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Partition Storage — 1 : Default Partition Sizes in 12c

11g 11.2.0.2 introduced a change whereby the default Initial Extent of a Table Partition was 8MB. However, this did not apply to Index Partitions which could still start with 64KB extents in an AutoAllocate Tablespace.

12cR1 now introduces a parameter to enable large Initial Extent for Index Partitions as well.

SQL> connect / as sysdba                          
Connected.
SQL> select banner from v$version where banner like 'Oracle Database%';

BANNER
--------------------------------------------------------------------------------
Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production

SQL> show parameter deferred

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
deferred_segment_creation boolean TRUE
SQL>
SQL> connect hemant/hemant
Connected.
SQL> create table my_part_tbl (id_column number(6), data_column varchar2(100))
2 partition by range(id_column)
3 (partition p_100 values less than (101),
4 partition p_200 values less than (201),
5 partition p_300 values less than (301),
6 partition p_400 values less than (401),
7 partition p_max values less than (maxvalue))
8 /

Table created.

SQL> create index my_part_tbl_ndx on my_part_tbl(id_column) local;

Index created.

SQL>
SQL> select segment_name, partition_name, segment_type, bytes/1024
2 from user_segments
3 where segment_name like 'MY_PART_%'
4 order by 1,2;

no rows selected

SQL>
SQL> insert into my_part_tbl values (51,'Fifty One');

1 row created.

SQL> insert into my_part_tbl values (151,'One Hundred Fifty One');

1 row created.

SQL> insert into my_part_tbl values (251, 'Two Hundred Fifty One');

1 row created.

SQL> select segment_name, partition_name, segment_type, bytes/1024
2 from user_segments
3 where segment_name like 'MY_PART_%'
4 order by 1,2;

SEGMENT_NAME PARTITION_NA SEGMENT_TYPE BYTES/1024
------------------------------ ------------ ------------------ ----------
MY_PART_TBL P_100 TABLE PARTITION 8192
MY_PART_TBL P_200 TABLE PARTITION 8192
MY_PART_TBL P_300 TABLE PARTITION 8192
MY_PART_TBL_NDX P_100 INDEX PARTITION 64
MY_PART_TBL_NDX P_200 INDEX PARTITION 64
MY_PART_TBL_NDX P_300 INDEX PARTITION 64

6 rows selected.

SQL>

I can enable large Index Partition Extent with a parameter (which can be set with ALTER SESSION)

SQL> alter session set "_index_partition_large_extents"=TRUE;

Session altered.

SQL> insert into my_part_tbl values (351,'Three Hundred Fifty One');

1 row created.

SQL> select segment_name, partition_name, segment_type, bytes/1024
2 from user_segments
3 where segment_name like 'MY_PART_%'
4 order by 1,2;

SEGMENT_NAME PARTITION_NA SEGMENT_TYPE BYTES/1024
------------------------------ ------------ ------------------ ----------
MY_PART_TBL P_100 TABLE PARTITION 8192
MY_PART_TBL P_200 TABLE PARTITION 8192
MY_PART_TBL P_300 TABLE PARTITION 8192
MY_PART_TBL P_400 TABLE PARTITION 8192
MY_PART_TBL_NDX P_100 INDEX PARTITION 64
MY_PART_TBL_NDX P_200 INDEX PARTITION 64
MY_PART_TBL_NDX P_300 INDEX PARTITION 64
MY_PART_TBL_NDX P_400 INDEX PARTITION 8192

8 rows selected.

SQL>

However, I can rebuild the Index Partition Extent as well :

SQL> alter index my_part_tbl_ndx rebuild partition p_400 storage (initial 64K);

Index altered.

SQL> select segment_name, partition_name, segment_type, bytes/1024
2 from user_segments
3 where segment_name like 'MY_PART_%'
4 order by 1,2;

SEGMENT_NAME PARTITION_NA SEGMENT_TYPE BYTES/1024
------------------------------ ------------ ------------------ ----------
MY_PART_TBL P_100 TABLE PARTITION 8192
MY_PART_TBL P_200 TABLE PARTITION 8192
MY_PART_TBL P_300 TABLE PARTITION 8192
MY_PART_TBL P_400 TABLE PARTITION 8192
MY_PART_TBL_NDX P_100 INDEX PARTITION 64
MY_PART_TBL_NDX P_200 INDEX PARTITION 64
MY_PART_TBL_NDX P_300 INDEX PARTITION 64
MY_PART_TBL_NDX P_400 INDEX PARTITION 64

8 rows selected.

SQL>

In the next post, we’ll see more Extents for the Partitions.
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