18 Partitioned Tables and IndexesThis chapter describes
partitioned tables and indexes. It covers the following topics:
Introducton to Parttonng Overvew of Parttonng Methods Overvew of
Parttoned Indexes Parttonng to Improve PerformanceNote:This
functionality is available only if you purchase the Partitioning
option.Introduction to PartitioningPartitioning addresses key ssues
n supportng very arge tabes and ndexes by ettng you decompose them
nto smaer and more manageabe peces caed partitions. SOL queres and
DML statements do not need to be moded n orderto access parttoned
tabes. However, after parttons are dened, DDL statements can access
and manpuate ndvduas parttons rather than entre tabes or ndexes.
Ths s how parttonng can smpfy the manageabty of arge database
ob|ects. Aso, parttonng s entrey transparent to appcatons.Each
partton of a tabe or ndex must have the same ogca attrbutes, such
as coumn names, datatypes, and constrants, but each partton can
have separate physca attrbutes such as pctfree, pctused, and
tabespaces.Parttonng s usefu for many dherent types of appcatons,
partcuary appcatons that manage arge voumes of data. OLTP systems
often benet from mprovements n manageabty and avaabty, whe data
warehousng systems benet from performance and manageabty.Note:All
partitions of a partitioned object ust reside in tablespaces of a
single bloc! si"e.See Also: "Mutpe Bock Szes" Oracle Database Data
Warehousing Guide and Oracle Database Administrator's Guide for
more nformaton about parttonngParttonng ohers these advantages:
Parttonng enabes data management operatons such data oads, ndex
creaton and rebudng, and backup/recovery at the partton eve, rather
than on the entre tabe. Ths resuts n sgncanty reduced tmes for
these operatons. Parttonng mproves query performance. In many
cases, the resuts of a query can be acheved by accessng a subset of
parttons, rather than the entre tabe. For some queres, ths technque
(caed partition pruning) can provde order-of-magntude gans n
performance. Parttonng can sgncanty reduce the mpact of schedued
downtme for mantenance operatons.Partton ndependence for partton
mantenance operatons ets you perform concurrent mantenance
operatons on dherent parttons of the same tabe or ndex. You can aso
run concurrent SELECT and DML operatons aganst parttons that are
unahected by mantenance operatons. Parttonng ncreases the avaabty
of msson-crtca databases f crtca tabesand ndexes are dvded nto
parttons to reduce the mantenance wndows, recovery tmes, and mpact
of faures. Parttonng can be mpemented wthout requrng any modcatons
to your appcatons. For exampe, you coud convert a nonparttoned tabe
to a parttoned tabe wthout needng to modfy any of the SELECT
statements or DMLstatements whch access that tabe. You do not need
to rewrte your appcaton code to take advantage of parttonng.Fgure
18-1 ohers a graphca vew of how parttoned tabes dher from
nonparttoned tabes.Figure 18-1 A View of Partitioned
Tables#escription of $%igure 18&1 A 'iew of Partitioned
Tables$Partition (eyEach row n a parttoned tabe s unambguousy
assgned to a snge partton. The partton key s a set of one or more
coumns that determnes the partton for each row. Orace automatcay
drects nsert, update, and deete operatons to the approprate partton
through the use of the partton key. A partton key: Conssts of an
ordered st of 1 to 16 coumns Cannot contan a LEVEL, ROWID, or
MLSLABEL pseudocoumn or a coumn of type ROWID Can contan coumns
that are NULLabePartitioned TablesTabes can be parttoned nto up to
1024K-1 separate parttons. Any tabe can be parttoned except those
tabes contanng coumns wth LONG or LONGRAW datatypes. You can,
however, use tabes contanng coumns wth CLOB or BLOB
datatypes.Note:To reduce dis! use and eory use )specifically* the
buffer cache+* you can store tables and partitioned tables in a
copressed forat inside the database. This often leads to a better
scaleup for read&only operations. Table copression can also
speed up ,uery execution. There is* however* a slight cost in -P.
overhead.See Also:$Table -opression$Partitioned Index&/rgani"ed
TablesYou can partton ndex-organzed tabes by range, st, or hash.
Parttoned ndex-organzed tabes are very usefu for provdng mproved
manageabty, avaabty, and performance for ndex-organzed tabes. In
addton, data cartrdges that use ndex-organzed tabes can take
advantage of the abty to partton ther stored data. Common exampes
of ths are the Image and interMeda cartrdges.For parttonng an
ndex-organzed tabe: Partton coumns must be a subset of prmary key
coumns Secondary ndexes can be parttoned - ocay and gobay OVERFLOW
data segments are aways equparttoned wth the tabe parttons/verview
of Partitioning 0ethodsOrace provdes the foowng parttonng methods:
Range Parttonng Lst Parttonng Hash Parttonng Composte
ParttonngFgure 18-2 ohers a graphca vew of the methods of
parttonng.Figure 18-2 List, Range, and Hash Partitioning#escription
of $%igure 18&1 2ist* 3ange* and 4ash Partitioning$Composte
parttonng s a combnaton of other parttonng methods. Orace supports
range-hash and range-st composte parttonng. Fgure 18-3ohers a
graphca vew of range-hash and range-st composte parttonng.Figure
18-3 o!"osite Partitioning#escription of $%igure 18&5 -oposite
Partitioning$3ange PartitioningRange parttonng maps data to
parttons based on ranges of partton key vaues that you estabsh for
each partton. It s the most common type of parttonng and s often
used wth dates. For exampe, you mght want to partton saes data nto
monthy parttons.When usng range parttonng, consder the foowng rues:
Each partton has a VALUES LESS THAN cause, whch speces a nonncusve
upper bound for the parttons. Any vaues of the partton key equa to
or hgher than ths tera are added to the next hgher partton. A
parttons, except the rst, have an mpct ower bound speced by the
VALUES LESS THAN cause on the prevous partton. A MAXVALUE tera can
be dened for the hghest partton. MAXVALUE represents a vrtua nnte
vaue that sorts hgher than any other possbe vaue for the partton
key, ncudng the nu vaue.A typca exampe s gven n the foowng secton.
The statement creates a tabe (sales_range) that s range parttoned
on the sales_date ed.3ange Partitioning 6xapleCREATE TABLE
sales_range (salesman_idNUMBER(5), salesman_name VARCHAR2(30),
sales_am!n"NUMBER(#0), sales_da"e$ATE)%ART&T&'N B(
RAN)E(sales_da"e) (%ART&T&'N sales_*an2000 VALUE+ LE++
THAN(T'_$ATE(,02-0#-2000,,,MM-$$-((((,)),%ART&T&'N
sales_.e/2000 VALUE+ LE++
THAN(T'_$ATE(,03-0#-2000,,,MM-$$-((((,)),%ART&T&'N
sales_mar2000 VALUE+ LE++
THAN(T'_$ATE(,00-0#-2000,,,MM-$$-((((,)),%ART&T&'N
sales_a1r2000 VALUE+ LE++
THAN(T'_$ATE(,05-0#-2000,,,MM-$$-((((,)))22ist PartitioningLst
parttonng enabes you to expcty contro how rows map to parttons. You
do ths by specfyng a st of dscrete vaues for the parttonng key n
the descrpton for each partton. Ths s dherent from range parttonng,
where a range of vaues s assocated wth a partton and from hash
parttonng, where a hash functon contros the row-to-partton mappng.
The advantage of st parttonng s that you can group and organze
unordered and unreated sets of data n a natura way.The detas of st
parttonng can best be descrbed wth an exampe. In ths case, et's say
you want to partton a saes tabe by regon. That means groupng states
together accordng to ther geographca ocaton as n the foowng
exampe.2ist Partitioning 6xapleCREATE TABLE
sales_lis"(salesman_idNUMBER(5), salesman_name
VARCHAR2(30),sales_s"a"e VARCHAR2(20),sales_am!n"NUMBER(#0),
sales_da"e$ATE)%ART&T&'N B(
L&+T(sales_s"a"e)(%ART&T&'N sales_3es"
VALUE+(,Cali.rnia,, ,Ha3aii,),%ART&T&'N sales_eas" VALUE+
(,Ne3 (r4,, ,Virginia,, ,5lrida,),%ART&T&'N sales_6en"ral
VALUE+(,Te7as,, ,&llinis,),%ART&T&'N sales_"8er
VALUE+($E5AULT))2A row s mapped to a partton by checkng whether the
vaue of the parttonng coumnfor a row fas wthn the set of vaues that
descrbes the partton. For exampe, the rowsare nserted as foows: (1,
!"#nes!, !Ha$a%%!, 1, !&'"AN'(!) maps to partton sales_$est
((1, !S)%t*!, !Fl#r%da!, 1&, !1&'"AN'(!) maps to partton
sales_east (+(, !Lee!, !C#l#rad#!, 1+, !(1'"AN'(!) maps to partton
sales_#t*erUnke range and hash parttonng, mutcoumn partton keys are
not supported for st parttonng. If a tabe s parttoned by st, the
parttonng key can ony consst of a snge coumn of the tabe.The
DEFAULT partton enabes you to avod specfyng a possbe vaues for a
st-parttoned tabe by usng a defaut partton, so that a rows that do
not map to any other partton do not generate an error.4ash
PartitioningHash parttonng enabes easy parttonng of data that does
not end tsef to range or st parttonng. It does ths wth a smpe
syntax and s easy to mpement. It s a better choce than range
parttonng when: You do not know beforehand how much data maps nto a
gven range The szes of range parttons woud dher qute substantay or
woud be dmcut to baance manuay Range parttonng woud cause the data
to be undesraby custered Performance features such as parae DML,
partton prunng, and partton-wse |ons are mportantThe concepts of
spttng, droppng or mergng parttons do not appy to hash
parttons.Instead, hash parttons can be added and coaesced.See
Also:Oracle Database Administrator's Guide for ore inforation about
partition tas!s such as splitting partitions4ash Partitioning
6xapleCREATE TABLE sales_8as8(salesman_idNUMBER(5), salesman_name
VARCHAR2(30), sales_am!n"NUMBER(#0), 3ee4_n NUMBER(2))
%ART&T&'N B( HA+H(salesman_id) %ART&T&'N+ 0 +T'RE
&N ("s#, "s2, "s3, "s0)2The precedng statement creates a tabe
sales_*as*, whch s hash parttoned on sales)an_%d ed. The tabespace
names are ts1, ts(, ts+, andts,. Wth ths syntax, we ensure that we
create the parttons n a round-robn manner across the speced
tabespaces.-oposite PartitioningComposte parttonng parttons data
usng the range method, and wthn each partton, subparttons t usng
the hash or st method. Composte range-hash parttonng provdes the
mproved manageabty of range parttonng and the data pacement,
strpng, and paraesm advantages of hash parttonng. Composte range-st
parttonng provdes the manageabty of range parttonng and the expct
contro of st parttonng for the subparttons.Composte parttonng
supports hstorca operatons, such as addng new range parttons, but
aso provdes hgher degrees of paraesm for DML operatons and ner
granuarty of data pacement through subparttonng.-oposite
Partitioning 3ange&4ash 6xapleCREATE TABLE sales_6m1si"e
(salesman_idNUMBER(5), salesman_name VARCHAR2(30),
sales_am!n"NUMBER(#0), sales_da"e$ATE)%ART&T&'N B(
RAN)E(sales_da"e) +UB%ART&T&'N B(
HA+H(salesman_id)+UB%ART&T&'N TEM%LATE(+UB%ART&T&'N
s1# TABLE+%ACE "s#,+UB%ART&T&'N s12 TABLE+%ACE
"s2,+UB%ART&T&'N s13 TABLE+%ACE "s3,+UB%ART&T&'N
s10 TABLE+%ACE "s0)(%ART&T&'N sales_*an2000 VALUE+ LE++
THAN(T'_$ATE(,02-0#-2000,,,MM-$$-((((,)) %ART&T&'N
sales_.e/2000 VALUE+ LE++ THAN(T'_$ATE(,03-0#-2000,,,MM-$$-((((,))
%ART&T&'N sales_mar2000 VALUE+ LE++
THAN(T'_$ATE(,00-0#-2000,,,MM-$$-((((,)) %ART&T&'N
sales_a1r2000 VALUE+ LE++ THAN(T'_$ATE(,05-0#-2000,,,MM-$$-((((,))
%ART&T&'N sales_ma92000 VALUE+ LE++
THAN(T'_$ATE(,0:-0#-2000,,,MM-$$-((((,)))2Ths statement creates a
tabe sales_-#).#s%te that s range parttoned on the sales_date ed
and hash subparttoned on sales)an_%d. When you use a tempate, Orace
names the subparttons by concatenatng the partton name, an
underscore, and the subpartton name from the tempate. Orace paces
ths subpartton n the tabespace speced n the tempate. In the prevous
statement, sales_/an(_s.1 s created and paced n tabespace ts1 whe
sales_/an(_s., s created and paced n tabespace ts,. In the same
manner, sales_a.r(_s.1 s created and paced n tabespace ts1 whe
sales_a.r(_s., s created and paced n tabespace ts,. Fgure18-4 ohers
a graphca vew of the prevous exampe.Figure 18-# o!"osite Range-Hash
Partitioning#escription of $%igure 18&7 -oposite 3ange&4ash
Partitioning$-oposite Partitioning 3ange&2ist 6xapleCREATE
TABLE /imn"8l9_reginal_sales(de1"n NUMBER, i"em_n VARCHAR2(20),
"7n_da"e $ATE, "7n_am!n" NUMBER, s"a"e
VARCHAR2(2))%ART&T&'N B( RAN)E
("7n_da"e)+UB%ART&T&'N B( L&+T
(s"a"e)+UB%ART&T&'N TEM%LATE(+UB%ART&T&'N eas"
VALUE+(,N(,, ,VA,, ,5L,) TABLE+%ACE "s#,+UB%ART&T&'N 3es"
VALUE+(,CA,, ,'R,, ,H&,) TABLE+%ACE "s2,+UB%ART&T&'N
6en"ral VALUE+(,&L,, ,T;,, ,M',) TABLE+%ACE
"s3)(%ART&T&'N *an.e/_2000 VALUE+ LE++ THAN (T'_$ATE(,#
