Now I know why SYSTEM tablespace comes with dictionary extent manament in a vendor application

It seems the database uses raw devices, and created manually (not using dbca), when the option is not specified explicitly, by default the SYSTEM tablespace is created  as DICTIONARY managed.

It seems quite a few article list disadvantages of DICTIONARY extent management, but don't where it come from.

Below is my testing.

default setting for SYSTEM datafile

-bash-3.2$ cat cre_db.sql

STARTUP NOMOUNT

CREATE DATABASE "RAWDB1"

    MAXLOGFILES 16

    MAXLOGMEMBERS 3

    MAXDATAFILES 100

    MAXINSTANCES 8

    MAXLOGHISTORY 292

DATAFILE '/software/oracle/admin/RAWDB1/conf/RAWDB1_system_raw_1000m' size 900m reuse

sysaux datafile '/software/oracle/admin/RAWDB1/conf/RAWDB1_sysaux_raw_600m'size 560m  reuse

undo tablespace "UNDOTBS1" datafile '/software/oracle/admin/RAWDB1/conf/RAWDB1_undotbs1_raw_500m' size 480m reuse

default temporary tablespace temp tempfile '/software/oracle/admin/RAWDB1/conf/RAWDB1_temp_raw_250m' size 200m reuse

LOGFILE

  GROUP 1 ('/software/oracle/admin/RAWDB1/conf/RAWDB1_redo1_1_raw_120m')  SIZE 50M reuse ,

  GROUP 2 ('/software/oracle/admin/RAWDB1/conf/RAWDB1_redo1_2_raw_120m')  SIZE 50M reuse

user sys identified by "oracle123" user  system identified by "oracle123" ;

 
and
run the $ORACLE_HOME/rdbms/admin/catalog.sql and $ORACLE_HOME/rdbms/admin/catproc.sql.

17:00:32 SYS@RAWDB1> select tablespace_name , extent_management from dba_tablespaces;

TABLESPACE_NAME                EXTENT_MAN

------------------------------ ----------

SYSTEM                         DICTIONARY

UNDOTBS1                       LOCAL

SYSAUX                         LOCAL

TEMP                           LOCAL

4 rows selected.

 

Create non-dictionary extent management for SYSTEM tablespace

-bash-3.2$ cat cre_db_non_dict_system.sql

STARTUP NOMOUNT

CREATE DATABASE "RAWDB1"

    MAXLOGFILES 16

    MAXLOGMEMBERS 3

    MAXDATAFILES 100

    MAXINSTANCES 8

    MAXLOGHISTORY 292

DATAFILE '/software/oracle/admin/RAWDB1/conf/RAWDB1_system_raw_1000m' size 900m reuse extent management local

sysaux datafile '/software/oracle/admin/RAWDB1/conf/RAWDB1_sysaux_raw_600m'size 560m  reuse

undo tablespace "UNDOTBS1" datafile '/software/oracle/admin/RAWDB1/conf/RAWDB1_undotbs1_raw_500m' size 480m reuse

default temporary tablespace temp tempfile '/software/oracle/admin/RAWDB1/conf/RAWDB1_temp_raw_250m' size 200m reuse

LOGFILE

  GROUP 1 ('/software/oracle/admin/RAWDB1/conf/RAWDB1_redo1_1_raw_120m')  SIZE 50M reuse ,

  GROUP 2 ('/software/oracle/admin/RAWDB1/conf/RAWDB1_redo1_2_raw_120m')  SIZE 50M reuse

user sys identified by "oracle123" user  system identified by "oracle123" ;

17:24:40 SYS@RAWDB1> select tablespace_name,  extent_management from dba_tablespaces;

TABLESPACE_NAME                EXTENT_MAN

------------------------------ ----------

SYSTEM                         LOCAL

UNDOTBS1                       LOCAL

SYSAUX                         LOCAL

TEMP                           LOCAL