©2011 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice

Miroslav DimitrovBoris Hristov

INSIDE TEMPDB(ALMOST LEVEL 500)

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Our agenda = answer the WWW questions…

1. Tempdb creation

2. Logging

3. Allocations

Tempdb creation

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Right after master, we create tempdbOpen model firstCreate tempdb based on model and propertiesNotify tempdb is readyIf we fail – server goes down!

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How?

Lock model and tempdb! Copy extents from model to tempdb (including objects)Fixup the tempdb data fileThen tlog fileCreate attach the other files

-f option1 primary data file the size of model (unlimited fixed auto grow)Build one primary log 516096 – 2vlfs + header = 516096 bytes (unlimited 10% autogrowth)DATA FolderOrginal sizes are retained

Demo

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How?

Lock model and tempdb! Copy extents from model to tempdb (including objects)Fixup the tempdb data fileThen tlog fileCreate attach the other files

-f option1 primary data file the size of model (unlimited fixed auto grow)Build one primary log 516096 – 2vlfs + header = 516096 bytes (unlimited 10% autogrowth)DATA FolderOrginal sizes are retained

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Before tempdb is ready – no one will use it

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Tempdb log

Minimize logging – after images for inserts and updates (only to heaps – temp tables)

No need for crash recovery – who cares?

Then why a tlog?

ONLY FOR ROLLBACK

Log is faster than you think (lazy commits – one note)

No normal checkpoint of pages – skips tempdb (hard Is supported) truncates the loginternal objects – mostly allocation logging

Tempdb logging

Demo

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After image logging

Table with value of 1

Tempdb allocations

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What is there in tempdb exactly?

User Objects

• Temp tables• Table variables• UDFs• Online index space• …

Internal Objects

• Sort tables• Worktables• Workfiles• Version Store

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Temporary table caching

We cache…• Stored procs• Triggers • Functions

Why?

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Internal objects

Internal

Objects

• Sort tables• Worktables• Workfiles• Version Store

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TempDB allocations

PFS / GAM / SGAM pages

The only place MS do non-logged allocations!

What about contention?

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How is a table created inside tempdb?

Build system catalog enries

Why?

Why?

Allocate IAM – fina a mixed extent and mark in PFS

Allocate 1 page Record allocation in

system tables

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Tempdb Algorithm – how to choose a file?

Round robin/proportio

nal fill approach

For each “allocation” we

switch to next file with “equal free

space”

Skip files that are not so free

We calculate the “proportion”- After recovery- When adding or removing

files- Every 8192 extent

allocations

Trace flag 1165 – dump numbers

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Allocation of user and tempdb

And why is SQL Server 2005 SP2 CU KB9836185 that important?

The pressure

• PFS, GAM and SGAM• Frequent create/drop of tables• Internal objects allocation/deallocation

The symptoms

• PAGELATCH waits• NOT PAGELATCHIO waits

The solution

• Temp table caching• Trace flag 1118• Multiple data files

(always restart after adding!)

The collision

TempDB Files - benchmark

Demo

THANK YOU