oracle performance tuning boot camp: 10 new problem-solving tips

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Oracle Performance Tuning Boot Camp: 10 New Problem-Solving Tips Using ASH & AWR

Graham Wood

Architect


3 types of Performance Management

Reactive Performance Management

Proactive Performance Management

Preventive Performance Management



1.Comparing Performance Across Two Time Periods

2. Database Hang Analysis

3.SQL Performance Analysis


Comparing Performance Across Two Periods

Inconsistent Performance

– Over utilization of system resources

– High load ad hoc query consuming resources

– Change in execution plan of query

– Parallel execution downgrade

Performance was fine yesterday, today my

application is really slow ?


Compare Period ADDM

• Full ADDM analysis across two AWR snapshot periods

• Detects causes, measure effects, then correlates them

• Causes: workload changes, configuration changes

• Effects: regressed SQL, reach resource limits (CPU, I/O, memory, interconnect)

• Makes actionable recommendations along with quantified impact

AWR Snapshot

Period 1

AWR Snapshot

Period 2 Analysis Report Compare

Period ADDM

SQL Commonality

Regressed SQL

I/O Bound

Undersized SGA


• 30% smaller Buffer cache

• 10% new SQL

Compare Period ADDM: Method

Identify what changed • Configuration changes, workload

changes

Quantify performance differences

• Uses DB Time as basis for measuring performance

Identify root cause • Correlate performance

differences with changes

• Top SQL increased 45%

• Read I/O up 55%

• Buffer cache reduction

caused read I/O increase




2.Database Hang Analysis


Compare Period ADDM


Database Hang Analysis

Database Hung state

– Blocking Sessions

– Memory allocation issues

– Library cache issues

– Unresponsive Storage (ASM)

– Interconnect problems

My database has hung ? I do not want to

bounce it again


Real-Time ADDM – Architecture

Enterprise

Manager

EM Agent

JDBC Connection

Diagnostic Connection

Database

ADDM

Analysis

Hangs

Latches

Deadlocks

• Uses a pre-established diagnostic connection for unresponsive systems

• Initiates a standard JDBC connection for real-time analysis

• Diagnostic connection collects data without holding latches or running SQL

• First intelligent advisor to diagnose problems in real-time as they occur, no matter

how sick the system is

Real time analysis

Unresponsive DB


Real-Time ADDM

• Real-time analysis of hung or slow database systems

• Holistically identify global resource contentions and deadlocks

• Quantified performance impact

• Precise, actionable recommendations

• Provide cluster-wide analysis for RAC






Compare Period ADDM

Real-Time ADDM


SQL Performance Analysis

I enabled parallel query, yet this query is taking

so long. Can you take a look ?

Parallel Downgrades

– Uncontrolled parallel execution

– Parallel Server availability

– Object level settings

– Session level settings


Real-Time SQL Monitoring Insert executed with parallel hint.


Real-Time SQL Monitoring Parallel Tab

• Parallel Coordinator busy for the entire duration !!


Real-Time SQL Monitoring Enabled Parallel DML

• Parallel Slaves busy for the entire duration !!!






Compare Period ADDM

Real-Time ADDM

SQL Monitoring



4.Proactively Monitoring Long Running Programs

5.Analyzing Transient Performance Problems

Understanding Workload Profile

6. Correlating ASH & AWR

7. Using ASH Analytics


Reactive Tracing of long running programs ? Can you trace my program ?

What is wrong with tracing ?

– A very reactive way of looking at problems

– Overhead of writing data to trace files

– Programs we want to trace are usually the ones

with issues

– Impacts the performance of the production

system


Real Time Database Operation Monitoring

Database Operation (DBOPs)

– Simple DBOP (already supported in 11g)

A SQL statement (e.g. SQL for DSS, batch/report SQL, runaway SQL)

A PL/SQL procedure/function

– Composite (new in 12g)

Session(s) activity between two points of time defined by application code / DBA

For example, SQL*Plus script, batch job, ETL processing, …

At most one DBOP per DB session

NEW


– Naming or Tagging

– Bracketing

Naming a Database Operation

BEGIN_OPERATION

END_OPERATION

SQL

PL/SQL Blocks

…

SQL

SQL

EXPLICIT

SQL

PL/SQL Blocks

…

SQL

SQL

DBOP (Tag)

IMPLICIT


Database monitoring of application jobs

– Grouping of SQLs, sessions for the application job

– Key scenarios: ETL operations, Quarter End Close job

Real time monitoring driven by application specified tagging

– Automatically tag Data pump jobs

– Tagging ability in PLSQL, OCI, JDBC

Avoids the overhead of SQLTrace

Visibility of Top SQL statements, system and session performance metrics

Real Time Database Operations Monitoring



4.Reactive Tracing of Long Running Programs



• 6. Correlating ASH & AWR

• 7. Using ASH Analytics

Database Operations


Analyzing Transient Performance Problems

What happened last night the batch job took

twice the time to finish ?

No way to detect transient issues

– We look at AWR data

Averaged out over the snapshot window

– On-disk ASH Data

Sampled every 10 seconds

– Very difficult to detect such issues in the “past”


Automatic Performance Diagnostics A

DD

M

• Diagnose persistent performance issues

• Uses AWR snapshots

• Regular interval

• Automatic or Manual C

om

pare

Period A

DD

M

• Coarse grain performance comparison across two periods

• Relies on AWR data

• Manual

Real-

Tim

e A

DD

M

• Hung or extremely slow databases

• Uses a normal and diagnostic mode connection

• Manual

Enha

nced R

eal-

Tim

e A

DD

M

• Proactively detect and diagnose transient high-impact problems

• Built inside the database

• Automatic

• Runs every 3 seconds

NEW


Automatic real time problem detection and analysis

– Looks for triggering conditions every 3 seconds

Database self-monitors for serious performance issues

– Recognize bad performance trends and trigger analysis :

High CPU, I/O spikes, memory, interconnect, hangs, deadlocks

– Identify a problem before it threatens application performance

Short duration (5 min spikes) ADDM analysis

– Actionable advice for critical issues

– Richer data set available for analysis

Reports (analysis and data) stored in AWR for historical analysis

– ADDM, SQL Monitoring reports

Real-Time ADDM NEW


Triggering Conditions

# Rule Condition

1 High Load Average active sessions greater than 3 times the number of CPU cores

2 I/O bound Impact on active sessions based on single block read performance

3 CPU bound Active sessions greater than 10% of total load and CPU utilization great

than 50%

4 Over-allocated

memory

Allocation over 95% of physical memory

5 Interconnect bound Single block interconnect transfer time based

6 Session Limit Session limit close to 100%

7 Process Limit Process limit close to 100%

8 Hung Session Significant number of hung sessions. If this number is greater than 10%

of total sessions

9 Deadlock Detected Any deadlock detected by hang analyzer


Real-Time ADDM Report








Database Operations

Real-Time ADDM


Understanding Workload Profile The SQL Response Metric crossed the warning

threshold. What is wrong?

Several factors can impact SQL Response time

– Increased or unusual load on system

– Hardware Issues

– Runaway queries consuming system resources

– Changes in execution plans

– Missing or stale object statistics

Need a mechanism to quickly analyze in-memory

performance data


DB Response time analysis - AWR

AWR top 5 section

shows the Wait Class

which contributes most

to DB wait time

Objects involved in TX row lock

contention can be identified in

Segment Statistics section of AWR

Foreground Wait Class section in

AWR to see distribution of DB waits

over Waits classes


From AWR to ASH

ASH report for the

period of increase

of Application waits

will show the same

waits as AWR

Can I get the Application

Module which suffered

from this type of

contention ?


Extracting more data from ASH

Identify SQL statements and sessions impacted by waits on

“Application” Wait Class


Extracting more data from ASH

Get a list of blocking sessions and DB objects !


Understanding Workload Profile: ASH Analytics

• Graphical ASH report for advanced analysis

• Provides visual filtering for recursive drill-downs

• Select any time period for analysis

• Analyze performance across many dimensions

• Different visualizations: Stacked chart or

Tree Map

• Collaborate with others using Active

Reports








Database Operations

Real-Time ADDM

AWR & ASH Reports

ASH Analytics



8.Prevent Regression After Upgrade

9.Ensure Optimal Resource Allocation

10.Prevent Performance Issues Due To Application Changes


SQL Tuning Challenges Change Causing Problems

Situation

– New SQL statements added as part of application patch deployment

– Database upgrades

– Database patching

Response

– Users: “How will the application perform after the changes?”

– DBA: “How do I ensure that our SLA remains intact after the changes are

rolled out?”

Challenge

– How to reduce business risk while absorbing new technologies?


SQL Tuning Advisor

• Analyzes statistics for accuracy

• Recommends SQL Profiles for transparent application tuning

• Suggest access structures and alternate SQL to speed up query execution

• Identifies alternative execution plans using real-time and historical performance

data to recover from plan regression

• Recommends appropriate degree of parallelism for best performance

SQL Profiling

Statistics Analysis

Access Path Analysis

SQL Restructure Analysis

Alternative Plan Analysis

Parallel Query Analysis

Automatic Tuning Optimizer

Administrator

Comprehensive SQL Tuning Recommendations

Gather Missing or Stale

Statistics

Create a SQL Profile

Add Missing Access

Structures

Modify SQL Constructs

Adopt Alternative

Execution Plan (11.2)

Create Parallel SQL

Profile (11.2)

SQL Tuning Advisor






SQL Tuning Advisor


Ensure Optimal Resource Allocation

In a consolidated environment how can I

ensure one database is not running away with

all my system resources ?

Database resource manager directives prevent

a single session to run away with all resources

In DB 12c CDB level resource plans ensure

optimal resource allocations across PDBs

Create a resource allocation strategy

Allocate appropriate CPU and I/O (Exadata)

across PDBs


Allocating Resources in DB 12c

• Gives maximum flexibility for each PDB

• Allows any PDB to consume all available resource

• Risky as one PDB can run away with all resources.

No Resource Allocation

• Ensures all PDBs get a specific share of the resources

• Allows any PDB to consume any unused resources

• Kicks in at 100% resource utilization.

• Assumes that not all PDBs will use its allocated resources

Specify a minimum allocation

• Ensures all PDBs get a specific share of the resources

• Prevents a PBD from taking more than the maximum value assigned.

• May result in unused capacity

Specify a minimum and maximum

NEW


Setting up Resource Manager in Oracle Enterprise Manager

• Extremely simple to manage the CDB resource plans using

Enterprise Manager UI






SQL Tuning Advisor

DB Resource Manager


Prevent performance issues due to Application Changes

The new BI system has very aggressive SLAs

defined. How can we ensure consistent

performance across the system ?

Code migration, new indices, objects can often

impact performance of the application

How do we validate the performance of critical

queries before rolling out these changes ?


Validate Impact of custom code migration

Use SPA Guided Workflow (recommended) or PL/SQL APIs

Create a SQL tuning set of the top X (20 or 30) queries

Establish first trial remotely using current state – baseline

Make change – Create the indexes or migrate custom code

Establish second trial remotely using the same SQL Tuning Set

Review SPA report and rollout or rollback changes.

Trial 2

Trial 1

State 1

State 2

State 1

Custom

Code Changes


Take the Guess Work Out!

Run your trial

before and after

migrating the

change

Make sure your

most important

queries are not

regressed

Take the guess

work out






SQL Tuning Advisor

DB Resource Manager

SQL Performance

Analyzer

oracle performance tuning boot camp: 10 new problem-solving tips

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