Case Study 10g

8/6/2019 Case Study 10g

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An Oracle 10g Upgrade CaseStudy: Looking at System

Performance Before and After

the Upgrade

Roger Schrag

Database Specialists, Inc.www.dbspecialists.com


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Today's Session The view from 30,000 feet:

Our Oracle environment, upgrade strategy

Impressions: upgrade process and compatibility Impressions: Oracle 10g in general

In greater detail:

Sizing the shared pool and SGA

Optimizer statistics collection and accuracy

Query optimization

SQL Tuning Advisor

Overhead


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Todays SessionGoal: Help you plan for your own Oracle 10g upgrade.

We will:

Look at one companys experience upgrading to 10g Discuss real-life experiences

Provide data so you can draw your own conclusions

We will not:

Walk through the actual upgrade steps Make any judgments about Oracle 10g


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Always Remember Each Oracle system is unique and will have its

own challenges.

Never take somebody elses word on anythingwhen it comes to Oracle technology.

In this session we are only relaying onecompanys experiences.

The only way for you to know how your specificsystem will fare on Oracle 10g is to try itin a testenvironmentand see.


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White Paper Contains additional topics and examples we won't

have time to discuss today

Contains additional supporting evidence forconclusions reached in today's session that wewon't have time to discuss or that wont fit legiblyon a PowerPoint slide

TKPROF reports, execution plans, AWR reports

Download: www.dbspecialists.com/presentations


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The View From 30,000 Feet Our Oracle environment

Our upgrade strategy

Impressions: upgrade process and compatibility

Impressions: Oracle 10g in general


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Our Oracle Environment Platform details:

Oracle 8.1.7 Standard Edition 32 bit

Sun Solaris 8 64 bit One production and one dev database

Production database 15 Gb in size


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Our Oracle Environment Application: Customer database monitoring tool

Backend daemons process inbound agent files from our

customers database servers in the field Web-based user interface for report generation, system

configuration

Almost all code is PL/SQL (roughly 50,000 lines)

Leverages Oracle 8i featureseg GTTs, table()About 50 SQL statements have hints


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Our Oracle Environment Oracle 8i production database was very stable

Figured out workarounds to 8i bugs long ago

Application enhancements are tested in dev beforeproduction deployment

Instance restarted 3-4 times per year

Designed and developed from the start by small group

of experienced Oracle DBAs, developers Well-architected for efficiency, performance, scalability

(in our opinion)


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Our Reasons to Upgrade to 10g Oracle 8i met all of our needs.

So why upgrade?

Oracle 8i desupport. (What difference does it make?) Gain Oracle 10g experience. (For us, a more

compelling reason.)


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Our Upgrade Strategy Restore production hot backup onto dedicated

test server.

Export Oracle 8i test database and import into

empty Oracle 10g test database.

Why export/import instead of upgrading in place?

Switch all tablespaces to LMTs

C

ompact all application segments (purges left holes) Change character set

Fresh data dictionary, database components

Worked out a strategy to keep the down time tolerable


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Our Upgrade Strategy Our Oracle 8i and 10g test databases started out

with the same datahandy for testing and

comparison. Two critical points to remember when comparing

these two test databases:

Application segments in Oracle 10g test database

occupied fewer blocks. Our Oracle 10g test database was 64 bit while our

Oracle 8i test database was 32 bit.


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Impressions: Upgrade Process Oracle 10g version 10.1.0.2 and patch set

10.1.0.3 installed very smoothly.

Oracle 10g import utility read our Oracle 8iexport file with no issues.

Oracle 10g Upgrade Information Tool accuratelypointed out necessary parameter changes.

I've done my share of Oracle installs over theyears, and honestly this was one of the smootherones. (Note: Solaris platform!)


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Impressions: Compatibility Encountered two compatibility issues:

EXTPROC needed reconfiguring (tighter security) and

recompiling (32 bit to 64 bit change). Oracle 10g PLSQL compiler did not like our Oracle 8i

wrapped PL/SQL code. (Cause is probably an Oracle8i export bug.) Rewrapping with Oracle 10g wrapperutility resolved this.

All other application code functioned correctly.

Retained Oracle 8i modplsql client initially.

No interoperability issues encountered.


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Impressions: Oracle 10g Discouraged by SQL Tuning Advisor. (But did not

test exhaustively due to frustration.)

The bottom line for us: Install and upgrade went better than we expected.

Increased overhead and heft are manageablea fairexchange for increased functionality and sophistication.

We expect to get more out of our system than waspossible with Oracle 8i, once we leverage newerfeatures. (But will proceed in this direction verycautiously!)


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Upgrade Issues in Greater Detail Sizing the shared pool and SGA

Optimizer statistics collection and accuracy

Query optimization SQL Tuning Advisor

Overhead


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Sizing the Shared Pool and SGA We like SGA to be only as large as necessary.

Oracle 8i settings:

shared_pool_size = 40 Mb Total SGA size was 84 Mb

Oracle 8i performance characteristics:

50,000 lines of PL/SQL code

15-20 executions per second Under 660 hard parses per day

Buffer cache hit ratio > 97%

Library cache hit ratio ~100%


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Sizing the Shared Pool and SGA Oracle 10g settings:

shared_pool_size = 144 Mb

Total SGA size is 194 Mb Why?

Minimum shared_pool_size setting for 64 bit platformsis 144 Mb according to Metalink document 263809.1

Recommended by Upgrade Information Tool as well


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Sizing the Shared Pool and SGA Just to satisfy a curiosity

shared_pool_size = 48 Mb on Oracle 10g:

Instance would not start


Instance started, but frequent ORA-4031 errors


Everything seemed to work properly

We run Oracle 10g in production with:

shared_pool_size = 144 Mb


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Reasons for Larger Shared Pool Three reasons why the shared_pool_size

setting needs to be increased when upgrading

to Oracle 10g:Allocation for overhead

Shared SQL area memory usage

SQL statements generated by Oracle


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Allocation for Overhead A portion of the shared pool is used to hold

internal memory structures (overhead).

Oracle 8i and 9i make the shared pool largerthan shared_pool_size specifies in order to allowspace for this overhead.

Oracle 10g does not make the shared pool

larger than shared_pool_size specifies. Thus Oracle 10g gives you less usable space in the

shared pool for the same shared_pool_size setting.

See Metalink document 270935.1.


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Allocation for Overhead On our Oracle 8i database the shared pool was

about 3 Mb (8%) larger than specified byshared_pool_size:

SQL> SELECT SUM (bytes) / 1024 / 1024 actual_pool_size2 FROM v$sgastat3 WHERE pool = 'shared pool';

ACTUAL_POOL_SIZE----------------

43.1291847SQL> SHOW PARAMETER shared_pool_size

NAME TYPE VALUE------------------------------------ ------- -------------------------shared_pool_size string 41943040

Weve seen the disparity as high as 27%.


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Shared SQL Area Memory Usage Individual SQL statements appear to occupy more

memory in the shared SQL area in Oracle 10g

than in Oracle 8i. In our environment the difference was almost 2x.

The move from 32 bit Oracle software to 64 bitaccounts for much of this growth.

How much, we dont know.


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Shared SQL Area Memory Usage On our Oracle 10g database:

SQL> SELECT A.username, COUNT(*), SUM (B.sharable_mem) sharable_mem,2 SUM (B.persistent_mem) persistent_mem,

3 SUM (B.runtime_mem) runtime_mem,4 SUM (B.sharable_mem + B.persistent_mem + B.runtime_mem)5 total_mem6 FROM dba_users A, v$sql B7 WHERE A.username = 'DBRX_OWNER8 AND B.parsing_user_id = A.user_id9 GROUP BY A.username;

USERNAME COUNT(*) SHARABLE_MEM PERSISTENT_MEM RUNTIME_MEM TOTAL_MEM------------ -------- ------------ -------------- ----------- ----------DBRX_OWNER 360 12,941,006 487,048 3,361,160 16,789,214


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SQL Generated by Oracle The shared SQL area on any Oracle instance will

contain statements issued by Oracle itself and not

by the application. Often called internal SQL or recursive SQL.

Automatic and self-management infrastructure inOracle 10g (database and EM Database Control)

generates a lot of internal SQL. The shared pool will need to be larger in order to

accommodate the extra statements.


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SQL Generated by Oracle Internal SQL took up an order of magnitude more

space in the shared SQL area of our Oracle 10g

test database than our Oracle 8i test database. Internal SQL took up more space in Oracle 10g

than our application code.

Caveat:

The Oracle 8i test database was Standard Edition withminimal options installed.

The Oracle 10g test database was Enterprise Editionwith default options installed.


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SQL Generated by Oracle On our Oracle 8i database:

SQL> SELECT A.username, COUNT(*), SUM (B.sharable_mem) sharable_mem,2 SUM (B.persistent_mem) persistent_mem,

3 SUM (B.runtime_mem) runtime_mem,4 SUM (B.sharable_mem + B.persistent_mem + B.runtime_mem)5 total_mem6 FROM dba_users A, v$sql B7 WHERE A.username IN ('DBSNMP', 'SYS', 'SYSTEM', 'SYSMAN')8 AND B.parsing_user_id = A.user_id9 GROUP BY A.username;

USERNAME COUNT(*) SHARABLE_MEM PERSISTENT_MEM RUNTIME_MEM TOTAL_MEM------------ -------- ------------ -------------- ----------- ----------SYS 192 2,331,619 125,356 569,688 3,026,663SYSTEM 30 810,325 19,644 163,480 993,449

------------ -------------- ----------- ----------sum 3,141,944 145,000 733,168 4,020,112


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SQL Generated by Oracle On our Oracle 10g database:

SQL> SELECT A.username, COUNT(*), SUM (B.sharable_mem) sharable_mem,2 SUM (B.persistent_mem) persistent_mem,3 SUM (B.runtime_mem) runtime_mem,4 SUM (B.sharable_mem + B.persistent_mem + B.runtime_mem)

5 total_mem6 FROM dba_users A, v$sql B7 WHERE A.username IN ('DBSNMP', 'SYS', 'SYSTEM', 'SYSMAN')8 AND B.parsing_user_id = A.user_id9 GROUP BY A.username;

USERNAME COUNT(*) SHARABLE_MEM PERSISTENT_MEM RUNTIME_MEM TOTAL_MEM------------ -------- ------------ -------------- ----------- ----------DBSNMP 99 4,161,758 137,504 1,701,032 6,000,294SYS 695 24,402,627 1,024,744 8,103,496 33,530,867SYSMAN 670 16,644,400 806,904 4,403,720 21,855,024SYSTEM 14 533,442 18,152 290,280 841,874

------------ -------------- ----------- ----------sum 45,742,227 1,987,304 14,498,528 62,228,059


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Optimizer Statistics Collected optimizer statistics weekly in Oracle 8i:

ANALYZE TABLE table_name ESTIMATE STATISTICS SAMPLE 5 PERCENT;

Oracle 10g uses gather_stats_job:Automatic job runs nightly 10 pm to 6 am.

Uses dbms_stats.

Only collects statistics where missing or stale.

Sample size and histograms automatic. This is all set up automatically out of the box.


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Optimizer Statistics: Cost Automatic statistics collection in Oracle 10g is

more resource intensive than ANALYZE was inOracle 8i:

Resources Used to CollectOptimizer Statistics

Oracle8i(ANALYZE)

Oracle 10g(automatic)

CPU seconds 1,101 2,595

Elapsed seconds 2,044 5,244

Logical reads 597,717 73,082,675

Physical reads 545,844 2,926,625


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Histogram Creation

Histograms are one reason statistics collectionin Oracle 10g is so much more expensive:

Our setup on Oracle 8i created no histograms. Oracle 10g created lots of histograms:

SQL> SELECT histogram, COUNT(*)2 FROM user_tab_columns3 GROUP BY histogram;

HISTOGRAM COUNT(*)--------------- ----------FREQUENCY 267HEIGHT BALANCED 74

NONE 1202----------

sum 1543


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Sample Size Sample size is another reason statistics collection

in Oracle 10g was so much more expensive.

Oracle 8i sample sizes were consistent: Sample sizes on tables over 1 Mb were 4.5 to 5.4%.

Sample sizes on smaller tables were 100%.

Oracle 10g sample sizes were all over the map:

Sample size on 80 Mb table: 100%

Sample size on 1,088 Mb table: 0.4%

Sample size on 760 Mb table: 100%


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Sample Size On our Oracle 10g database:

SQL> SELECT A.table_name, A.num_rows, B.bytes / 1024 / 1024 mb,2 100 * (A.sample_size / A.num_rows) sample_pct3 FROM user_tables A, user_segments B4 WHERE A.table_name IN5 ('SAMPLE_DATA_FILES', 'SAMPLE_JOBS',6 'COMMON_SQL_PLAN_PARTS', 'SAMPLE_SQL_TEXTS',7 'SAMPLE_LIBRARY_CACHE_STATS')8 AND B.segment_type = 'TABLE9 AND B.segment_name = A.table_name10 ORDER BY sample_pct;

TABLE_NAME NUM_ROWS MB SAMPLE_PCT-------------------------- ----------- ---------- ----------SAMPLE_DATA_FILES 14,938,632 1,088.00 0.4SAMPLE_JOBS 1,360,429 54.00 4.1COMMON_SQL_PLAN_PARTS 174,851 9.00 6.9SAMPLE_LIBRARY_CACHE_STATS 1,414,830 80.00 100.0SAMPLE_SQL_TEXTS 6,346,638 760.00 100.0


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Sample Size How Oracle 10g came to sample every row in a

760 Mb table:

First, Oracle sampled all 35 columns of the table on0.0892929621% of the rows.

Next, Oracle sampled 8 of the columns on0.8929296209% of the rows.

Next, Oracle sampled 3 of the columns on8.9292962091% of the rows.

Finally, Oracle performed a COUNT (DISTINCT) onone of the columns without a SAMPLE clause.


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Optimizer Statistics: Accuracy Oracle 10g optimizer statistics did not appear to

be particularly more accurate than those collected

by ANALYZE

in Oracle 8i. In particular Oracle 10gs estimate of distinct

column values was sometimes less accurate thanOracle 8is.

Could have been caused by excessively small samplesize on some tables (just a guess)


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Optimizer Statistics: Accuracy How accurate do optimizer statistics need to be?

If every business process on your system gives

satisfactory response time, then the statistics areaccurate enough.

But if a business process runs too slowly, can youblame the optimizer statistics?

W

e will see some queries that got unsatisfactoryexecution plans in our Oracle 10g testenvironment.

Is it the statistics? We dont know.


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Query Optimization Queries in our application follow an OLTP

workload model.

All run quickly (except for quarterly purge). Quick, but some are complex.

We believe weve written practical, logical SQL.

Oracle 8i ran most of our SQL efficiently:

We added hints to SQL only when response timeconcerns arose.

About 50 statements throughout the application havehints.


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Query Optimization Did not expect things to run faster in Oracle 10g.

Queries already had efficient execution plans in 8i.

We expect the gains to come when we leverageOracle 9i and 10g new features.

Concern: What if some queries run slower inOracle 10g?

In a business process with 100 SQL statements, it onlytakes one bad execution plan to slow the wholeprocess down.


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The Executive Summary

Most SQL in our application consumedroughly the same CPU time and number of

logical reads in Oracle 10g as in Oracle 8i. Some statements ran a little faster, and a

few ran a little slower.

Most workload operations yielded similar

response times in both versions of Oracle. Only a very few SQL statements were slow

enough on Oracle 10g to cause concern.


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Query Optimizer Challenge Could Oracle 10g find efficient execution

plans for the queries that required hints in

Oracle 8i? Is adding hints to queries a thing of the past?

Well not yet:

Oracle 10g ran the troublesome queries faster

without hints than Oracle 8i without hints. However, both versions of Oracle ran the

queries faster with hints than Oracle 10g didwithout hints.


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Query Optimization in Detail SQL that ran similarly in Oracle 8i and 10g

SQL that ran faster in Oracle 10g

SQL that ran faster in Oracle 8i


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SQLT

hat Ran Similarly Loader Daemon comparison

Performance Summary report comparison

See the white paper for TKPROF reportexcerpts


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Loader Daemon Comparison Loader Daemon parses, validates, and loads

files from our monitoring agents into the

database for analysis and reporting. PL/SQL package roughly 7,800 lines long.

7 SQL statements in the package have hints.

Starting out with the same data in the Oracle

8i and 10g test databases, we traced theLoader Daemon on each database whileloading the same agent file into each.


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Performance Report Comparison Performance Summary report provides a

summary of performance statistics for one

monitored Oracle database over a specifiedperiod of time (like a Statspack report).

PL/SQL package roughly 3,200 lines long.

4 SQL statements in the package have hints.

Starting out with the same data in the Oracle8i and 10g test databases, we traced sessionsthat called the report with the sameparameters on each database.


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Performance Report ComparisonResources Used by Performance

Summary ReportOracle 8i Oracle 10g

User SQL statements traced 98 98

Internal SQL statements traced 10 10

Unique SQL statements traced 98 97

Total OCI calls 654 531

CPU seconds 0.89 0.88

Logical reads 4,641 3,661

Physical reads 1 0


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Performance Report Comparison Business process gave roughly same response

time and load profile on Oracle 8i and 10g.

Fewer logical reads on Oracle 10g again. Fewer total OCI calls in Oracle 10g:

Same number of parse and execute calls.

Oracle 8i had twice as many fetch calls as 10g.

It appears as if Oracle 8i did extra fetch calls to makesure it had retrieved all rows from a cursor, whileperhaps Oracle 10g asked for more rows up front.


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SQLT

hat Ran Faster in 10g We did not expect noticeable response time

improvements on Oracle 10g because

everything already ran fast enough on 8i. We removed the hints from queries that had

been slow in Oracle 8i to see if Oracle 10gcould find the right execution plan.

In several cases Oracle 10g did better than8i did without hints, but 10gs execution planwas still far inferior to that chosen when thehints were in place.


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Recent Event Notifications Query appears in several reports.

Retrieves a list of recent event notifications for

all databases to which the specified user hasaccess.

Joins 7 tables and includes a subquery.

To get the query to run efficiently in Oracle 8i

we had added a hint to specify join order andwhich join algorithm to use for each table.

Not a trivial query, nor the most complex.


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Recent Event NotificationsSELECT /*+ ORDERED INDEX (privs) USE_NL (i s ar acr) USE_HASH (t l) */

t.test_severity_id severity, i.instance_id,NVL (privs.instance_nickname, i.current_instance_name) inst_name,ar.first_detected, t.short_description brief_description,l.report_section_id

FROM customer_user_instance_privs privs, customer_instances i,samples s, analysis_results ar, analysis_common_results acr,

analysis_tests t, lookup_report_40000_formats l WHERE privs.user_id = :cp_user_id AND privs.current_cust_user_priv_level IN ('admin', 'read only') AND i.instance_id = privs.instance_id AND privs.user_wishes_to_see = 'y' AND s.instance_id = i.instance_id AND s.sample_type IN ('ping', 'full_stat') AND s.sample_date_db_local_time >

(SELECT s2.sample_date_db_local_time -

(i.display_events_for_so_many_hrs / 24)FROM samples s2

WHERE s2.sample_id = rpt_util.most_recent_analyzed_sample (i.instance_id))

AND ar.sample_id = s.sample_id AND acr.analysis_common_result_id = ar.analysis_common_result_id AND t.test_id = acr.test_id AND t.alert_type = 'event' AND l.test_id = t.test_idORDER BY severity, first_detected DESC, inst_name;


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Oracle 8iW

ithoutH

intRows Execution Plan------- ---------------------------------------------------

0 SELECT STATEMENT MODE: CHOOSE0 SORT (ORDER BY)0 FILTER

7093 HASH JOIN

71 TABLE ACCESS MODE: ANALYZED (FULL) OF 'LOOKUP_REPORT_40000_FORMATS7092 HASH JOIN

4 TABLE ACCESS MODE: ANALYZED (FULL) OF 'ANALYSIS_TESTS'512382 HASH JOIN512382 NESTED LOOPS832470 HASH JOIN465504 HASH JOIN

41 TABLE ACCESS MODE: ANALYZED (FULL) OF 'CUSTOMER_INSTANCES'

465504 TABLE ACCESS MODE: ANALYZED (FULL) OF 'SAMPLES'832469 INDEX MODE: ANALYZED (FAST FULL SCAN) OF 'ANALYSIS_RESULTS_PK'512382 INDEX MODE: ANALYZED (UNIQUE SCAN) OF 'CUSTOMER_USER_INST_PRIVS126110 INDEX MODE: ANALYZED (FAST FULL SCAN) OF 'ANALYSIS_COMMON_RESULT

42 TABLE ACCESS MODE: ANALYZED (BY INDEX ROWID) OF 'SAMPLES'42 INDEX MODE: ANALYZED (UNIQUE SCAN) OF 'SAMPLES_PK' (UNIQUE)


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Oracle 10gW

ithoutH

intRows Row Source Operation------- ---------------------------------------------------

0 SORT ORDER BY (cr=4212 pr=0 pw=0 time=3573213 us)0 HASH JOIN (cr=4212 pr=0 pw=0 time=3573077 us)

71 TABLE ACCESS FULL LOOKUP_REPORT_40000_FORMATS (cr=3 pr=0 pw=0 time=4890 HASH JOIN (cr=4209 pr=0 pw=0 time=3562005 us)

4 TABLE ACCESS FULL ANALYSIS_TESTS (cr=18 pr=0 pw=0 time=853 us)243 HASH JOIN (cr=4191 pr=0 pw=0 time=3554047 us)

126110 INDEX FAST FULL SCAN ANALYSIS_COMMON_RESULTS_N1 (cr=341 pr=0 pw=0 ti243 HASH JOIN (cr=3850 pr=0 pw=0 time=2830427 us)343 TABLE ACCESS BY INDEX ROWID SAMPLES (cr=391 pr=0 pw=0 time=19666 us359 NESTED LOOPS (cr=292 pr=0 pw=0 time=578919 us)15 NESTED LOOPS (cr=58 pr=0 pw=0 time=1791 us)41 TABLE ACCESS FULL CUSTOMER_INSTANCES (cr=15 pr=0 pw=0 time=759 u

15 INDEX UNIQUE SCAN CUSTOMER_USER_INST_PRIVS_PK (cr=43 pr=0 pw=0 t343 INLIST ITERATOR (cr=234 pr=0 pw=0 time=40802 us)343 INDEX RANGE SCAN SAMPLES_UK2 (cr=234 pr=0 pw=0 time=40979 us)(ob14 TABLE ACCESS BY INDEX ROWID SAMPLES (cr=147 pr=0 pw=0 time=336414 INDEX UNIQUE SCAN SAMPLES_PK (cr=133 pr=0 pw=0 time=33165 us)(

832469 INDEX FAST FULL SCAN ANALYSIS_RESULTS_PK (cr=3459 pr=0 pw=0 time=16


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SQLT

hat Ran Slower in 10g SQL noticeably slower in very few cases on 10g.

A report ran unacceptably slower after the

upgrade: CPU time doubled.

Logical reads increased by order of magnitude.

Slowdown attributed to one query (which runs

many times):SELECT B.valueFROM common_stat_names A, sample_sysstats B WHERE A.name = :p_statname AND B.common_stat_name_id = A.common_stat_name_id AND B.sample_id = :p_sample_id;


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Sample Stats Query On our Oracle 8i database:

call count cpu elapsed disk query current rows------- ------ -------- ---------- --------- --------- --------- ---------

Parse 1 0.00 0.00 0 0 0 0Execute 1 0.00 0.00 0 0 0 0Fetch 2 0.00 0.00 0 6 0 1------- ------ -------- ---------- --------- --------- --------- ---------total 4 0.00 0.00 0 6 0 1

Rows Execution Plan------- ---------------------------------------------------

0 SELECT STATEMENT MODE: CHOOSE1 NESTED LOOPS2 INDEX MODE: ANALYZED (RANGE SCAN) OF 'COMMON_STAT_NAMES_PK' (UNIQU1 INDEX MODE: ANALYZED (UNIQUE SCAN) OF 'SAMPLE_SYSSTATS_PK' (UNIQUE


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Sample Stats Query On our Oracle 10g database:

call count cpu elapsed disk query current rows------- ------ -------- ---------- --------- --------- --------- ---------

Parse 1 0.00 0.00 0 0 0 0Execute 1 0.00 0.00 0 0 0 0Fetch 2 0.01 0.01 0 244 0 1------- ------ -------- ---------- --------- --------- --------- ---------total 4 0.01 0.01 0 244 0 1

Rows Row Source Operation------- ---------------------------------------------------

1 NESTED LOOPS (cr=244 pr=0 pw=0 time=893 us)234 INDEX RANGE SCAN SAMPLE_SYSSTATS_PK (cr=5 pr=0 pw=0 time=1152 us)1 INDEX RANGE SCAN COMMON_STAT_NAMES_UK1 (cr=239 pr=0 pw=0 time=9472 us


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Sample Stats Query Who cares about a 0.01 second query?

Suppose the query runs 50+ times each time apopular report is viewed?

Adding an ORDERED hint to the query madeOracle 10g choose the correct execution plan.

The same exact behavior occurred in both our

test and production Oracle 10g environments. Both tables in the query are IOTs.

Oracle has determined this is a problem with theoptimizer caching cost model.


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SQLT

uning Advisor Cool sounding Oracle 10g feature that studies

a query and makes recommendations:

You tell Advisor how long to study the query.Advisor could recommend rewrite.

Advisor could collect additional statistics that canbe saved in data dictionary as a profile to be usedwhenever the statement is parsed in the future.

Opens the door to fixing bad queries withoutmodifying the application code.


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SQLT

uning Advisor We had already added hints to all queries that

ran unacceptably slow.

Weve already discussed that taking thosehints away in Oracle 10g led to inferiorresponse times.

So what if we took the hints away and let the

SQL Tuning Advisor recommend a solution foreach troublesome query?


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Recent Event NotificationsSQL> SELECT dbms_sqltune.report_tuning_task2 ('Tuning case 47696', 'TEXT', 'ALL', 'ALL')3 FROM SYS.dual;

DBMS_SQLTUNE.REPORT_TUNING_TASK('TUNINGCASE47696','TEXT','ALL','ALL')---------------------------------------------------------------------GENERAL INFORMATION SECTION

---------------------------------------------------------------------Tuning Task Name : Tuning case 47696Tuning Task ID : 951Scope : COMPREHENSIVETime Limit(seconds): 600Completion Status : COMPLETEDStarted at : 01/27/2005 13:42:34Completed at : 01/27/2005 13:42:48

---------------------------------------------------------------------SQL ID : b6c2qka14951zSQL Text: SELECT t.test_severity_id severity, i.instance_id,

...ORDER BY severity, first_detected DESC, inst_name

---------------------------------------------------------------------There are no recommendations to improve the statement.


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Sample Stats QuerySQL> SELECT dbms_sqltune.report_tuning_task2 ('Tuning case 47694', 'TEXT', 'ALL', 'ALL')3 FROM SYS.dual;



---------------------------------------------------------------------SQL ID : g5pqqgcuq8pmaSQL Text: SELECT B.value /* tuning case 47694 */

FROM common_stat_names A, sample_sysstats B WHERE A.name = :p_statname AND B.common_stat_name_id = A.common_stat_name_id AND B.sample_id = :p_sample_id

---------------------------------------------------------------------

There are no recommendations to improve the statement.


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A Trivial QuerySQL> SELECT dbms_sqltune.report_tuning_task

2 ('Tuning case 47702', 'TEXT', 'ALL', 'ALL')3 FROM SYS.dual;



---------------------------------------------------------------------SQL ID : 9cz4z8xvtxbm1SQL Text: SELECT instance_id, sample_type, sample_date_db_local_time

/* tuning case 47702 */FROM samplesWHERE sample_id + 1 = :sample_id


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A Trivial Query-------------------------------------------------------------------------------FINDINGS SECTION (1 finding)-------------------------------------------------------------------------------1- Restructure SQL finding (see plan 1 in explain plans section)----------------------------------------------------------------The predicate "SAMPLES"."SAMPLE_ID"+1=:B1 used at line ID 1 of the execution

plan contains an expression on indexed column "SAMPLE_ID". This expressionprevents the optimizer from selecting indices on table"DBRX_OWNER"."SAMPLES".

Recommendation--------------Rewrite the predicate into an equivalent form to take advantage ofindices. Alternatively, create a function-based index on the expression.

Rationale---------The optimizer is unable to use an index if the predicate is an inequalitycondition or if there is an expression or an implicit data type conversionon the indexed column.


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A Trivial Query-------------------------------------------------------------------------------EXPLAIN PLANS SECTION-------------------------------------------------------------------------------

1- Original-----------

Plan hash value: 3806118825

-----------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |-----------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 4656 | 122K| 2375 (4)| 00:00:29 || 1 | TABLE ACCESS FULL| SAMPLES | 4656 | 122K| 2375 (4)| 00:00:29 |

-----------------------------------------------------------------------------

Query Block Name / Object Alias (identified by operation id):-------------------------------------------------------------

1 - SEL$1 / SAMPLES@SEL$1-------------------------------------------------------------------------------


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Overhead

What does the automation, self-management,and new functionality of Oracle 10g cost us?

For example: Memory usage

The cost of a parse

CPU usage by automation and self-mgmt processes

As you would expect, all of these go upnoticeably with Oracle 10g.

For us, the increases were all manageable.


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Memory Usage

Process stats from prstat and top

Total VM size includes SGA

Remember: 32 bit to 64 bit change

Oracle Dedicated Server Processes Oracle 8i Oracle 10g

Resident set size of Oracle process 97 Mb 224 Mb

Total virtual memory size of Oracle process 121 Mb 301 Mb

SGA size according to v$sgastat 84 Mb 197 Mb

Size of the Oracle executable 32 Mb 95 Mb


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Hard Parse Cost

Hard parses have been expensive in Oracle for along time.

Mechanisms to reduce the need for hard parses: Shared SQL area

Bind variables

Hard parses should be a one-time expense in

properly designed systems. As the optimizer gets more sophisticated you

might expect hard parses to get more expensive.

In Oracle 10g, they do.


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Hard Parse Cost Comparison

Resources used by Loader DaemonAgent File 1 (hard parse)

Oracle 8i Oracle 10g


Internal SQL statements traced 402 977Unique SQL statements traced 139 149

Total OCI calls 9,094 10,754



Physical reads 695 959


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Resources used by Loader DaemonAgent File 2 (soft parse)







Physical reads 8 13


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Resources used by Loader DaemonDifference







Physical reads 687 946


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CPU Used by Oracle Daemons

How much additional CPU time will Oracle10g daemons consume?

Simple test: MeasureC

PU usage on an idleinstance.

Flaws in this test:

Some Oracle features probably use more

resources on a busy database than an idle one(eg AWR).

How do you measure CPU time accurately?(We used sar.)


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CPU Usage Comparison

No Oracle processes running:02:00:03 %usr %sys %wio %idle02:05:03 0 4 0 9602:10:03 0 4 0 9602:15:03 0 4 0 96

Idle Oracle 8i instance:02:00:03 %usr %sys %wio %idle02:05:03 1 4 1 9402:10:03 0 4 1 9502:15:03 0 4 0 95

Idle Oracle 10g instance plus EMDC:13:00:05 %usr %sys %wio %idle13:05:05 5 6 3 8713:10:05 3 6 2 8913:15:05 3 6 4 88


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Activity in Idle Oracle 10g

An AWR report for a one hour period on anOracle 10g instance with no user activityshowed:

27,000 statement executions

49 CPU seconds used

8 Mb redo generated


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Wrapping Up

Weve been happy with Oracle 10g:

Installed easily

Upgrade went smoothly

No serious compatibility issues

Very few response time issues caused by upgrade

New features ought to justify increased heft,complexity, and overhead

For us, the upgrade justification boiled down togetting the experience. Technology-wise, Oracle8i was already meeting our needs.


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Always Remember

Each Oracle system is unique and will have itsown challenges.

Never take somebody elses word on anythingwhen it comes to Oracle technology.

In this session we are only relaying onecompanys experiences.

The only way for you to know how your specificsystem will fare on Oracle 10g is to try itin atest environmentand see.


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White Paper

Contains additional topics and examples wedidnt have time to discuss today

Contains additional "supporting evidence" forconclusions reached in today's session that we

didnt have time to discuss or that couldnt fitlegibly on a PowerPoint slide

TKPROF reports, execution plans, AWR reports Download: www.dbspecialists.com/presentations


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Contact Information

Roger SchragDatabase Specialists, Inc.

388 Market Street, Suite 400

San Francisco, CA 94111

Tel: 415/344-0500

Email: [email protected]

Web: www.dbspecialists.com

Date post:	08-Apr-2018
Category:	Documents
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Case Study 10g

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