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SQLBalls

Bradley Ball is a MCITP SQL 2005 & MCTS 2008 DBA with over 10 years of IT experience. Bradley spent 8 years working as a Defense contractor for clients such as the U.S. Army and The Executive Office of the President of the United States. He is currently a Sr. Consultant for Pragmatic Works. He has presented at SQL Saturdays 62, 74, 79, 85, 86, 131, for the MAGICPASS & OPASS SSUG’s, SQL Rally 2011 & 2012, SQL Dev Connections 2012, the PASS Summit in 2011, and is scheduled for the PASS Summit 2012 and SQL Live 360 later this year. He recently finished Chapter 14 of Expert SQL Server Practices on Page & Row Compression and can be found blogging on http://www.sqlballs.com.

Tales from the Query Processor: II

Hello Dear Reader!  Today is Halloween, October 31st.  My Daughter turns a big 15 today!  Happy Birthday Ches!!!!!

To celebrate two years ago I posted my first Halloween Blog.  Tales from the Query Processor.  It was a lot of fun to write a fiction/horror story revolving around SQL Server and computers.  I wanted to do this last year but got a little busy with family stuff. 

Leading up to this year, I wanted to do it again.  This is one of those stories that's been sitting in the back of my head for a while.  I hope you enjoy it!  



INTO THE DARK

“It’s the same dream every night Doctor, and I don’t know how to make it stop and it just keeps happening.”  The panic in my voice was clear.  “I’m just a simple data page, I don’t know how to stop something like this!”

“Settle down, and start from the beginning,” was the doctor’s soothing reply. 

I settled in on the doctor’s couch, take a deep breath.  I’m in a safe place, I tell myself.  I’m in the buffer far from the disk, there’s plenty of room in the cache and the LRU algorithm is fast asleep.  Nothing can get me here.

CRASH!!!!

“WHAT WAS THAT!”, I screamed as I bolted straight up.

“Settle down,” said the doctor his tone growing a bit frustrated.  “It was just a stray hash bucket.  I’m sure it was nothing.  Lie back down, that's it. You were about to tell me about your dreams.”

Another deep breath, I’m in a safe… oh the hell with relaxing, “It always begins the same…. “

I’m at home in the disk.  I’m at the bottom of the B-Tree where data pages live.  Everyone is going about their business as usual.  It seems darker than normal, but I’m the only one who notices.  The lights of Data Center cascading through the rack, the blink of packets coming and going during their commute, the hustle and bustle of page splits and re-orgs.  It’s all there.  But there’s a fog.  Like I’m the only one that can see it.  A haze in the air, and everything is in slow motion.  I move myself out of physical order, changing my pointer so I can be found and maintain logical order.

My table is large and there are many IAM pages I can hop to.  I transverse the chain trying to get a better view.  The spinning of the disk heads are in the air, their normal beat and pulse that we’ve all come to expect.  It comforts us, like a baby in the womb.  I stare out into the vastness.  Pages so far it looks like the hex starts to fall off the end of the world into nothing but darkness.  That deep darkness captures me.  I cannot look away.  It's deep like a night with no stars and no moon.  Objects just start to melt in it.  The longer I look at it the larger it grows. Instantly have a stab of panic.  I know that I should stop looking.  But I can't!

It’s out there!  It sees me!  I shouldn’t have gone looking for it!  I should have stayed where I was.  I was safe back in my allocated space.  And I'm still staring!  I want to tear my eyes away from the darkness but I can't.  It's so empty and vast.  At least I thought it was.  The hairs on my neck stand up.  I can feel it.  I'm the only one looking for it and now it can see me.

I’m to close now.  I still can’t see it, but I can feel it with a certainty.  IT IS OUT THERE.  The normal spinning of the disk feels wrong.  It feels off.  Like a 757 flying 300 feet off the ground at 500 miles per hour, the disk continues to spin.  But if you watch it, you just know that any second somethings going to happen.  And that’s when I see it.

It lights up the sky with its spark.  Everyone else is still sitting there, like it’s a picnic on a sunny day.  Be lazy, enjoy the moment.  But I know.  I KNOW.  

I shouldn’t see it.  BUT I DO.  The light caused it to be visible.  The light that was some how gone a moment ago, the vile of fog has been pierced.  Worst of all, now I know that it sees me too.  I was the only one looking for it.  I stood out on the edge, and IT SAW ME.

It’s big and malformed.  It’s hideous.  It shouldn’t be there.  I know it.  Now it must catch me and add me to it or I’ll tell everyone.

I start running.  I need to get back to my allocated position.  I’ve got 10 IAM pages to transverse to get there.  524,288 pages per allocation.  I’m running and running.  This should be taking nanoseconds, but the pages are stretching before me, more, and more, and more.  It’s taking microseconds just to transverse one page.  I can feel the ground quake behind me.  I can feel it closer to me.

I’m terrified.  Running.  This is the end and I know it.  I see my spark starting to go out in the darkness.  I know it wants my bits and it wants to re-arrange them. 

I scream and there is no sound.  I’m trying to get the Checksum’s attention.  Screaming and Screaming, but there’s no sound!  Everyone is still going about their business.  Sunday picnic’s!  Maintenance windows, Read-ahead’s from a query, none of them see it!

READ-AHEAD’S!  If I can grab onto one it can pull me up!  There’s a chance!  There’s a chance I can make it!  But the GAM Allocation stretches out even further.  I extend my hand, like that will do any good.  Reach for as far as I can.  But it’s no good.  It falls on me.

“And that’s where I wake up”

The Doctor was on the edge of his chair.  Moments ago, he would have thought this simple data page another fragmented mess just in need of a bit of re-ordering.  Unknowingly he has stopped taking notes, and his right hand is digging deep into the arm of his chair.

“What was it?”, asks the Doctor.

“Doc, you know what it was as well as I do.  I don’t want to say it.”

“No of course not,” said the doctor.  Forcibly relaxing.  “Look, dreams like this are somewhat common for data pages.  I wouldn’t worry about it.” 

“Really?”

“Yes I’m sure everything is fine.  Often times dreams are just subliminal ways of dealing with a long day.  Head on home and let’s meet again next week,” he says jotting down some notes.  “Can I see your insurance card and driver’s license one more time?  I’ve want to make sure I get all the numbers down correctly.”

“Sure,” I say handing them over.  “So next week then.”

“mmmhmmm”, mutters the Doctor and he copies down the number next to his notes.
I rise.  The doctor is right I feel a little better just getting it off my chest.  We smile shake hands and I leave the office.

I’m almost to the door when I realize my keys feel out of my pocket.  I go back to the knock on the door, it’s still cracked open.  That’s when I hear him.

The Doctor is yelling into the phone.  “What DO YOU MEAN THERE’S NO ALERTS ON THE SUSPECT_PAGES TABLE!  We need to raise some sort of alert!  They need to check the Windows Error Log! NO NO YOU FOOL, 823 & 824 DON’T APPEAR IN THE SQL ERROR LOG IT’S GOT TO BE WINDOWS!”

The other end of the phone squabbles back.  The Doctor cuts him off sharply.

“Look I know damn well CHECKSUM is not ON!  I just had a torn page in my office!  IN MY OFFICE!  CHECKSUM was enabled at some point, but it must have been disabled.” 

“Doctor, I’m a torn Page!”, I say announcing my presence at the door.

“CHECKPOINT!!” The Doctor yells into the phone, “CHECKPOINT!!!”


And the world went white.


WRAP UP

As Always Dear Reader, Thanks for stopping by.  And Happy Halloween!

Thanks,

Brad

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