Oracle DBA – A lifelong learning experience

Discrepancies in v$parameter default values in 12c

Posted by John Hallas on April 10, 2015

In my last blog about security parameters I mentioned I had found some oddities in the default values for parameters in 12.1.0.2, this is a more in-depth analysis of my findings.

Taking the parameter SEC_RETURN_SERVER_RELEASE_BANNER as an example.

Prior to 12c the default value for this parameter was ‘FALSE’, whereas the documentation for 12c (https://docs.oracle.com/database/121/REFRN/refrn10275.htm) states that the default is ‘TRUE’.

To confirm this, I made a connection to a 12c (12.1.0.2) database and ran the following query:

select name, value,  default_value,  isdefault

from v$parameter

where name = 'sec_return_server_release_banner';
NAME                                     VALUE               DEFAULT_VALUE       ISDEFAULT
---------------------------------------- -------------------- -------------------- ---------
sec_return_server_release_banner         FALSE               TRUE                 TRUE

After confirming that the parameter had not been explicitly set in the parameter file, or as part of an alter system/session command, we could see that the actual value, held in ‘VALUE’, given to the parameter does not match the value provided by ‘DEFAULT_VALUE’ nor did it match the value it should have been assigned according to the documentation. Read the rest of this entry »

Posted in 11g new features, 12c new features, Oracle | Tagged: , , , , , , , | 2 Comments »

Getting sql statements out of a trace file

Posted by John Hallas on March 15, 2015

The focus on this post started off in one direction and ended up in another. Originally I had been running a drop user script which had hung and even when I killed the process I could not drop the users as it gave a “ORA-01940: cannot drop a user that is currently connected” – despite the users having left the company months ago and there being no chance of them actually having connected sessions. My suspicions were that the drop user command actually took a lock on the users or connected as them whilst dropping them.  I was also intrigued by the length of time it took to drop users who had no objects.  Therefore I created a user, dropped it and traced the session to see what was happening. I was amazed by the size of the output file and that is where the direction changed. I wanted to find an easy way to get all the lines of code out of  trace file so that I could review them quickly.

SQL*Plus: Release 11.2.0.2.0 Production on Sat Mar 14 06:55:08 2015
Connected to:
Oracle Database 11g Express Edition Release 11.2.0.2.0 - 64bit Production

create user test identified by test;
User created.
set timing on
ALTER SESSION SET sql_trace=TRUE;
Session altered.
Elapsed: 00:00:00.00
drop user test;
User dropped.
Elapsed: 00:00:00.26
ALTER SESSION SET sql_trace=FALSE;
Session altered.
Elapsed: 00:00:00.00

I now had a trace file and I used the insert=filename parameter of tkprof to produce a script containing all the sql_statements in the trace file, in the same order.

tkprof xe_ora_5796.trc xe_ora_5796.tkp insert=xe_ora_5796.sql

Edit the sql file that is produced (xe_ora_57967.sql in my example) , changing the field SQL_STATEMENT from LONG to a varchar2(4000) Read the rest of this entry »

Posted in Oracle | Tagged: , , , , , , , , , | 1 Comment »

Running two oracle installations from the same terminal

Posted by John Hallas on February 23, 2015

Two posts from me on the same day. The other one about Datapatch is about a brand new utility in 12c and is probably new to most people. This post caused mixed reactions when I mentioned it at work last week. Some people laughed at my naivety in not knowing about it, others took the same view as me and were interested to hear about it as it may prove useful one day.

A colleague had a double installation of new Oracle binaries on primary and standby servers and I suggested he get someone else to run one in parallel as he could not run two installers at the same time. He came back later on to show how it could be done and prove me wrong.

When starting up Xming using the Launch script the first window that comes up has a Display number of 0 at the bottom

xming_1

 

That maps to the :0 in the DISPLAY command you export

export DISPLAY=10.3.127.4:0.0

 So if you want a second installer to run you change the display number to 1 and use

export DISPLAY=10.3.127.4:1.0

And voila you can have 2 xming installer sessions running in parallel

The last 0 (.0) is used to have multiple screens within the same display – something that is not used very frequently these days.

So if you think I have wasted your time feel free to ignore this post and if you have found it useful I would happy to get comments saying so.

 

Posted in Oracle | Tagged: , , , , | Leave a Comment »

Issue with Datapatch – AKA SQL Patching Tool after cloning a database

Posted by John Hallas on February 23, 2015

There have been a few changes in the way patches are managed and monitored in 12c and whilst looking at this I found a potential problem that might occur when you clone or copy databases around, or even build them from a template file.

Firstly when you apply a PSU and run an opatch lsinventory command you now see a description of the patch rather than just a patch number – here showing that PSU 1 has been applied. This came in at 11.2.0.3 and in my opinion is really helpful. Read the rest of this entry »

Posted in 12c new features, Oracle | Tagged: , , , , , | Leave a Comment »

opatch lsinventory gives “line 384: [: =: unary operator expected”

Posted by John Hallas on February 19, 2015

I noticed the error message when running lsinventory against a  12.1.0.2 Oracle_Home. As the command worked I didn’t think anymore of it until on the same server against an 11.2.0.1 home I got the same error message.

opatch lsinventory
 tr: extra operand `y'
 Try `tr --help' for more information.
 /app/oracle/product/11.2.0.1/dbhome_1/OPatch/opatch: line 384: [: =: unary operator expected

There is a Mos note which provides a solution – 1551584.1

Modify following line (line number 384) in file $ORACLE_HOME/OPatch/opatch
if [ `echo $arg | tr [A-Z] [a-z]` = "-invptrloc" ]; then
to
if [ `echo $arg | tr A-Z a-z` = "-invptrloc" ]; then

However the real problem is caused by the presence of a file with a single character name in the current directory. Indeed there was such a file ‘x’ and once that was removed then the opatch lsinventory command worked as normal.

This bug appears when a new version of opatch is installed , in my case I had just added opatch version 12.1.0.6

Posted in Oracle | Tagged: , | 2 Comments »

Changing a database link password

Posted by John Hallas on February 13, 2015

I recently found out  that it is possible to change a database link password without dropping and recreating a database link in its entirety.

To be honest I thought this might have existed forever and I had just never come across it but it actually come out in 11GR2

The ALTER DATABASE LINK statement can be used and you do not need to specify the target service either  – all you need  is to run the following command from the user that owns a pre-existing database link

ALTER DATABASE LINK JOHN connect to USER identified by  PASSWORD;

I know it is not a major change but a quick canvas amongst fellow DBAs and nobody had noticed it’s arrival either so a heads-up might be helpful to someone

Posted in 11g new features, Oracle | Tagged: , | 2 Comments »

New ASM power levels in 11.2.0.2 and beyond

Posted by John Hallas on February 13, 2015

I recently saw the following command in a script that was to be run and thought an error had been made and the power level should have been 5 not 500.

ALTER DISKGROUP DATA REBALANCE POWER 500;

Upon doing some research it was not a mistype but a new method of disk balancing which came in from 11.2.0.2

Previously setting the power limit from 0 to 11 basically caused an additional number of ARBx process to be created to match the power level and these were removed once the rebalance had finished.

That was a nice simple situation which I had no problem with. The range was adequate and I normally used between 4 and 7 depending on the usage of the system and any performance impact that might be caused. The impact was easy to monitor using a variety of tools as top or glance on a *nix platform

Now from 11GR2 onwards and when a database has disk group ASM compatibility set to 11.2.0.2 or greater the operational range of values is 0 to 1024 for the rebalance power. Note that if the value of the POWER clause is specified larger than 11 for a disk group with ASM compatibility set to less than 11.2.0.2, then a warning is displayed and a POWER value equal to 11 is used for rebalancing. Second point to note is that if a disk group is altered to a higher RDBMS value this operation cannot be reversed.

So what does that mean in practise? Well in my eyes it seems to be a basic change but it now seems very hard, well-nigh impossible to see the impact that the re-balance is having on the server and consequently I do not see the advantages of it other than possibly on massively high-end systems. Read the rest of this entry »

Posted in 11g new features, ASM, Oracle | Tagged: , , | 2 Comments »

Stopping one ASM listener in Flex ASM environment takes down ASM instance

Posted by John Hallas on January 6, 2015

Stopping one ASM listener in Flex ASM environment takes down ASM instance

This is a heads-up about behaviour we are seeing during OAT testing on a 12c environment. We are running OAT tests on a new 12.1.0.2 Grid Infrastructure environment using Flex ASM (OEL 5.8) and when taking down one of the two ASMNETLSNR listeners on one of the nodes, the ASM instance running on that node is taken down. We assume this is due to a hard dependency between the listener and the ASM instance. Unfortunately this does not give us a great deal of resilience: as we have two ASMNETLSNR listeners normally running on each node we would expect to be able to lose one of them without losing an ASM instance.

ps -ef | grep tns
root 769 2 0 Nov10 ? 00:00:00 [netns]
oracle 8386 1 0 Nov19 ? 00:00:09 /app/gridsoft/12.1.0.2/bin/tnslsnr ASMNET1LSNR_ASM -no_crs_notify -inherit
oracle 8389 1 0 Nov19 ? 00:00:12 /app/gridsoft/12.1.0.2/bin/tnslsnr LISTENER_DG -inherit
oracle 8500 1 0 Nov19 ? 00:00:51 /app/gridsoft/12.1.0.2/bin/tnslsnr LISTENER -no_crs_notify -inherit
oracle 8621 1 0 Nov19 ? 00:00:13 /app/gridsoft/12.1.0.2/bin/tnslsnr LISTENER_SCAN1 -no_crs_notify -inherit
oracle 117429 1 0 13:57 ? 00:00:00 /app/gridsoft/12.1.0.2/bin/tnslsnr ASMNET2LSNR_ASM -no_crs_notify -inherit 

We are stopping the listener in a consistent and standard manner

srvctl stop listener ASMNET... -n node_name –f

 

Oracle did refer us to the following note.
Bug 14155526 : [12100-LIN64] BC: FAILED TO STOP ASM LISTENER WITH DEPENDENCY OF “ORA.ASM” RES >> this bug is closed as not bug . since its expected behavior.

This is expected behavior. ASM cannot be stopped on the node where the CRSD PE is running.

However we thought that you should be able to take an ASM listener down without forcing the database down as well. We have HAIP with two ASM Listeners per node. If we take one of the ASM listeners on a node down surely the other ASM Listener should be able to service the ASM instance on that node without the need for ASM going down. So why is there a hard dependency for the ASM listener?

 

Oracle said that this was expected behaviour but we still did not agree. They took the view that it works as per the design – confirmed by their dev team.

Based on the internal   <a href="https://support.oracle.com/epmos/faces/BugDisplay?id=14347014">Bug 14347014</a> : LNX64-12.1-SRVM-FPF:NEED AN OPTION TO REMOVE ASM LISTENER ALSO UPDATE DEPENDENCY

there is option provided by dev team to remove asm listener and update the dependency

A new command

srvctl update listener [-listener  -asm -remove [-force]]

is provided to remove asm listener and update dependency

note: srvctl update listener -listener listener_asm3 -remove -asm [-force]

If '-remove' and '-asm' are not specified together, then we should error out

 

We were  still not satisfied that this is how it should work if there are multiple ASM listeners/interfaces.
I can understand that if there is only one interface for the ASM instances to communicate on via the ASM listener, then it could be argued that taking the listener down should take down the non-critical ASM instances. But we have set up HAIP and are utilising two network interfaces, the whole point of this configuration is to provide greater resilience, therefore we should be able to lose one listener, either through failure or a need to restart it, without killing ASM instances.
It looks like the hard dependencies have been configured so that ASM will fail if ANY of the ASM listeners are not present, it should be configured so that ASM should only fail if ALL of the ASM listeners are not present.

Oracle have now confirmed that in 12.2 there will be an enhancement to change the dependencies between ASM and the ASM listener.

If you are testing resilience between nodes on a new 12c cluster then it might be worth stopping an ASM listener and seeing what the impact is.

Posted in 12c new features, ASM, Oracle | Tagged: , | 3 Comments »

My bizarre question of 2015 already

Posted by John Hallas on January 5, 2015

To be honest it was asked 2 years ago in a blog about ASM and rebalancing and someone asked the following question

Can I upgrade ASM from 10205 to 11203 while ASM rebalancing is in progress?
and the answer, unsurprisingly, was
No.
Why would anyone even think of asking that question never mind contemplating the idea of running an upgrade under such circumstances.
Needless to say my next blog post is about ASM related activities – coming very shortly

Posted in ASM, Oracle | Tagged: | Leave a Comment »

 
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