Last Season's Performance Tuning Techniques

Brent, Ozar, Founder, Brent Ozar Unlimited

Erik Darling, Consultant, Brent Ozar Unlimited

Moderated By: Damu Venkatesan

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OCT 31 – NOV 3 SEATTLE WA

Last Season’sPerformance Tuning Techniques

Brent Ozar and Erik Darling

Developer stuff

What are you wearing to PASS?

Erik Darling

SQL or whatever

You’re a carb.

DBA stuff

Bo-ring, let’s go take pictures of food we’re not gonna eat.Ew. Old people.

Over it.

Quelle horreur!

WANNA FOLLOW ALONG?

Get the slides & demos: BrentOzar.com/go/fashion

Brent Ozar

PRETTY GOOD AT DATABASES

Microsoft Certified Master, working with SQL Server for 20+ years.

EXTREMELY BAD AT FASHION

And plenty of photo albums from over the years to prove it.Facebook.com/BrentOzar

@BrentO

LinkedIn.com/in/BrentOzar

Today’s topic: unfashionable performance skills.

WE ALL LEARN THIS STUFF AS WE GO

We don’t grow up with Stacy London and Karl Lagerfeld giving us style advice, nor does Joe Celko mentor us as we write our first T-SQL.

WE JUST NEED TO CATCH UP

Every now and then, we need to revisit our clothes and our database skills and make sure that they still work in today’s world.

WE THINK WE’RE COOL AT THE TIME

We emulate things we see on TV or read about online, like copy/pasting code from random answers on Stack Overflow or techniques from really old blog posts.

Tracking Page Splits to Reduce Fragmentation

Rocket science fashion told me,”Fragmentation is really bad.”

REMEMBER YOUR PARENTS’ SQL SERVER?

It had two hard drives for the data files, and two hard drives for the log files,and a vinyl record player to install SQL Server.

SO WE WATCHED FRAGMENTATION CAREFULLY.

And we watched any indicators that might mean fragmentation was happening.

REMEMBER WINDOWS DEFRAG?

It shuffled your pages around to put them in order because sequential access was so much faster than random access.

“Page splits mean fragmentation is happening.”

SQL SERVER STORES STUFF IN 8KB PAGES.

You saw How to Think Like the Engine last year at the Summit, right?

THE NEW PAGE WOULDN’T BE IN ORDER.

It’s added wherever there happened to be free space in the data file. That meant fragmentation! So we watched page splits carefully. I tracked them on my Swatch.

A FULL PAGE IS LIKE A POPPED COLLAR:YOU CAN’T POP IT ANY FURTHER.

When you try to insert a new row into it, or update an existing row to make it wider, SQL Server can’t cram any more data in – so it splits the page.

“I like gold chains, K-Swiss sneakers, and long demos in the park.”

Perfmon’s Page Splits/sec is the Milli Vanilli of metrics.

GIRL YOU KNOW IT’S FALSE.

Even if you believe out-of-order pages on disk represents a performance problem, the Page Splits per Second counter doesn’t mean things are getting worse.

And if you’ve been adjusting Fill Factor in order to reduce page splits per second, you might have been making things even worse.

Like wearing a formal ”gold” watch with an OP shirt, print pants, and sneakers.

Table Variables Are Just As Good As Temp Tables

I know what you’re up to

When you create temp objects, it’s a real coin-toss

• One day it might be a temp table

Heads I win

One day it might be a table variable

Tails you lose

One day it might be laziness

Past results, future performance

You’ve heard some bad things about table variables

• Modifications are forced serial

• You always get a 1 row estimate

• Unless you RECOMPILE

And you’ve finally let go of the only-in-memory mantra

• Big surprise, a 10 GB table won’t fit in 8 GB of RAM

But you say he’s just an estimated plan

But on the flip side, what about SELECT queries?

• Well, they still can go parallel with a table variable

• But…

Demo

Separating Data & Log Files for Better Performance

I did what I was told.

They told me magnetic hard drives were:

• Really fast at sequential activities

• Really slow at random activities

Then they told me that SQL Server’s:

• Log file writes were sequential

• Data file reads & writes were random

So they said I needed to keep log files on their own volume so they’d be sequential and fast.

(They also said striped socks and striped shorts match.)

Some of this is still true today.

Even today, solid state drives are:

• Really fast at sequential activities

• Really slow Sorta fast at random activities

(Striped socks and striped shorts do actually match, but it turns out that you don’t want matchy-matchy.)

But part of it is a lie.

SQL Server’s log file writes are sequential –but only for one database’s log file writes.

Most of us have more than one database.

And our databases don’t take turns to write.

And when you put more than one log file on a volume, that volume’s access is random.

(They also said striped socks and striped shorts match.)

Inseparable.

Even when you try to separate data & logs,you’re usually using one pool of disks.

If they’re sharing drives anyway,especially sharing with multiple servers,what’s the point of separation?

To make your servers more reliable? Debunked:https://www.brentozar.com/archive/2017/06/separating-data-log-files-make-server-reliable/

Separating log filesis like wearing racing stripes.

It doesn’t magically make you faster or more reliable.

CTEs Are Better For Performance

NANANANANANANANANANANANA

There are some things I always hear about CTEs

• They don’t use indexes

• They’re in memory

• SQL persists the results like a temp table

• They’re better than derived tables

Exhausted by Basic DBAs

“I tried them but they didn’t work”

>mfw

It’s a cruel, cruel winterDressing me in acid washed jeans

Many people saying these things call themselves “Senior”

• These are pretty lousy misconceptions

• Especially for people with 10+ years of experience

CTEs have many fine uses

• Making query intent more clear

• Paging queries

• Getting around ‘wide’ queries

Demo

Functions Are Optimized Like Stored Procedures

I hate functions.*

Scalar valued functions.

No more words

Demo

Believing theMissing Index Hints

If you’ve used open source databases,

SSMS is a wonderful gift.

It’s the thought that counts,and some gifts aren’t thoughtful.

THE MISSING INDEX HINTS ARE JUST A QUICK GIFT.

SQL Server only casually throws these out as a byproduct of building a plan.

OR YOU COULD PICK A WORSE ONE.

I actually bought this entire outfit with my own money. Top down: mullet, gold chain over sweater, wannabe Cosby sweater, wool pants, boat shoes. Not pictured: taste.

YOU COULD PICK A BETTER GIFT YOURSELF.

SQL Server only puts a few milliseconds into building these, and you could do way, way better by thinking through the query yourself.

Wanna come over to my place,

watch a demo, and make fun of

my baggy acid-washed jeans?

Missing index hintsaren’t thinking too much.

YOU ONLY SEE THE FIRST ONE.

Go into the XML and search for the word “missing” to check for more.

FIELDS MAY BE MISSING ENTIRELY.

SQL Server typically suggests indexes for the WHERE clause and ignores ordering, grouping, having clauses.

When you see a missing index, smile, nod, and come up with your own.

FIELDS AREN’T SHOWN IN ORDER.

It’s just a comma-delimited list of things you should think about indexing.

>2017>Still using trace flags

Flags of our fathers

It used to be that if you wanted performance

• Especially if you’re running a ‘big box’

• You needed about one trace flag per core

If tempdb performance sucked

• 1117 and 1118

If you hit CMEMTHREAD waits

• 8048

If stats didn’t update often enough automatically

• 2371

The list goes on and on

1204

1222

2301

2389

2390

2549

2562

3226

4199

7470

9024

Hey kid, want some Trace Flags?

You

what?

No more rocket surgery

SQL Server 2016 makes some good choices for you

• Trace Flags for tempdb are automatic

• And they only apply to tempdb

• Plus smart tempdb config at startup

Auto update stats threshold based on # of rows

• Just like 2371!

Automatic memory partitioning

• No more 8048!

• No more CMEMTHREAD!

• Kinda…

Recap

Your performance skillsmight be out of fashion.

WERE YOU SURPRISED BY STUFF TODAY?

It’s okay: so were we as our careers progressed. Learning is a good thing.

GOOD NEWS: WE’VE GOT A PRE-CON TO HELP.

We’re teaching Expert Performance Tuning for SQL Server 2016 & 2017.

Your job is making SQL Server go faster, but you haven’t been to a performance tuning class since 2016 came out. You’ve heard things have gotten way better with 2016 and 2017, but you haven’t had the chance to dig into the new plan cache tools, DMVs, adaptive joins, and wait stats updates.

In one fun-filled day, Brent Ozar and Erik Darling will future-proof your tuning skills. You’ll learn our most in-depth techniques to tune SQL Server leveraging DMVs, query plans, sp_BlitzCache, and sp_BlitzFirst. You’ll find your server’s bottleneck, identify the right queries to tune, and understand why they're killing your server. If you bring a laptop with SQL Server 2016 and 120GB free space, you can follow along with us in the Stack Overflow database, too.

Learn more now: BrentOzar.com/go/summit

QUESTIONS?

Coming up next!

Create and Load a Staging Environment from Scratch in an Hour with BimlScott Currie

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