INDEXES AND INDEXING IN ORACLE 12C -...

INDEXES AND INDEXING IN ORACLE 12C

© Oren Nakdimon

Oren Nakdimon

www.db-oriented.com

[email protected]

+972-54-4393763

@DBoriented

This presentation is available in http://db-oriented.com/presentations © O

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WHO AM I? A CHRONOLOGY BY “ORACLE YEARS”

When What Where

Oracle 6/7 1991-1997 Developer IAF

Oracle 8 1997-1998 Server Group Manager Golden Screens

Oracle 8i/9i 1998-2003 DBA Group Manager TELEknowledge

Oracle 10g/11g 2004-2011 VP R&D and Israel Site Manager

Olista

Oracle 11g/12c 2011-2015 Freelance Consultant

2015- Database Expert

http://www.db-oriented.com/blog [English]

http://www.db-oriented.com/blog-2 [Hebrew]

http://db-oriented.com/presentations



http://www.db-oriented.com/blog



http://www.db-oriented.com/blog-2/






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AGENDA

Multiple indexes on the same column list

Indexes and extended strings

Online operations

Asynchronous global index maintenance

Partial indexes

Advanced index compression





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THE USUAL WARNING

Before you decide to apply any of the presented features in production, make sure:

to thoroughly test them for your applications and environments

that you have the required license to use them




Multiple Indexes on the Same Column List


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INVISIBLE INDEXES (11G)

An invisible index is:

Maintained by DML

Invisible to the optimizer Unless optimizer_use_invisible_indexes is true

@iind





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MULTIPLE INDEXES ON THE SAME COLUMN LIST

Before 12c

Impossible to define several indexes on the same column list

In 12c

It is possible, as long as Only one of the indexes is visible

The indexes are different somehow; for example:

Unique vs. non-unique

B*tree vs. bitmap

Partitioned vs. non-partitioned

@mind




Extended Strings


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EXTENDED STRINGS

By default, maximum length of:

VARCHAR2 and NVARCHAR2 columns is 4KB

RAW columns is 2KB

If MAX_STRING_SIZE = EXTENDED, it is 32KB

Implemented like LOBs

SQL string functions can return 32KB

@32k





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EXTENDED STRINGS – ENABLING

MAX_STRING_SIZE can be changed from STANDARD to EXTENDED, but not from EXTENDED to STANDARD

COMPATIBLE must be set to 12.0.0.0 or higher

Can be done only in UPGRADE mode

The script utl32k.sql must be executed

Objects may be invalidated

Instructions: http://docs.oracle.com/cloud/latest/db121/REFRN/refrn10321.htm




http://docs.oracle.com/cloud/latest/db121/REFRN/refrn10321.htm






Online DDL Operations


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ONLINE DDL OPERATIONS

In 12c more operations can be executed online:

ALTER INDEX VISIBLE

ALTER INDEX INVISIBLE

DROP INDEX ONLINE

ALTER INDEX UNUSABLE ONLINE

ALTER TABLE MOVE SUB/PARTITION ONLINE

@online1|2|3|4





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Offline Operations Online Operations





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Get ORA-54 due to active transactions

Wait for active transactions to end





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Block new DML statements Do not block new DML statements





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ALTER INDEX UNUSABLE drops the index segment

ALTER INDEX UNUSABLE keeps the index segment





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ALTER INDEX UNUSABLE drops the index segment

ALTER INDEX UNUSABLE keeps the index segment

MOVE PARTITION may lead to unusable indexes

MOVE PARTITION keeps the indexes usable




Asynchronous Global Index Maintenance


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ASYNC GLOBAL INDEX MAINTENANCE

DROP/TRUNCATE PARTITION

Before 12c: either fast operation or keeping global indexes usable

In 12c: both fast operation and keeping global indexes usable

New data dictionary column ORPHANED_ENTRIES

Orphaned index entries are:

Not deleted as part of the operation

Not reused (usually)

@async1





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ASYNC GLOBAL INDEX MAINTENANCE

Cleaning out the orphaned entries:

Alter index rebuild

Alter index coalesce cleanup

DBMS_PART.CLEANUP_GIDX

PMO_DEFERRED_GIDX_MAINT_JOB

@async2




Partial Indexes


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PARTIAL INDEXES

In 12c it is possible to create an index on a subset of partitions

Supported for both local and global indexes

The optimizer is aware of it

INDEXING ON | INDEXING OFF

At table/partition level

INDEXING PARTIAL

At index level

New data dictionary columns: INDEXING

@pind




Advanced Index Compression


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INDEX COMPRESSION CONCEPT CREATE INDEX PEOPLE_IDX ON PEOPLE

(LAST_NAME,FIRST_NAME)

Allen,Alex,rowid

Allen,Barbara,rowid

Allen,David,rowid

Allen,James,rowid

Allen,John,rowid

Allen,Linda,rowid

Allen,Mary,rowid

Allen,Michael,rowid

Allen,Patricia,rowid

Allen,Robert,rowid

Blake,David,rowid

Blake,James,rowid

Blake,Lisa,rowid

Blake,Maria,rowid

Blake,William,rowid

#1=Allen

#2=Blake

#1,Alex,rowid

#1,Barbara,rowid

#1,David,rowid

#1,James,rowid

#1,John,rowid

#1,Linda,rowid

#1,Mary,rowid

#1,Michael,rowid

#1,Patricia,rowid

#1,Robert,rowid

#2,David,rowid

#2,James,rowid

#2,Lisa,rowid

#2,Maria,rowid

#2,William,rowid

COMPRESS 1





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INDEX COMPRESSION CONCEPT – CONT.

Smith,Alex,rowid

Smith,Alex,rowid

Smith,Alex,rowid

Smith,Alex,rowid

Smith,Barbara,rowid

Smith,Barbara,rowid

Smith,Barbara,rowid

Smith,Barbara,rowid

Smith,Barbara,rowid

Smith,David,rowid

Smith,David,rowid

Smith,David,rowid

Smith,David,rowid

Smith,David,rowid

Smith,David,rowid

#1=Smith

#1,Alex,rowid

#1,Alex,rowid

#1,Alex,rowid

#1,Alex,rowid

#1,Barbara,rowid

#1,Barbara,rowid

#1,Barbara,rowid

#1,Barbara,rowid

#1,Barbara,rowid

#1,David,rowid

#1,David,rowid

#1,David,rowid

#1,David,rowid

#1,David,rowid

#1,David,rowid





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INDEX COMPRESSION CONCEPT – CONT.

Xa,Alex,rowid

Xander,Barbara,rowid

Xanders,David,rowid

Xanthopoulos,Kevin,rowid

Xanthos,Sandra,rowid

Xavier,Sarah,rowid

Xayachack,Scott,rowid

Xayarath,Martin,rowid

Xayasane,Donna,rowid

Xayavong,Edward,rowid

#1=Xa #2=Xander

#3=Xanders #4=Xanthopoulos

#5=Xanthos #6=Xavier

#7=Xayachack #8=Xayarath

#9=Xayasane #a=Xayavong

#1,Alex,rowid

#2,Barbara,rowid

#3,David,rowid

#4,Kevin,rowid

#5,Sandra,rowid

#6,Sarah,rowid

#7,Scott,rowid

#8,Martin,rowid

#9,Donna,rowid

#a,Edward,rowid

@acmp





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PREFIX INDEX COMPRESSION (SINCE ORACLE8I)

Implemented in the leaf block level

May reduce the size of the index

Today’s optimal prefix length may be suboptimal tomorrow

All the index blocks are compressed the same way





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ADVANCED INDEX COMPRESSION

Same mechanism, but:

Each block may be compressed or not

Each block may have different number of columns in the prefix table

And it’s automatic




INDEXES AND INDEXING IN ORACLE 12C -...

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