARAMETER1 PARAMETER2 PARAMETER3 WAIT_CLASS
------ ------------------------------------- ---------- ---------- ---------- ---------------
   524 PGA memory operation                                                   Other

Well, that doesn’t help…

back to the basics: ALTER TABLE MOVE vs SHRINK

It’s time for the next article with ODBV visualisation </p />
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back to the basics: ALTER TABLE MOVE vs SHRINK

It’s time for the next article with ODBV visualisation </p />
</p></div>

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back to the basics: truncate table reuse storage vs drop storage

From time to time I get questions on my trainings, what is the difference between TRUNCATE TABLE and TRUNCATE TABLE DROP STORAGE… well, there is no difference because DROP STORAGE is default </p />
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Advanced Oracle memory profiling using pin tool ‘pinatrace’

In my previous post, I introduced Intel Pin. If you are new to pin, please follow this link to my previous post on how to set it up and how to run it.

One of the things you can do with Pin, is profile memory access. Profiling memory access using the pin tool ‘pinatrace’ is done in the following way:

$ cd ~/pin/pin-3.0-76991-gcc-linux
$ ./pin -pid 12284 -t source/tools/SimpleExamples/obj-intel64/pinatrace.so

The pid is a pid of an oracle database foreground process. Now execute something in the session you attached pin to and you find the ‘pinatrace’ output in $ORACLE_HOME/dbs:

Introduction to Intel Pin

This blogpost is an introduction to Intel’s Pin dynamic instrumentation framework. Pin and the pintools were brought to my attention by Mahmoud Hatem in his blogpost Tracing Memory access of an oracle process: Intel PinTools. The Pin framework provides an API that abstracts instruction-set specifics (on the CPU layer). Because this is a dynamic binary instrumentation tool, it requires no recompiling of source code. This means we can use it with programs like the Oracle database executable.
The Pin framework download comes with a set of pre-created tools called ‘Pintools’. Some of these tools are really useful for Oracle investigation and research.

Oracle 12cR2: Database parameters

For those in a desperate need to learn all 4841 database parameter variations of the…

Oracle Database Block Visualizer

Recently I wanted to demonstrate to some people on my training, how Oracle database maintains blocks in a datafile – what happens after truncate, truncate with drop storage clause, delete, regular insert, direct path insert and so on…

I didn’t find any tool for that so I’ve written my own. It’s core code is based on my previous database block research – project RICO http://blog.ora-600.pl/2015/09/03/rico/

Tool is very small and simple and right now it supports only regular blocks with data and no compression.

And this is how it works – let’s create a tablespace and 3 new tables in HR schema:

Oracle Database Block Visualizer

Recently I wanted to demonstrate to some people on my training, how Oracle database maintains blocks in a datafile – what happens after truncate, truncate with drop storage clause, delete, regular insert, direct path insert and so on…

I didn’t find any tool for that so I’ve written my own. It’s core code is based on my previous database block research – project RICO http://blog.ora-600.pl/2015/09/03/rico/

Tool is very small and simple and right now it supports only regular blocks with data and no compression.

And this is how it works – let’s create a tablespace and 3 new tables in HR schema:

Watching is in the eye of the beholder

Recently I was investigating the inner working of Oracle. One of the things that is fundamental to the Oracle database is the SCN (system change number). SCNs are used to synchronise changes in the database. There is one source for SCNs in every instance (kcbgscn; the global or current SCN in the fixed SGA), and there are multiple tasks for which Oracle keeps track of synchronisation using SCNs. A few of these tasks for which Oracle stores and uses SCNs to keep track of progress are on disk SCN and lwn SCN.

This blogpost is about some oddities I found when using gdb (the GNU debugger) to watch memory locations of a running Oracle database. This should not be done on a production instance, and is purely for research purposes. Only use the methods mentioned in this article if you are absolutely sure what you are doing, and/or if you are using an Oracle instance that can be crashed and can be restored.