ausoug partitioning
TRANSCRIPT
Partitioning – Let’s Divide and Conquer!
Gavin Soorma,Senior Oracle DBA, Bankwest
Agenda
• The what, who and why of Partitioning• Partitioning – decisions and challenges• Partitioning – It’s evolution • Types of Partitioning• What’s new in Oracle11g?• Partitioned Indexes• Composite Partitioning• Partition Maintenance Operations• Partitioning and the Cost-based Optimizer• Converting a non-partitioned table to a partitioned table
What is Partitioning?
a) A Structure dividing a space into parts (noun)b) To divide or separate (verb)
Source: Oxford English Dictionary
• Additional licensable option of the Oracle Enterprise Edition.
• Partitioning allows a table, index or index-organized table to be divided and subdivided into smaller pieces called partitions and sub-partitions.
• A partitioned object has multiple pieces that can be managed either collectively or individually.
• Each partition has its own name, and may optionally have its own storage characteristics.
• Tables are partitioned using a 'partitioning key', a set of column/columns which determine in which partition a given row will reside.
Really BigTable
Rea
lly
Big
Tab
le
Partitioning stores a data segment (Table, Index, LOB) asmultiple segments while retaining a logically massive structure.
Partition
Partition
Partition
Partition
Partition
Partition
Partition
Partition
Partition
Partition
Partition
Partition
Partition
Partition
Who Partitions?
• Deciding on what and how to partition is both a Developer and DBA job.
• A good of understanding of the business rules needs to be known about how the data is utilized within Oracle. For example, how data is loaded and queried by the application?
• A great portion of care needs to done in selection of the type of partitioning along with the partition key.
• Poor selection of partition or partition key could lead to poor DML and DDL performance.
• Always test, test, and test again prior to implementing in production.
Why Partition?• For Manageability
Partitioning enables data management operations such data loads, index creation and rebuilding, and backup/recovery at the partition level, rather than on the entire table. This results in significantly reduced times for these operations.
• For Performance
Partitioning improves query performance. In many cases, the results of a query can be achieved by accessing a subset of partitions, rather than the entire table. Partition Pruning and Partition-wise joins can provide order-of-magnitude gains in performance.
• For AvailabilityPartitioning increases the availability of mission-critical databases if critical tables and indexes are divided into partitions to reduce the maintenance windows, recovery times, and impact of failures.
Decisions and Challenges• License cost of Partitioning option (~11,000$ per CPU)
• Number of Partitions.
• Choosing the partitioning key column.
• Partitioning Key – single column, multiple column.
• Choosing the type of partitioning: Range, Hash-List, Range-Hash, Range-List, List-List, Range-Range ….
• Which tables to Partition …. All tables > 2GB (Oracle says so …)
• Think about it if table is > 1 million rows (I say so …)
• Partitioned tables with non partitioned or partitioned index
• Global Index vs Local Index
Oracle Partitioning10 years of innovation…
Database Release Core Functionality
Oracle 8.0 (1997) Range Partitioning
Oracle 8i Hash and Composite Partitioning
Oracle 9i List Partitioning
Oracle 9i Release 2 Composite Range-List Partitioning
Oracle 10g Global Hash Indexes
Oracle 10g Release 2 1M partitions per table
Oracle 11g Interval Partitioning, System Partitioning, REF Partitioning, Virtual Column Partitioning, Partition Advisor , Composite All Partitioning
Partitioning Methods Oracle provides the following partitioning methods(pre 11g):
• Range Partitioning• List Partitioning• Hash Partitioning• Composite Partitioning
Composite Partitioning is a combination of the methods shown above
Composite PartitioningRange-Hash
Partitioned by date_of_salethen ….
Partitioned by salesman_id
Range-List
Partitioned by date_of_salethen ….
Partitioned by sales_region
RANGE Partitioning
• Introduced in Oracle 8.0
• Useful when Data has logical ranges into which it can be distributed by – example, a range of dates
• Data is mapped to partitions based on ranges of partition key values established for each partition
• Each partition has a VALUES LESS THAN clause, which specifies a non inclusive upper bound for the partitions.
• All partitions, except the first, have an implicit lower bound specified by the VALUES LESS THAN clause on the previous partition
• A MAXVALUE literal can be defined for the highest partition. MAXVALUE represents a virtual infinite value
Range Partitioning
create table order_details (order_id number, order_date date) partition by range (order_date) (partition p_jan values less than (to_date('01-FEB-2009','DD-MON-
YYYY')), partition p_feb values less than (to_date('01-MAR-2009','DD-MON-
YYYY')), partition p_mar values less than (to_date('01-APR-2009','DD-MON-
YYYY')), partition p_2009 values less than (MAXVALUE) ) ;
Partitioning Method
Partitioning Column (Key)
Partition descriptions identifying partition bounds
Hash Partitioning
• Introduced in Oracle 8i.• Enables partitioning of data that does not lend itself to
either range or list partitioning• As a better alternative to range partitioning when:
We do not know beforehand how much data maps to a
particular range.
The size of range partitions would differ substantially.
Range partitioning would cause the data to be undesirably clustered.
Hash Partitioning
• Hash function applied to the partitioning key column to place row in required partition.
• Balances the data distribution between all partitions.
• Is an effective means of distributing data, because Oracle hashes the data into a number of partitions, each of which can reside on a separate device.
• Hash Partitioning enables the use of performance features like Partition-wise joins when two tables are hash partitioned on the join key.
Hash Partitioning
• Not suitable for purging and archiving data models.
• Partition pruning is limited to using equality or IN-list predicates.
• User has no control of the row to partition mapping.
• Partition maintenance tasks like splitting, dropping and merging cannot be carried out.
• Partitions can only be added and coalesced.
CREATE TABLE employees ( empno NUMBER(4), ename VARCHAR2(30), sal NUMBER)
PARTITION BY HASH (empno) ( PARTITION h1 TABLESPACE t1, PARTITION h2 TABLESPACE t2, PARTITION h3 TABLESPACE t3, PARTITION h4 TABLESPACE t4);
CREATE TABLE employees (empno NUMBER(4), ename VARCHAR2(30), sal NUMBER) PARTITION BY HASH(empno)PARTITIONS 3STORE IN (t1,t2,t3);
List Partitioning
• Introduced in Oracle 9i.
• List Partitioning is useful for data that has discrete or distinct values.
• Enables to group and organize unordered and unrelated sets of data.
• Gives data warehouse administrators precise control over which data belongs in each partition.
• Enables the partitioning strategy to closely model underlying business processes.
• Unlike range and hash partitioning, multicolumn partition keys are not supported for list partitioning.
CREATE TABLE sales_list(salesman_id NUMBER(5), salesman_name VARCHAR2(30),sales_state VARCHAR2(20),sales_amount NUMBER(10), sales_date DATE)PARTITION BY LIST(sales_state)(PARTITION sales_west VALUES ('California', 'Hawaii'),PARTITION sales_east VALUES ('New York', 'Virginia', 'Florida'),PARTITION sales_central VALUES ('Texas', 'Illinois'),PARTITION sales_other VALUES (DEFAULT));
11g Interval partitioning
• Pre 11g new partitions must be created in advance for new data.
• Additional partitioning management overhead.
• 11g interval partitioning automates partition management.
• Extension of range partitioning.
• Automatic creation of range partitions based on interval.
• Segments are allocated as soon as new data arrives.
• Local indexes are created and maintained as well
CREATE TABLE order_details
(order_id NUMBER,
order_date DATE)
PARTITION BY RANGE (order_date)
INTERVAL (NUMTOYMINTERVAL(1,'MONTH'))
(PARTITION P_FIRST VALUES LESS THAN ('01-JAN-2009'))
;
SQL> select partition_name from user_tab_partitionswhere table_name='ORDER_DETAILS';
PARTITION_NAME------------------------------P_FIRST
SQL> insert into order_detailsvalues(10001,'15-JAN-2009');
1 row created.
SQL> commit;
Commit complete.
SQL> select partition_name from user_tab_partitionswhere table_name='ORDER_DETAILS';
PARTITION_NAME------------------------------P_FIRSTSYS_P101
REF Partitioning
• Related tables benefit from the same partitioning strategy.Example:Orders and Line Items table
• Redundant storage of the same data solves the problem.But Data and maintenance overhead …
• Oracle 11g introduces REF partitioning
Child table inherits the same partitioning strategy as the parent table via PK-FK relationships.
Enhanced performance as well as manageability.
Partition maintenance operations on parent table cascade to child table.
Before REF Partitioning
… …
… …
Table ORDERS
Table LINEITEMS
RANGE(order_date)
PRIMARY KEY(order_id)
RANGE(order_date)
FOREIGN KEY(order_id)
Redundant storage of order_date
Jan 2009 Feb 2009
Jan 2009 Feb 2009
Dec 2009
Dec 2009
11g REF Partitioning
… …
… …
Table ORDERS
Table LINEITEMS
RANGE(order_date)
PRIMARY KEY(order_id)
RANGE(order_date)
FOREIGN KEY(order_id)
Partition By ReferencePartitioning Key in Child TableInherited through PK-FKrelationship
Jan 2009 Feb 2009
Jan 2009 Feb 2009
CREATE TABLE mycustomers
(cust_id NUMBER,
cust_first_name VARCHAR2(20),
cust_last_name VARCHAR2(20),
cust_gender CHAR(1))
PARTITION BY LIST (cust_gender)
(PARTITION p_male VALUES ('M'),
PARTITION p_female VALUES ('F')
);
SQL> ALTER TABLE mycustomers ADD CONSTRAINT p_cust_id PRIMARY KEY (cust_id);
Table altered.
CREATE TABLE mysales
(cust_id NUMBER NOT NULL, quantity_sold NUMBER(10,2),
amount_sold NUMBER(10,2),
CONSTRAINT fk_sales_01
FOREIGN KEY (cust_id)
REFERENCES mycustomers(cust_id))
PARTITION BY REFERENCE (fk_sales_01);
SQL> SELECT TABLE_NAME, PARTITIONING_TYPE,
REF_PTN_CONSTRAINT_NAME FROM USER_PART_TABLES WHERE
TABLE_NAME IN ('MYCUSTOMERS','MYSALES');
TABLE_NAME PARTITION REF_PTN_CONSTRAINT_NAME------------------------------ --------- --------------------------MYCUSTOMERS LISTMYSALES REFERENCE FK_SALES_01
Extended Composite Partitioning
Range List Hash
Range 11g 9i 8i
List 11g 11g 11g
Range/Range Order Date, Shipping DateList/Range Salesman, Date of SaleList/List State, County
Data is partitioned along two dimesions
Introduced in Oracle 8i with Range/Hash
9i extended to Range/List
11g extended to all combinations
Range-Range Partitioning
…
…
…
… … … …
… … … …
Order_date
Ship_date
Jan 08 Feb 08 Mar 08 Dec 08
Jan 08
Feb 08
Dec 08
11g Virtual Column Partitioning
• Virtual columns introduced in Oracle 11g.
• Virtual columns using functions and expressions.
• Virtual column not stored physically.
• Partition data as per business rules and requirements – not just based on application requirements.
• Treated as real columns – only DML not allowed.
• Enhanced performance and manageability
CREATE TABLE emp_year_sal
(ename VARCHAR2(20),
sal NUMBER,
yearly_sal AS (sal*12) VIRTUAL)
PARTITION BY RANGE (yearly_sal)
(PARTITION low_sal VALUES LESS THAN (20000),
PARTITION mid_sal VALUES LESS THAN (40000),
PARTITION high_sal VALUES LESS THAN (60000),
PARTITION others VALUES LESS THAN (MAXVALUE));
SQL> SELECT ename,sal,yearly_sal FROM emp_year_sal;
ENAME SAL YEARLY_SAL---------- ---------- ----------SMITH 800 9600ALLEN 1600 19200WARD 1250 15000JONES 2975 35700MARTIN 1250 15000BLAKE 2850 34200CLARK 2450 29400SCOTT 3000 36000
SQL> SELECT ename,sal,yearly_sal FROM emp_year_sal PARTITION (low_sal);
ENAME SAL YEARLY_SAL-------------------- ---------- ----------SMITH 800 9600ALLEN 1600 19200WARD 1250 15000MARTIN 1250 15000TURNER 1500 18000ADAMS 1100 13200
SQL> SELECT ename,sal,yearly_sal FROM emp_year_sal PARTITION(mid_sal);
ENAME SAL YEARLY_SAL-------------------- ---------- ----------JONES 2975 35700BLAKE 2850 34200CLARK 2450 29400SCOTT 3000 36000FORD 3000 36000
Partitioning Strategy Data Distribution Sample Business Usage
Range Partitioning Based on consecutive ranges of values
Orders table range
partitioned by order_date
List Partitioning Based on unordered lists of
values.
Orders table list partitioned
by country
Hash Partitioning Based on a hash algorithm. Orders table hash partitioned
by customer_id
Composite Partitioning• Range-Range• Range-List• Range-Hash• List-List• List-Range• List-Hash
Based on a combination of two of the above-mentioned basic
techniques of Range, List,
Hash, and Interval Partitioning
•Orders table is range
partitioned by order_date
and sub-partitioned by hash
on customer_id•Orders table is range
partitioned by order_date
and sub-partitioned by range
on shipment_date
10g Partitioning - Summary
11g Partitioning - SummaryPartitioning Extension Partitioning Key Sample Business Usage
Interval Partitioning• Interval•Interval-Range• Interval-List• Interval-Hash
An extension to Range
Partition. Defined by an
interval, providing equi-width
ranges. With the exception of
the first partition all partitions
are automatically created ondemand
when matching data
arrives.
Orders table partitioned by
order_date with a predefined
daily interval, starting with
'01-Jan-2007'
REF Partitioning Partitioning for a child table is
inherited from the parent table
through a primary key –
foreign key relationship. The
partitioning keys are not stored
in actual columns in the child
table.
(Parent) Orders table range
partitioned by order_date
and inherits the partitioning
technique to (child) order
lines table. Column
order_date is only present in
the parent orders table
Virtual column based
Partitioning
Defined by one of the abovementioned
partition techniques
and the partitioning key is
based on a virtual column.
Virtual columns are not stored
on disk and only exist as
metadata.
Orders table has a virtual
column that derives the sales
region based on the first
three digits of the customer
account number. The orders
table is then list partitioned
by sales region.
Partition Data Dictionary Views
• DBA_PART_TABLES• DBA_TAB_PARTITIONS• DBA_TAB_SUBPARTITIONS• DBA_PART_KEY_COLUMNS• DBA_PART_HISTOGRAMS• DBA_PART_INDEXES• DBA_IND_PARTITIONS
DBA_IND_SUBPARTITIONS
Working with Partitions
SQL> select order_date from order_details partition(p_jan);
SQL> select count(*) from SALES_DATA_COMP subpartition(SALES_2000_SP2);
$ exp system/manager TABLES=(order_details:p_jan)
$ exp system/manager TABLES=(order_details:p_jan, order_details:p_jan_subpart1)
Local and Global Indexes
LOCAL INDEX
Index partition
equipartitioned
with table
Single index partition
only contains rows from
corresponding table partition
GLOBAL INDEX
Index partition can
contain rows from
several table
partitions
LOCAL Partitioned Index• Equi-partitioned – each partition of local index exactly associated with
corresponding partition of the table.
• Cannot explicitly add or drop local index partitions – partitions to the index are added or dropped based on partitions being added or dropped from base table.
• Provide higher availability and ease of maintenance.
• Partition maintenance operations on base table will only affect corresponding local index partition – other partitions of the index are not affected improving availability.
• Most suited for DSS environments - easier to manage during data loads and during partition-maintenance operations
SQL> select partition_name from user_tab_partitions where table_name='ORDER_DETAILS';
PARTITION_NAME---------------P_FIRSTSYS_P81SYS_P82
SQL> create index order_det_ind_local on order_details (order_date)
LOCAL << NO PARTITIONING KEY DEFINED (partition p1_ind tablespace users,
partition p2_ind tablespace example);
create index order_det_ind_local on order_details (order_date) *ERROR at line 1:ORA-14024: number of partitions of LOCAL index must equal that of
the underlying table
SQL> create index order_det_ind_local on order_details (order_date)
LOCALtablespace example;
Index created.
SQL> select partition_name,tablespace_name from user_ind_partitions where index_name='ORDER_DET_IND_LOCAL';
PARTITION_NAME TABLESPACE_NAME--------------- ------------------------------P_FIRST EXAMPLESYS_P102 EXAMPLESYS_P103 EXAMPLE
Global Partitioned Index
• Index partitioning key is independent of the table partitioning method.
• Better suited for OLTP environments than local indexes.
• Better performance as they minimise the number of index partition probes.
• Lower availability than local indexes as partition maintenance operations can affect all the index partitions.
Global Partitioned Indexes
• Highest partition of the global index needs to have a MAXVALUE clause to ensure all rows of the underlying table are represented – this partition cannot be dropped.
• Can be created as a global hash or global range partitioned index.
• Can enable partition pruning to take place at the index level even if not possible on the underlying partitioned table
CREATE INDEX order_id_ind_global
ON order_details (order_id)
GLOBAL PARTITION BY RANGE (order_id)
(PARTITION p_ind1 values less than (100001),
PARTITION p_ind2 values less than (200001),
PARTITION p_ind3 values less than (300001)); PARTITION p_ind3 values less than (300001))
*
ERROR at line 6:
ORA-14021: MAXVALUE must be specified for all columns
CREATE INDEX order_id_ind_global ON order_details (order_id)GLOBAL PARTITION BY RANGE (order_id) (PARTITION p_ind1 values less than (100001),PARTITION p_ind2 values less than (200001), PARTITION p_ind3 values less than (300001), PARTITION p_ind_others values less than (MAXVALUE));
Table Partitionedon order_date
Partition Maintenance Operations
• Add • Coalesce• Drop• Truncate• Split• Exchange• Move• Rename• Merge
….
Consider the effect of these operations on Index partitions …..
Partition Maintenance
ALTER TABLE sales ADD PARTITION jan96 VALUES LESS THAN ( '01-FEB-1999' ) TABLESPACE tsx;
ALTER TABLE scubagear ADD PARTITION p_named TABLESPACE gear5;
ALTER TABLE parts MOVE PARTITION depot2 TABLESPACE ts094
NOLOGGING COMPRESS;
ALTER TABLE order_details
SPLIT PARTITION p_2009 AT (TO_DATE ('01-JUL-2009','DD-MON-YYYY'))
INTO (PARTITION p_2009h1, PARTITION p_2009h2);
ALTER TABLE four_seasons MERGE PARTITIONS quarter_one,
quarter_two INTO PARTITION quarter_two ;
Index Maintenance
• Indexes in UNUSABLE state is one of the major issues in dealing with partitioned tables and indexes.
• SELECT or DML statement that accesses index in such state will return an ORA-01502 error.
• Partition maintenance operations will mark the affected local index partition and ALL global index partitions as UNUSABLE.
ALTER TABLE MOVE PARTITION
ALTER TABLE SPLIT PARTITION
ALTER TABLE TRUNCATE PARTITION
ALTER INDEX SPLIT PARTITION
• SQL*Loader operations which bypass index maintenance
SQL> SELECT PARTITION_NAME FROM USER_IND_PARTITIONSWHERE INDEX_NAME='SALES_DATA_IND';
PARTITION_NAME------------------------------SALES_1998SALES_1999SALES_2000SALES_2001P_2009
SQL> ALTER TABLE sales_data MOVE PARTITION sales_1999 TABLESPACE users;
Table altered.
SQL> SELECT PARTITION_NAME,STATUS FROM USER_IND_PARTITIONS WHERE INDEX_NAME='SALES_DATA_IND';
PARTITION_NAME STATUS------------------------------ --------SALES_1998 USABLESALES_1999 UNUSABLESALES_2000 USABLESALES_2001 USABLEP_2009 USABLE
LOCAL Index
SQL> ALTER TABLE sales_data TRUNCATE PARTITION sales_1999_h2;
Table truncated.
SQL> select partition_name,status from user_ind_partitions where index_name='PROD_ID_IND';
PARTITION_NAME STATUS------------------------------ --------P1 UNUSABLEP2 UNUSABLEP_OTHERS UNUSABLE
ALL Global Index Partitions are marked as UNUSABLE even though only one single table partition has been accessed
SQL> SELECT COUNT (*) FROM sales_data WHERE time_id ='01-DEC-1999'
*ERROR at line 1:ORA-01502: index 'SH.SALES_DATA_IND' or partition of such index is
in unusable state
SQL> ALTER SESSION SET SKIP_UNUSABLE_INDEXES=TRUE;
System altered.
SQL> SELECT COUNT (*) FROM sales_data WHERE time_id ='01-DEC-1999‘
COUNT(*)----------
310
SQL> EXPLAIN PLAN FOR SELECT COUNT(*) FROM sales_data WHERE time_id ='01-DEC-1999';
Explained.
SQL> SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY);
PLAN_TABLE_OUTPUT------------------------------------------------------------------------------------------------------Plan hash value: 1021418022------------------------------------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | Pstart| Pstop |------------------------------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 1 | 9 | 342 (26)| 00:00:05 | | || 1 | SORT AGGREGATE | | 1 | 9 | | | | || 2 | PARTITION RANGE SINGLE| | 276 | 2484 | 342 (26)| 00:00:05 | 2 | 2 ||* 3 | TABLE ACCESS FULL | SALES_DATA | 276 | 2484 | 342 (26)| 00:00:05 | 2 | 2 |------------------------------------------------------------------------------------------------------
Because index partition is in an UNUSABLE state, a full table scan is beingperformed of the SALES_DATA table
SQL> ALTER INDEX sales_data_ind REBUILD PARTITION sales_1999;
Index altered.
SQL> EXPLAIN PLAN FOR SELECT COUNT(*) FROM sales_data WHERE time_id ='01-DEC-1999';
Explained.
SQL> SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY);
PLAN_TABLE_OUTPUT---------------------------------------------------------------------------------------------------------------
---------Plan hash value: 3608419564----------------------------------------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | Pstart| Pstop |----------------------------------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 1 | 9 | 5 (0)| 00:00:01 | | || 1 | SORT AGGREGATE | | 1 | 9 | | | | || 2 | PARTITION RANGE SINGLE| | 310 | 2790 | 5 (0)| 00:00:01 | 2 | 2 ||* 3 | INDEX RANGE SCAN | SALES_DATA_IND | 310 | 2790 | 5 (0)| 00:00:01 | 2 | 2 |----------------------------------------------------------------------------------------------------------
Update Global Indexes
• By default, many table maintenance operations on partitioned tables invalidate (mark UNUSABLE) global indexes.
• We can override this default behaviour if you specify UPDATE GLOBAL INDEXES.
• Partition DDL statement takes longer to execute since indexes which were previously marked UNUSABLE are updated
SQL> ALTER TABLE sales_data move partition sales_2000 tablespace example UPDATE GLOBAL INDEXES;
SQL> SELECT PARTITION_NAME,STATUS FROM USER_IND_PARTITIONS WHERE INDEX_NAME='PROD_ID_IND';
PARTITION_NAME STATUS------------------------------ --------P1 USABLEP2 USABLEP_OTHERS USABLE
Partition Pruning• Very important feature for VLDB and Data Warehouses.
• CBO eliminates unneeded partitions when building a partition access list.
• Operations performed only on partitions relevant to the SQL statement dramatically reduce the amount of disk reads as well as CPU time.
• If using global partitioned indexes, can perform partition pruning on the index partitions by eliminating index partitions even if table partitions cannot be eliminated
• Range Partitioning– range, equality and IN-list predicates
• Hash Partitioning – equality and IN-list predicates
SQL> EXPLAIN PLAN FOR SELECT COUNT(*) FROM sales_data WHERE time_id='21-JAN-2000';
Explained.
SQL> SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY);
PLAN_TABLE_OUTPUT---------------------------------------------------------------------------------------------------------------
---------Plan hash value: 1021418022------------------------------------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | Pstart| Pstop |------------------------------------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 1 | 8 | 246 (3)| 00:00:03 | | || 1 | SORT AGGREGATE | | 1 | 8 | | | | || 2 | PARTITION RANGE SINGLE| | 468 | 3744 | 246 (3)| 00:00:03 | 5 | 5 ||* 3 | TABLE ACCESS FULL | SALES_DATA | 468 | 3744 | 246 (3)| 00:00:03 | 5 | 5 |------------------------------------------------------------------------------------------------------
The Pstart and Pstop columns indicate that a single partition has been accessed by the optimizer even though the “TABLE ACCESS FULL” operation is indicated
Partition-wise Joins
• Significantly improve the performance when joining tables with millions of rows.
• Useful in VLDB and DSS environments.
• Applies to Merge and Hash joins and not to Nested Loop joins.
• Two tables that are equi-partitioned on the join column.
• Optimizer breaks the join operation into a number of smaller joins that can be performed sequentially or in parallel.
• If using parallel joins, will minimise the data exchanged by parallel slaves
CREATE TABLE "SH"."SALES_DATA_HASH" ( "PROD_ID" NUMBER NOT NULL ENABLE, "CUST_ID" NUMBER NOT NULL ENABLE, "TIME_ID" DATE NOT NULL ENABLE, "CHANNEL_ID" NUMBER NOT NULL ENABLE, "PROMO_ID" NUMBER NOT NULL ENABLE, "QUANTITY_SOLD" NUMBER(10,2) NOT NULL ENABLE, "AMOUNT_SOLD" NUMBER(10,2) NOT NULL ENABLE )
PCTFREE 5 PCTUSED 40 INITRANS 1 MAXTRANS 255 NOCOMPRESS NOLOGGING PARTITION BY HASH ("CUST_ID") PARTITIONS 4 STORE IN (EXAMPLE, USERS)
;
CREATE TABLE SH.CUSTOMERS_HASH(CUST_ID NUMBER, CUST_FIRST_NAME VARCHAR2(20),CUST_LAST_NAME VARCHAR2(40),CUST_CITY VARCHAR2(30))PARTITION BY HASH (CUST_ID) PARTITIONS 4 STORE IN (EXAMPLE, USERS)
;
Both tables are hash partitioned on the CUST_ID column
SQL> EXPLAIN PLAN FOR
SELECT SUM (a.amount_sold),b.cust_city
FROM sales_data_hash a, customers_hash b
WHERE a.cust_id =b.cust_id
GROUP BY b.cust_city;
Explained.
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------
Plan hash value: 4232629991
--------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | Pstart| Pstop |
--------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 839K| 44M| 1158 (10)| 00:00:14 | | |
| 1 | HASH GROUP BY | | 839K| 44M| 1158 (10)| 00:00:14 | | |
| 2 | PARTITION HASH ALL | | 839K| 44M| 1085 (4)| 00:00:14 | 1 | 4 |
|* 3 | HASH JOIN | | 839K| 44M| 1085 (4)| 00:00:14 | | |
| 4 | TABLE ACCESS FULL| CUSTOMERS_HASH | 62069 | 1818K| 61 (2)| 00:00:01 | 1 | 4 |
| 5 | TABLE ACCESS FULL| SALES_DATA_HASH | 839K| 20M| 1012 (3)| 00:00:13 | 1 | 4 |
Statistics---------------------------------------------------------- 7 recursive calls 0 db block gets 4794 consistent gets 296 physical reads 0 redo size 18197 bytes sent via SQL*Net to client 932 bytes received via SQL*Net from client 42 SQL*Net roundtrips to/from client 2 sorts (memory) 0 sorts (disk)
Statistics-------------------------------------------- 7 recursive calls 0 db block gets 6039 consistent gets 4100 physical reads 0 redo size 18197 bytes sent via SQL*Net to client 932 bytes received via SQL*Net from client 42 SQL*Net roundtrips to/from client 2 sorts (memory) 0 sorts (disk) 608 rows processed
Note the physical reads and consistentgets using the Partition wise join on Hash Partitioned versus Non Partitioned tables
Using DBMS_REDEFINITION
SQL> EXEC DBMS_REDEFINITION.CAN_REDEF_TABLE('SH','SALES_NO_PART');
PL/SQL PROCEDURE SUCCESSFULLY COMPLETED.
CREATE TABLE "SH"."SALES_INTERIM"
( "PROD_ID" NUMBER NOT NULL ENABLE,
...
) PCTFREE 5 PCTUSED 40 INITRANS 1 MAXTRANS 255 NOCOMPRESS
TABLESPACE "EXAMPLE"
PARTITION BY RANGE ("TIME_ID")
(PARTITION SALES_1998 VALUES LESS THAN (TO_DATE('01-JAN-1999','DD-MON-YYYY')),
...
...
PARTITION SALES_2001 VALUES LESS THAN (TO_DATE('01-JAN-2002','DD-MON-YYYY')),
PARTITION P_2009 VALUES LESS THAN (MAXVALUE)
);
DECLAREERROR_COUNT PLS_INTEGER := 0;BEGINDBMS_REDEFINITION.COPY_TABLE_DEPENDENTS('SH', 'SALES_NO_PART', 'SALES_INTERIM',1, TRUE, TRUE, TRUE, FALSE,ERROR_COUNT); DBMS_OUTPUT.PUT_LINE('ERRORS := ' || TO_CHAR(ERROR_COUNT)); END; /
SQL> EXEC DBMS_REDEFINITION.FINISH_REDEF_TABLE ('SH','SALES_NO_PART','SALES_INTERIM');
PL/SQL PROCEDURE SUCCESSFULLY COMPLETED.
SQL> SELECT PARTITION_NAME FROM USER_TAB_PARTITIONS WHERE TABLE_NAME='SALES_NO_PART';
PARTITION_NAME
------------------------------
SALES_1998
SALES_1999
SALES_2000
SALES_2001
P_2009
SQL> SELECT COUNT(*) FROM SALES_NO_PART PARTITION(SALES_1999);
COUNT(*)
----------
247945
SQL> DROP TABLE SALES_INTERIM;
TABLE DROPPED.
Exchange Partition
SQL> select partition_name from user_tab_partitions where table_name='SALES_NO_PART';
PARTITION_NAME------------------------------SALES_1998SALES_1999SALES_2000
SQL> select count(*) from sales_2001; << NON PARTITIONED TABLE
COUNT(*)---------- 259418
SQL> alter table sales_no_part add partition sales_2001 2 values less than ('01-JAN-2002') tablespace example;
Table altered.
SQL> select partition_name from user_tab_partitions where table_name='SALES_NO_PART';
PARTITION_NAME------------------------------SALES_1998SALES_1999SALES_2000SALES_2001
SQL> ALTER TABLE sales_no_partEXCHANGE PARTITION sales_2001WITH TABLE sales_2001
UPDATE GLOBAL INDEXES;
Table altered.
SQL> select count(*) from sales_no_part partition(sales_2001);
COUNT(*)---------- 259418
