Performance Tuning of the Transaction Log

Performance Tuning of the Transaction Log

A Peek in the most Critical and Misunderstood Part of SQL Server

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About me

Senior SQL Server DBA at HP Guest Lecturer at Sofia

University MCITP: SQL 2008 MCSE: Data Platform MCSA: Windows Server 2012 @miro_dd miroslav.dimitrov89@gmail.com

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Agenda

Introduction to Log

Transaction Log Structure

Top reasons for Log Performance Problems

Delayed Durability

Configuration Best Practices

Log Monitoring

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Introduction

What is it actually?

Write Ahead Logging

Log Cache

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Transaction Log Structure

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Virtual Log Files

Log Blocks

Log Records

Top Reasons for Log Performance problems

Unused Non-clustered Indexes

Log Autogrowth Setting

High Availability Features

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sys.dm_db_index_usage_stats

DEMO

Top Reasons for Log Performance problems (2)

Fragmented Indexes

Many tiny transactions

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https://www.flickr.com/photos/83633410@N07/7658225516

sys.dm_db_index_physical_stats

sys.dm_io_virtual_file_stats

sys.dm_io_pending_io_requests

DEMO

Delayed Durability

SQL 2014 Feature

Deferred Log Flushing

Tiny Transactions

Tolerate Data Loss!

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DEMO

Configuration Best Practices

Initial Size

Number of VLFs

TEMPDB Log

Shrinking

Multiple Log Files

Reverting from Snapshot

Physical Location

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https://www.flickr.com/photos/m-i-k-e/7231298090

Log Monitoring

DMVs/DMFs

Performance Monitor Counters

Extended Events

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DEMO

Key Takeaways

Transaction Log is crucial for the SQL performance

Many factors can have effect on it

Indexes – too many, fragmented

Configuration

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Useful Links

Paul Randal: http://sqlperformance.com/2012/12/io-subsyst

em/trimming-t-log-fat

http://sqlperformance.com/2013/02/system-configuration/transaction-log-configuration

Kimberly Tripp: http://www.sqlskills.com/blogs/kimberly/8-step

s-to-better-transaction-log-throughput/

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Thank You!

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