1 Forgotten Features Julian Dyke Independent Consultant Web Version juliandyke.com © 2005 Julian...

1

Forgotten Features

Julian Dyke

Independent Consultant

Web Version

juliandyke.com

© 2005 Julian Dyke

2

© 2005 Julian Dykejuliandyke.com

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 and

Auditing

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TRACEFILE_IDENTIFIER Initialisation Parameter Introduced in Oracle 8.1.7

tracefile_identifier = '<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 SESSION SET 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 operators

SELECT 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 ISBEGIN

RETURN x + y - BITAND (x,y);END;/

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

RETURN BITOR (x,y) - BITAND (x,y);END;/

Beware of overflows

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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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System Triggers Introduced in Oracle 8.1.5 Must be created by SYS (as SYSDBA)

CREATE OR REPLACE TRIGGER us01_logonAFTER LOGON ON us01.SCHEMABEGIN

dbms_session.set_sql_trace (TRUE);END;

CREATE OR REPLACE TRIGGER us01_logoffBEFORE LOGOFF ON us01.SCHEMABEGIN

dbms_session.set_sql_trace (FALSE);END;

ALTER TRIGGER us01_login ENABLE;

ALTER TRIGGER us01_login DISABLE;

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DBMS_MONITOR Introduced in Oracle 10.1 To enable trace in another session use

DBMS_MONITOR.SESSION_TRACE_ENABLE( SESSION_ID NUMBER, -- SID

SERIAL_NUM NUMBER, -- Serial Number WAITS BOOLEAN, -- Include Waits BINDS BOOLEAN -- Include Binds

);

To disable trace in another session use

DBMS_MONITOR.SESSION_TRACE_DISABLE( SESSION_ID NUMBER, -- SID

SERIAL_NUM NUMBER -- Serial Number );

Waits (event 10046 level 8) are enabled by default Binds (event 10046 level 4) are disabled by default

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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 Waits

BINDS 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 );

12


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 trigger1BEFORE INSERT ON table1 FOR EACH ROWDECLARE

PRAGMA AUTONOMOUS_TRANSACTION;BEGIN

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

END;/

13


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

user can be audited.

To enable SYS auditing set AUDIT_SYS_OPERATIONS parameter to TRUE

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

Default directory is $ORACLE_HOME/rdbms/audit

Filename is ora_<pid>.aud where pid is the operating system process ID

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Testing and

Benchmarking

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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.SEED

procedure

SAMPLE clause Can be made deterministic by enabling event 10193 Level specifies seed

ALTER SESSION SET EVENTS ‘10193 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 cache

ALTER SYSTEM FLUSH BUFFER_CACHE;

In Oracle 9.0.1 and above the following command has the same effect

ALTER SESSION SET EVENTS ‘IMMEDIATE 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# NUMBEROBJECT_OWNER VARCHAR2(30)OBJECT_NAME VARCHAR2(64)OPTIMIZER VARCHAR2(20)ID NUMBERPARENT_ID NUMBERDEPTH NUMBERPOSITION NUMBERCOST 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 why execution 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 partition pruning, 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 FOR SET STATEMENT_ID = 'STATEMENT1' FORSELECT t1.c2, t2.c2FROM t1, t2WHERE t1.c1 = t2.c1AND t1.c2 = 10;

SELECT * FROM TABLE (

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 Parallel execution queries are automatically formatted e.g.

EXPLAIN PLAN FOR SELECT /*+ ORDERED PARALLEL (t1 2) USE_MERGE (t1 t2) */

t1.c2, t2.c2FROM t1, t2WHERE t1.c1 = t2.c1AND t1.c2 = 10;


The plan table can be queried using

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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 FOR SELECT 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)

);


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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"<250)

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DBMS_XPLAN In Oracle 10.1 and above

New DISPLAY_CURSOR function By default displays plan for last statement executed in

session

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 more

user 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 ‘<sid>,<serial#>’;

For example

ALTER SYSTEM KILL SESSION ‘133,523’;

Next command issued by killed session will return error

ORA-00028: your session has been killed

36


Renaming Database Objects To rename a table:

RENAME oldname TO newname;

In Oracle 9.2 and above to rename a column

ALTER TABLE t1 RENAME COLUMN oldname TO newname;

ALTER TABLE t1 RENAME CONSTRAINT oldname TO newname;

In Oracle 10.1 and above to rename a tablespaceALTER 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;

37


Dropping Columns Introduced in 8.1.5

Columns can be dropped from a table using the ALTER TABLE 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 restarted from the point of failure

38


Dropping Columns To drop a column immediately use

ALTER TABLE table1 DROP COLUMN column2;

Columns can also be marked unused immediately and 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

39


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 DATABASE DEFAULT TEMPORARY TABLESPACE <tablespace>;

In Oracle 10.1 and above a default permanent tablespace can be defined

ALTER DATABASE DEFAULT TABLESPACE <tablespace>;

41


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

42


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

43


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 tablespace ‘TS99’

4 – Error is written to alert log

44


Resumable Statements5 – (Optional) DBA is notified by message generated by AFTER SUSPEND trigger

6 – DBA queries DBA_RESUMABLE view for details of suspended operation

7 – DBA fixes error condition e.g.

ALTER TABLESPACE TS99ADD DATAFILE <filename> SIZE <size>;

8 – Suspended operation resumes automatically

9 – Operation completes successfully

45


Resumable Statements In Oracle 10.1 and above resumable statements can be

enabled at instance levelALTER SYSTEM SET resumable_timeout = <timeout>;

Resumable statements can be disabled at instance level using

ALTER SYSTEM SET resumable_timeout = 0;

Resumable statements can be enabled at session level using

ALTER SESSION SET resumable_timeout = <timeout>;

Resumable statements can be disabled at session level using

ALTER SESSION SET 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 deletes Oracle Managed Files

47


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 tablespaces following a database restart use:

ALTER DATABASE END BACKUP;

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Tables

49


Row Movement In Oracle 8.0 updating the partition key columns in a range

partitioned table fails if it would cause the row to be migrated to another 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

50


Row Movement

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

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

CREATE TABLE table1 (

column1 NUMBER,column2 NUMBER

)PARTITION BY ….ENABLE ROW MOVEMENT;

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

51


External Tables External tables

read-only tables definition is stored in data dictionary data is stored outside the database in operating system

flat files 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

52


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’)

);

53


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 ARCHIVING

modes

Description Time in seconds

NoArchiving Archiving

Use SQL*Loader with CONVENTIONAL path load to INSERT 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 from internal table to internal table

15 283

54


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 achieve optimal compression ratios

A segment may contain compressed and uncompressed blocks

55


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

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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

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Data Segment Compression

1993Ayrton Senna4

1996Olivier PanisLigier

19943 2

19953 2

19971 2

20024 0

20011 2

20004 0

19991 2

19984 Mika Hakkinen

SymbolTable

Row Data

2 David Coulthard0

3 Ferrari1

5 Michael Schumacher2

Benetton3 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

58


Data Segment Compression Compression ratios vary with

number of rows number of columns cardinality of rows

For example – loading SALES table from sales history demo schema

$ORACLE_HOME/demo/schema/sales_history

Block Size

Uncompressed Size (Blocks)

Compressed Size (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

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

table

Compressed Blocks Elapsed TIme (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 compressed table

SELECT SUM (quantity_sold) FROM sales;

Compressed Blocks Elapsed TIme (Secs)

CPU Time (Secs)

No 4398 3.41 2.77

Yes 2850 3.78 3.53

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Indexes

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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

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Index Leaf Compression

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

Italy

Milan

Rome

Prefix Row

Prefix Row

Prefix Row

Suffix Row

Suffix Row

Suffix Row

Suffix Row

Suffix Row

Suffix Row CREATE 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;

64


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

65


Index Rebuild Online Introduced in 8.1.5

create or rebuild index whilst allowing concurrent DML operations

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

66


Index Rebuild Online To build an index online use

ALTER INDEX index1 REBUILD ONLINE;

Can be executed in parallel

Three phasesprepare phase

index created data dictionary updated

build phase index populated changes written to journal table

merge phaserows in journal table are merged

67


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

68


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 Oracle updates a table in the data dictionary when that index is included 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

69


Index Monitoring

SELECT index_name,monitoring FROM 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

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Index Monitoring Execute all possible statements against the table

SELECT index_name,used FROM 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

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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 fail with the following error:

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

72


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 leading column

If the index is non-partitioned, table, column and index statistics 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;

73


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

74


Undoand

Redo

75


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 user’s sort space can overflow to sort segment in user’s temporary

tablespace

Indexes can be created against global temporary tables same scope and duration

76


Global Temporary Tables 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

77


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;


No rows returned

78


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

79


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 operations requiring 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;

80


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;

81


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 level

ALTER 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

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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;

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Native Dynamic SQL In Oracle 8.1.5 and above EXECUTE IMMEDIATE can execute DDL

statements

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’;

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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);

BEGIN l_str := 'SELECT c0l1 FROM tab1 WHERE c2 = 20';

EXECUTE IMMEDIATE l_str INTO l_c1;DBMS_OUTPUT.PUT_LINE ('Result is ‘ || l_c1);

END;

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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

DECLAREl_c1 NUMBER;l_str VARCHAR2(1000);

BEGIN l_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;

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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

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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;LOOP

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

END LOOP; CLOSE c1; END;

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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 set grows

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

FETCH c1 BULK COLLECT INTO l_c3 LIMIT 1000;

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FORALL 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

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FORALL Example DECLARE

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;

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FORALL Performance Performance of FORALL statement degrades for very large

tables

Rows FOR FORALL

100000 28 4

1000000 240 360

Times in seconds

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Conclusion Every release contains many new features and enhancements

that are not highlighted in the marketing material

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

Study the New Features documentation when you upgrade

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Thank you for your interest

For more information and to provide feedback

please contact me

My e-mail address is:[email protected]

My website address is:

www.juliandyke.com

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