Getting the Oracle Homes in a server from the oraInventory

The information contained in the oratab should always be updated, but it is not always reliable. If you want to know what Oracle installations you have in a server, better to get it from the Oracle Universal Installer or, if you want some shortcuts, do some grep magics inside the inventory with the shell.

The following diagram is a simplified structure of the inventory that shows what entries are present in the central inventory (one per server) and the local inventories (one per Oracle Home).

inventory_structureYou can use this simple function to get some content out of it, including the edition (that information is a step deeper in the local inventory).

HTH

Loading resolved Adaptive Plans in the SQL Plan Management

In my previous post, I have shown that loading Adaptive Plans in the SQL Plan Baseline leads to using the original plan. Well, actually, this is true when you capture them via the OPTIMIZER_CAPTURE_SQL_PLAN_BASELINES parameter.

Thanks to a tweet by Neil Chandler, I’ve realized that it was a good idea to show also the case when the plan is loaded manually.

When the adaptive plan switches to the alternative plan, the plan_hash_value also changes, and can be loaded manually in the baseline with DBMS_SPM.

Let’s reset everything and retry quickly to:

  • Capture the plan automatically (this will lead to the original plan)
  • Load the plan manually (I will specify to load the alternative plan, if resolved)
  • Drop the plan captured automatically
  • Use the newly accepted baseline

To recap:

  • The capture process will always load the original plan
  • It is possible to decide to load manually the original one or the alternative one (if resolved)
  • Using automatic capture is a bad idea

HTH

Ludo

How Adaptive Plans work with SQL Plan Baselines?

Disclaimer: after writing this post (but before publishing it) I have seen that other people already blogged about it, so I am ashamed of publishing it anyway… but that’s blogger’s life 🙂

Wednesday I have got a nice question after my presentation about Adaptive Features at the DOAG16 conference:

What happens when you load an adaptive plan in a SQL Plan Baseline?
Does it load only the final plan or does it load the whole plan including the inactive operations? Will the plan be evaluated again using the inflection point?

I have decided to do some tests in order to give the best possible answer. I did not spend the time to rethink about producing an adaptive plan. Tim Hall already did an excellent test case to create and alter an adaptive plan in his blog, so I have reused massively most of its code. Thanks Tim :-).

I will not post all the code (please find it in Tim’s post), I will go straight to the plans.

First: I have an adaptive plan that resolves to NESTED LOOPS:

Second: I load the plan (lazy way: using baseline capture at session level)

Third: re-run the statement and check the plan

It does not look adaptive, but I can also check from the function DBMS_XPLAN.DISPLAY_SQL_PLAN_BASELINE:

Again, despite in the Note section it says it is adaptive, it does not look like an adaptive plan.

Can I trust this information? Of course I did not and tried to check the plan with and without baseline after changing the rows to force a plan switch to HJ (again taking Tim’s example):

After changing the rows:

  • when I do not use the baseline, the plan resolves to HASH JOIN
  • when I use it, the baseline forces to NESTED LOOPS.

So the plan in the baseline is not adaptive and it forces to what has been loaded. Is it the final plan or the original one? I have to capture it again to see if a new baseline appears:

A new baseline does not appear, so it looks that the original plan is considered by the capture process and not the resolved one! To be 100% sure, let’s try to drop the existing one and redo the test:

So, despite the fact that I have an adaptive plan that switches from NL to HJ, only the NESTED LOOPS operations are captured in the baseline, I can infer the only the original plan is loaded as SQL Plan Baseline.

References:

Autumn: a season of conferences and travels

It is not a news that autumn is the busiest season for people involved in the Oracle Community. Thanks to the OTN Nordic Tour this year I am setting my new record 🙂

In the next 2 months I will give 15 presentations in 8 distinct countries and in 3 distinct languages (Italian, French, English).

If you are based in one of those countries, you can join and say hello 🙂

Date/Time Event
11/10/2016
11:00 am - 12:00 pm
Adaptive Features or: How I Learned to Stop Worrying and Troubleshoot the Bomb [Nordic Tour 2016 - Denmark]
Oracle Denmark, Ballerup
11/10/2016
2:10 pm - 3:10 pm
Migrating to 12c: 300 DBs in 300 days. What we learned [Nordic Tour 2016 - Denmark]
Oracle Denmark, Ballerup
12/10/2016
11:15 am - 12:00 pm
Migrating to 12c: 300 DBs in 300 days. What we learned. [Nordic Tour 2016 - Norway]
Felix Conference Center, Oslo
12/10/2016
1:00 pm - 1:45 pm
Self-Service Database Operations made easy with APEX [Nordic Tour 2016 - Norway]
Felix Conference Center, Oslo
12/10/2016
3:00 pm - 3:45 pm
Database Migration Assistant for Unicode (DMU): a Real Customer Case [Nordic Tour 2016 - Norway]
Felix Conference Center, Oslo
13/10/2016
3:10 pm - 4:00 pm
Migrating to 12c: 300 DBs in 300 days. What we learned. [Nordic Tour 2016 - Finland]
Accenture Finland, Helsinki
14/10/2016
9:00 am - 9:45 am
Migrating to 12c: 300 DBs in 300 days. What we learned. [Nordic Tour 2016 - Sweden]
Stockholm, Stockholm
14/10/2016
10:00 am - 10:45 am
Adaptive Features or: How I Learned to Stop Worrying and Troubleshoot the Bomb. [Nordic Tour 2016 - Sweden]
Stockholm, Stockholm
11/11/2016
9:30 am - 10:15 am
Migrating to 12c: 300 DBs in 300 days. What we learned. [ITOUG Tech Day 2016]
UNA Hotel Century, Milano
11/11/2016
12:00 pm - 12:45 pm
Adaptive Features or: How I Learned to Stop Worrying and Troubleshoot the Bomb.
UNA Hotel Century, Milano
16/11/2016
11:00 am - 11:45 am
Adaptive Features or: How I Learned to Stop Worrying and Troubleshoot the Bomb [DOAG 2016]
DOAG Konferenz 2016, Nürnberg
22/11/2016
10:50 am - 11:30 am
Montée en version de 300 bases de données vers Oracle 12c en 300 jours. Quels problèmes peut-on rencontrer ? [Swiss Data Forum 16]
Aquatis Hotel, Lausanne
23/11/2016
9:00 am - 12:00 pm
Migrating to Oracle Database 12c: 300 Databases in 300 Days [Oracle Tech Breakfast]
Oracle Business Breakfast, Oracle Suisse SA, Geneva
07/12/2016
12:30 pm - 1:15 pm
Upgrading 300 Databases to 12c in 300 Days. What Can Go Wrong? [UKOUG_Tech16]
International Convention Centre, Birmingham, Birmingham
07/12/2016
3:10 pm - 4:00 pm
Adaptive Features or: How I Learned to Stop Worrying & Troubleshoot the Bomb [UKOUG Tech16]
International Convention Centre, Birmingham, Birmingham

The updated list of upcoming events can be found here.

How to fix CPU usage problem in 12c due to DBMS_FEATURE_AWR

I love my job because I always have suprises. This week’s surprise has been another problem related to SQL Plan Directives in 12c. Because it is a common problem that potentially affects ALL the customers, I am glad to share the solution on my blog 😀

Symptom of the problem: High CPU usage on the server

My customer’s DBA team has spotted a consistent high CPU utilisation on its servers:

spd_awr_high_cpu_sar

Everyday, at the same time, and for 20-40 minutes, the servers hosting the Oracle databases run literally out of CPU.

spd_awr_high_cpu_em

 

Troubleshooting

Ok, it would be too easy to give the solution now. If you cannot wait, jump at the end of this post. But what I like more is to explain how I came to it.

First, I gave a look at the processes consuming CPU. Most of the servers have many consolidated databases on them. Surprisingly, this is what I have found:

spd_awr_high_cpu_m001It seems that the source of the problem is not a single database, but all of them. Isn’t it? And I see another pattern here: the CPU usage comes always from the [m001] process, so it is not related to a user process.

My customer has Diagnostic Pack so it is easy to go deeper, but you can get the same result with other free tools like s-ash, statspack and snapper. However, this is what I have found in the Instance Top Activity:

spd_awr_high_cpu_instOk, everything comes from a single query with sql_id auyf8px9ywc6j. This is the full sql_text:

It looks like something made by a DBA, but it comes from the MMON.

Looking around, it seems closely related to two PL/SQL calls that I could find in the SQL Monitor and that systematically fail every day:

spd_cpu_sql_monitorDBMS_FEATURE_AWR function calls internally the SQL auyf8px9ywc6j.

The MOS does not know anything about that query, but the internet does:

spd_awr_franckOh no, not Franck again! He always discovers new stuff and blogs about it before I do 🙂

In his blog post, he points out that the query fails because of error ORA-12751 (resource plan limiting CPU usage) and that  it is a problem of Adaptive Dynamic Sampling. Is it true?

What I like to do when I have a problematic sql_id, is to run sqld360 from Mauro Pagano, but the resulting zip file does not contain anything useful, because actually there are no executions and no plans.

During the execution of the statement (or better, during the period with high CPU usage), there is an entry in v$sql, but no plans associated:

And this is very likely because the statement is still parsing, and all the time is due to the Dynamic Sampling. But because the plan is not there yet, I cannot check it in the DBMS_XPLAN.DISPLAY_CURSOR.

I decided then to trace it with those two statements:

At the next execution I see indeed the Adaptive Dynamic Sampling in the trace file, the errror due to the exhausted CPU in the resource plan, and the directives that caused the Adaptive Dynamic Sampling:

 

 

So, there are some SQL Plan Directives that force the CBO to run ADS for this query.

This query touches three tables, so instead of relying on the DIRECTIVE_IDs, it’s better to get the directives by object name:

Solution

At this point, the solution is the same already pointed out in one of my previous blog posts: disable the directives individually!

This very same PL/SQL block must be run on ALL the 12c databases affected by this Adaptive Dynamic Sampling problem on the sql_id auyf8px9ywc6j.

If you have just migrated the database to 12c, it would make even more sense to programmatically “inject” the disabled SQL Plan Directives into every freshly created or upgraded 12c database (until Oracle releases a patch for this non-bug).

It comes without saying that the next execution has been very quick, consuming almost no CPU and without using ADS.

HTH

Ludovico

 

Bash tips & tricks [ep. 7]: Cleanup on EXIT with a trap

This is the seventh epidose of a small series.

Description:

Pipes, temporary files, lock files, processes spawned in background, rows inserted in a status table that need to be updated… Everything need to be cleaned up if the script exits, even when the exit condition is not triggered inside the script.

BAD:

The worst practice is, of course, to forget to cleanup the tempfiles, leaving my output and temporary directories full of files *.tmp, *.pipe, *.lck, etc. I will not show the code because the list of bad practices is quite long…

Better than forgiving to cleanup, but still very bad, is to cleanup everything just before triggering the exit command (in the following example, F_check_exit is a function that exits the script if the first argument is non-zero, as defined it in the previous episode):

A better approach, would be to put all the cleanup tasks in a Cleanup()  function and then call this function instead of duplicating all the code everywhere:

But still, I need to make sure that I insert this piece of code everywhere. Not optimal yet.

I may include the Cleanup function inside the F_check_exit function, but then I have two inconvenients:
1 – I need to define the Cleanup function in every script that includes my include file
2 – still there will be exit conditions that are not trapped

GOOD:

The good approach would be to trap the EXIT signal with the Cleanup function:

Much better! But what if my include script has some logic that also creates some temporary files?

I can create a global F_Cleanup function that eventually executes the local Cleanup function, if defined. Let me show this:

Include script:

Main script:

The Cleanup function will be executed only if defined.

No Cleanup function: no worries, but still the F_Cleanup function can do some global cleanup not specific to the main script.

Bash tips & tricks [ep. 6]: Check the exit code

This is the sixth epidose of a small series.

Description:

Every command in a script may fail due to external reasons. Bash programming is not functional programming! 🙂

After running a command, make sure that you check the exit code and either raise a warning or exit with an error, depending on how a failure can impact the execution of the script.

BAD:

The worst example is not to check the exit code at all:

Next one is better, but you may have a lot of additional code to type:

Again, Log_Close, eok, eerror, etc are functions defined using the previous Bash Tips & Tricks in this series.

GOOD:

Define once the check functions that you will use after every command:

 

Bash tips & tricks [ep. 5]: Write the output to a logfile

This is the fifth epidose of a small series.

Description:

Logging the output of the scripts to a file is very important. There are several ways to achieve it, I will just show one of my favorites.

BAD:

You can log badly either from the script to a log file:

or by redirecting badly the standard output of the script:

 GOOD:

My favorite solution is to automatically open a pipe that will receive from the standard output and redirect to the logfile. With this solution, I can programmatically define my logfile name inside the script (based on the script name and input parameters for example) and forget about redirecting the output everytime that I run a command.

(*) the functions edebug, einfo, etc, have to be created using the guidelines I have used in this post: Bash tips & tricks [ep. 4]: Use logging levels

The -Z parameter can be used to intentionally avoid logging.

Again, all this stuff (function definitions and variables) should be put in a global include file.

If I execute it:

 

Bash tips & tricks [ep. 4]: Use logging levels

This is the fourth epidose of a small series.

Description:

Support different logging levels natively in your scripts so that your code will be more stable and maintainable.

BAD:

 

 GOOD:

Nothing to invent, there are already a few blog posts around about the best practices for log messages. I personally like the one from Michael Wayne Goodman:

http://www.goodmami.org/2011/07/04/Simple-logging-in-BASH-scripts.html

I have reused his code in my scripts with very few modifications to fit my needs:

The edumpvar is handy to have the status of several variables at once:

If you couple the verbosity level with input parameters you can have something quite clever (e.g. -s for silent, -V for verbose, -G for debug). I’m putting everything into one single snippet just as example, but as you can imagine, you should seriously put all the fixed variables and functions inside an external file that you will systematically include in your scripts:

Example:

bash-colour-output-normal

bash-colour-output-verbose

bash-colour-output-debug

It does not take into account the output file. That will be part of the next tip 🙂

Bash tips & tricks [ep. 3]: Colour your terminal!

This is the third epidose of a small series.

Description:

The days of monochrome green-on-black screens are over, in a remote shell  terminal you can have something fancier!

BAD:

bash_prompt_nocolor

GOOD:

Define a series of variables as shortcuts for color escape codes, there are plenty of examples on internet.

Use them whenever you need to highlight the output of a script, and eventually integrate them in a smart prompt (like the one I’ve blogged about sometimes ago).bash_prompt_color

The echo builtin command requires -e in order to make the colours work. When reading files, cat works, less requires -r. vi may work with some hacking, but it’s not worth to spend too much time, IMHO.