Diagnosing SQL Performance Using SQL Health-Check (SQLHC)

8/11/2019 Diagnosing SQL Performance Using SQL Health-Check (SQLHC)

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Copyright 2013, Oracle and/or its affiliates.1


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Diagnosing SQL Performanceusing SQL Health-Check

(SQLHC)

Carlos SierraConsulting Technical Advisor

Center of Expertise (CoE)


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Carlos Sierra

SQL Tuner handyman: developer, advisor, trainer, sup

IT: Oracle(17), UNISYS(12), Ford(3), others(3)

Florida(17), Venezuela(3), Puerto Rico(6), Michigan(1),

Tools: SQLTXPLAIN(SQLT), SQLHC, TRCANLZR(TRC

Motto: Life is good!

Oracle Server Technologies(ST) Center of Expertise(CoE)


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Agenda

SQL Health-Check Tool (SQLHC)

What, Why, When and How?

Health Checks performed

Output sample

Demo


5/42Copyright 2013, Oracle and/or its affiliates.5

What is the SQL Health-Check Tool?

Stand-alone SQL script

By the Server Technologies (ST) Center of Expertise (CoE)

SQL Health Check (HC) does not install schema objec

Centric to one SQL statement per use


6/42Copyright 2013, Oracle and/or its affiliates.6

What is the SQL Health Check Tool?

Inputs one SQL_ID

Outputs

Results of several Health Checks

Additional information

Execute as SYS (or DBA)

Works on 11g and 10.2

UNIX, Linux and Windows


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Why would I want to use the SQL HC?

Verify environment around one SQL

Executes in a few minutes

Minimum resources utilization

Documents state around one SQL

Does not pollute the application


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Why would I want to use the SQL HC?

Acting upon output of relevant Health Checks

may improve execution plan thus performance Output is small and easy to digest

Requires intermediate SQL Tuning expertise

Safe to use on DML statements


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When should I use the SQL HC Tool?

When a quick sanity check of the environment aroun

SQL is needed On a poorly performing SQL

As per AWR or StatsPack reports

On any SQL statement

Out of a Trace or TKPROF


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When should I use the SQL HC Tool?

When using SQLTXPLAIN (SQLT) MOS 215187.1 is

not a short term option When there had been recent changes on the system

And a SQL has regressed in terms of performance

When performance of a SQL is not consistent


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How do I use SQL HC Tool?

Download latest version of sqlhc.sql

Out of MOS (Metalink) 1366133.1

Execute connected as SYS

Or a user with DBA privileges

Parameters

Oracle Diagnostics or Oracle Tuning Pack licenses?

SQL_ID for the SQL statement to be analyzed


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How do I use the SQL HC Tool?

Review and digest content of HTML output reports

Focus first on Health-Check report (number 1)

Act upon those Observations reported by HC

Some may be more relevant than others in each case


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Health Checks performed

Levels

Global Table

Index

Purpose

Highlight SQL Tuning opportunities

Highlight concerns


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Global Health Checks

Using STATISTICS_LEVEL = ALL on LINUX

CBO parameters with non-default values

optimizer_features_enable rdbms_version

optimizer_dynamic_sampling between 1 and 3

db_file_multiblock_read_count is set

nls_sort is not binary


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DBMS_STATS automatic gathering

High version count

Using first rows

Fixed objects missing statistics


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SQL with policies as per v$vpd_policy

Materialized views with rewrite enabled Table with bitmap index(es)

Index in plan no longer exists

System statistics not gathered


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mreadtim < sreadtim

sreadtim < 2 mreadtim < 3

sreadtim > 18

mreadtim > 522


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SQL Plan Baseline contains non-reproducible Plans

Sizes of SQL Plan History and SQL Plan Baseline SQL Profile combined VPD policies

Multiple CBO environments


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INTERNAL_FUNCTION in a Filter Predicate

Plan Operations with Cost 0 and Cardinality 1 SREADTIM differs from actual db file sequential read

MREADTIM differs from actual db file scattered read


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Table Health Checks

empty_blocks > blocks

Table DOP is set Table has indexes with DOP set

Index degree Table degree

No statistics


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Table Health Checks

No rows

Siebel: small tables with statistics Small sample size

Old statistics

Extended statistics


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Table Health Checks

Columns with no statistics

Columns missing low/high values Columns with old statistics

More nulls than rows

More distinct values than rows


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Table Health Checks

Zero distinct values on columns with value

Incorrect NDV in long char column with histogram Frequency histograms with less buckets than NDV

Frequency histogram with 1 bucket

Height balanced histogram with no popular values


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Table Health Checks

ANALYZE command was used

Tables with stale statistics SQL with policies as per dba_policies

SQL with policies as per dba_audit_policies


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Table Health Checks

Table partitions with no statistics

Table partitions where num rows = 0 Table partitions with outdated statistics

Partitions with no column statistics

Partition columns with outdated statistics


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Table Health Checks

Derived statistics in Tables or Partitions

Table has locked statistics

I d H lth Ch k


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Index Health Checks

No statistics

More rows in index than its table Clustering factor > rows in table

Statistics on zero while columns have value

Table/Index statistics out of sync

I d H lth Ch k


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Index Health Checks

NDV on column > num_rows in single-column index

NDV is zero but column has values in single-column inde No column statistics in single-column index

ANALYZE was used

I d H lth Ch k


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Index Health Checks

NDV NDK in single-column index

Index partitions with no statistics Index partitions where num rows = 0

Index partitions with outdated statistics

Derived statistics in Index or Partitions

I d H lth Ch k


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Index Health Checks

Indexes with UNUSABLE segments

INVISIBLE Indexes Index in a Plan with UNUSABLE segments

Index in a Plan is now INVISIBLE

Wh t i th t t?


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What is the output?

Health-Checks

Diagnostics Execution Plans

SQL Detail Report

SQL Monitor Report(s)

Event 10053 Trace from Cursor SQL Dynamic eXtractor (SQLDX)

Health Checks section


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Health-Checks section

Identification

Observations (Health-Checks results) SQL Text

Tables Summary

Indexes Summary

Observations section


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Observations section

Global then Table then Index

All observations include a verbose explanation Some observations have pointers to pertinent MOS docu

Some are more relevant than others for your particula

Test any change before implementing in Production

Tables Summary


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Tables Summary

Content

Table level CBO statistics Indexes and Columns counts

Columns with Histograms counts

Average sample sizes for Indexes and Columns

Purpose

Quick quantitative view of Tables statistics health

Ease a compare between two systems believed to be simila

Indexes Summary


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Indexes Summary

Content

Index level CBO statistics Indication if Index is referenced in an Execution Plan

Columns counts and columns with Histograms counts

Average sample sizes for Columns

Purpose

Quick quantitative view of Indexes statistics health

Ease a compare between two systems believed to be simila

Diagnostics output


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Diagnostics output

Output sample


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Output sample

Output sample


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Output sample

Output sample


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Output sample


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D E M O N S T R A T I O

My Oracle Support Notes and Contact


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My Oracle Support Notes and Contact

1366133.1SQL Tuning Health-Check Script (SQLHC) 215187.1SQLTXPLAIN (SQLT) Tool Download

MOS (Metalink) Notes

carlos.sierra@ora

http://carlos-sierra @csierra_usa


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