Forgotten Features

8/4/2019 Forgotten Features

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1

ForgottenFeatures

Julian Dyke

Independent ConsultantWeb Version

juliandyke.com2005 Julian Dyke


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2005 Julian Dyke juliandyke.com2

Agenda

Introduction Forgotten Features

Tracing and Auditing

Testing and Benchmarking

Administration

Execution Plans

Tables

Indexes

SQL

PL/SQL Conclusion


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Criteria for an Oracle feature Easy to understand

Easy to implement

Works in first release

Documented in first release

Compatible with other features

Improves Productivity or Manageability Saves resources / money

Intellectually stimulating


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Tracing

andAuditing


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TRACEFILE_IDENTIFIER Initialisation Parameter

Introduced in Oracle 8.1.7

tracefile_identifier = ''

e.g. in Oracle 9.2 if a trace file is called

ss92001_ora_1760.trc

ss92001_ora_1760_test.trc

then the statement

will change the file name to

ALTER SESSIONSET tracefile_identifier = 'test';


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DBMS_SYSTEM.KSDWRT DBMS_SYSTEM

undocumented package installed in all databases

owned by SYS

To write messages to trace files and/or alert log use

DBMS_SYSTEM.KSDWRT(

DEST NUMBER, -- 1 = Trace File, 2 = Alert Log, 3 = BothTST VARCHAR2 -- Message

);

For example

BEGINDBMS_SYSTEM.KSDWRT (1, Output to trace file);DBMS_SYSTEM.KSDWRT (2, Output to alert log);DBMS_SYSTEM.KSDWRT (3, Output to both);

END;/


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BITAND Initially undocumented built-in function

Performs a bit-wise AND between two operatorsSELECT BITAND (42,1) FROM dual;

Can be used as basis for OR and XOR functions

CREATE OR REPLACE FUNCTION bitor (x NUMBER, y NUMBER)

RETURN NUMBER ISBEGINRETURN x + y - BITAND (x,y);

END;/

CREATE OR REPLACE FUNCTION bitxor (x NUMBER, y NUMBER)

RETURN NUMBER ISBEGINRETURN BITOR (x,y) - BITAND (x,y);

END;/

Beware of overflows



Hexadecimal Format Masks Introduced in Oracle 8.1.5

Convert decimal numbers to and from hexadecimal To convert from decimal to hex

SELECT TO_CHAR (1048576,XXXXXXXX) FROM dual;

returns 100000

To convert from hex to decimal

SELECT TO_NUMBER (100000,XXXXXXXX) FROM dual;

returns 1048576


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DBMS_MONITOR Introduced in Oracle 10.1

To enable trace in another session useDBMS_MONITOR.SESSION_TRACE_ENABLE(

SESSION_ID NUMBER, -- SIDSERIAL_NUM NUMBER, -- Serial NumberWAITS BOOLEAN, -- Include Waits

BINDS BOOLEAN -- Include Binds);

To disable trace in another session useDBMS_MONITOR.SESSION_TRACE_DISABLE(

SESSION_ID NUMBER, -- SIDSERIAL_NUM NUMBER -- Serial Number

);

Waits (event 10046 level 8) are enabled by default

Binds (event 10046 level 4) are disabled by default



DBMS_MONITOR Can be enabled at database level in Oracle 10.2

To enable trace for all database sessions use

DBMS_MONITOR.DATABASE_TRACE_ENABLE(

WAITS BOOLEAN, -- Include WaitsBINDS BOOLEAN -- Include BindsINSTANCE_NAME VARCHAR2 -- Instance Name

);

To disable trace for all database sessions use

DBMS_MONITOR.DATABASE_TRACE_DISABLE(

INSTANCE_NAME VARCHAR2 -- Instance Name);



Autonomous Transactions Introduced in Oracle 8.1.5

Recursive transaction started by main transaction

Can commit or rollback independently of main transaction

Committed data unaffected if main transaction rolls back

Often used for auditing

CREATE OR REPLACE TRIGGER trigger1

BEFORE INSERT ON table1 FOR EACH ROWDECLARE

PRAGMA AUTONOMOUS_TRANSACTION;BEGIN

INSERT INTO log1 VALUES (:new.col1,:new.col2,SYSDATE);COMMIT;

END;/



SYS Auditing In Oracle 9.2 and above, operations performed by the SYS

user can be audited.

To enable SYS auditing set AUDIT_SYS_OPERATIONSparameter to TRUE

Auditing information will be written to text file in directoryspecified by AUDIT_DUMP_DEST parameter

Default directory is $ORACLE_HOME/rdbms/audit

Filename is ora_.aud where pid is the operating systemprocess ID



Testing

andBenchmarking



Fixed Date Initialization Parameter

Useful for deterministic testing In Oracle 8.0 and above can be set dynamically using

ALTER SYSTEM

To set date only use

FIXED_DATE = DD-MON-YY

Sets time to 00:00:00

To set date and time use

FIXED_DATE = YYYY-MM-DD-HH24:MI:SS


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Random Functions To guarantee consistent tests, random functions should

return deterministic results

DBMS_RANDOM package

Seed can be specified using DBMS_RANDOM.SEEDprocedure

SAMPLE clause

Can be made deterministic by enabling event 10193

Level specifies seed

ALTER SESSION SET EVENTS10193 trace name context forever, level 42;


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Checkpoints and Logfiles To force a checkpoint

ALTER SYSTEM CHECKPOINT;

To force a log file switch

To force a log file switch and archive the log file

ALTER SYSTEM SWITCH LOGFILE;

Useful when dumping log files

ALTER SYSTEM ARCHIVE LOG CURRENT;

Useful for testing archive log creation with

Physical standby database

Logical standby database


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Flushing the Shared Pool Introduced in Oracle 8.0

Flushes all unpinned objects from library cache

ALTER SYSTEM FLUSH SHARED_POOL;

Useful for deterministic testing but

After issuing this statement

All unpinned cursors need reparsing

All unpinned packages need recompilation


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Flushing the Buffer Cache Introduced in Oracle 10.1

Flushes all unpinned buffers from the buffer cacheALTER SYSTEM FLUSH BUFFER_CACHE;

In Oracle 9.0.1 and above the following command has the

same effectALTER SESSION SET EVENTSIMMEDIATE TRACE NAME FLUSH_CACHE;

Useful for deterministic testing but

After issuing this statement

Warm up the cache before testing workloads


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PerformanceTuning


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V$SQL_PLAN Introduced in Oracle 9.0.1

Shows actual execution plan in memory

Enhanced in Oracle 9.2 to include

Access Predicates (Joins)

Filter Predicates

Related views include

V$SQL_PLAN_WORKAREA

V$SQL_PLAN_STATISTICS V$SQL_PLAN_STATISTICS_ALL


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V$SQL_PLAN

ADDRESS RAW(4)

HASH_VALUE NUMBERCHILD_NUMBER NUMBEROPERATION VARCHAR2(30)OPTIONS VARCHAR2(30)OBJECT_NODE VARCHAR2(10)OBJECT# NUMBER

OBJECT_OWNER VARCHAR2(30)OBJECT_NAME VARCHAR2(64)OPTIMIZER VARCHAR2(20)ID NUMBERPARENT_ID NUMBERDEPTH NUMBERPOSITION NUMBER

COST NUMBERCARDINALITY NUMBER

BYTES NUMBEROTHER_TAG VARCHAR(35)PARTITION_START VARCHAR2(5)PARTITION_STOP VARCHAR2(5)PARTITION_ID NUMBEROTHER VARCHAR2(4000)DISTRIBUTION VARCHAR2(20)CPU_COST NUMBERIO_COST NUMBERTEMP_SPACE NUMBERACCESS_PREDICATES VARCHAR2(4000)

FILTER_PREDICATES VARCHAR2(4000)PROJECTION VARCHAR2(4000)TIME NUMBERQBLOCK_NAME VARCHAR2(31)REMARKS VARCHAR2(4000)


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Optimizer Environment Variables In Oracle 10.1 and above, optimizer environment variables are

externalized at :

instance level - V$SYS_OPTIMIZER_ENV

session level - V$SES_OPTIMIZER_ENV

statement level - V$SQL_OPTIMIZER_ENV

Use the values in these views when determining whyexecution plans differ


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Optimizer Environment Variables Optimizer Environment Variable values reported by the

dynamic performance views include:

active_instance_count parallel_dml_mode

bitmap_merge_area_size parallel_execution_enabled

cpu_count parallel_query_mode

cursor_sharing parallel_threads_per_cpu

db_file_multiblock_read_count pga_aggregate_target

hash_area_size query_rewrite_enabled

optimizer_dynamic_sampling query_rewrite_integrity

optimizer_features_enable skip_unusable_indexes

optimizer_index_caching sort_area_retained_size

optimizer_index_cost_adj sort_area_size

optimizer_mode star_transformation_enabled

optimizer_mode_hinted statistics_level

parallel_ddl_mode workarea_size_policy


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DBMS_XPLAN Introduced in Oracle 9.2

Formats PLAN_TABLE contents generated by EXPLAIN PLAN

SELECT * FROM TABLE (dbms_xplan.display);

DISPLAY function parameters include

TABLE_NAME name of plan table

STATEMENT_ID statement ID in plan table FORMAT as below

Value Description

BASIC Operation ID, object name and operation/option only

TYPICAL (Default) Most relevant information including partitionpruning, parallelism and predicates where appropriate

ALL As TYPICAL plus parallel execution server statements

SERIAL As TYPICAL without parallel execution server statements


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DBMS_XPLAN For example explain a query

EXPLAIN PLAN FORSET STATEMENT_ID = 'STATEMENT1' FORSELECT t1.c2, t2.c2FROM t1, t2WHERE t1.c1 = t2.c1AND t1.c2 = 10;

SELECT * FROMTABLE(

dbms_xplan.display ('PLAN_TABLE','STATEMENT1'));

The plan table can be queried using


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DBMS_XPLAN Example output with predicates

Id Operation Name Rows Bytes Cost

0 SELECT STATEMENT 10 590 66

* 1 HASH JOIN 10 590 66

* 2 TABLE ACCESS FULL T1 10 60 58

3 TABLE ACCESS FULL T2 1000 53000 7

Predicate Information (identified by operation id):

1 - access("T1"."C1"="T2"."C1")2 - filter("T1"."C2"=10)


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DBMS_XPLAN Example output for parallel execution

Id Operation Name Rows Bytes Cost TQ IN-OUT PQ Distrib


1 MERGE JOIN 10 590 79 78,02 P->S QC(RANDOM)

2 SORT JOIN 10 60 33 78,02 PCWP

* 3 TABLE ACCESS FULL T1 10 60 29 78,01 P->P HASH* 4 SORT JOIN 1000 53000 47 78,02 PCWP

5 TABLE ACCESS FULL T2 1000 53000 7 78,00 S->P HASH


3 - filter("T1"."C2"=10)4 - access("T1"."C1"="T2"."C1")

filter("T1"."C1"="T2"."C1")


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DBMS_XPLAN Partition pruning information can also be included e.g. for a

range partitioned table

EXPLAIN PLAN FORSELECT c2 FROM t1

WHERE c1 >= 150 AND c1 < 250;

CREATE TABLE t1 (c1 NUMBER,c2 NUMBER,c3 CHAR(50))PARTITION BY RANGE (c1)(

PARTITION p1 VALUES LESS THAN (100),PARTITION p2 VALUES LESS THAN (200),

PARTITION p3 VALUES LESS THAN (300),PARTITION p4 VALUES LESS THAN (400));

SELECT * FROM TABLE (dbms_xplan.display);


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DBMS_XPLAN Example output for partition pruning

Id Operation Name Rows Bytes Cost PStart PStop


1 PARTITION RANGE ITERATOR 2 3

* 2 TABLE ACCESS FULL T1 1 26 2 2 3


2 - filter("T1"."C1">=150 AND "T1"."C1"


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DBMS_XPLAN In Oracle 10.1 and above

New DISPLAY_CURSOR function

By default displays plan for last statement executed insession

SQL> SELECT COUNT(*) FROM t1;

SQL > SELECT * FROM TABLE (dbms_xplan.display_cursor);

Id Operation Name Rows Cost (%CPU) Time

0 SELECT STATEMENT 160 (100)

1 SORT AGGREGATE 1

2 TABLE ACCESS FULL T1 51809 160 (2) 00:00:02


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V$SESSION_WAIT_HISTORY Introduced in Oracle 10.1

SID NUMBERSEQ# NUMBEREVENT NUMBEREVENT VARCHAR2(64)P1TEXT VARCHAR2(64)P1 NUMBERP2TEXT VARCHAR2(64)P2 NUMBERP3TEXT VARCHAR2(64)P3 NUMBERWAIT_TIME NUMBERWAIT_COUNT NUMBER

Externalises last 10 wait events for each session

Similar information to V$SESSION_WAIT but much moreuser friendly


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Administration


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Kill Session For example to kill a session for user US01

Identify the SID and serial number

SELECT sid, serial#FROM v$sessionWHERE username = US01;

Kill the session using

ALTER SYSTEM KILL SESSION ,;

For example

ALTER SYSTEM KILL SESSION 133,523;

Next command issued by killed session will return error

ORA-00028: your session has been killed


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Renaming Database Objects To rename a table:

RENAME oldname TO newname;

In Oracle 9.2 and above to rename a columnALTER TABLE t1 RENAME COLUMN oldname TO newname;

ALTER TABLE t1 RENAME CONSTRAINT oldname TO newname;

In Oracle 10.1 and above to rename a tablespace

ALTER TABLESPACE oldname RENAME TO newname;

In Oracle 9.2 and above to rename a constraint

To rename an index

ALTER INDEX oldname RENAME TO newname;


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Dropping Columns Introduced in 8.1.5

Columns can be dropped from a table using the ALTERTABLE statement

Columns can be

marked unused immediately and deleted at a later time deleted immediately

If the delete operation fails at any point it can be restartedfrom the point of failure


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Dropping Columns To drop a column immediately use

ALTER TABLE table1 DROP COLUMN column2;

Columns can also be marked unused immediatelyand subsequently dropped

To mark a column unused use

ALTER TABLE table1 SET UNUSED COLUMN column2;

ALTER TABLE table1 DROP UNUSED COLUMNS;

To drop all unused columns from a table use


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Dropping Columns If instance is shutdown while column is being dropped, drop

column statement can be continued when instance restarted

ALTER TABLE table1 DROP COLUMNS CONTINUE;

DBA_PARTIAL_DROP_TABS describes partially dropped columns

DBA_UNUSED_COL_TABS describes columns marked unused,but not yet dropped


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Default Tablespaces In Oracle 9.0.1 and above a default temporary tablespace can

be defined

ALTER DATABASEDEFAULT TEMPORARY TABLESPACE ;

In Oracle 10.1 and above a default permanent tablespace canbe defined

ALTER DATABASEDEFAULT TABLESPACE ;


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Resumable Statements Oracle 9.0.1 and above long running operations encountering

out of space errors can be resumed

Resumable operations include

Queries

DML Statements

SQL*Loader operations Import operations

DDL statements

Out of space errors include

Tablespace full

Maximum number of extents reached for object

Tablespace quota exceeded for a user


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Resumable Statements When resumable space allocation is enabled

Operation suspends if an out of space error occurs

Details of the error are written to DBA_RESUMABLE

DBA can optionally be alerted

DBA can either

fix the error

abort the operation Operation automatically resumes execution when error is

fixed

If a further error is detected, operation will suspend again


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Resumable Statements1 Resumable space allocation is enabled

ALTER SESSION ENABLE RESUMABLENAME Batch Update TIMEOUT 3600;

2 Resumable operation starts

INSERT INTO t2SELECT * FROM t1;

3 Out of space error occurs

ORA-01653: unable to extend table US01.T2 by 210 in tablespaceTS99

4 Error is written to alert log


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Resumable Statements

5 (Optional) DBA is notified by message generated by

AFTER SUSPEND trigger

6 DBA queries DBA_RESUMABLE view for details ofsuspended operation

7 DBA fixes error condition e.g.

ALTER TABLESPACE TS99ADD DATAFILE SIZE ;

8 Suspended operation resumes automatically

9 Operation completes successfully


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Resumable Statements In Oracle 10.1 and above resumable statements can be

enabled at instance level

ALTER SYSTEMSET resumable_timeout = ;

Resumable statements can be disabled at instance level using

ALTER SYSTEMSET resumable_timeout = 0;

Resumable statements can be enabled at session level using

ALTER SESSIONSET resumable_timeout = ;

Resumable statements can be disabled at session level using

ALTER SESSIONSET resumable_timeout = 0;


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Automatic Datafile Deletion In Oracle 9.0.1 and above, DROP TABLESPACE has been

extended to optionally delete its datafiles

DROP TABLESPACE tablespace_nameINCLUDING CONTENTS AND DATAFILES;

The DROP TABLESPACE command automatically deletesOracle Managed Files


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Database Level Backups In Oracle 10.1 and above to enable/disable backup mode for

all tablespaces in single statement use:

Useful with three-way mirror or snapshot backups

ALTER DATABASE BEGIN BACKUP;ALTER DATABASE END BACKUP;

In Oracle 9.2 to disable backup mode for all tablespacesfollowing a database restart use:

ALTER DATABASE END BACKUP;


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Tables


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Row Movement

In Oracle 8.0 updating the partition key columns in a rangepartitioned table fails if it would cause the row to be migrated toanother partition

ORA-14402: updating partition key column would cause a partition change

In Oracle 8.1.5 and above row movement can be enabled a row may be migrated to another partition if its partition key

columns are updated

By default row movement is disabled


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Row Movement

ALTER TABLE table1 ENABLE ROW MOVEMENT;ALTER TABLE table1 DISABLE ROW MOVEMENT;

Row movement can be enabled when the partitioned table iscreated e.g.

CREATE TABLE table1(

column1 NUMBER,column2 NUMBER

)PARTITION BY .ENABLE ROW MOVEMENT;

Row movement can be also be enabled and disabled from anexisting table e.g.


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External Tables External tables

read-only tables

definition is stored in data dictionary

data is stored outside the database in operating system flatfiles

can be queried using SQL

can be queried in parallel can be included in DML statement subqueries

No DML operations are allowed on external table

No indexes can be created on external table

E l T bl


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External Tables Example

CREATE DIRECTORY ext_dir AS '/v01/external';

CREATE TABLE transactions(

account NUMBER,value NUMBER

)ORGANIZATION EXTERNAL(

TYPE ORACLE_LOADERDEFAULT DIRECTORY ext_dirACCESS PARAMETERS(

RECORDS DELIMITED BY NEWLINEFIELDS TERMINATED BY ,

)LOCATION (transactions.csv)

);

E l T bl


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External Tables The following tests were based on a 1,000,000 row flat file.

Each row contained 74 bytes of data and 4 bytes of separators

Tests were performed in NOARCHIVING and ARCHIVINGmodes

Description Time in seconds

NoArchiving Archiving

Use SQL*Loader with CONVENTIONAL path load toINSERT rows

318 322

Use SQL*Loader with DIRECT load to INSERT rows 28 285

Use CREATE TABLE AS SELECT to copy data from

external table to internal table

20 290

Use CREATE TABLE AS SELECT to copy data frominternal table to internal table

15 283

D S C i


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Data Segment Compression Introduced in Oracle 9.2

Data is compressed when it is written to a block decompressed when it is read from the block

Compression is applied at block level

Blocks will only be compressed if data is sufficiently large to fill the block rows have low enough cardinality

Columns can be reordered within each block to achieveoptimal compression ratios

A segment may contain compressed and uncompressedblocks

D t S t C i


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Data Segment Compression Compression can be specified for new tables

CREATE TABLE t1 (c01 NUMBER,c02 VARCHAR2(30)) COMPRESS;

Compression can also be specified for existing tables

ALTER TABLE t2 COMPRESS;

Existing tables can be compressed using

ALTER TABLE t3 MOVE COMPRESS;

Compression can also be specified for

range and list partitioned tables

materialized views nested tables

D t S t C i


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Data Segment Compression Only works with direct path inserts

For example

CREATE TABLE AS SELECT

INSERT /*+ APPEND */

ALTER TABLE MOVE

Materialized View Refresh SQL*Loader

Online Reorganization

Does not work with INSERT /*+ NOAPPEND */

UPDATE

DELETE

D t S t C i


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Data Segment Compression

1993Ayrton Senna4

1996Olivier PanisLigier

19943 2

19953 2

19971 2

20024 0

20011 220004 0

19991 2

19984 Mika Hakkinen

SymbolTable

RowData

2 David Coulthard0

3 Ferrari1

5 Michael Schumacher2Benetton3 2

4 4 McLaren

Year Driver Team

1993 Ayrton Senna McLaren

1994 Michael Schumacher Benetton

1995 Michael Schumacher Benetton

1996 Olivier Panis Ligier

1997 Michael Schumacher Ferrari

1998 Mika Hakkinen McLaren


2000 David Coulthard McLaren


2002 David Coulthard McLaren

Monaco Grand PrixWinners 1993-2002

D t S t C i


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Data Segment Compression Compression ratios vary with

number of rows

number of columns

cardinality of rows

For example loading SALES table from sales history demoschema

$ORACLE_HOME/demo/schema/sales_history

BlockSize

UncompressedSize (Blocks)

CompressedSize (Blocks)

Ratio %

2048 18777 13433 71.5

4096 8983 6106 68.0

8192 4398 2850 64.7

16384 2179 1353 62.0

Table contains 1016271 rows

D t S t C i


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Data Segment Compression Test1 Loading the SALES table from a flat file into an empty

table

Compressed Blocks ElapsedTIme (Secs)

CPU Time(Secs)

No 4398 31.77 4.13

Yes 2850 71.08 43.86

Test2 Selecting one column from all rows in the compressedtable

SELECT SUM (quantity_sold) FROM sales;

Compressed Blocks ElapsedTIme (Secs) CPU Time(Secs)

No 4398 3.41 2.77

Yes 2850 3.78 3.53


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Indexes

Inde Leaf Compression


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Index Leaf Compression Introduced in Oracle 8.1.5

Compresses leading columns in index

Must be specified when index is created or rebuilt

CREATE INDEX i1 ON t1 (c1, c2, c3) COMPRESS 2;

ALTER INDEX i1 REBUILD ONLINE COMPRESS 1;

Benefits

Reduces number of blocks to hold index

Reduction in physical I/O for scans

Improved cache efficiency

Potential reduction in index height

CBO more likely to use index

Index Leaf Compression


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Country City

France Paris

Germany Berlin

Germany Frankfurt

Germany Munich

Italy Milan

Italy Rome

Suffix Slot Array

Prefix Slot Array

1600 120013001400 9001000

15001700 11001 4 6

1700

1500

1400

1300

1200

1100

1600

1000

900

France

Paris

Germany

Berlin

Frankfurt

Munich

ItalyMilan

Rome

Prefix Row

Prefix Row

Prefix Row

Suffix Row

Suffix Row

Suffix Row

Suffix Row

Suffix Row

Suffix RowCREATE INDEX i1ON TABLE t1 (country, city)COMPRESS 1;



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Index Leaf Compression Number and size of prefixed rows can be verified using

Useful INDEX_STATS columns include

PRE_ROWS

Number of prefix rows PRE_ROWS_LEN

Sum of lengths of all prefix rows

OPT_CMPR_COUNT

Optimal key compression length

OPT_CMPR_PCTSAVE

Space saved by implementing optimal key length

ANALYZE INDEX i1 VALIDATE STRUCTURE;SELECT * FROM index_stats;



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Index Leaf Compression Can also be used with IOTs

CREATE TABLE t1(

c1 NUMBER,c2 NUMBER,c3 NUMBER,c4 NUMBERCONSTRAINT pk1 PRIMARY KEY (c1,c2,c3)

)ORGANIZATION INDEXCOMPRESS 2;

ALTER TABLE t1 MOVE COMPRESS 1;

To rebuild existing IOT

Index Rebuild Online


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Introduced in 8.1.5

create or rebuild index whilst allowing concurrent DMLoperations

Works with

B*tree indexes (non-partitioned and partitioned) 8.1.5

IOTs (non-partitioned and partitioned) 8.1.5

Reverse key indexes 9.0.1

Function-based indexes 9.0.1

Compressed indexes 9.0.1

IOT Secondary indexes 9.0.1



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Index Rebuild Online To build an index online use

ALTER INDEX index1 REBUILD ONLINE;

Can be executed in parallel

Three phases

prepare phase index created

data dictionary updated

build phase

index populated

changes written to journal tablemerge phase

rows in journal table are merged

ANALYZE INDEX ONLINE


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ANALYZE INDEX ONLINE Prior to Oracle 9.0.1, index structure can be analyzed using

ANALYZE INDEX index_nameVALIDATE STRUCTURE;

No DML possible against index while it is being analyzed

In Oracle 9.0.1 and above indexes can be analyzed online

ANALYZE INDEX index_nameVALIDATE STRUCTURE ONLINE;

DML statements unaffected

Index Monitoring


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Index Monitoring In Oracle 9.0.1 indexes can be monitored to determine if they

are being used

If index monitoring is enabled for an index, then Oracleupdates a table in the data dictionary when that index isincluded in an execution plan by the parser

Indexes are only monitored at parse time

Only SELECT statements and subqueries monitored

Also works for bitmap indexes

Index Monitoring


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Index Monitoring

SELECT index_name,monitoringFROM v$object_usage;

This example assumes the following definitions

ALTER INDEX index1 MONITORING USAGE;ALTER INDEX index2 MONITORING USAGE;

CREATE TABLE table1 (col1 NUMBER, col2 NUMBER);CREATE INDEX index1 ON table1 (col1);CREATE INDEX index2 ON table1 (col2);

Enable index monitoring using

To check which indexes are being monitored use

INDEX_NAME MONITORING

INDEX1 YES

INDEX2 YES

Index Monitoring


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Index Monitoring Execute all possible statements against the table

SELECT index_name,usedFROM v$object_usage;

ALTER INDEX index1 NOMONITORING USAGE;ALTER INDEX index2 NOMONITORING USAGE;

SELECT /*+ INDEX (table1 index1) */ * FROM table1WHERE col1 = 0;

Check which indexes have been used using

Disable index monitoring using

INDEX_NAME USED

INDEX1 YES

INDEX2 NO

Create Index NOSORT


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Create Index NOSORT Specify the NOSORT option to avoid sorting index columns

when creating an index

CREATE INDEX index1 ON table1 (column1) NOSORT

If columns are not in sorted order then index creation will failwith the following error:

ORA-01409: NOSORT option may not be used;rows are not in ascending order

Create Index Compute Statistics


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Create Index Compute Statistics Introduced in Oracle 8.1.5

To compute statistics when creating an index use:

CREATE INDEX index1 ON table1 (column1) COMPUTE STATISTICS;

Statistics will be computed (not estimated)

If the index is composite, statistics only generated for leadingcolumn

If the index is non-partitioned, table, column and indexstatistics are gathered

If the index is partitioned only index statistics are gathered

To compute statistics when rebuilding an index use:

ALTER INDEX index1 REBUILD COMPUTE STATISTICS;

Global Index Maintenance


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Global Index Maintenance In Oracle 9.0.1 and above UPDATE GLOBAL INDEXES can be

specified for DDL statements on partitioned tables

Global indexes remain available during the operation

Updates to the global index are logged

UPDATE GLOBAL INDEXES can be used with the following

partition DDL statements

ALTER TABLE table1DROP PARTITION table1_p1UPDATE GLOBAL INDEXES;

ADD SPLIT

DROP MERGE

MOVE EXCHANGE

TRUNCATE COALESCE

For example


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Undo

andRedo

Global Temporary Tables


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Global Temporary Tables Introduced in Oracle 8.1.5

Defined in data dictionary definition available to all sessions

Data

only visible to current session

retained for duration of current transaction or session stored in users sort space

can overflow to sort segment in users temporary

tablespace

Indexes

can be created against global temporary tables

same scope and duration



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Can define triggers and views

Views cannot join permanent and temporary tables

Benefits

Reduction in DDL

Reduction in amount of redo generated

DML statements against global temporary tables

Generate undo

Generate redo for undo

Do not generate redo for block changes



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Global Temporary Tables ON COMMIT DELETE ROWS

rows are only visible to the current transaction

CREATE GLOBAL TEMPORARY TABLE temp1 (column1 NUMBER)ON COMMIT DELETE ROWS;

INSERT INTO temp1 VALUES (1);

SELECT * FROM temp1;Column11

COMMIT;

SELECT * FROM temp1;

No rows returned



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Global Temporary Tables ON COMMIT PRESERVE ROWS

rows are visible throughout current session

CREATE GLOBAL TEMPORARY TABLE temp2 (column1 NUMBER)ON COMMIT PRESERVE ROWS;

INSERT INTO temp2 VALUES (1);


Column11

COMMIT;


Column11

Guaranteed Undo Retention


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Guaranteed Undo Retention Introduced in Oracle 10.1

To specify that unexpired undo should be preserved in all

undo segments even if this makes current operationsrequiring undo space fail use

Only applies to undo tablespaces

Useful while flashback queries are running

To specify default behaviour use

ALTER TABLESPACE tablespace_nameRETENTION GUARANTEE;

ALTER TABLESPACE tablespace_nameRETENTION NOGUARANTEE;

Enabling NOLOGGING


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Enabling NOLOGGING UNRECOVERABLE clause introduced in Oracle 7.3

NOLOGGING clause introduced in Oracle 8.0

Enabled at object level

ALTER TABLE table NOLOGGING ;

Can be used by

SQL*Loader direct loads CREATE TABLE direct loads

CREATE INDEX direct loads

INSERT /*+ APPEND */

INSERT LOB NOCACHE

Writes reduced redo

Cannot be recovered

CREATE INDEX index1 ON table1(column1) NOLOGGING;

Disabling NOLOGGING


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Disabling NOLOGGING If NOLOGGING option is specified

Limited redo is written

Changes cannot be recovered

Changes cannot be transported to standby database

In Oracle 9.2 and above NOLOGGING can be disabled

At database levelALTER DATABASE FORCE LOGGING ;ALTER DATABASE NO FORCE LOGGING;

ALTER TABLESPACE tablespace_name FORCE LOGGING ;ALTER TABLESPACE tablespace_name NO FORCE LOGGING;

At tablespace level


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PL/SQL

Native Dynamic SQL


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Native Dynamic SQL Prior to Oracle 8.1.5 PL/SQL DDL statements were executed

using DBMS_SQL package

DECLAREl_cursor INTEGER;l_result INTEGER;

BEGINl_cursor := DBMS_SQL.OPEN_CURSOR;

DBMS_SQL.PARSE (l_cursor,ALTER SYSTEM SWITCH LOGFILE,DBMS_SQL.V7);

l_result := DBMS_SQL.EXECUTE (l_cursor);

DBMS_SQL.CLOSE_CURSOR (l_cursor);END;

Native Dynamic SQL


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Native Dynamic SQL

In Oracle 8.1.5 and above EXECUTE IMMEDIATE can execute DDLstatements

EXECUTE IMMEDIATE 'INSERT INTO tab1 (c1,c2) VALUES (1,10)';EXECUTE IMMEDIATE 'UPDATE tab1 SET c1 = 4 WHERE c2 = 10';EXECUTE IMMEDIATE 'DELETE FROM tab1 WHERE c2 = 10';

EXECUTE IMMEDIATE can also execute DML statements

EXECUTE IMMEDIATE 'CREATE TABLE tab1 (c1 NUMBER)';EXECUTE IMMEDIATE 'ALTER TABLE tab1 ADD (c2 NUMBER)';EXECUTE IMMEDIATE DROP TABLE tab1;

Native Dynamic SQL


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Native Dynamic SQL EXECUTE IMMEDIATE can also be used for SELECT

statements

INTO clause is used to define fetch variables

For example

DECLAREl_c1 NUMBER;l_str VARCHAR2(1000);

BEGINl_str := 'SELECT c0l1 FROM tab1 WHERE c2 = 20';

EXECUTE IMMEDIATE l_str INTO l_c1;

DBMS_OUTPUT.PUT_LINE ('Result is || l_c1);END;

Native Dynamic SQL


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Native Dynamic SQL EXECUTE IMMEDIATE can also use bind variables

USING clause is used to specify bind variable positions

For example

DECLARE

l_c1 NUMBER;l_str VARCHAR2(1000);

BEGINl_str := 'SELECT c1 FROM t1 WHERE c2 = :p1';

EXECUTE IMMEDIATE l_str INTO l_c0l1 USING 10;DBMS_OUTPUT.PUT_LINE ('Result is '||l_c1);

EXECUTE IMMEDIATE l_str INTO l_c0l1 USING 30;DBMS_OUTPUT.PUT_LINE ('Result is '||l_c1);

END;

Bulk Collect


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Bulk Collect Introduced in Oracle 8.1.5

Returns result set in single operation

Can be used with

SELECT INTO

FETCH INTO RETURNING INTO

Bulk Collect - Example


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Bulk Collect ExampleDECLARE -- 100000 row table

l_c3 NUMBER;CURSOR c1 IS SELECT c3 FROM t1;

BEGINOPEN c1;LOOP

FETCH c1 INTO l_c3; -- 3.052 secondsEXIT WHEN c1%NOTFOUND;

END LOOP;CLOSE c1;

END;DECLARE -- 100000 row table

TYPE NUMTYPE IS TABLE OF NUMBER(6) INDEX BY BINARY_INTEGER;l_c3 NUMTYPE;CURSOR c1 IS SELECT c3 FROM t1;

BEGINOPEN c1;

LOOPFETCH c1 BULK COLLECT INTO l_c3; -- 0.119 secondsEXIT WHEN c1%NOTFOUND;

END LOOP;CLOSE c1;

END;

Bulk Collect Limit Clause


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Bulk Collect Limit Clause Bulk collect performance improves as optimum result set size

is approached

Thereafter bulk collect performance degrades as result setgrows

In Oracle 8.1.6 and above the number of rows returned byFETCH INTO can be restricted using the LIMIT clause

FETCH c1 BULK COLLECT INTO l_c3 LIMIT 1000;

FORALL


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O Introduced in Oracle 8.1.5

Sends INSERT, UPDATE or DELETE statements in batches

Can only repeat single DML statement

Works with PL/SQL collections including TABLE, VARRAY,NESTED TABLE etc.

Much faster than equivalent for-loop

Limited functionality

FORALL Example


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pDECLARE

TYPE NUMTYPE IS TABLE OF NUMBER(6) INDEX BY BINARY_INTEGER;TYPE NAMETYPE IS TABLE OF VARCHAR2(30) INDEX BY BINARY_INTEGER;l_c1 NUMTYPE;l_c2 NAMETYPE;l_c3 NUMTYPE;

BEGINFOR i IN 1..100000 LOOP

l_c1(i) := i;l_c2(i) := LPAD (TO_CHAR (i),30,0);l_c3(i) := MOD (i, 100);

END LOOP;

FOR i IN 1..100000 LOOP -- FOR Loop 28 secondsINSERT INTO t1 VALUES (l_c1 (i), l_c2 (i), l_c3(i));

END LOOP;

FORALL f IN 1..100000 LOOP -- FORALL Loop 4 secondsINSERT INTO t1 VALUES (l_c1 (i), l_c2 (i), l_c3(i));

END;

FORALL Performance


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Performance of FORALL statement degrades for very largetables

Rows FOR FORALL

100000 28 4

1000000 240 360

Times in seconds

Conclusion


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Every release contains many new features and enhancementsthat are not highlighted in the marketing material

Oracle assumes all customers will move on to new versionswhen they are released

Study the New Features documentation when you upgrade

Thank you for your interest


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y y

For more information and to provide feedbackplease contact me

My e-mail address is:

[email protected]

My website address is:

www.juliandyke.com

Date post:	07-Apr-2018
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