Tuesday Mar 22, 2016

GC Freelist Session Waits causing slowness and hangs

Best Practice Hint

One of the best things in my job:
I learn from you folks out there. Everyday. 

Credits here go to Maciej Tokar who did explain the below topic to me via LinkedIn - thanks a lot, Maciej! 
.

Locks are not being closed fast enough, resulting in gc freelist waits

You can find a reference for Global Cache Freelist in the Oracle Documentation. This issue here can or will lead to database being slow, up to complete hangs. Based on my research it looks as the issue is not related to RAC only but a general thing. In your session waits you'll spot this:

Event                               Event Class        % Event   Sessions
----------------------------------- --------------- ---------- ----------
gc freelist                         Cluster              41.37       8.61

This has been logged as a bugs 21352465 (public) and 18228629 (not public). It causes locks are not being closed fast enough, resulting in gc freelist waits. In conjunction the default for _gc_element_percent seemed to be too low at 120 (or 110 in 11.2.0.4).

Actually the issue can affect not only Oracle Database 12.1.0.2 but also Oracle Database 11.2.0.3 and 11.2.0.4.

See MOS Note:2055409.1 (Database Hangs with High "gc freelist" wait ) for further details.
.

Solution

  • Apply the patch for bug 18228629 on top of a PSU or BP where available
    • See the drop-down list to the right labeled "Release" to access the correct patch for your release
    • Unlike the above MOS Note states in Oracle Database 12.1.0.2 it is only available on top of the January 2016 PSU and BP and two other Exadata BPs - and on Linux only!
      .
  • Use the workaround and set _gc_element_percent = 200
    • This will require an instance restart as the parameter can't be changed dynamically:
      alter system set "_gc_element_percent"=200 scope=spfile;
      .

Epilogue

We've had a lot of discussions about underscore parameter in the past weeks. And I'm not a big fan of underscores especially when it comes to upgrades as experiences has shown that having underscores set one day may make it hard to remove them the other day - and underscores can significantly impact the upgrade duration in a negative way.

But on the other hand, if an issue is seriously affecting many customers, and there's no patch available for your platform and environment right now, what else can one do?
.

--Mike

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Wednesday Sep 02, 2015

No patches anymore for Oracle Database 11.2.0.3

Just in case you've missed the date please be aware:

No bug fixes, no patches, no CPU/SPUs, no PSUs, no BPs will be produced for Oracle Database 11.2.0.3 since Augugst 28, 2015

I know from the many emails I'm receiving that people are a bit disturbed since the Oracle Lifetime Support Policy brochure (Lifetime Support Policy and Brochure for Technology Products ) doesn't talk explicitly about patch sets but offers support for Oracle 11.2 until January 2018.

Oracle 11.2 Lifetime Support Policy

But this - as always - applies to the terminal patch set only - i.e. Oracle Database 11.2.0.4.

For a detailed description please see MOS Note:742060.1 and my previous blog posts from:

I have visited customers with hundreds of Oracle 11.2.0.3 databases in the past months. If you are now sitting there with one or many or many many Oracle 11.2.0.3 instances don't even think of moving to Oracle 11.2.0.4. The amount of work you'll spend in evaluating Oracle 11.2.0.4 is exactly the same as testing Oracle 12.1.0.2. Move to Oracle Database 12.1.0.2 - NOW!

And keep in mind: there's no such thing as a 2nd release anymore. Every patch set release is a full release - no matter if we talk about 11.2.0.4 or 12.1.0.2. Both have new features, new behavior etc etc.

--Mike

Monday Jun 29, 2015

Premier Support for Oracle 11.2 has ended months ago

PLEASE FIND AN UPDATED BLOG POST HERE:

https://blogs.oracle.com/UPGRADE/entry/no_extra_fee_for_extended


I have blogged many times about the End of Premier Support for Oracle Database 11.2 and the different stages and regulations for Extended Support for this release. But still I'm getting inquiries almost every day, internally and externally.

Let me first point out that I'm not a rep of Oracle Support. I'm just a Product Manager with some Oracle Support background. So you'll always have to consult our officially available documents and sources as regulations may change after I published this blog post. I'm just trying to summarize what I know at the moment to help you avoid some of the usual misunderstandings.

Premier Support for Oracle 11.2 has already ended

Fact. Premier Support for Oracle 11.2 has ended on Jan 31, 2015. Period. Regardless of the patch level you may be on. No further discussion here please. Just for your notes: this has happened a while ago in case you've missed the date:

PLEASE FIND AN UPDATED BLOG POST HERE:

https://blogs.oracle.com/UPGRADE/entry/no_extra_fee_for_extended


--Mike 

Wednesday Feb 15, 2012

Why is every patchset now a full release?

This question got posted by Naveen in the previous entry today - and I found it worth it to create a new blog entry as this question gets raised in nearly every 2nd workshop as well - so others might be interested as well.

Mike,

A question has been bothering me for a while and I thought I'll throw it out there. I didn't raise a support ticket, I knew what the response is going to be.

So here is the question. I have an 11g ORACLE HOME that was built as 11.2.0.1. Now if I want to upgrade to 11.2.0.2 or 11.2.0.3, I guess there is no easy way to upgrade the existing ORACLE HOME. Why didn't Oracle give the option to just apply a patch (opatch) and upgrade to 11.2.0.2 (or .3). For a customer to create a new ORACLE HOME is just a lot of work and breaks a lot of things. We have to copy over so many configs from the old home to the new home.

I'm sure there is a good reason, I'm just trying to understand what they are.

Thanks
Naveen

Naveen, thanks for your question. And the answer has many aspects.

Install into your existing ORACLE Home

First of all you can still install the new patch set (which is now a full release since Oracle 11.2.0.2) into your existing $ORACLE_HOME. But you'll have to detach your current home from the OUI's inventory first. Please see slide 41 of the Upgrade and Migration workshop deck. Please backup the contents of $ORACLE_HOME/dbs and $ORACLE_HOME/network/admin first as you'll have to copy them back later.

$ ./runInstaller -detachHome ORACLE_HOME=/u01/orahomes/11.2.0

Starting Oracle Universal Installer...

Checking swap space: must be greater than 500 MB. Actual 10047 MB Passed

The inventory pointer is located at /etc/oraInst.loc

The inventory is located at /u01/orabase

'DetachHome' was successful.

Once you've done that you'll install into your existing (old) directory.  And finally you'll copy back your dbs and network/admin files.

Why customers might use this procedure?

There are basically two reason why a customer chooses this strategy:
(a) Home naming conventions not allowing an Oracle 11.2.0.2 home and another Oracle 11.2.0.3 home
(b) Space issues
Both are valid reasons and therefore you can stay with the old strategy.

Why did we change from patchsets to full release patchsets?

Simple reason: Customers did ask us for a looooong time why we are delivering 3GB large patchsets instead of full releases. So we'd follow this wish. And second it will decrease the overall downtime when you'd install into your new Oracle Home. If you apply patchset software to your existing Oracle Home every Oracle process serviced by that home must be shut down as well - obviously including the database(s). And furthermore if something fails you'll have to restore your OUI's inventory plus all home contents - or reinstall your previous Oracle software.

Besides that we recommend to patch this home first with important one-offs (see links in MOS Note 161818.1) and the latest PSU or CPU. If you'd do that to your already emptied old home it will simply increase again your overall downtime.

And this is the reason why we recommend:
Always install into a new Oracle home beginning with Oracle Database 11.2 - don't erase your old home to reuse it unless there's no significant need for that procedure.

About

Mike Dietrich - Oracle Mike Dietrich
Master Product Manager - Database Upgrade & Migrations - Oracle

Based in Germany. Interlink between customers/partners and the Upgrade Development. Running workshops between Arctic and Antartica. Assisting customers in their reference projects onsite and remotely. Connect via:

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