分区默认segment大小变化(64k—>8M)

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标题：分区默认segment大小变化(64k—>8M)

作者：惜分飞©版权所有[未经本人同意,不得以任何形式转载,否则有进一步追究法律责任的权利.]

在11.2.0.3(从11.2.0.2开始)创建分区表,每个分区默认大小为8M,是由_partition_large_extents参数控制,可以算是11.2.0.2开始的一个新特性,为了减少extent数量,提高分区表性能,而设置的一个参数,默认为true，即分区表的每个extent为8M,这里对于_partition_large_extents为true和false的情况进行了测试
_partition_large_extents=true

SQL> select * from v$version;
BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - Production
PL/SQL Release 11.2.0.3.0 - Production
CORE    11.2.0.3.0      Production
TNS for Linux: Version 11.2.0.3.0 - Production
NLSRTL Version 11.2.0.3.0 - Production
SQL> show parameter deferred_segment_creation
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
deferred_segment_creation            boolean     TRUE
SQL> show parameter _partition_large_extents;
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
_partition_large_extents             string      FALSE
SQL> create table test_com_partition_1
  2  (
  3  name varchar2(4000) not null,
  4  aaaaa number not null,
  5  bbbbb varchar2(180) not null,
  6  ccccc varchar2(4000),
  7  constraint pk_test_com_partition_1 primary key(name)
  8  )
  9  partition by range(aaaaa) interval (1)
 10  subpartition by range (bbbbb)
 11  subpartition template
 12  (
 13  subpartition sp_2008 values less than ('2009') tablespace sp_2008,
 14  subpartition sp_2009 values less than ('2010') tablespace sp_2009,
 15  subpartition sp_2010 values less than ('2011') tablespace sp_2010,
 16  subpartition sp_2011 values less than ('2012') tablespace sp_2011,
 17  subpartition sp_2012 values less than ('2013') tablespace sp_2012,
 18  subpartition sp_2013 values less than ('2014') tablespace sp_2013,
 19  subpartition sp_2014 values less than ('2015') tablespace sp_2014,
 20  subpartition sp_2015 values less than ('2016') tablespace sp_2015,
 21  subpartition sp_2016 values less than ('2017') tablespace sp_2016,
 22  subpartition sp_2017 values less than ('2018') tablespace sp_2017,
 23  subpartition sp_2018 values less than ('2019') tablespace sp_2018,
 24  subpartition sp_2019 values less than ('2020') tablespace sp_2019,
 25  subpartition sp_2020 values less than ('2021') tablespace sp_2020,
 26  subpartition sp_2021 values less than ('2022') tablespace sp_2021,
 27  subpartition sp_2022 values less than ('2023') tablespace sp_2022,
 28  subpartition sp_2023 values less than ('2024') tablespace sp_2023,
 29  subpartition sp_2024 values less than ('2025') tablespace sp_2024,
 30  subpartition sp_2025 values less than ('2026') tablespace sp_2025,
 31  subpartition sp_max values less than (maxvalue) tablespace sp_max
 32  )
 33  (partition part_init values less than (1))
 34  enable row movement;
Table created.
--数据库延迟对象创建
SQL> select TABLESPACE_NAME,sum(bytes)/1024/1024 from dba_segments  where tablespace_name
   2 like 'SP%' group by TABLESPACE_NAME;
no rows selected
--只插入一个分区1,2013
SQL> insert into test_com_partition_1 values (lpad('xifenfei',3900,'wwww.xifenfei'),1,'2013',
   2 rpad('aaafdfafd',4000,'b'));
1 row created.
SQL> commit;
Commit complete.
--所有分区全部都创建了segment
SQL> select TABLESPACE_NAME,sum(bytes)/1024/1024 from dba_segments  where tablespace_name like 'SP%'
   2 group by TABLESPACE_NAME;
TABLESPACE_NAME                SUM(BYTES)/1024/1024
------------------------------ --------------------
SP_2018                                           8
SP_2022                                           8
SP_2021                                           8
SP_2025                                           8
SP_2011                                           8
SP_2008                                           8
SP_MAX                                            8
SP_2020                                           8
SP_2012                                           8
SP_2010                                           8
SP_2024                                           8
SP_2019                                           8
SP_2015                                           8
SP_2014                                           8
SP_2013                                           8
SP_2023                                           8
SP_2017                                           8
SP_2016                                           8
SP_2009                                           8
19 rows selected.
SQL> begin
  2  for i in 3 .. 200 loop
  3  insert into test_com_partition_1 values (to_char(i)||lpad('xifenfei',3900,'wwww.xifenfei'),mod(i,5),
     '2013',rpad('xifenfei',4000,'www.xifenfei.com'));
  4  end loop;
  5  commit;
  6  end;
  7  /
PL/SQL procedure successfully completed.
--只是在2013的分区(1,子分区2013)中插入了对象,但是其他分区也都创建了segment(extent)
SQL>  select TABLESPACE_NAME,sum(bytes)/1024/1024 from dba_segments  where tablespace_name
   2  like 'SP%' group by TABLESPACE_NAME;
TABLESPACE_NAME                SUM(BYTES)/1024/1024
------------------------------ --------------------
SP_2018                                          32
SP_2021                                          32
SP_2022                                          32
SP_2008                                          32
SP_2011                                          32
SP_2025                                          32
SP_2010                                          32
SP_2012                                          32
SP_2020                                          32
SP_MAX                                           32
SP_2015                                          32
SP_2019                                          32
SP_2024                                          32
SP_2013                                          40
SP_2014                                          32
SP_2023                                          32
SP_2009                                          32
SP_2016                                          32
SP_2017                                          32
19 rows selected.
SQL> select PARTITION_NAME,TABLESPACE_NAME from dba_segments where TABLESPACE_NAME='SP_2015';
PARTITION_NAME                 TABLESPACE_NAME
------------------------------ ------------------------------
SYS_SUBP128                    SP_2015
SYS_SUBP148                    SP_2015
SYS_SUBP168                    SP_2015
SYS_SUBP188                    SP_2015
--因为在创建表语句中有partition part_init values less than (1)，隐藏之类对于小于1的分区没有子分区，只有PART_INIT_SP_2013
SQL> select PARTITION_NAME,TABLESPACE_NAME from dba_segments where TABLESPACE_NAME='SP_2013';
PARTITION_NAME                 TABLESPACE_NAME
------------------------------ ------------------------------
PART_INIT_SP_2013              SP_2013
SYS_SUBP126                    SP_2013
SYS_SUBP146                    SP_2013
SYS_SUBP166                    SP_2013
SYS_SUBP186                    SP_2013

_partition_large_extents=false

SQL> alter system set "_partition_large_extents"=false;
System altered.
SQL> show parameter _partition_large_extents
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
_partition_large_extents             string      FALSE
SQL> drop table test_com_partition_1 purge;
Table dropped.
SQL> alter system set deferred_segment_creation=true;
System altered.
SQL> create table test_com_partition_1
  2  (
  3  name varchar2(4000) not null,
  4  aaaaa number not null,
  5  bbbbb varchar2(180) not null,
  6  ccccc varchar2(4000),
  7  constraint pk_test_com_partition_1 primary key(name)
  8  )
  9  partition by range(aaaaa) interval (1)
 10  subpartition by range (bbbbb)
 11  subpartition template
 12  (
 13  subpartition sp_2008 values less than ('2009') tablespace sp_2008,
 14  subpartition sp_2009 values less than ('2010') tablespace sp_2009,
 15  subpartition sp_2010 values less than ('2011') tablespace sp_2010,
 16  subpartition sp_2011 values less than ('2012') tablespace sp_2011,
 17  subpartition sp_2012 values less than ('2013') tablespace sp_2012,
 18  subpartition sp_2013 values less than ('2014') tablespace sp_2013,
 19  subpartition sp_2014 values less than ('2015') tablespace sp_2014,
 20  subpartition sp_2015 values less than ('2016') tablespace sp_2015,
 21  subpartition sp_2016 values less than ('2017') tablespace sp_2016,
 22  subpartition sp_2017 values less than ('2018') tablespace sp_2017,
 23  subpartition sp_2018 values less than ('2019') tablespace sp_2018,
 24  subpartition sp_2019 values less than ('2020') tablespace sp_2019,
 25  subpartition sp_2020 values less than ('2021') tablespace sp_2020,
 26  subpartition sp_2021 values less than ('2022') tablespace sp_2021,
 27  subpartition sp_2022 values less than ('2023') tablespace sp_2022,
 28  subpartition sp_2023 values less than ('2024') tablespace sp_2023,
 29  subpartition sp_2024 values less than ('2025') tablespace sp_2024,
 30  subpartition sp_2025 values less than ('2026') tablespace sp_2025,
 31  subpartition sp_max values less than (maxvalue) tablespace sp_max
 32  )
 33  (partition part_init values less than (1))
 34  enable row movement;
Table created.
SQL> select TABLESPACE_NAME,sum(bytes)/1024/1024 from dba_segments
   2 where tablespace_name like 'SP%' group by TABLESPACE_NAME;
no rows selected
SQL> insert into test_com_partition_1 values (lpad('xifenfei',3900,'wwww.xifenfei'),
   2 1,'2013',rpad('aaafdfafd',4000,'b'));
1 row created.
SQL> commit;
Commit complete.
SQL>  select TABLESPACE_NAME,sum(bytes)/1024/1024 from dba_segments  where tablespace_name
   2 like 'SP%' group by TABLESPACE_NAME;
Tablespace           SUM(BYTES)/1024/1024
-------------------- --------------------
SP_2018                             .0625
SP_2021                             .0625
SP_2022                             .0625
SP_2008                             .0625
SP_2011                             .0625
SP_2025                             .0625
SP_2010                             .0625
SP_2012                             .0625
SP_2020                             .0625
SP_MAX                              .0625
SP_2015                             .0625
SP_2019                             .0625
SP_2024                             .0625
SP_2013                             .0625
SP_2014                             .0625
SP_2023                             .0625
SP_2009                             .0625
SP_2016                             .0625
SP_2017                             .0625
19 rows selected.
SQL> select PARTITION_NAME,TABLESPACE_NAME from dba_segments where TABLESPACE_NAME='SP_2015';
Partition Name       Tablespace
-------------------- --------------------
SYS_SUBP328          SP_2015
SQL>  select PARTITION_NAME,TABLESPACE_NAME from dba_segments where TABLESPACE_NAME='SP_2013';
Partition Name       Tablespace
-------------------- --------------------
SYS_SUBP326          SP_2013
SQL> begin
  2  for i in 3 .. 2000 loop
  3  insert into test_com_partition_1 values (to_char(i)||lpad('xifenfei',3900,'wwww.xifenfei'),
     mod(i,5),'2013',rpad('xifenfei',4000,'www.xifenfei.com'));
  4  end loop;
  5  commit;
  6  end;
  7  /
PL/SQL procedure successfully completed.
SQL> select PARTITION_NAME,TABLESPACE_NAME from dba_segments where TABLESPACE_NAME='SP_2015';
Partition Name       Tablespace
-------------------- --------------------
SYS_SUBP328          SP_2015
SYS_SUBP348          SP_2015
SYS_SUBP368          SP_2015
SYS_SUBP388          SP_2015
SQL> select PARTITION_NAME,TABLESPACE_NAME from dba_segments where TABLESPACE_NAME='SP_2013';
Partition Name       Tablespace
-------------------- --------------------
PART_INIT_SP_2013    SP_2013
SYS_SUBP326          SP_2013
SYS_SUBP346          SP_2013
SYS_SUBP366          SP_2013
SYS_SUBP386          SP_2013

通过测试证明,设置_partition_large_extents参数确实是能够控制分区表的extent大小,而且对于分区表,deferred_segment_creation虽然为true，但是在一个分区表中如果有一个子分区插入了记录,那么其他子分区会同时创建segment.对于数据量不多，而且数据大量集中在某几个分区,那强烈建议设置_partition_large_extents为false,节约空间.如果数据量较大,而且数据分布较为均匀,建议设置_partition_large_extents为true.另外对于分区的index也有同样的参数为_index_partition_large_extents

One thought on “分区默认segment大小变化(64k—>8M)”

  1. 参考MOS:Initial Extent Size of a Partition Changed to 8MB from 64KB After Upgrade to 11.2.0.2 or Later (Doc ID 1295484.1)

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