It’s not about ego … it’s about knowledge

Take a quick look at this blog post by Jonathan Lewis

Anyone that has been working with Oracle for any length of time probably knows that Jonathan has a great depth of knowledge in the Oracle database, and is a regular blogger.  But this post is a good example to inspire anyone that is working with Oracle (or any technology for that matter) to start blogging and sharing their experiences with the community, no matter what their level of experience is.

If you read the post, you’ll see that Jonathan presented a well-crafted test case, and presented a hypothesis about NVARCHAR2 and potential side effects of adding columns of this data type to an existing table.

Turns out the hypothesis was wrong, and the observations were unrelated to NVARCHAR2 at all.  A comment from a reader pointed out the true cause of the side effect.

But here’s the important thing.

Has the blog post been deleted ? No

Has the comment been deleted ? No.

Publishing information for the community to digest is not (as we say in Australia) a pissing contest ( to show who is the smartest or the fastest or the cleverest.  It is about collectively growing the knowledge base of one’s self and the community.

So don’t be afraid to publish your experiences so that all may benefit.  If your findings or claims are incorrect, then good people in the community will correct you gently and professionally.  And those not-so-good people that choose to point out errors in a condescending or derogatory tone…well….they’ll be doing a lot more damage to their online reputations than they could ever possibly do to yours.

Happy New Year!

2017–what grabbed your attention

Here are the blog posts that you hit on most this year.  Thanks for supporting the blog, and always, there will be more content next year !

Buffer cache hit ratio–blast from the past

I was perusing some old content during a hard drive “spring clean” the other day, and I found an old gem from way back in 2001.  A time when the database community were trying to dispel the myth that all database performance issues could be tracked back to,  and solved via, the database buffer cache hit ratio.  Thankfully, much of that folklore has now passed into the realm of fiction, but I remember at the time, as a means of showing how silly some of the claims were, I published a routine that would generate any buffer cache hit ratio you desired.  It just simply ran a query to burn through logical I/O’s (and burn a whole in your CPU!) until the required number of operations bumped up the buffer cache hit ratio to whatever number you liked Smile 

Less performance, more work done…. all to get a nice summary number.

The kinds of statistics that the database collects, and what each one represents has changed over the years and versions of Oracle, but I figured I’d present the routine in original form as a nostalgic reminder that statistics without an understanding behind them are as good as no statistics at all.

Enjoy !

create or replace
procedure choose_a_hit_ratio(p_ratio number default 99,p_show_only boolean default false) is
  v_phy                number;
  v_db                 number;
  v_con                number;
  v_count              number;
  v_additional_congets number;
  v_hit number;
  procedure show_hit is
    select p.value, d.value, c.value
    into v_phy, v_db, v_con
      ( select value from v$sysstat where name = 'physical reads' ) p,
      ( select value from v$sysstat where name = 'db block gets' ) d,
      ( select value from v$sysstat where name = 'consistent gets' ) c;
    v_hit := 1-(v_phy/(v_db+v_con));
    dbms_output.put_line('Current ratio is: '||round(v_hit*100,5));
-- First we work out the ratio in the normal fashion

  if p_ratio/100 < v_hit or p_ratio > 99.9999999 then
    dbms_output.put_line('Sorry - I cannot help you');
  end if;
-- Flipping the formula we can work out how many more consistent gets
-- we need to increase the hit ratio
  v_additional_congets := trunc(v_phy/(1-p_ratio/100)-v_db - v_con);

  dbms_output.put_line('Another '||v_additional_congets||' consistent gets needed...');

  if p_show_only then return; end if;
-- Create a simple table to hold 200 rows in a single block
    execute immediate 'drop table dummy';
    when others then null;

  execute immediate 'create table dummy (n primary key) organization index as '||
                    'select rownum n from all_objects where rownum <= 200';
-- Turn off any new 9i connect-by features to ensure we still do lots of 
-- logical IO
    execute immediate 'alter session set "_old_connect_by_enabled" = true';
    when others then null;
-- Grind away until we do all those additional gets
  execute immediate '
    select count(*) 
    from (
      select n
      from dummy
      connect by n > prior n
      start with n = 1 )
    where rownum < :v_additional_congets' into v_count using v_additional_congets;


And some output to keep the hit ratio fanatics happy!

SQL> exec choose_a_hit_ratio(85,true);
Current ratio is: 82.30833
Another 29385 consistent gets needed...

PL/SQL procedure successfully completed.

SQL> exec choose_a_hit_ratio(85);
Current ratio is: 82.30833
Another 29385 consistent gets needed...
Current ratio is: 86.24548

PL/SQL procedure successfully completed.

SQL> exec choose_a_hit_ratio(90,true);
Current ratio is: 86.24731
Another 79053 consistent gets needed...

PL/SQL procedure successfully completed.

SQL> exec choose_a_hit_ratio(90);
Current ratio is: 86.24731
Another 79053 consistent gets needed...
Current ratio is: 90.5702

PL/SQL procedure successfully completed.

SQL> exec choose_a_hit_ratio(98,true);
Current ratio is: 90.5709
Another 1141299 consistent gets needed...

PL/SQL procedure successfully completed.

SQL> exec choose_a_hit_ratio(98);
Current ratio is: 90.5709
Another 1141299 consistent gets needed...
Current ratio is: 98.02386

PL/SQL procedure successfully completed.

Why being wrong can be awesome

OK, Now that I’ve started the post with a nice click-bait heading, let’s get down to the business of being wrong. Smile

I did a lot of conference presentations last year, and the great thing about that for me was that I got to meet a lot of new people in the Oracle community in the Developer and DBA space. One of the questions that came up over and over again was about putting one’s knowledge “out there” in the community and how to deal with the repercussions of that.  In particular, “What if you publish something that is proven wrong?”

Here’s the thing about being wrong …. there’s two likely outcomes:

  • Someone tells you that you are wrong, or
  • You never know that you’re wrong and you wallow about in flawed darkness for all eternity.

Which would you prefer ? Smile

This is really all about perception from both the blogger and the reader, and the way they behave.

If you are the reader and you find something that is incorrect, you have choices:

  • Absolutely go ballistic on the author via comments, insult their intelligence, tell them how much smarter than them you are, and that they should never have been born, or
  • Initiate a reasoned discussion about where the errors might be, how the author may have come to that point, discuss boundary conditions and both leave the discussion more knowledgeable as a result.

Rest assured, if you take the former position, no amount of smarts is going outweigh the public reputation you’ve just acquired as being a schmuck.

And similarly, as an author of content, when someone points out an error you can:

  • take it in good faith, and work toward improving your knowledge by investigating further and collaborating with the person who discovered it, or
  • just deny it, and lose your mind at them and denigrate them so that you don’t lose your fine public standing.

If you do the latter….guess what you just lost?  Yup, your fine public standing.

And here’s the thing. Even if the person pointing out the error is indeed lacking the basic skills of civility, and is demonstrating their “schmucky-ness” all over your blog, just put that aside and focus on improving the content.  Other readers will pick up on this, and they’ll value your contribution to the community much more than Joe Schmuck.  They’ll be “red flagged” in the minds of the community as “one of those members that just isn’t worth the time of day”.

And if you’re wondering what the motivation for this post is – just this morning on an AskTOM answer, one of the Product Managers inside Oracle reached out to me and said “Hey Connor – I don’t think that answer is completely correct” and gave some me some additional content about the cause, and how to improve the answer.  The net result of that:

  • I learn some new stuff!
  • The community gets better content from AskTOM!
  • I make a new contact within the Oracle organization!

So don’t ever let being wrong stop you from contributing to the community.  It’s the best way of improving yourself and the community as well.

The devastating death PC emoji of doom

So there I am.  Sitting at Perth airport.  My flight from Perth to Sydney, the first leg on my trip to OpenWorld 2017 is delayed.  Of course, delays are not unusual and do not normally bother me.  Because I can just flip open my laptop, knock off a few AskTOM questions while I wait.

But not this time.  I press the Power button and I get this:

Image result for windows 10 collectin memory dump

That is the first time I’ve ever seen that on my nice Dell XPS 13 laptop, but I figure “No big drama.  Probably just some sleep glitch” and let the machine reboot.

That is when the real fun started.  As it is restarting I get a similar screen (which I can’t screen dump…because the laptop isn’t booting!) saying the machine cannot boot.

Now I’m starting to be concerned.  Because I’m a few days out from 6 conference talks at the biggest Oracle conference of the year.  The laptop then goes into a “Cannot boot, so we’ll reboot” cycle which I don’t seem to be able to escape from, and then boarding call comes out over the public address system at the airport.


So I have to do a forced power off on the laptop, jump on the plane…and now sit there in a cold sweat for 5 hours while I fly to Sydney (because I’m now too scared to tackle this issue without a power supply).

I arrive in Sydney and renew the battle.  I power it up, and the laptop says “I cannot boot”, but this time says … “Would I like to repair the startup?”.  Why it has changed I have no idea, but I give it a shot.  After a lot of progress bars, and messages about how long this might take, the laptop finally displays the normal login screen.

Phew !!!!!!!!!

But all is not totally right.  If I sleep or shutdown the laptop, then on boot up, the first message I get is a sad emoji BSOD like the one above, after which it reboots again and then appears fine.

So … here I am, at the hotel with a working laptop… and zero confidence in it.  Grrrrrr.

Not the best start to the week 😦

The village idiot

If you are not familiar with the term Village Idiot, then Wikipedia provides a sufficient definition from which I can base this blog post.

“The village idiot … is a person known for ignorance or stupidity”

Over the past couple of weeks I’ve been flying a bit.  First was OpenWorld and OracleCode in New Delhi in India, and from there, I was heading straight from there to Cleveland, Ohio for the GLOC users conference for the first time.  Being a fairly seasoned traveller, this should have been a relatively straightforward affair.

Well… things didn’t turn out that way. 

To get to Cleveland, first I had to get to the United States, so I had two flights, as you can see from the picture  – one from New Delhi to a transfer in Shanghai, and then from Shanghai to San Francisco. 




The problems started due to the simplest of issues.  The night before I was due to fly, I picked up my itinerary, saw “11:40pm” and thought “Cool…I can sleep in tomorrow, do some AskTOM, get some work done, and stroll out to the airport after the evening traffic has subsided”.  And I did precisely that.  I got to the airport at about 9pm, paid my driver, collected my suitcase and headed over to the airport entrance.

For those of you that have not been the India, the airports work a little differently.  You cannot actually enter the airport unless you have a valid ticket.  I assume this is both for security reasons and due simply to the volume of people that pass through the doors.  At the entrance, security personnel check your passport and ticket and let you in.  I produced my details and after a short pause, the officer looked at me and said:

“You cannot come in”

I asked why ?  I had given him my passport and all my flight details. 

He said “Your ticket is no longer valid”

And that’s when it hit me….The boarding time for both of my flights was 11:40… But for the first flight, it was 11:40am, and for the second flight was 11:40pm.  The night before, I had checked the wrong itinerary – I was mentally cued in to the time being “11:40” so when I saw “11:40pm” I assumed I was looking at the right document.

So this was the start of problems.  Here I was, on the sidewalk, not even being able to enter the airport, having missed a flight that left some 8 hours before I even got to the airport.  This first leg was with Air India, and the second leg was with United, so I was already thinking – how am I going to re-arrange these flights and get everything coordinated across two carriers. 

But first things first…I wandered down to the one part of the airport where you are allowed to enter – the ticketing section.  And, now nearly 10pm, no-one was manning the Air India desk.  So I tried calling them, and even whilst on hold, I realised the futility of this, because if you’ve ever stood outside in Indian traffic, you cannot hear a single thing.

I knew I would not be flying anywhere tonight so the next job was to get to an airport hotel….and of course, there are no onsite airport hotels at New Delhi airport Smile  So then it was a case of walking from taxi to taxi outside the airport trying to see if any of them take a credit card (which is rare for taxis in India) because, like most people, I had carefully spent all of my Indian currency because I thought I was about to leave the country !  Finally a car that looked less like a taxi and more like a hotel car was driving past, so I flagged him down, and asked him which hotel he was from and how far away it was.  5km later I was at a hotel, now nearing midnight, and the job of sorting out flights commenced.

Sorting out 2 flights with different vendors is not pleasant.  To try avoid the hassles, I phoned my travel agency because they’d have access across carriers.  After 20 mins (on mobile phone international roaming rates!) of “Please hold, your call is important to us” I gave up.  So first it was a call to Air India to see if I could get on the same flight tomorrow, but I could book nothing because then it was a call to United to see if I could get the next day flight from Shanghai. Then back to Air India to actually book, and then back to United and book with them.  Rest assured, on a mobile phone with brittle coverage, nothing is more annoying that voice-controlled automation ! 

Bot: “In a few words, tell us how we can direct your call”…
Me:  “Flight Reservation”
Bot: “I think you said ‘Cargo’. Is that right?”

I dont know why…but it does indeed make you feel better to swear at a bot Smile
So after a couple of hours of sweat and tears (and expense) I have more or less the same flights booked for 24 hours later.  I get some much needed sleep to let the adrenalin seep out…

Next morning, I’m back where I started – at the airport entrance, but this time, I’m straight through the entrance with no difficulties…phew.  After the standard 30min queue to check in, when I get to the counter, the Air India agent says to me:

“I’m sorry…We cannot check you in”

I go pale…. “WHY ?!?!?!”

“You do not have a visa for China.”

I tell him I do not need one, because I’m not staying there – it is just transit.  But apparently with the re-booking of the flights, they are no longer “connected”.  So now I have to prove that I indeed have a connecting flight out of China, and my existing hard copy printouts are useless, because they refer to a flight that already left yesterday !  And thus, here I am, at the checkin desk, trying to once again navigate the stupid voice bot as I try to contact United over shoddy cell service with international roam, so they can tell my Air India checkin agent about my flight.  I’ve discovered this is not a good way to be popular in an indian airport, with 500 people queued up behind you because you have become a bottleneck.

After 10mins on the phone, passing it back and forth to the agent and myself, I am finally allowed to check in.  My Air India agent is very apologetic and offers to check my bags all the way through to San Francisco to make transit more convenient.  I am thankful for small mercies at this point.

8 hours later and touchdown…I have made it to Shanghai.  Unsurprisingly, all of the signage is in Chinese, so navigating my way around is not easy.  For the life of me, after much wandering, I cannot find the International Transfer. Eventually I give up and figure, even if I go out through Customs, I can just come back through security in the normal way.  After another long queue, I get to the front of the line at Customs, and the two officials, resplendent in their semi-automatic machine guns, look at my passport, and my ticket, pause, and just shake their head.

That’s all.  Just a shake of the head, and I’m not allowed to pass.

Now I’m panicking.  I’m starting to think of that movie where the guy could not get out of the airport for months. 

I ask why, but their English is just as good my Chinese, ie, non-existent.  I can feel the sweat on forehead, so I’m sure they are starting to think I’m a terrorist or threat to the nation in some way.  And they are mighty big machine guns.

Some feeble gesturing and “sign language” from me doesn’t seem to be helping but at least I’m not being locked up yet.  Eventually one of the officials gets my onward boarding pass to San Francisco, and points at the sign on the wall, which is mainly Chinese but I can make out that it is referring to “24 hours” being the limit you can stay in the country without having a visa.

Now I’m very stressed and very confused.  I’ve given them my onward boarding pass, which shows I’m (hopefully) out of the country in 5 hours…so what could possibly be the issue. More desperate hand waving from me.  The official gets my boarding pass and circles two items:

Departure Date: May 12
Boarding Time: 23:40

and then points to the “24 hour” sign again.  And then … the penny drops.  My flight leaves at 00:30 on May 12, but the boarding pass says “Boarding at 23:40” (which is actually boarding on May 11 for a May 12 flight!), but the Customs person is interpreting this to be late at night on the 12th, which is more than 24 hours…hence violating their entry rules.

So now it’s me drawing pictures of clock hands, and calendars, and departure boards …. and after 10 terrifying minutes, we finally are in agreement – I can indeed pass through and pass back to leave the country !  At this point, I’m still not even sure if I was meant to come through Customs but at least I’m seem to be making some progress. 

It’s at this moment I realise that Friday night is peak hour at Shanghai airport.  Often as travellers, we’re critical of security checks when the queues are long and only a handful of staff are working.  I cannot say this about Shanghai.  They had every single departure check open, and equally as many X-ray machines all going concurrently – perhaps as many as 15.  But it counts for nought when a bazillion people are trying to fly somewhere.  I spent 2 hours in the familiar snake lines going through the standard departure checks and x-ray screening before finally getting to the United departure gate with about 40mins to spare.

The stress finally seems to be over…I sit and relax.  And then…

“Paging Mr Connor McDonald…can you come to the gate desk urgently”

By this point, I’m convinced that I will never be seen again by family and friends.  I trudge up to the desk. 

“We’re sorry sir, but the Air India checkin agent should not have checked your bags through to San Francisco.  As you’ve seen, there is no international transfer in Shanghai – all passengers must retrieve their bags when transferring”.

Well…this explains why I could not find the international transfer….there isn’t one !  And then comes the kicker..

“…So we’ll need to go back through Customs and collect your suitcase and come through security again”

There was long pause at this moment… a long pause where I considered the well being of the person telling me this, and what the implications would be if I were to remove their spleen with the plastic fork I had been eating my salad with Smile

“NNNNNNOOOOOOOOOOOO!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!”  I bellowed at them, knowing that I could no way make it back in time, and moreover, there was no way I was going through the explanations of 24hour clocks again.

The result ?  I did get on my plane and I did land in San Francisco…albeit a day later than originally planned.

The suit case ?  Well… it didn’t.  So the next day, I was back in a taxi, heading out to San Francisco airport to pick up the suitcase that made its own way on its own schedule to San Francisco.

So there you have it.  All of this grief…and why ?  Because I could not read a piece of paper correctly.  I’m not just the village idiot.  I think if you took the village idiot from the all villages, and then made a village of those idiots…then I’d be the village idiot in that village !

So I’m writing this post somewhat as part of my “penance”.  After all, if you can do something as silly as I did, then it only seems an appropriate punishment to share it with one’s peers 🙂