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A Wider View: Experimentations and ruminations on Oracle performance analysis

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Oracle Database performance tuning and analysis experimentation and ruminations.Craig Shallahamer, President/Founder, OraPub
Updated: 1 day 23 hours ago

11 Tips To Get Your Conference Abstract Accepted

Wed, 2014-10-08 19:21
11 Ways To Get Your Conference Abstract Accepted
This is what happens when your abstract is selected!Ready for some fun!? It's that time of year again and the competition will be intense. The "call for abstracts" for a number of Oracle Database conferences are about to close.

The focus of this posting is how you can get a conference abstract accepted.

As a mentor, Track Manager and active conference speaker I've been helping DBAs get their abstracts accepted for many years. If you follow my 11 tips below, I'm willing to bet you will get a free pass to any conference you wish in any part of the world.

1. No Surprises! 
Track Manager After A SurpriseThe Track Manager wants no surprises, great content and a great presentation. Believe me when I say, they are looking for ways to reduce the risk of a botched presentation, a cancelation or a no show. Your abstract submissions is your first way to show you are serious and will help make the track incredibly awesome.

Tip: In all your conference communications, demonstrate a commitment to follow through.

2. Creative Title.
The first thing everyone sees is the title. I can personally tell you, if the title does not peak my curiosity without sounding stupid, then unless I know the speaker is popular I will not read the abstract. Why do I do this? Because as a Track Manager, I know conference attendees will do the same thing! And as a Track Manager, I want attendees to want to attend sessions in my track.

Tip: Find two people, read the title to them and ask what they think. If they say something like, "What are you going to talk about?" that's bad. Rework the title.

3. Tell A Story
The abstract must tell a compelling story. Oracle conferences are not academic conferences! There needs to be some problem along with a solution complete with drama woven into the story.

Tip: People forget bullet points, but they never forget a good story.

4. Easy To Read
The abstract must be easy to review. The abstract reviewers may have over a hundred abstracts to review. Make it a good quick read for the reviewers and your chances increase.

Tip: Have your computer read your abstract back to you. If you don't say, "Wow!" rework the abstract. 

5. Be A Grown-Up
You can increase the perception you will physically show up and put on a great show at the conference by NOT putting into your abstract emoji, bullet points, your name and title or pushing a product or service. NEVER copy/paste from a powerpoint outline into the abstract or outline. (I've seen people do this!)

Tip: Track Managers do not want to baby sit you. They want an adult who will help make their track great.

6. Submit Introductory Level Abstracts
I finally figured this out a couple years ago. Not everyone is ready for a detailed understanding of cache buffer chain architecture, diagnosis, and solution development. Think of it from a business perspective. Your market (audience) will be larger if your presentation is less technical. If this bothers you, read my next point.

Tip: Submit both an introductory level version and advanced level version of your topic.

7. Topics Must Be Filled
Not even the Track Manager knows what people will submit. And you do not know what the Track Manager is looking for. And you do not know what other people are submitting. Mash this together and it means you must submit more than one abstract. I know you really, really want to present on topic X. But would you rather not have an abstract accepted?

Tip: Submit abstracts on multiple topics. It increases your chances of being accepted.

8. Submit Abstract To Multiple Tracks
This is similar to submitting both an introductory version of your abstract. Here's an example: If there is a DBA Bootcamp track and a Performance & Internals Track, craft your abstract to Bootcamp version has a more foundational/core feel to it. And craft your Performance & Internals version to feel more technical and advanced.

Do not simply change the title and the abstract can not be the same.  If the conference managers or the Track Manager feels you are trying to game the conference, you present a risk to the conference and their track and your abstracts will be rejected. So be careful and thoughtful.

Tip: Look for ways to adjust your topic to fit into multiple tracks.

9. Great Outline Shows Commitment
If the reviewers have read your title and abstract, they are taking your abstract seriously. Now is the time to close the deal by demonstrating you will put on a great show. And this means you already have in mind an organized and well thought out delivery. You convey this with a fantastic outline. I know it is difficult to create an outline BUT the reviewers also know this AND having a solid outline demonstrates to them you are serious, you will show up, and put on a great show.

Tip: Develop your abstract and outline together. This strengthens both and develops a kind of package the reviewers like to see.

10. Learning Objectives Show Value
You show the obvious value of your topic through the learning objectives. Personally, I use these to help keep me focused on my listener, just not what I'm interested in at the moment. Because I love my work, I tend to think everyone also does... not so. I must force myself to answer the question, "Why would a DBA care about this topic?"

Tip: Develop your learning objectives by asking yourself, "When my presentation is over, what do I want the attendees to remember?"

11. Submit About Problems You Solved
Submit on the topics you have personally explored and found fascinating. Every year, every DBA has had to drill deep into at least one problem. This concentrated effort means you know the topic very well. And this means you are qualified to tell others about it! People love to hear from people who are fascinated about something. Spread the good news resulting from a "bad" experience.

Tip: Submit on topics you have explored and are fascinated with.

How Many Abstracts Should I Submit?
It depends on the conference, but for a big North America conference like ODTUG, RMOUG and IOUG I suggest at least four.

Based on what I wrote above, pick three topics, perhaps create both an introductory and advanced version and look to see if it makes sense to submit to multiple tracks. That means you'll probably submit at least four abstracts. It's not as bad as it sounds, because you will only have perhaps three core abstracts. All the others are modifications to fit a specific need. Believe when you receive the acceptance email, it will all be worth it!

See you at the conference!


Categories: DBA Blogs

Comparing SQL Execution Times From Different Systems

Mon, 2014-10-06 18:17
Comparing SQL Execution Times From Different Systems
Suppose it's your job to identify SQL that may run slower in the about-to-be-upgrated Oracle Database. It's tricky because no two systems are alike. Just because the SQL run time is faster in the test environment doesn't mean the decision to upgrade is a good one. In fact, it could be disastrous.

For example; If a SQL statement runs 10 seconds in production and runs 20 seconds in QAT, but the production system is twice as fast as QAT, is that a problem? It's difficult to compare SQL runs times when the same SQL resides in different environments.

In this posting, I present a way to remove the CPU speed differences, so an appropriate "apples to apples" SQL elapsed time comparison can be made, thereby improving our ability to more correctly detect risky SQL that may be placed into the upgraded production system.

And, there is a cool, free, downloadable tool involved!

Why SQL Can Run Slower In Different Environments
There are a number of reasons why a SQL's run time is different in different systems. An obvious reason is a different execution plan. A less obvious and much more complex reason is a workload intensity or type difference. In this posting, I will focus on CPU speed differences. Actually, what I'll show you is how to remove the CPU speed differences so you can appropriately compare two SQL statements. It's pretty cool.

The Mental Gymnastics
If a SQL statement's elapsed time in production is 10 seconds and 20 seconds in QAT, that’s NOT an issue IF the production system is twice as fast.

If this makes sense to you, then what you did was mentally adjust one of the systems so it could be appropriately compared. This is how I did it:

10 seconds in production * production is 2 times as fast as QA  = 20 seconds 
And in QA the sql ran in 20 seconds… so really they ran “the same” in both environments. If I am considering placing the SQL from the test environment into the production environment, then this scenario does not raise any risk flags. The "trick" is determining "production is 2 times as fast as QA" and then creatively use that information.
Determining The "Speed Value"
Fortunately, there are many ways to determine a system's "speed value." Basing the speed value on Oracle's ability to process buffers in memory has many advantages: a real load is not required or even desired, real Oracle code is being run at a particular version, real operating systems are being run and the processing of an Oracle buffer highly correlates with CPU consumption.
Keep in mind, this type of CPU speed test is not an indicator of scalability (benefit of adding additional CPUs) in any way shape or form. It is simply a measure of brut force Oracle buffer cache logical IO processing speed based on a number of factors. If you are architecting a system, other tests will be required.
As you might expect, I have a free tool you can download to determine the "true speed" rating. I recently updated it to be more accurate, require less Oracle privileges, and also show the execution plan of the speed test tool SQL. (A special thanks to Steve for the execution plan enhancement!) If the execution plan used in the speed tool is difference on the various systems, then obviously we can't expect the "true speeds" to be comparable.
You can download the tool HERE.
How To Analyze The Risk
Before we can analyze the risk, we need the "speed value" for both systems. Suppose a faster system means its speed rating is larger. If the production system speed rating is 600 and the QAT system speed rating is 300, then production is deemed "twice as fast."
Now let's put this all together and quickly go through three examples.
This is the core math:
standardized elapsed time = sql elapsed time * system speed value
So if the SQL elapsed time is 25 seconds and the system speed value is 200, then the standardized "apples-to-apples" elapsed time is 5000 which is 25*200. The "standardized elapsed time" is simply a way to compare SQL elapsed times, not what users will feel and not the true SQL elapsed time.
To make this a little more interesting, I'll quickly go through three scenarios focusing on identifying risk.
1. The SQL truly runs the same in both systems.
Here is the math:
QAT standardized elapsed time = 20 seconds X 300 = 6000 seconds
PRD standardized elapsed time = 10 seconds X 600 = 6000 seconds
In this scenario, the true speed situation is, QAT = PRD. This means, the SQL effectively runs just as fast in QAT as in production. If someone says the SQL is running slower in QAT and therefore this presents a risk to the upgrade, you can confidently say it's because the PRD system is twice as fast! In this scenario, the QAT SQL will not be flagged as presenting a significant risk when upgrading from QAT to PRD.
2. The SQL runs faster in production.
Now suppose the SQL runs for 30 seconds in QAT and for 10 seconds in PRD. If someone was to say, "Well of course it's runs slower in QAT because QAT is slower than the PRD system." Really? Everything is OK? Again, to make a fare comparison, we must compare the system using a standardizing metric, which I have been calling the, "standardized elapsed time."
Here are the scenario numbers:
QAT standardized elapsed time = 30 seconds X 300 = 9000 secondsPRD standardized elapsed time = 10 seconds X 600 = 6000 seconds
In this scenario, the QAT standard elapsed time is greater than the PRD standardized elapsed time. This means the QAT SQL is truly running slower in QAT compared to PRD. Specifically, this means the slower SQL in QAT can not be fully explained by the slower QAT system. Said another way, while we expect the SQL in QAT to run slower then in the PRD system, we didn't expect it to be quite so slow in QAT. There must another reason for this slowness, which we are not accounting for. In this scenario, the QAT SQL should be flagged as presenting a significant risk when upgrading from QAT to PRD.
3. The SQL runs faster in QAT.
In this final scenario, the SQL runs for 15 seconds in QAT and for 10 seconds in PRD. Suppose someone was to say, "Well of course the SQL runs slower in QAT. So everything is OK." Really? Everything is OK? To get a better understanding of the true situation, we need to look at their standardized elapsed times.
QAT standardized elapsed time = 15 seconds X 300 = 4500 secondsPRD standardized elapsed time = 10 seconds X 600 = 6000 seconds 
In this scenario, QAT standard elapsed time is less then the PRD standardized elapsed time. This means the QAT SQL is actually running faster in the QAT, even though the QAT wall time is 15 seconds and the PRD wall time is only 10 seconds. So while most people would flag this QAT SQL as "high risk" we know better! We know the QAT SQL is actually running faster in QAT than in production! In this scenario, the QAT SQL will not be flagged as presenting a significant risk when upgrading from QAT to PRD.
In Summary...
Identify risk is extremely important while planning for an upgrade. It is unlikely the QAT and production system will be identical in every way. This mismatch makes identifying risk more difficult. One of the common differences in systems is their CPU processing speeds. What I demonstrated was a way to remove the CPU speed differences, so an appropriate "apples to apples" SQL elapsed time comparison can be made, thereby improving our ability to more correctly detect risky SQL that may be placed into the upgraded production system.
What's Next?
Looking at the "standardized elapsed time" based on Oracle LIO processing is important, but it's just one reason why a SQL may have a different elapsed time in a different environment. One of the big "gotchas" in load testing is comparing production performance to a QAT environment with a different workload. Creating an equivalent workload on different systems is extremely difficult to do. But with some very cool math and a clear understanding of performance analysis, we can also create a more "apples-to-apples" comparison, just like we have done with CPU speeds. But I'll save that for another posting.

All the best in your Oracle performance work!


Categories: DBA Blogs

Top 7 Reasons Why Oracle Conferences Rock!

Wed, 2014-09-24 10:56
Top 7 Reasons Why Oracle Conferences Rock!
Why take the time and make the effort to attend an Oracle database conference or Oracle user group meeting? We're all busy, so there had better be some super good reasons to make the effort! For me, the benefits definitely exceed the cost.

There are many different conferences to choose from. There are professional conferences, leadership conferences, scientific conferences and business focused conferences. So why an Oracle Database conference? What's the big deal?

This is difficult for me to explain, so I've summarized why I love Oracle conferences into a "Top 7" list.

Number 7. Get free stuff from vendorsI suspect 50% of Oracle DBAs attend conferences because they love getting free stuff. If you want to maximize the good stuff, timing is everything. Get to the booth when the exhibition hall first opens, because vendors have tons of stuff to give away and they are full of energy. Also, just before the exhibition hall closes on the final day show up again. Vendors are tired and want to get rid of as much stuff as possible... and you just happen to be there!

Number 6. Become known in your industryIf you want to focus and excel in your career in a particular area, then pass on what you know. If you hold on to what you learn, no one will know you're an expert but you... and that's lonely. One of the best ways to become known and enjoy conferences is to speak at them. If this is something you want to do, please email me. I'll mentor you. I'm serious.

Number 5. Talk to others, if you want toWant to talk with people who care about Oracle technology as much as you do? Conferences are a great way to break out of your rut and think... and if you want to talk. One of the reasons I like conferences is it gives me a chance to meet with past students.

Number 4. Learn, if you want toThere are always opportunities to learn at conferences. How many times have I heard someone say they were in a lame session. But when I ask if they read the abstract first, they say no. If you want to increase your chances of attending great sessions, read the abstract. Second, look for speakers you like. Third, sit next to the door just in case you need to make a quick exit! The worst you can do is look at the agenda and pick the sessions you want to attend. Do a little research and you'll be surprised how many good sessions there are.

Number 3. Be inspired!How many places can you go to receive inspiration? Not many, is my answer! Because I can chill for a bit at conferences, observe what's going on in our industry and interact with a wide variety of people associated with Oracle technology, I tend to leave with a fresher and more refined view... or better said, "A Wider View." That in itself is worth the cost of any conference.

Number 2. Network with vendors, speakers, colleaguesI take it one step at a time. I always cruise the exhibition halls looking for new products and touching base with the vendors I know. Personally, I like to encourage the new vendors because it is a massive investment for them to exhibit. When I'm cruising, that's where I typically reconnect with students and other DBAs. It's a more comfortable and relaxing environment for me. If you want to speak with an expert face-to-face, a conference is a natural place to do this. If someone walks up to me with an AWR report, I'll make time for them. If they email me the week before, I'll do whatever I can to schedule some time with them.

Number 1. Be with friendsThis one is personal. When I'm teaching or consulting, it's very intense and compressed. But at conferences, I get a chance to unwind, sit back, have a beer, and talk. I'm really involved with the IOUG conference and each year I look forward to reconnecting with this small group of friends. It's such a good feeling to be with "Oracle friends" without having to talk... about Oracle. I can just sit and listen without anyone wondering... What's wrong with Craig? You can do the same thing. Find an Oracle user group and volunteer.

Why Attend? Because Oracle conferences rock!There you have it. Seven reasons why Oracle conferences and Oracle User Groups rock! If you're not planning to attend any, you're missing a great way to connect, advance your career, and have a lot of fun. See you there!!

All the best in your Oracle performance work!


Categories: DBA Blogs

Top 7 Reasons Why Oracle Conferences Are A Waste Of Time

Mon, 2014-09-15 16:38
Top 7 Reasons Why Oracle Conferences Are A Waste Of Time
Want to turn a lame Oracle Database conference experience into a great one? You may not believe this, but I think Oracle conferences are a waste of time. That is, unless I take action. I've been to hundreds of Oracle conferences, so I'm kind of an expert in this field.

Here is my "Top 7" list about why Oracle conferences are time suckers AND how you can turn them into a GREAT educational, social and networking experience.

Number 7. Sleeper Presentations. You forgot to read that session abstract before you sat down? You're not alone! Here my secret: Sit by the door. But when you walk out, remember that the speaker probably
knows how you feel but is doing they best they can. Out of respect for them and the poor souls who are actually enjoying the session, be quiet when you leave.

Number 6. My System Is Bigger Than Your System. How many times have we all heard someone talking about their, "50 node RAC global system with 5 million active users." Really? Is that even possible? Here are four proven options. Option 1 is to ask a question to shut them up. For example, "So how do you deal with the enqueue contention?" Another option is to simply walk away. If you feel that's rude, then Option 3 is to suddenly grab your phone to answer "that" call and walk away...never to return. If you're feeling feisty then combining Option 2 and 3 is wonderful. Ask the question "So how do you deal with upgrading 50 nodes?" AND THEN suddenly grab your phone and walk away.

Number 5. Not Another New Feature Presentation! Oracle Corporation and their marketing minions love to talk about futures. If you're depressed from hearing about new features you won't get to touch for the next five years, here's what to do. First, remember that Oracle Corporation user group sponsorship is important to user group conferences. Without the help from Oracle, most conferences would not occur. Second, the more Oracle sponsors an event, the more they influence the content. The money source always drives the content. The solution is to look at number of presentations given by non-Oracle employees versus Oracle employees... before you register.

Number 4. Can't Afford It Unless Oracle Sales Pays. Yes you can! I know training and traveling budgets have been cut. What you need is a free pass, right? I figured this one out while still working for Oracle. Submit an abstract to speak. If speaking freaks you out, click HERE. If you won't speak, then volunteer. Believe me when I say, EVERY CONFERENCE NEEDS VOLUNTEERS.

Number 3. Boring Conference. I totally get that. Want to know the secret about boring conferences? Avoid them...unless you take action. My conference of choice is Collaborate/IOUG. I love that conference... because I'm really involved, have been for years and look forward to working with the conference team and seeing them each year. It's kind of like family to me.

Number 2. I Feel Like A Dork. Because I speak a lot, people don't realize that much of the time I feel like a social idiot. Strange, but put me on stage or in a mentoring situation and I'm fine. It's taken me 20 years of conferences to figure this one out. Here's what to do: Go with a colleague or volunteer so you'll always have someone to hang out with. If that doesn't work and you're a guy, look for the stupid games because that's where you'll find DBAs just like you (and me).

Number 1. Stupid Drunks. I get so tired of drunk people yelling in my face! Especially when I can feel the spit from their mouths poke me in the eye. It only took a few years to figure this one out. The solution? Step back a couple of feet. And if that doesn't work, then walk away. Don't worry about offending them, because they won't remember you anyways.

Make It A Great Conference!

There you have it, my "Top 7" list about why Oracle conferences are time suckers AND how you can turn them into a GREAT educational, social and networking experience.

See you at IOUG this April in Las Vegas!

All the best in your Oracle performance work,

Categories: DBA Blogs

Watch Oracle DB Elapsed Time and Wall Time With Parallel Query

Sun, 2014-09-07 09:09
Watch Oracle Elapsed Time and Wall Time With Parallel Query
In my recent postings I wrote that when using the Oracle Database parallel query a SQL statement's wall time should be equal to its elapsed time divided by the number of parallel query slaves plus some overhead.

That may seem correct, but is it really true? To check I ran an experiment and posted the results here. The results are both obvious and illuminating.

If you don't want to read but just sit on the couch, have a beer and watch TV you're in luck! I took a clip from my Tuning Oracle Using An AWR Report online video seminar put it on youtube.  You can watch the video clip on YouTube HERE or simply click on the movie below.

The Math, For Review Purposes
In my previous recent postings I detailed the key time parameters; DB Time, DB CPU, non-idle wait time, elapsed time, parallelism and effective parallelism. To save you some clicking, the key parameters and their relationships are shown below.


Elapsed Time = Sum of DB Time

Wall Time = ( Elapsed Time / Parallelism ) + Parallelism Overhead

Wall Time = Elapsed Time / Effective Parallelism

Test Results: When Oracle Parallel Query was NOT involved.
If you want to see my notes, snippets, etc. they can be found in this text file HERE.

Here is the non-parallel SQL statement.

select /*+ FULL(big2) NOPARALLEL (big2) */ count(*)
into   i_var
from   big2 
where  rownum < 9000000

When the SQL statement was running, I was monitoring the session using my Realtime Session Sampler OSM tool, rss.sql. Since I knew the server process session ID and wanted to sample every second and wanted to see everything just for this session, this is the rss.sql syntax:
SQL>@rss.sql 16 16 827 827 % % 1
For details on any OSM tool syntax, run the OSM menu script, osmi.sql. You can download my OSM Toolkit HERE.

The rss.sql tool output is written to a text file, which I was doing a "tail -f" on. Here is a very small snippet of the output. The columns are sample number, sample time, session SID, session serial#, Oracle username, CPU or WAIT, SQL_ID, OraPub wait category, wait event, [p1,p2,p3].

We can see the session is consuming CPU and waiting. When waiting, the wait event is "direct path read", which is asynchronous (we hope) block read requests to the IO subsystem that will NOT be buffered in the Oracle buffer cache.

Now for the timing results, which are shown in the below table. I took five samples.  It's VERY important to know that the wait time (WAIT_TIME_S), DB CPU (DB_CPU_S), and DB Time (DB_TIME_S) values are related to ONLY server process SID 16. In blazing contrast, the wall time (WALL_S), elapsed time (EL_VSQL_S), and SQL statement CPU consumption (CPU_VSQL_S) is related the entire SQL_ID statement execution.

Here are the "no parallel" experimental results.
SQL> select * from op_results;

---------- ---------- ---------- ---------- ----------- ---------- ----------
1 35.480252 35.470015 9.764407 24.97 9.428506 34.152294
2 35.670021 35.659748 9.778554 25.15 9.774984 35.541861
3 35.749926 35.739473 9.774375 25.12 9.31266 34.126285
4 35.868076 35.857752 9.772321 25.32 9.345398 34.273479
5 36.193062 36.18378 9.712962 25.46 9.548465 35.499693
Let's check the math. For simplicity and clarity, please allow me to round and use only sample 5.
35.5 = 9.5 + 25.5 = 35.0
The DB Time is pretty close (35.5 vs 35.0). Close enough to demonstrate the time statistic relationships.
Elapsed Time (EL_VSQL_S) = DB_TIME_S
35.5 = 34.2
The Elapsed Time is off by around 4% (35.5 vs 34.2), but still closely to demonstrate the time statistic relationships.
Wall Time (WALL_S) = Elapsed Time (EL_VSQL_S) / Effective Parallelism
35.5 = 35.5 / 1
Nice! The Wall Time results matched perfectly. (35.5 vs 35.5)

To summarize in a non parallel query (i.e., single server process) situation, the time math results are what we expected! (and hoped for)

Test Results: When Oracle Parallel Query WAS involved.
The only difference in the "non parallel" SQL statement above and the SQL statement below is the parallel hint. Below is the "parallel" SQL statement.
select /*+  FULL(big2) PARALLEL(big2,3)  */ count(*) into i_var from big2 where rownum<9000000>
When the "parallel" SQL statement was running, because Oracle parallel query was involved resulting in multiple related Oracle sessions, when monitoring using my rss.sql tool, I need to open the session ID (and serial#) to include all sessions. I still sampled every second. Here is the rss.sql syntax:
SQL>@rss.sql 0 9999 0 9999 % % 1
The tool output is written to a text file, which I was doing a "tail -f" on. Here is a very small snippet of the output. I manually inserted the blank lines to make it easier to see the different sample periods.

There is only one SQL statement being run on this idle test system. And because there is no DML involved, we don't see much background process activity. If you look closely above, sessions 168 (see third column) must be a log write process because the wait event is "log file parallel write". I checked and session 6 is a background process as well.

It's no surprise to typically see only four session involved. One session is the parallel query coordinator and the three parallel query slaves! Interestingly, the main server process session that I executed the query from is session number 16. It never showed up in any of my samples! I suspect it was "waiting" on an idle wait event and I'm only showing processes consuming CPU or waiting on a non-idle wait event. Very cool.

Now for the timing results. I took five samples.  Again, it's VERY important to know that the wait time (WAIT_TIME_S), DB CPU (DB_CPU_S), and DB Time (DB_TIME_S) values are related to ONLY calling server process, which in this case is session 16. In blazing contrast, the wall time (WALL_S), elapsed time (EL_VSQL_S), and SQL statement CPU consumption (CPU_VSQL_S) is related the entire SQL statement execution.

Here are the "parallel" experimental results.
 SQL>  select * from op_results;

---------- ---------- ---------- ---------- ----------- ---------- ----------
1 46.305951 132.174453 19.53818 .01 4.069579 4.664083
2 46.982111 132.797536 19.371063 .02 3.809439 4.959602
3 47.79761 134.338069 19.739735 .02 4.170921 4.555491
4 45.97324 131.809249 19.397557 .01 3.790226 4.159572
5 46.053922 131.765983 19.754143 .01 4.062703 4.461175
Let's check the math. So simplicity and clarity, please allow me to round and use sample 5.
4.5 = 4.1 + 0
The DB Time shown above is kind of close... 10% off. (4.5 vs 4.1) But there is for sure timing error in my collection sript. I take the position, this is close enough to demonstrate the time statistic relationships. Now look below.
Elapsed Time (EL_VSQL_S)  = DB_TIME_S
131.7 != 4.5
Woah! What happened here? (131.7 vs 4.5) Actually, everything is OK (so far aways) because the DB Time is related to the session (Session ID 16), whereas the elapsed time is ALL the DB Time for ALL the processes involved in the SQL statement. Since parallel query is involved, resulting in four additional sessions (1 coordinator, 3 slaves) we would expect the elapsed time to be greater than the DB Time. Now let's look at the wall time.
Wall Time (WALL_S) = ( Elapsed Time (EL_VSQL_S) / Parallelism ) + overhead
46.1 = ( 131.8 / 3 ) + 2.2
Nice! Clearly the effective parallelism is greater than 3 because there is some overhead (2.2). But the numbers makes sense because:

1. The wall time is less than the elapsed time because parallel query is involved.

2. The wall time is close to the elapsed time divided by the parallelism. And we can even see the parallelism overhead.

So it looks like our time math is correct!

Reality And The AWR Or Statspack Report
This is really important. In the SQL Statement section of any AWR or Statspack Report, you will see the total elapsed time over the snapshot interval and perhaps the average SQL ID elapsed time per execution. So what is the wall time? What are users experiencing? The short answer is, we do NOT have enough information.

To know the wall time, we need to know the parallelism situation. If you are NOT using parallel query, than based on the time math demonstrated above, the elapsed time per execution will be close to what the user experiencing (unless there is an issue outside of Oracle). However, if parallelism is involved, you can expect the wall time (i.e, user's experience) to be much less than the elapsed time per execution shown in the AWR or Statspack report.

Another way of looking at this is: If a user is reporting a query is taking 10 seconds, but the average elapsed time is showing as as 60 seconds, parallel query is probably involved. Also, as I mentioned above, never forget the average value is not always the typical value. (More? Check out my video seminar entitled, Using Skewed Data To Your Advantage HERE.)

Thanks for reading!

Categories: DBA Blogs

What Is Oracle Elapsed Time And Wall Time With A Parallelism Twist

Mon, 2014-08-18 09:14

What Is Oracle Elapsed Time And Wall Time With A Parallelism Twist
In this post I'm focusing on Oracle Database SQL elapsed time, adding parallelism into the mix and then revisiting wall time. What initially seems simple can take some very interesting twists!

If you are into tuning Oracle Database systems, you care about time. And if you care about time, then you need to understand the most important time parameters: what they are, their differences, how they relate to each other and how to use them in your performance tuning work.

A couple weeks ago I wrote about Oracle DB Time, non-idle wait time, and server process CPU consumption (DB CPU) time. If you have not read that posting, HERE is the link. It must be a good read because it quickly become my most viewed post ever! In this posting, the focus is SQL elapsed time, parallelism, and again wall time. Enjoy!

Quick Review
In my previous related post, I covered non-idle wait time, DB CPU, and DB Time. Here is a very quick summary of each.

Non-Idle Wait Time occurs when an Oracle process is not consuming CPU, the session pauses (i.e., waits) and Oracle considers the wait time important for performance tuning. An example of a non-idle wait event is direct path read temp. An example of an idle wait event is SQL*Net message from client or pmon timer.

DB CPU is Oracle server/foreground/shadow process CPU consumption. This is not include Oracle background process CPU consumption.

DB Time is DB CPU plus Non-Idle Wait Time. Remember that DB Time does not include background process CPU consumption and Oracle Corporation determines which wait events are considered idle.

Elapsed Time
Elapsed Time (ET) is all DB Time related to a defined task. A "defined task" could be a SQL statement, group of SQL statements, pl/sql procedure, batch job, etc. It is whatever makes sense in your tuning situation.

The elapsed time for a SQL_ID can be found in v$sql. But be careful because this elapsed time is related to "all" the SQL_ID executions. Thankfully, there is an "executions" column in v$sql.

Elapsed time is displayed in a number of areas within an Oracle Database AWR and Statspack report. Looking at the above screen shot, the "top" elapsed time SQL has an elapsed time of 268561 seconds. This means that over the AWR report's snapshot interval, for all this SQL's executions, its total DB Time is 268561 seconds. Said another way, if we were to add up all this SQL's DB CPU and non-idle wait time for all its executions within the snapshot interval, the value should be 268561.

There is a lot of great information provided in the AWR and Statspack SQL reports. For example, because the elapsed time and the CPU time (DB CPU) is shown above, we can calculate the non-idle wait time for the "top" elapsed time SQL ID.

non idle wait time = elapsed time - cpu time
268465 = 268561 - 96

For the "top" elapsed SQL, its elapsed time 268561 and it's DB CPU is 96 therefore its non-idle wait time is 268465. Wow! This statement has tons of associated wait time compared to CPU consumption time.

But it gets even better! Because the total Elapsed Time and the total number Executions over the snapshot interval is displayed, we can determine the average elapsed time!

average elapsed time = total elapsed time / executions
746.03 = 268561 / 36

Do not be deceived! The average elapsed time is unlikely what the user is experiencing. Two possibility examples for this deception are skewed elapsed times and parallelism.

For most DBAs this is unexpected. It also causes performance perception problems yet solutions are available to understand what's really going on.

I've spent so much time researching this topic and seen it increase my consulting value, I've posted a number of blog entries on this subject. Plus I created an OraPub Online Institute seminar focused specifically on this subject. It's called Using Skewed Performance Data To Your Advantage. Check it out. I'm really proud how it turned out. I also have a couple of OSM scripts dedicated to this topic, sqlelget[11].sql.

Revisiting Wall Time With A Parallelism Twist
Now it's time to put this all together.

DB CPU is the Oracle server process CPU consumption.

Non-Idle Wait Time (NIWT) is the time when an Oracle process can not consume CPU and must pause and we care about this time.

DB Time is the Oracle server process CPU consumption and all non-idle wait time.

Elapsed Time (ET) is the sum (i.e., all) DB Time related to a task, such as a SQL_ID.

Wall Time is what we hope the user experiences. I'll assume there is no time gap between Oracle and the user, therefore the wall time will equal the user's experience.

Effective Parallelism is the effective number of Oracle parallel slaves or some other form of parallelism, such as designed-in application parallelism. (For simplicity, I'm only going to mention Oracle parallel query.) If Oracle parallel query is not involved, then the effective parallelism is one. If two parallel query slaves are involved, then the effective parallelism will be a little less than 2

Parallelism can reduce wall time because we can simultaneously "burn time" in multiple places. For example, 60 seconds of elapsed time with a process running serially, results in a wall time of 60 seconds. But if we have two parallel query slaves, while the elapsed time (i.e., all the DB Time) is still 60 seconds (plus some overhead time), the wall time will be around 30 seconds (plus some overhead time).

The math is really simple...that is until you factor in scalability (i.e., the overhead), which I won't. If you're interested, read the last chapter of my book, Forecasting Oracle Performance.

Let's simplify this by using some mathematical notation.


Elapsed Time = Sum of DB Time

Wall Time = Elapsed Time / Effective Parallelism

Pretty straightforward, eh? Below is a short video clip summarizing the key time parameters taken from the OraPub Online Institute seminar, Tuning Oracle Using an AWR Report - Part 2. If you can't see the video, click HERE watch it on YouTube.

Test You Knowledge
True or False? If the total elapsed time is 60 seconds and parallel query is not involved, the total wall time will also be 60 seconds. True

True or False? If the elapsed time per execution is 60 seconds and the wall time is 30 seconds, then parallel query is involved. True

True or False? Bonus question yet very important to understand: If the elapsed time per execution is 60 seconds and two PQ slaves are involved, then the wall time will be 30 seconds.

The last question is false because there is overhead when parallelizing. Parallelism is not free. Because of this, the wall time will hopefully drop to perhaps 35 seconds. That 5 seconds is the parallelization overhead.

Coming Up Next: Video Proof!
While the above may seem correct, I ran some SQL statements and captured the relevant time statistics. There is quite a bit of detail and I ran two different tests, so I'll post that in a week or two.

Thanks for reading,

Categories: DBA Blogs

Watch Oracle DB Session Activity With The Real-Time Session Sampler

Mon, 2014-08-11 16:38
Watch Oracle DB Session Activity With My Real-Time Session Sampler
Watching session activity is a great way to diagnose and learn about Oracle Database tuning. There are many approaches to this. I wanted something simple, useful, modifiable, no Oracle licensing
issues and that I could give away. The result is what I call the Oracle Real-Time Session Sampler (OSM: rss.sql).

The tool is simple to use.  Based on a number filtering command line inputs, it repeatedly samples active Oracle sessions and writes the output to a file in /tmp. You can do a "tail -f" on the file to watch session activity in real time!

The rss.sql tool is included in the OraPub System Monitor (OSM) toolkit (v13j), which can be downloaded HERE.

If you simply want to watch a video demo, watch below or click HERE.

The Back-Story
Over the past two months I have been creating my next OraPub Online Institute seminar about how to tune Oracle with an AWR/Statspack report using a quantitative time based approach. Yeah... I know the title is long. Technically I could have used Oracle's Active Session History view (v$active_session_history) but I didn't want anyone to worry about ASH licensing issues. And ASH is not available with Oracle Standard Edition.

The Real-Time Session Sampler is used in a few places in the online seminar where I teach about Oracle session CPU consumption and wait time. I needed something visual that would obviously convey the point I wanted to make. The Real-Time Session Sampler worked perfectly for this.

What It Does
Based on a number of command line inputs, rss.sql repeatedly samples active Oracle sessions and writes the output to file in /tmp. The script contains no dml statements. You can do a "tail -f" on the output file to see session activity in real time. You can look at all sessions, a single session, sessions that are consuming CPU or waiting or both, etc. You can even change the sample rate. For example, once every 5.0 seconds or once every 0.25 seconds! It's very flexible and it's fascinating to watch.

Here is an example of some real output.

How To Use RSS.SQL
The tool is run within SQL*Plus and the output is written to the file /tmp/rss_sql.txt. You need two windows: one to sample the sessions and other other to look at the output file. Here are the script parameter options:

rss.sql  low_sid  high_sid  low_serial  high_serial  session_state  wait_event_partial|%  sample_delay

low_sid is the low Oracle session id.
high_sid is the high Oracle session id.
low_serial is the low Oracle session's serial number.
high_serial is the high Oracle session's serial number.
session_state is the current state of the session at the moment of sampling: "cpu", "wait" or for both "%".
wait_event_partial is when the session is waiting, select the session only with this wait event. Always set this to "%" unless you want to tighten the filtering.
sample_delay is the delay between samples, in seconds.

Examples You May Want To Try
By looking at the below examples, you'll quickly grasp that this tool can be used in a variety of situations.

Situation: I want to sample a single session (sid:10 serial:50) once every five seconds.

SQL>@rss.sql  10 10 50 50 % % 5.0

Situation: I want to essentially stream a single session's (sid:10 serial:50) activity.

SQL>@rss.sql 10 10 50 50 % % 0.125

Situation: I want to see what sessions are waiting for an row level lock while sampling once every second.

SQL>@rss.sql 0 99999 0 99999 wait enq%tx%row% 1.0

Situation: I want to see which sessions are consuming CPU, while sampling once every half second.

SQL>@rss.sql 0 99999 0 99999 cpu % 0.50

Be Responsible... It's Not OraPub's Fault!
Have fun and explore...but watch out! Any time you are sample repeatedly, you run the risk of impacting the system under observation. You can reduce this risk by sampling less often (perhaps once every 5 seconds), by limiting the sessions you want to sample (not 0 to 99999) and by only select sessions in either a "cpu" or "wait" state.

A smart lower impact strategy would be to initially keep a broader selection criteria but sample less often; perhaps once every 15 seconds. Once you know what you want to look for, tighten the selection criteria and sample more frequently. If you have identified a specific session of interest, then you stream the activity (if appropriate) every half second or perhaps every quarter second.

All the best in your Oracle Database tuning work,

Categories: DBA Blogs

What Is Oracle DB Time, DB CPU, Wall Time and Non-Idle Wait Time

Tue, 2014-08-05 05:30
What Is Oracle DB Time, DB CPU, Wall Time and Non-Idle Wait Time
If you are into tuning Oracle Database systems, you care about time. And if you care about time, then you need to understand the most important time parameters: what they are, their differences, how they relate to each other and how to use them in your performance tuning work.

The key Oracle Database time parameters are elapsed time, database time (DB Time), non-idle wait time and server process CPU consumption (DB CPU) time.

This first post is pretty basic, yet core fundamental stuff. So in the following two posts I'll introduce elapsed time, add parallelism into the mix and revisit wall time. What initially seems simple can some take very interesting twists!

You probably know that I am all about quantitative Oracle performance analysis. I research, write, teach, and speak about it. I even have an OraPub Online Institute seminar about how to tune your Oracle Database systems from a standard AWR or Statspack report using an Oracle Time Based Analysis (OTBA) framework.

So let's get started!

Wall Time & Run Time
I'll start with Wall Time because that is close (hopefully) to what a user experiences. In fact, if there is no time gap between the Oracle Database and the user, then we can do a little math and figure out what the users are, on average, experiencing. I'll get back to wall time in the next post, where I include elapsed time and parallelism into the equation.

DB CPU is Oracle server/foreground/shadow process CPU consumption. Each Oracle server process gathers its own CPU consumption using the time and/or getrusage C function system call. So unless there is a major screw-up by either the operating system or the Oracle kernel developers, the time will be good... very good. The name DB CPU is taken from the actual statistic name, which is found in both v$sess_time_model and v$sys_time_model.

If you look at any AWR or Statspack report in the "Time Model" section, you will see DB CPU. The value shown will be all server process CPU consumption within the reporting snapshot interval, converted to seconds. (The raw statistic is stored in microseconds.)

Below is an example Time Model Statistics screen shot from a standard AWR report. I've highlighted DB CPU.

If you run one of my OraPub System Monitor (OSM) time related tools like ttpctx.sql or rtpctx.sql you see a CPU time statistic. That contains both the DB CPU (i.e., server process) and "background process cpu" statistics. Here's an example.

SQL> @ttpctx.sql
Remember: This report must be run twice so both the initial and
final values are available. If no output, press ENTER about 11 times.

Database: prod35 31-JUL-14 12:09pm
Report: ttpctx.sql OSM by OraPub, Inc. Page 1
Total Time Activity (142 sec interval)

Avg Time Time Wait
Time Component % TT % WT Waited (ms) (sec) Count(k)
------------------------------------- ------- ------- ----------- ----------- --------
CPU consumption: Oracle SP + BG procs 95.95 0.00 0.000 347.212 0
PX Deq: Slave Session Stats 1.45 35.74 0.113 5.240 47
library cache: mutex X 0.58 14.26 0.136 2.090 15
PX Deq: Slave Join Frag 0.43 10.57 0.067 1.550 23
PX Deq: Signal ACK EXT 0.29 7.16 0.045 1.050 23
control file parallel write 0.28 7.03 20.600 1.030 0
PX qref latch 0.27 6.75 0.012 0.990 85
latch free 0.20 4.91 0.090 0.720 8
log file parallel write 0.16 4.02 12.826 0.590 0

Non-Idle Wait Time
When an Oracle process can not consume CPU, it will pause. As an Oracle DBA, we know this as wait time. Sometimes a process waits and it's not a performance problem, so we call this Idle Wait Time. Oracle background processes typically have lots of idle wait time. However, when a user is waiting for sometime to complete and way down deep their Oracle server process is waiting to get perhaps a lock or latch, this is Non-Idle Wait Time. Obviously, when tuning Oracle we care a lot about non-idle wait time.

Below is a simple query showing wait event classifications. In this system there are 119 Idle wait events, so all the rest would be classified as non-idle wait events.

Oracle uses a variety of methods to determine wait time. I have a number of postings and educational content available about this. You'll see them if you do an OraPub or blog search for "time".

When working with non-idle wait time, remember the 80/20 rule. Most of the wait time we care about will be contained with in the largest ("top") two to four wait events. Don't waste YOUR time focusing on the 20%.

Here's an example. In the screen shot below, while not shown the total wait time is 1966 seconds.
If you add up the displayed "top" four wait events, their combined wait time is 1857. This is about 95% of all the non-idle wait time. This is a good example demonstrating that most of the wait time is found in the top two to four events.

My OSM toolkit has many wait time related tools. Most start with "sw" for "session wait" but the both ttpctx.sql or rtpctx.sql will contain the non-idle wait time and also CPU consumption. This is a good time to transition into DB Time.

DB Time
DB Time is a time model statistic that is the sum of Oracle process CPU consumption and non-idle wait time. When optimizing Oracle systems we typically focus on reducing "time", though many times database work is also part of the equation. This "time" is essentially DB Time, though sometimes I take control over what I consider idle wait time.

The name DB Time comes from the actual statistic name in both v$sess_time_model and v$sys_time_model.

If you look at any AWR or Statspack report in the "Time Model" section, you will see DB Time.
The DB time value is technically all server process CPU consumption plus the non-idle wait time within the reporting snapshot interval, converted to seconds. (The raw statistic is stored in microseconds.) Surprisingly, Oracle does not include "background cpu time" in the DB Time statistic. There are both good and not so good reasons the background CPU time is not include, but that's a topic for another posting.

A Little Math
We have enough detail to relate DB Time, DB CPU and non-idle wait time together... using a little math.

DB Time = DB CPU + non_idle_wait_time

And of course,

non_idle_wait_time = DB Time - DB CPU

This is important, because there is no single statistic that shows all the non-idle wait time. This must be derived. Shown above is one way to derive the non-idle wait time. Take a look at the AWR report snippet below.

In the Non-Idle Wait Time section above, I stated that the total non-idle wait time was 1966 seconds. I derived this from the Time Model screen shown above. I simply did:

non_idle_wait_time = DB Time - DB CPU
1966.16 = 4032.03 - 2065.87

Coming Up Next
I wanted to keep this post short, which means I left out the more interesting topics. So in the next post I'll merge into the picture elapsed time along with parallelism and revisit wall time. Then in the third post (that's my guess at this point), I'll actually demonstrate this in two different systems.

Thanks for reading,

Categories: DBA Blogs

Four Options For Oracle DBA Tuning Training

Mon, 2014-07-28 09:00
Four Options For Oracle DBA Tuning Training
Oracle DBAs are constantly solving problems... mysteries. That requires a constant knowledge increase. I received more personal emails from my Oracle DBA Training Options Are Changing posting than ever before. Many of these were from frustrated, angry, and "stuck" DBAs. But in some way, almost all asked the question, "What should I do?"

In response to the "What should I do?" question, I came up with four types of Oracle DBA performance tuning training that are available today. Here they are:

Instructor Led Training (ILT) 
Instructor Led Training (ILT) is the best because you have a personal connection with the teacher. I can't speak for other companies, but I strive to connect with every student and every student knows they can personally email or call me...even years after the training. In fact, I practically beg them to do what we do in class on their production systems and send me the results so I can continue helping them. To me being a great teacher is more than being a great communicator. It's about connection. ILT makes connecting with students easy.

Content Aggregators
Content Aggregators are the folks who pull together free content from various sources, organize and display it. Oh yeah... and they profit from it. Sometimes the content value is high, sometimes not. I tend to think of content aggregators like patent trolls, yet many times they can be a great resource. The problem is you're not dealing with the creator of the content. However, the creator of the content actually knows the subject matter. You can somtimes contact I encourage my students and readers to do.

Content Creators
Content Creators are the folks who create content based on their experiences. We receive that content through their blogs, videos, conference presentations and sometimes through their training. I am a content creator but with an original, almost child-like curiosity, performance research twist. Content creators rarely directly profit from their posted content, but somehow try to transform it into a revenue stream. I can personally attest, it can be a risky financial strategy...but it's personally very rewarding. Since I love do research, it's easy and enjoyable to post my findings so others may benefit.

Online Training (OLT)
Online Training (OLT) is something I have put off for years. The online Oracle training I have seen is mostly complete and total crap. The content is usually technically low and mechanical. The production quality is something a six year old can do on their PC. The teaching quality is ridiculous and the experience puts you to sleep. I do not ever want to be associated with that kind of crowd.

I was determined to do something different. It had to be the highest quality. I have invested thousands of dollars in time, labor, and equipment to make online video training
Craig teaching in an OraPub Online Institute Seminarwork. Based on the encouraging feedback I receive it's working!

This totally caught me by surprise. I have discovered that I can do things through special effects and a highly organized delivery that is impossible to do in a classroom. (Just watch my seminar introductions on YouTube and you'll quickly see what I mean.) This makes the content rich and highly compressed. One hour of OraPub Online Institute training is easily equivalent to two to four hours of classroom training. Easily. I have also strive to keep the price super low, the production at a professional level and ensure the video can be streamed anywhere in the world and on any device. Online training is an option, but you have to search for it.

So there you have it. Because of economics and the devaluation of DBAs as human beings coupled with new technologies, the Oracle DBA still has at least four main sources of training and knowledge expansion. Don't give up learning!

Some of you reading may be surprised that I'm writing about this topic because it will hurt my traditional instructor led training (public or on-site) classes. I don't think so. If people can attend my classes in person, they will. Otherwise, I hope they will register for an OraPub Online Institute seminar. Or, at least subscribe to my blog (see upper left of page).

All the best in your quest to do great work,

Categories: DBA Blogs

Oracle DBA Training Options Are Changing

Tue, 2014-07-15 07:43
Oracle DBA Training Options Are Changing
Training options for Oracle Database DBAs are changing. Generally, I don't think they are for the better. Companies don't value Oracle Database Administrators like they used to. And, it shows in the lack of their professional development investment.

When I travel a long way from home, I tend to get very reflective about life, death and beyond. On my way home from teaching an onsite two-day Oracle performance tuning seminar coupled with a one-day predictive analysis (forecasting) class in Ghana (yes, Ghana as in AFRICA) I started thinking about how fortunate the Ghana DBAs I taught are. Clearly their management is willing to invest in their DBAs' future. This is very, very rare.

Today most Oracle DBAs receive what I call, "Training By Google." You know, blog posts, YouTube videos and various syntax websites. While these are all valuable (I am a content creator myself with my blog posts and videos), they are no substitute for instructor led training. Not even close! So what is happening that is forcing Oracle DBAs to change their training habits?

So Why The Change? Three Reasons
1. Training Budget. Over the past five years I have been disappointed (more like disturbed) that most companies do not provide the training DBAs need. They just won't do it. IT managers (not typically DBA managers) believe their staff can get by with "Training By Google." It's stupid and foolish. It tells DBAs they are worthless and leaves them unprepared to perform at their best. And, of course, that ends up hurting the company they work for. Stupid and foolish.

Are we then surprised with the results from poor performing systems, down production systems, massive security breaches, and DBAs hopping from one company to another?

2. Travel Budget. A nasty tactic many companies use is to provide a minimal training budget but without a travel budget. If you want specialized and advanced training, you'll probably have to travel to get to it. Maybe not hundreds or thousands of miles, but probably more than you want to commute each day.

Essentially the company is splitting the training cost with the DBA and ensuring the DBA really, really wants the training. OK, I can respect that. But, I think a company that does not truly provide training for its employees (human beings that spend a significant portion of their lives doing whatever it takes to get the job done) is cruel and frankly immoral.

3. More Training Options. The good news for Oracle DBAs is there is more information and training options available today than ever before. When the website began in 1995, doing a "tail -f" on the web log was a lesson in world geography. It was amazing watching line after line stream by as DBAs from all over the world were looking for Oracle performance materials through the web. Now there is much more available. Training options for Oracle DBAs now include traditional instructor led training (ILT), web sites from content aggregators (people who pull together content for us), content creators (like myself), and online training. I'm very excited about online training and have made a significant investment in OraPub's Online Institute.

So there you have it. Because of economics, the devaluation of DBAs as human beings and the increase in training options, the Oracle DBA training landscape is changing. If you believe this, the next question is, "What is good content?" That will be the subject of my next posting!

Enjoy your work and thanks for reading!

Categories: DBA Blogs